Lee Jackