Questions-and-Answers

Here I’ll post Your Questions and My Answers, from the E-mails I receive every week from around the World.
These include everything from Lee Jackson Products, Ampeg , Crate , Fender and Marshall amplifiers and general questions about equipment.

Hello, I own an Ampeg VL-503 and while re-tubing it today I couldn’t recall which of the 6 preamp slots is which. V1, V2, V3, V4, V5 are preamp tube slots and V6 & V7 are the power tubes.:

On the VL-503 Tube order:
V1 is the tube socket towards the left edge.
V1 – Preamp – All three channels
V2 – Preamp – channel 2
V3/V4 – Preamp – channel 3
V5 – Phase inverter
V6/V7 – output tubes
Effects loop is solid-state.

On the Vl-1002 and VL-502 Tube order:
I need to know which one that is? Which preamp tubes control what?

On the tubes:
The first tube and the second tube are used on both channel one and two.
The third tube and fourth is only on channel two.
The fifth tube is for the reverb
The sixth tube is the effects send and the overall amp mixer tube.
The seventh tube is the phase inverter

Question about power tubes for my amp:
What kind of power tubes can be used?
6L6, EL34, 6CA7? KT77?, KT88? All?
I currently have a quad of Tesla E34Ls in it.
Does the amp need to be biased each time the tubes are changed or is it self-biasing?
Should I buy a matched quad?
What tubes do you recommend for early Van Halen 1 sound? Best Tube Brand?
They will all work except the KT88’s, the tube is to big to fit in the sockets.
In most cases you will not need to have the amp biased as long as you have the bias selector set to the correct tube.
Set amp bias selector for EL34 for EL34/6CA7/KT77.
Set amp bias selector for 6550 for 6550/6L6/KT88
Matched Quads are best when available
Eddie uses Sylvania 6CA7’s, the new 6CA7’s are not even close to the Sylvania’s,
You can still find Sylvania’s.
http://www.hitestguitars.com/power-tubes.htm

Can the “key” be disabled on the Ampeg VL1002?
Yes it can, it is wired in line with the main power switch,
And can be bypassed. Take it to your local amp repair shop,
And they will be able to do this for you.
This also can be done on all the VL-Series with the key lock.

Impedance Selector for M-1000 / XLS / XLA / VL’s:
On all these amps, we used the same Impedance selector, it is made by Schurter Part # 0033.4032 . Here is a Part Description.

Will KT88’s operate in a VL amplifier:
The problem is not with the KT88’s operating, the problem is with the output tube socket spacing.
The sockets on the VL’s are too close to get the large bulb KT88’s to fit.
If they fit they work just fine in the VL’s
If you really wanted to hear the KT88 sound in your amp, You could use just two of them, and use the two outer sockets.

No output sound on a VL amplifier:
HI I recently emailed you about a volume issue with my vl 501 after about 5 minutes of play the volume would just drop way down and go up and down randomly. You recommended changing out the molex connectors with 18 gauge wires which I did and it didn’t fix the problem and now the volume doesn’t fluctuate it’s just very low all the time now just curious if you could please give me any more suggestions on what to do because I’m at a loss with it.
Assuming the molex repair was done without a problem, like a wire in the wrong position. When the molex connector are taken out there will be one wire in the bundle not used at all it was used as a spacer, so if you didn’t allow for that then the wire positions could be wrong.

Next the original problem could have been either a output transformer failing or a bad impedance selector on the back of the amp. If you have access to an ohm meter, if you set it to the lowest resistance setting and check the switch to make sure it is making a connection from the center pin to the outside pins on the impedance select, If the impedance selector is good then it is a good chance the output transformer is bad.
Output transformers of the VL’s don’t general die, you have to play the amp loud without a speaker plugged in or if an impedance selector fails while your playing loud, that can cause an out transformer to fail. If the transformer failed, mercury magnets are making great replacement transformers for the VL’s.
Make sure before you do anything the amp is unplugged and off for a while, so there is no power in the power supply capacitors.

I have a question about the Ampeg V412TC cabinet designed by Lee Jackson, and I have a question that I hope he or someone can answer, since Ampeg no longer supports that product.
On the back, it is switchable between 4 and 16 ohms mono, and the question is: Which one is better for the amp/cabinet? I run a 4/8/16 ohm switchable Rivera amplifier, and I’m curious if the lower impedance is better for the longevity of the amp, or if there is any noticeable tone differences, etc.

On the Ampeg V412TC Lee Jackson cabinet
The switch not only changes the impedance it also changes the way the speakers are wired. In the (16 ohm) position, the cabinet is wired series parallel, like any standard marshall cab. In the (4 ohm) position the cab is wired in parallel.
And we have found just that sounds different from each setting.
Now on amplifier impedance, the closer the impedance is matched to the cabinet, The better frequency range and power output is achieved. So experiment, make sure you put the amp on standby before changing any setting, On either the cab or the amplifier. And the Question about Longevity of the amp, lower impedance’s are harder to drive , So the amp will work harder and hotter at lower impedance’s. And heat is not your amps friend.

VL-Series Cabinets:
I did design the ampeg cabs, there were two models.
One model came with Celestion Vintage 30’s and the other cabinet was made with cheaper wood and Eminence speakers. It is easy to tell, the cabs with the vintage 30’s has a little plate in the front of the cab that says vintage 30’s. Also the Cabs with the Cheaper speakers to not have the Mono Stereo plate on the back.

The Differences between the XLS and the VL Series Amps:
The XLS and the VL’s are a lot the same, I designed the VL’s first, so the XLS’s are an extension of the VL’s. I changed stuff I didn’t like about the VL’s, like the effects loop which I see is one of your questions. It is a hybrid of tube and solidstate, whereas the XLS is all tube with individual trim controls.Don’t get me wrong, I love the VL’s, ampeg made me put the effects loop in to save money, other than the loop the amp rocks.

VL-Series Amplifiers Front Panel Keys:
The Amps originally came with an extra key on the inside of the head stapled to the side of the head cab. The original key switch was special and had to be UL approved for the voltages.You can try and get one from the Ampeg service center 1-800-727-4512 The key is only needed if you want to dis able the amp from coming on. If the amp is stuck in the off position, a tech can bypass the switch internally.

VL-1002 – No Sound – Logo Doesn’t Light:
0ne of the things that fail with the VL-1002’s is the Tube Heater supply, Ampeg used a Molex connector between the main board and the tube board, these connector would fail, To do the repair correct they would have needed to dis-assemble the amp and replace the wiring between the boards, taking the connectors out. We have a Video’s that shows the whole Service and Repair, Bias etc (This work should only be done by a tech) Get Here

VL-1002 and VL-502 Tube Placement and use:
Starting from the far right, looking from back.
Tube 1 is for both input channels, Tube 2 is for Channel 1, Tube 3 is for Channel 2, Tube 4 is for channel 2 Gain, Tube 5 is reverb, Tube 6 is mixer and Tube 7 is phase inverter.

VL-502 and VL1002 Foot switch:
On the VL-502 and VL-1002, Foot switch you can use a Daul button Foot switch (On/Off) to switch the channels, Use a stereo cord, Because it will turn off your reverb when you plug into the foot switch jack with a mono guitar cord, If you want to use a single Foot switch, You will need to do is put a stereo 1/4″ plug on the end that plugs into the amp, and connect the wires to only the Tip and ground and leave the ring open. This will allow the reverb to work and you can change channels.
We make a custom foot switch for the VL’s Here

VL-503 Foot Switch:
The Foot switch cable is a Cat 5 cable, you can get at any computer store. You need to get one that is straight and not twisted pair, Both ends have to be the same: pin 1 has to go to pin 1 on the other end. and so on. I think the one you do not want to use is the Cat 5 reverse cable. The VL-503 is a custom foot switch, Ampeg is no longer producing them, and there is not a substitute, your only option is to have someone near you to make one. Here is the foot switch schematic: Here

I own a VL 502 and would like to know how to adjust the hum balance?
Make sure you are in a quiet room,
Also make sure a cabinet is plugged in, Do Not plug in a cable or instrument. Adjust the Hum Balance for the quietest position.

VL-1002 and VL-502 Reverb Pan:
It is an Accutronics 4AB3C1B

VL-Series Front Panel Key Types:
There were two different key switches through the VL production. the only way to tell the difference is to think of the front of the switch like a clock face, On one of the switches, the the key goes from 12 to 2, and the other Switch it goes from 12 to 3. Both Switches use a different key. You can get the keys at the Ampeg service center, call 1-800-727-4512

VL-Series Light Bulbs:
The bulb is a Incandescent Lamp #47
Chicago Miniature Incandescent Base Bayonet T-3 1/4 6.3V .15A
You can find them at www.mouser.com.

VL-1002 – Tubes:
On your Vl-1002, KT-88’s will not fit in the output tube sockets,
They are too big around.

VL-1002 Bias Switch:
Don’t switch the bias switch without changing the output tubes, the switch is only good for switching bias between 6550’s and EL-34’s output tubes. If you have 6550’s in the amp and switch the bias switch to EL-34’s, the amp will melt the output tubes. The opposite would cause the amp to sound horrible and cold. A fellow musician (Jimmy Page), did the exact same thing and just melted His Vl-1002 amp, because when he saw the switch saying EL-34 / 6550. He though the amp would give him both sounds (EL-34 or 6550). I later put the switch on the inside on my XLS-1000 amps.

I’ve got a VL1002 with a problem thats got me stumped. the #1 channel sounds like its being really overdriven (starts breaking up @10 o’clock or so) and past that point its really oversaturated to the point it actually starts backing up on its self (volume wise) but the #2 channel is fine.both the pre and master vols appear to function fine on both channels. i’ve checked all components within the #1channel including the tubes and everything appears fine (caps for value and leakage, resistors in tolerence, voltages) the molex and switching cap mods have already been done prior to me getting this unit.
So here are some of the things that will cause the channel to have gain problems.

1. The LDR’s, the little black boxes with 4 wires coming out of them, these fail in all kinds of weird ways, One of them is level.
2. The 100k plate resistors, R6, R10 if they start failing, it will cause that.
3. The 22uf/25v caps C3

VL amp Foot Switch Question: Can a regular 1/4 in jack be used to access the channels ? I saw the picture of the channel-switch you are offering on your site . It appears to have a “stereo ring end” on it , and I’m guessing that would be to control the channels and the reverb function. Would a regular 1/4 in. jack work for just the channels ?
On the VL’s they use a Stereo 1/4″ jack, the tip is the Channel Switching and the Ring is the Reverb on/off, If you plug a standard 1/4″ plug into the foot switch jack, it turns the Reverb Off. You can use a standard single foot switch, you just have to put a Stereo 1/4″ plug on the end,
and leave the Ring of the plug open.

Information on the Ampeg VL-501.Could you tell me the tube layout of the preamp,and which position is the cathode follower.Do the 501 and 1001 have the same issues as the 502 and 1002,such as the molex connectors?And finally I have found the schematic for the preamp of the 501,but nothing for the power section or power supply board.
On the VL’s the tubes start from the far right looking from the back, start with V1, V2, V3 etc.. moving to the left. You can look at your schematic and see what tube does what function.
Yes that the VL-1001 will have the same Molex issues as the VL-1002.
On both the 501 and 502, it is not as critical because there are less tubes drawing current on the connectors. You can use the VL-1002 service dvd to do the molex repair and updates, on the VL-501 and 1001. (This has to done by a amp tech, it isn’t a simple job). I included a schematic of the 1002 output section, it is the same as the 1001 and 501, on the 501 we just removed the outside two output tubes. Everything else is the same.

Lee Jackson and Ampeg 4 x 12 Cab Dimensions:
The cab Dimensions: (H) 29 1/4 x (W) 30″ x (D) 14″, They weight about 85 lbs.

GT-50 – Half power Mod:
On your Stealth Amps you can take out either the center two 6V6’s or the outside two 6V6’s
Generally if you buy a good set of 6v6’s, you will not have to rebias your amp.
We have a service dvd for that model, it shows you how to service and bias your amp. Here

Converting Stealth GT-50 to 6L6’s:
On the stealths, you can NOT use the 6L6’s, the reason is first the current draw of the heaters would melt the power transformer and second, the bias supply would not adjust in the range to bias the tubes. You need to change all four 6V6’s with a matched quad, the electroharmonix 6V6’s are good, I like the tung sol 6V6’s too,The good news if you put a new set of 6v6’s in, you wont have to rebias the amp.

Crate GT-100H Power Section:
On the Crate 100 watt Stealth I used the same parts in the output section as I did on my VL-1002 amps, so the amp really rocks.

Crate Stealth GT-100H Output Jacks:
Hey man just to start things off I absolutely love this head and has served me well for many many years. Now though i have noticed that the main speaker out in the back has become slightly warped and or has melted. It still works just as it should but every now and again if the speaker cord isn’t placed in there just right it won’t work at all. Is this a problem that a decent tech can fix? I hope so. Yes it can be done by any good amp tech and should be done immediately.
The reason the jack is warped or melted is because the jack is not making a good contact with the speaker cord and getting hot, and is arcing.
The big bummer if you keep playing with this condition is it will cause the output transformer to fail, and this is very expensive to replace. A new transformer could cost upwards of a couple hundred dollars plus the cost of someone installing it.
New jacks should cost you under $10.00 plus installation.

I just re-tubed my GT-50C with a matched quad of JJ 6V6 S and their high gain 12AX7 with a triode matching one for the PI and I was adjusting the bias but ran into a little bit of a wall.  From what I can tell, I can’t get above 17mA at 385V according to my bias probe, I can go as low as 3.2mA at 399V.  Unless my math is off, I get around a 50% bias that’s reading out at 17mA (your video I think had it at 28mA?).  This is with the trimpot maxed without forcing/breaking it.  Would I need to replace the bias resistor?
On the GT-50’s you can raise and lower the overall bias voltage with resistor (R93) which is a 33.2k resistor.
By lowering the value of the resistor you increase the overall bias voltage.
Because of the state of the new tubes available now, we still feel using a scope to bias, is better then setting it by current draw. Lower the bias voltage increases current draw, this can be done by increasing the value of your (R93) resistor.
Make sure you pull the output tubes out till you are sure your bias voltage is in range, Not doing so could bake a set of tubes quickly.

Concert Mod Difficulty:
The concert mod does make the concert sound warm and smooth.
The difficulty in doing the mod isn’t too bad, if you have anyone near that services amps could follow the dvd and install the parts.It takes about 2 hours to do the mod.
(Concert Mod Here)

I was wondering if the dvd for the fender concert mod (rivera era) comes with the necessary parts for the mod or if i will have to get them separately?   i also was wondering what all the mod does and what the voicing of the amp is changed to?  i have read on the forums that it changes the amp to be dumble like and that it changes it to be more old school boogie.I want it to be more dumble like than anything.
Both the physical and downloaded Video’s come with a parts list of the parts that are needed.
You can purchase the parts off of the web, at Mouser.com or tubesandmore.com As for the sound, it can sound both dumble and boogie, you can really tailor your sound after the mod,
With the preamp and power amp tubes you use, for example, sovtek tubes are going to push you more to the boogie sound,
Where as The new tunsol and Mullard’s you get you in the dumble area. If you can find some old GE 6L6’s I have heard them sound amazing in the concert.

Concert Mod _ Mid Mod on Clean Channel:
On the mid control for the clean channel, there is several things that can be done.
On the back of the Bass control on the clean channel, there is a resistor soldered to ground.
You can either exchange the resistor for another control pot (10K), or change the resistor value till you get the mids your looking for.I think the resistor that is in there is a 6.8k, so you can try from 680 ohm to 10k.

Effects Chain Line up:
On the effects chain, Guitar – Tuners – to Wha’s – (EQ’s) – Compressors – Distortion pedals – Chorus/flangers – (EQ’s) – Delays – Reverbs – amp The same goes for the Amp Effects loop, except you DO NOT want to put Distortion pedals in the Loop.

“TRUEBYPASS”:
Can I have a word here about “TRUEBYPASS”, because I get a lot of email concerning this.
Ok, in the 50’s 60’s 70’s electronics and especially solidstate electronics, was a new frontier and A LOT of the companies had no idea what they were doing, and really didn’t care as long as it was selling. So yes…A Lot of those earlier effects suck all the life out of your instrument if you leave it in line. We are now in the 2000’s and as designers we now know how to design circuits that do not suck tone and actually enhance it. With that said, I have ONLY heard how playing Through Mr Springgy has improved there Tone On and Off.
Power attenuator Question.
I would be mostly playing it in my living room, so that’s a potential issue. (I know it sounds incredibly dumb to be looking at a high-gain 59-Watt tube head for a living-room amp, but curcumstances seem to have conspired to make it a possible option, and like I said, it’s a great-sounding amp) If I were to consider some type of attenuator, would there be a particular type you would reccomend? I’ve looked at the Marshall Powerbrake, THD Hot Plate, Weber Mass, and even a couple of old Tom Scholz Power Soak units.

On power attenuators….a BIG NO!
The reason, it is not because they don’t sound good.
It is because it allows you to crank the amp at volumes you would never stand, which causes the output transformer core to heat up to levels it would not normally get to. Which finally causes the copper wire to fail… And fail in not a good way… Failing in a way that makes your wonderful vintage transformer sound like you put a carpet over your speaker cabinet.

AMP output Power Soaks:
External Power Soaks are bad on output transformers, they will make you amp permanently sound dull after a while of playing. They over heat the transformer windings, causing a physical breakdown.

Quantity of Lee Jackson Products Around the World:
I was just talking to Ampeg the other day to get the production numbers of my products, I’m updating Vintage Guitar Buyers guide and they need production numbers. Between Metaltronix, Perfect Connection, Lee Jackson Amps, Ampeg, and Crate, I have more than a 200,000 pieces worldwide.

On tubes if you would like some suggestions:
On Tubes, you have multiple choices with the VL’s,
You can use EL-34’s, I like the J/J and Electroharmonix EL-34’s
You can use 6550’s, My fav’s right now are the Tungsol 6550’s (Note: these will not fit in the XLA’s, XLS’s, VL’s) If not them, then Svetlana 6550’s If you use 6L6, I do like the Sovtek wxt’s and the 5881 wxt’s. On 12ax7’s I like the sovtek’s, the Electroharmonix 12ax7EH and the Tungsol 12ax7’s
Do not ever buy the J/J 12ax7’s. they suck, they are really dull sounding. If you play more drop tunings, I like the 6550’s they have great low end, great at concert levels. The EL-34’s are going to have the marshall sound, more distorted, great at club volumes. The 5881/6L6 are smoother, less output, good low end.

A Word on KT-88’s. 6550’s, EL-34’s and 6L6’s:
Selection of tubes (kt-88, 6550, EL-34’s) depends on how loud you play. If you play clubs then the EL-34’s would be best if you want a smooth lead sound, Kt-88 are really clean and keep there note definition at extreme volumes. There not as smooth as EL-34’s, but EL-34’s do not have the bottom end of Kt-88’s or 6550’s. If you can find Sylvania 6CA7’s there the best of all worlds, they distort like an EL-34 and have the power of a 6550. There really expensive when you find them, (100.00 each), eddie vanhalen uses them in all his marshalls because of the way they sound. Another tube we put in a lot of our amps is the 6L6, Sovtek has a great one (6L6 WXT), again the amp has to be biased for it. The 6L6 has great low end and the distortion is smooth for solos.

240 v or 120 v- Which sounds better:
Most English amps do have multitap transformer which allow them to work at 100 -120- 220- 240 volt ac. It is best to set them at the voltage of your country ie…U.S 120 v, Europe 240 v What I have found true is the English amps do sound better at 240 v “BUT” that is at 50 hz which can only be done in Europe, so the variac will not help you. We have found even our Amps sounded better at 240 vac, when we were at the Summer Frankfurt Namm Show.

Using a Variac:
The variac can be used to turn down the voltage to make the amp distort more at lower volumes, That is what eddie vanhalen did on the early VH Albums. You can only go so low before the Tube Heaters Turn Off.

ALL Power transformers:
If the fuse blows with all the secondary wires from the transformer are dis connected including the heaters, then the transformer is bad. If the Transformer secondaries are connected and the Primary Fuse blows, we have found in extreme cases it was the output transformer center tap that was bad and shorted, so to test for that you need to unsolder the output transformer center tap wire and test again.

Tubes are really subjective:
It depends on guitars, pickups and the volume you play at, because each tube acts differently at different volumes.The Vl’s originally came with GE6550’s which sound great especially at extreme volumes, they sound clean at lower volumes, compared to EL-34’s.6L6’s and 5881’s sound great at lower volumes, but don’t have the output like the 6550’s, Akira (Loudness) uses 6L6’s in his amps. On 12ax7’s they make a big difference too. My favorites are the Chinese 12ax7’s, the problem is you have to go through a box of them to get quiet ones, and when you do they sound great.The best right out of the box is the sovtek 12ax7’s, stay away from the J/J 12ax7’s they a dull.The Electroharmonix 12ax7 sounds great too Their really is no way other than just trying them all out, to really hear the difference.

Install Tube Effects Loop on Non Master Volume Amps:
The problem is when you put the loop right after the treble control, the signal level is so high that you compress the send of the loop, you can try to put a 220k -470k resistor in line with the input of the loop circuit. Also every effect handles signal different.

Checking Tube Effects Loop:
On the Loop, Unplug anything from the loop, turn the loop off. Play the amp at the volume your going to play at, turn the effects send down to the 9:00 position. Put a guitar cable from the send to the return, turn on the loop set the loops return level so there is no change between the loop being on or off. Now plug in your Effect and set its controls so there is no difference between the loop being on or off.

Installing Tube Reverb
For about a year or so Ive been looking oround the net for a good reverb schematic to put in my Modified Marshall amp,but to no avail. The circut on the AmpPeg VL-502/1002 would probly work but Iam having trouble shorting out where to put the circut in the JCM 800,before the FX loop, or after the loop and also finding the input and output of the ampegs reverb circut.

So By your question, you want to install a spring reverb.
There are a couple things you can not get around if you want a great sounding reverb. The circuit you should be looking at, is like an old Fender Twinn with reverb,
The reason is, your going to need a mixer circuit, and there pretty standard with a 3.3meg resistor feeding the grid of another tube stage.
You’ll need a fender reverb driver transformer , another 1 – 2 tube sockets, I used only one with the VL’s and it worked just fine. 1/2 the tube to driver the reverb transformer and the other 1/2 as the reverb return.
The last thing is a good pan, you can choose from 2 – 3 string long decay, get the Accutronics pans.
Now with that said…if you ever wondered why most my amps do not have reverb is because there is no way you will put the reverb in with out changing the sound of the amp.
The original VL-1001’s did not come with reverb, it was ampeg that pressured me into installing it on the VL-1002’s. Musicians swear they like the 1001’s better..
So with that said, know your giving something up for it.

Level Control on Effect Loops with out Levels:
Most amplifiers have there master volumes after the preamp section, and before the power amp section. So when you plug into the effects return you are plugging directly into the power amp section. If you needed a volume control there, you could make a simple box with a 1 meg control pot and two 1/4″ jacks. Connect one side of the pot to the input jack, the other side to ground and the middle (wiper) to the output jack. This will allow you to control the overall volume.

Amplifier NOT Switching Channels: (Tech’s Only)
You can put a jump across the Opto to see if it bad, if you short it and the sound comes on then the Opto is bad, or the switching circuit is not working. Take a volt meter and see if the voltage changes across the LED part of the Opto. If there is no change when you push the channel switch button then the switching transistors are bad.

GP-1000 – The Different Models:
On the GP-1000’s, the first model was designed after my Fender mods, and the Sencond model, Was designed after my Marshall mods, two completely different sounding pre’s.

You can visually tell the differenc by the back of the preamp, on the Fender style one, it has a Tube XLR direct output. The Marshall style one, only has the two outputs, no XLR direct out.
We no longer make the GP-1000 preamp, we are going to be making the new GP-1000II.
It will have the same circuitry, ALL TUBE plus It will have several added features, and it will be in pedal form.

GP-1000 – The Different Models II:
I a real fan of your excellent products. In particular I used for many many years two GP-1000 preamps. I have really a lot of preamps but I am going to bring the ’88 version of GP-1000 in my next european tour.
They sound quite different, and I would like to ask you 3 questions:
1. The difference between the two preamps is that one was the “Fender style” and the other the “Marshall style”, is it so? If yes, which of the two was supposed to be “Fender” and which “Marshall”? If not, what is the conceptual difference between them?
2. There is a sort of screw system inside, what does it control exactly?
3. In the last years I enjoyed a lot using Mullard 12at7 in my ’88 version. I know is not really orthodox but I love the sound. Can I damage the preamp in this way?
It great seeing the two different GP-1000’s.

To answer your questions on them, the 87 is the Fender version, designed after my modified fenders that I was doing for the session players in Hollywood, That is why it has the handmade Jenson output transformer there on the back. it is a smoother sound with less gain then the 88, which is modeled after my marshal mod sound.
I made the changes to the GP-1000 because the majority of the players wanted that sound over the Fender style sound.
The trim control that is on both of your preamps does two different things, one thing it does is set the level when you pull the distortion control on,
The other thing it does, is trim back the gain if you have a tube that feeds back on it self, This way you can try all kinds of different tubes and trim it back if the tubes starts to howl. On tube selection, there is nothing that you can do that can hurt the preamp, as long as you use standard 9 pin preamp tubes, Like 12ax7, 12aT7, 12au7,any of the military equivalents etc.. Each tube type and tube brand will drastically change the way the preamp sounds, The only thing I suggest is to turn the preamp off between changing tubes out and in, Because if you possibly shorted a pin with the power on, you could cause severe damage to the GP-1000 and you.

Foot Switching a GP-1000 Preamp:
You can use any generic on/off 1/4″ foot-switch, just never use a switching pedal that has the same ground as your guitar. Not to be confusing, just use a footswitch box by itself that does not have a common ground with any of your other pedals.

GP-1000 Tubes:
I used hand selected chinese 12ax7, you can still find them and you will have to go through a stack of them to find quiet ones. The other tube that sounds good in the GP’s is the sovtek, the new Tungsol 12ax7 is a great sounding tube, with the GP’s because it uses the 12ax7’s to create its sound, the kind of 12ax7’s make a big difference..

GP-1000, SP-1000 and BP-1000 – Changing International Voltages:
It depends on the SP-1000, we did make a lot of the international models. We did make US only models too, these have only one transformer tap at 120 vac. So, open the top on the SP-1000, on the Flat torriod transformer in the middle. Follow the leads from the power fuse and power switch, if there black, it is US only. If they are colored, then it is an international transformer which can be powered by 100 -110 – 120 – 220 – 240. I included a schematic (Here) for the transformer, the SP-1000 uses the same colors as the M-1000 transformer.

Bridging SP-1000 Outputs:
The way the SP-1000’s are designed, it will not work to bridge the outputs. The only way to biamp is to use an active crossover and then plug into each side. Output 100 watts a side at 4 ohms, 75 watts at 8 ohms and 50 watts at 16 ohms. That there is an internal fuse on each channel if you short the outputs, so if you find one of the sides not working, the fuse inside is probably blown.

The Differences between the XLS and the VL Series Amps:
The XLS and the VL’s are a lot the same, I designed the VL’s first, so the XLS’s are an extension of the VL’s. I changed stuff I didn’t like about the VL’s, like the effects loop which I see is one of your questions. It is a hybrid of tube and solidstate, whereas the XLS is all tube with individual trim controls.Don’t get me wrong, I love the VL’s, ampeg made me put the effects loop in to save money, other than the loop the amp rocks.

Question about the Bias slider switch
I just picked up a XLS1000 Combo that had some changes made (Speakers and Tubes). I noticed right off that the impedance was not set correctly so I wanted to inspect the Power Tubes to check the Bias switch was set correctly. Of course the Bias sticker is missing on this Combo amp so I am comparing it to the sticker on my XLS1000 head. It appears to be set wrong. My question for you, is the Bias switch setting the same for the Combos and Heads? (switch set closest to the power tubes are for 6550, 5881, 6L6 ; and set away from power tubes for EL34, 6CA7)?
Generally they are wired in the same direction,
I would have a tech check it though. In one direction the bias voltage should be between -40 to -47 which is for EL-34’s, 6CA7’s and the other direction should be between -50 to -57 which is for 6L6’s, 5881’s and 6550’s

Question about power tubes for my amp:
What kind of power tubes can be used?
6L6, EL34, 6CA7? KT77?, KT88? All?
I currently have a quad of Tesla E34Ls in it.
Does the amp need to be biased each time the tubes are changed or is it self-biasing?
Should I buy a matched quad?
What tubes do you recommend for early Van Halen 1 sound? Best Tube Brand?
They will all work except the KT88’s, the tube is to big to fit in the sockets.
In most cases you will not need to have the amp biased as long as you have the bias selector set to the correct tube.
Set amp bias selector for EL34 for EL34/6CA7/KT77.
Set amp bias selector for 6550 for 6550/6L6/KT88
Matched Quads are best when available
Eddie uses Sylvania 6CA7’s, the new 6CA7’s are not even close to the Sylvania’s,
You can still find Sylvania’s.
http://www.hitestguitars.com/power-tubes.htm

I have a Lee Jackson XLS-1000 combo amp that I bought new many moons ago. Love the amp!
Question: The back of the amp has two speaker outputs.
The combo amp has two 16 Ohm speakers wired in parallel. So running just those two speakers together, I set the ohm switch to 8 ohms.
1.) If I add a marshall 4×12 cabinet along with the two combo speakers, what total ohm Marshall cabinet would I want and what would I set the back of the amp to?
2.) Are the two output jacks on the back of the amp wired in parallel? In other words, if I ran two marshall 4×12 cabs (no using the Lee Jackson combo speakers) and each cab was 8 Ohms output, would I set the amp to 4 ohms?
3.) Does the Line Out signal on the back of the amp come after the pre-amp or after the main power amp?
Here are your answers
The speaker jacks are wired in parallel, so you have to set the impedance selector for overall impedance.
2 x 16 ohm loads set the impedance 8 ohms – 2 x 8 ohm loads set the impedance 4 ohms
On mismatched impedance’s like using the internal speakers which are 8 ohms, and a 16 ohm speaker the impedance would be about 6 ohms,
so I would use the 4 ohm impedance setting.
The line out is on the Main Power amp speaker out.

Can I put KT-88 tubes in my XLS-1000?
The KT-88’s will operate fine in the XLS with re-biasing,
The problem is they will not fit, the tube sockets are to close to each other for the Kt-88’s. If they made a KT-88 with a small sized bulb, something the size of a 6550, Then you could.

Lee Jackson and Ampeg 4 x 12 Cab Dimensions:
The cab Dimensions: (H) 29 1/4 x (W) 30″ x (D) 14″, They weight about 85 lbs.

Impedance Selector for M-1000 / XLS / XLA / VL’s:
On all these amps, we used the same Impedance selector, it is made by Schurter Part # 0033.4032 . Here is a Part Description.

Fuse Holder for XLS / XLA / VL’s:
On all these amps, we used the same Fuse Holder, it is made by Schurter Part #031.3577 . Here is a Part Description.

On the XLS Head, what the order is on the preamp tubes? Like which ones are for the effects loop, etc…?
The first 12ax7 closest to the edge , is the input stage for both channels, the 2rd is the second stage for the Clean and Hot channel, the 3rd is for the Hot channel Gain, the 4th is the Effects Loop tube and the last is for the phase inverter (driver tube).

I’ve started using the amp at a clean, low gain setting (which sounds fantastic!).  However, at this setting I’ve noticed that the effects loop has a lot of hiss when engaged.  I never noticed this before because I was using mainly hi-gain settings.  I read in your QandA section that Ampeg made you omit trim controls for the effects loop in order to save money.  Is there anything you can recommend to tame the hiss?
So I looked over the schematic, there were some things done, the easiest is to use a lower gain tube in the effects loop, the other is to take the amp to a tech and have a couple values changed to lower the gain, less gain = Less Hiss
There is a lot of gain that can be lowered.
First try changing resistor R1 from 68k to 6.8k, then the next thing to try is changing R13 sets gain for return from loop, lowering the value lowers the gain.
Then on the tube , it is V6A is the effects loop tube, only one side is used, the other side is reverb return (count in 6 12ax7’s from the end, another thing that would make sure you had the right tube, is to take it out and see if the loop turns off, make sure the amplifier is off before removing tube).
The best thing for the loop is to have send and return controls to control the levels, if the unit you are plugging into has great level controls then the amp does not need them as much.

I have Questions on my Lee Jackson XLS-1000
1. What tubes came “stock” in this amp, both power and pre amp.
2. What are the recommended tubes for the # 5,4 , Phase invert, and effects loop, and the Hi Gain(HOT) channel
3. Can I run Two KT88 paired for 50 wts, or for that matter, KT77, or KT66
4. Is it ok to mix power tubes with the ones it will run, in pairs, ie, inside position/outside position

The original tubes were sovtek 12ax7wxt’s and the Sovtek 5881’s in the output.
Tubes are subjective to playing style.
On the KT66, KT77 or KT88’s it is up to the size of the glass as to if they can fit.
Generally the KT88’s glass blub is to big around to fit 4 of them in the XLS-1000.
What you can do is use two of them, and use the two out side sockets.
All of the KT series do bias a little different then the Standard 6L6 or 6550.
So you can set the bias selector to the 6L6/6550 position, but I would still have a amp tech check the internal bias to be sure.
You can mix and match tubes of the same bias type like a KT88 and a Svetlana 6550, or a KT66 and a Sovtek 6L6.
But you can not mix and match tubes that bias differently like a 6550 and a EL-34, You could if you biased the amp for 6550’s and put in a EL-34, because the hi bias would cause the EL-34 to run cold. If you did the opposite and biased the amp for a EL-34 and put 6550’s or 6L6’s, you literally melt the tubes in there sockets, which would be very bad for you and your pocket book.

Which Marshall’s are Best to Modify:
The best marshall’s to mod are the early 1969 marshall 100 watters, they are really expensive though when you find them, Next would be the early single channel JCM 800’s 100 watters that came out in the late 70’s early 80’s. All the re -issues mod up well too, so the Plexi re -issues and 4 input re -issues sound great modded,You want to stay away from any of the channel switching models, or if the have reverb in them, they generally never sound good. The general rule is if they sound good un modded, they even sound better modded, because if you have a dull output transformer, The amp is just going to sound dull. Check out our Marshall Modification Dvd’s Here

Are the mod kits good for “early jcm 800s”:
On the earlier 80’s 2204’s they had the four and two input jacks on the front. On the 2 input jack model, normally they were vertical, on a couple runs of the model, they made some with two horizontal input jacks, They are harder to mod, because everything is mounted to the PC board.With all that said, any qualified tech can do the work and some feel the Versions with Horizontal jacks sound better.

Ozzmosis tone and gear?
OK, so a quick couple of questions. I already bought the DVD Marshall Mods 2 and it ain’t getting me that Zakk tone. What mods if any do I need to do to get my JCM800 2203 sounding like Zakks. I’m trying to get his sound on the Ozzmosis album. What speakers was he using on that album in his cab that was being mic’d. What effects was he using? Was he using an effects loop installed on the JCM800 he was using or going in the front door of the amp? Was he using those EVM 12L in his cabs or Something else? What kind of pickups? The EMG stuff? I know this is 1995.

I know it was 1995, and I can actually still remember back then.
First thing I did for Zakk was modify his Marshall’s with my Mod that I show on my Volume One Dvd, you need to add the extra tube to get the sound on “No Rest for the wicked” CD. We did add Effects Loops to his heads. Zakk also used a DS-1, an Octave pedal, and of coarse a Vox Wha. I remember Ozzie walking around the Studio yelling at Zakk; do you really need to play Wha on everything!
We also had three GP-1000’s powering a stereo 800 watt mosfet amp. All of this went into four 4 x 12 cabs loaded with Vintage 30’s and Celestion 65 watters. Live we had to change to 75 watt speakers, because Zakk kept blowing them. Because of the 800 watt mosfet amps, he was pushing the cabs pretty hard. By the end of the tour we replaced out his modified Marshall’s with My Metaltronix M-1000 heads. Zakk’s Les Paul did and does now have EMG’s in it. My employee named Scott Quinn sold Zakk that signature Guitar with the Bulls-eye.
I was at my shop when Zakk and Ozzie came by to hear his new rig, Zakk forgot his guitar and Scott handed him his, the rest is history, there are pictures in our picture area of Zakk playing the Les Paul without the Bulls-eye Strips.

What kind of Mod you would have to do on a Marshall JCM 800 – 100 watt. To convert the amp from 6550B Tubes to EL 34 Tubes?
On the bias difference between the 6550 and the el-34’s, all you have to do is add or subtract a resistor value. The 6550’s operate at a higher voltage -50 to -58,
EL-34’s operate between -40 to -48, As always, this should be done by a qualified tech.

JCM800 No Sound Coming out:
Greetings,I’m having some problems with my jcm 800
I’ve owned this amp for about 12 years now and I’ve re tubed it when needed and have always took care of it.a few weeks ago I noticed a static like noise coming out of it after a few minutes it went away,for a few days it was working properly then all of a sudden it was dead.sound will come out of it only when I crank up the volume and even with the volume at full its barely audible and its a very staticy distorted sound….I popped new tubes in it and still nothing then I hooked the cabinet up to another amp to make sure the speakers weren’t blown or something and the cabinet was fine…all the tunes light up like normal,just no sound.

On your Marshall, it can be several things, did you check the B+ fuse? Take it out and check it.
The first really bad thing that comes to mind is the output transformer, it will do exactly what you are explaining, even down to the low volume cranked up
A bad impedance selector, can cause this and cause your output transformer to fail.
Another is the 100k plate resistors on each preamp tube.

Marshall JCM 800 with LOUD HUMM:
I hope you could give me a pointer or two on what might be going on with it.  It started one night about half way through a gig ,,, a big HUM with the Vol on the guitar up or down,,unpluged or pluged,,,HUM,,,I thought it is time for some power tubes,,,,I bought some new 6550’s TUNG-SOL  While I was setting the bias I set it at 70% I did notice that the Plate voltage was slightly unstable,,,,IT would go up and down a few volts every few min.  from about 424V to about 455V so I used the 1ohm tied to pins 8 and 1 going to ground and set tne mv at about 55mv. ,,,,,still HUM,,,,,,I thought,,,put in some new pre-amp tubes,,,HUM,,,,,,I changed out every cap in the pre,tone,and phase stages,,,,, still HUM,,,,,,

It’s humming because it doesn’t know the words…
Ok, it sounds like the large filter caps have failed.
The things that cause hum, bad tubes are first, the next is bad plate resistors, then it is the power supply caps, the 50uf/500 v. If you take take out all the preamp tubes out and turn it on, and it stops humming it is in the preamp section.
If it hums with the tubes out then it is the supply caps.
If they have never been changed, change them all.
The plate voltage is completely dependent on your wall voltage, as it goes up and down so does the plate voltage, so I wouldn’t worry.

Hello Mr Jackson, I’m very impressed by the work you’ve done for Zakk Wylde in the eighties. I’ve read many times that you have made all his sound system for him in 1988-89. I’ve also seen the different pictures of his rig on your website. The sound Zakk Wylde had at this specific period of his career was absolutely wonderful. In my humble opinion much better than on the latter years. I’ve spent a lot of time trying to learn how this rack worked…
I have 2 questions for you and I would really appreciate if you could answer.
Do you remember what was the purpose of the Simmons (and after a Akai) line mixer in the rig ? Was it to connect simultaneously the gp-1000 preamps and the Metaltronix heads ?
Also, in 1989 Zakk Wylde said in that the yamaha SPX 90 that you put in his rack was for the clean sound. But the rack also contains 2 Roland Dep-5 processors. Do you remember what was the purpose of the Roland Dep-5 ?

On Zakk’s rig:
From his wireless system, it plugged into one of our custom splitters that split his signal into multiple outputs that feed all the inputs to the heads and all the preamps,
The the preamp outputs went into the Akai drum mixer, the effects processors were also plugged into the Akai because we could access them when needed for the GP-1000’s. His whole rig was run by midi so we could have a controller at the front of the stage, and one that the guitar tech had so we could make changes at the side of the stage, if zakk was too far from it when changes needed to happen.
The heads channel switching was controlled by a midi switch, so we could change the heads to be in harmony with the GP-1000’s, the Akai was basically a router so we could call up what preamp we wanted on with what head setting.
The system was stereo, so there was always two heads on with at least one Gp-1000 on, there was three GP-1000’s and one was set for clean, one for rhythm, and one for solo’s. The midi also controlled the effects processors so all the different programs could be accessed, and changed for the different songs. The heads went straight to cabs and the Akai feed a 800 watt mosfet power amp into 2 cabs, so all together we feed 4 cabinets with 70 watt celestions, which had to be changed out regularly because he would run the 800 watt power amps way up.
The rig was awesome to hear live and we had two identical systems on stage at important gigs, like the live HBO special,
I was there with master button to switch systems if anything went wrong.

Install Tube Effects Loop on Non Master Volume Amps:
The problem is when you put the loop right after the treble control, the signal level is so high that you compress the send of the loop, you can try to put a 220k -470k resistor in line with the input of the loop circuit. Also every effect handles signal different.

I just got the tube buffered effects loop Dvd in the mail, it shows you putting it into a marshall master volume model, I want to put it into a non master volume marshall with four inputs, can I still do it or do I have to put a master volume in it ? Also can I put this same effects loop in my friends peavey butcher it has a pregain and a post gain.
On placement of loop , that is up to you.
You can put the loop after the Treble control on most single channel Non Master volume Marshall amps. You can also put the loop just in front of the phase inverter on a multi channel amp, So the loop works on both channels.
The mod that I mention earlier, is needed if you install the effects loop any place the signal is hot, like after the Treble control. On the Four Input marshall, I would start with a 220k 1/2 watt. On other amps, the amp probably has a power amp Input Jack, install it there. And of Fender amps I would put it before the Phase inverter (Power-amp). Schematic

Checking Tube Effects Loop:
On the Loop, Unplug anything from the loop, turn the loop off. Play the amp at the volume your going to play at, turn the effects send down to the 9:00 position. Put a guitar cable from the send to the return, turn on the loop set the loops return level so there is no change between the loop being on or off.
Now plug in your Effect and set its controls so there is no difference between the loop being on or off.

The cab Dimensions:
(H) 29 1/4 x (W) 30″ x (D) 14″, They weight about 85 lbs.

Metaltronix M-1000 Blues59 – Changing International Voltages:
On the M-1000, I used a multi tape transformer, so there is not problem getting the different voltages, On the Gp-1000 I used a multi tap on some and a lot I did not, so the only way to know is to look at the transformer, and see if it has (6) input (primary) wires, if it only has (2) your out of luck. I will include a M-1000 transformer schematic, which will be the same for the GP-1000 if it does have the Multi tap. For 240vac operation you would connect mains (input) to the black and the orange wires, and you would tie the white and brown together. I would always use a variac to to power up the amp after changing any wiring to make sure you have wired it right. You can use the heater supply (6.3vac) as a reference.

M-1000 Bias Voltage:
On the M-1000 the plate voltage is so high that I generally just set the bias voltage around -45v for EL34’s and -55v for 6550’s.

I need a little help from you, if that’s possible. I have the Master vol 100W, but at small gigs and rehearsals, I can only run the amp at say number one. Doing this, I lose a lot of gain. Larger gigs, cranked up, it sounds great.
The other lad in the band, has a 50W Marshall, runs it at three for rehearsal, still sounds great. I have read that some people, remove two paired valves and adjust the impedance, to knock the amp down to 50W. My question to you is, is there a mod to add some kind of switch, to take out two valves.

Yes you can,
Of coarse the amp has to be unplugged and dis charged before starting.
On each of the output tubes, PIN 1 goes to ground.
Use a heavy duty DPDT switch, you can use an extra speaker jack hole,
if you don’t want to drill one.
Detach from the two center tubes the PIN 1 from ground.
Put each tube pin 1 to each side of the DPDT switch, put a wire from both center pins of the switch to ground.
So all your doing is grounding and un grounding PIN 1 on the two center tubes.
The impedance isn’t as critical, as long as you have 8 – 16 ohms on the speakers, you”l be fine. If you want the frequency range to be exact, then you need to have the impedance set at half the cabinet impedance.

Impedance Selector for M-1000 / XLS / XLA / VL’s:
On all these amps, we used the same Impedance selector, it is made by Schurter Part # 0033.4032 . Here is a Part Description.

Powering Mr Springgy:
Mr Springgy can be powered by any standard Boss style power supply .Just make sure it has at least 100 ma at 9 – 12 vdc , and the plug is 2.1 mm negative tip.

Mr Spinggy Battery Life:
Mr Springgy® does NOT like a low battery, and will make a High Pitch Squeal and Stop Working,

Battery is “TOO LOW” even if Blue LED is Bright. It is best to power Mr Springgy on a power supply (battery eliminator). Mr Springgy® can drain a battery pretty fast if left plugged in for long periods of time, so unplug after each use.

Mr Springgy Dimensions:
Mr Springgy is 3 1/2″ Wide and 4 1/2″ Long, ands about 2″ to the top of the Knob.

Mr Springgy Operation:
Mr Springgy is quieter than the Fender reverb unit it is recreating, Mr Springgy acts just like the Fender unit, meaning it works in the front of the amp for clean and with a little gain, If you use a lot of gain, then Mr Springgy needs to be in the loop of the amp.

Mr Springgy question:
I have a 59 Bassman LTD 410 combo amp with four inputs. I would like to know if i can make use of both of the pedal output into this amp and get the stero effect? This allows you to use jumper in the four input to make use of both channels. i dont want to try it if it will damage my or my new pedal. I was thinking that all i have to do is slide the internal switch to the left and use both of the pedal outputs to two of the amp inputs.

It is always great to experiment, Don’t worry about hurting the pedal, The only thing that can hurt the pedal is plugging in the wrong power supply,
If you use a power supply, make sure it is a standard (Boss Style) (2.1mm) 9 vdc center tip ground supply. You can definitely use the Main out as a WET only by switching the small switch inside the Mr Springgy. I would use the Dry straight on your main amp channel (#1), and the wet (main) output on the second amp channel (#2), This way you can mix the reverb into your sound with out effecting your main sound.

Effects Chain Line up:
On the effects chain, Guitar – Tuners – to Wha’s – (EQ’s) – Compressors – Distortion pedals – Chorus/flangers – (EQ’s) – Delays – Reverbs – amp The same goes for the Amp Effects loop, except you DO NOT want to put Distortion pedals in the Loop.

Lee Jackson Metaltronix Amplifiers Marshall Fender Modifications and Effects

Lee Jackson Metaltronix Amplifiers Marshall Fender Modifications and Effects

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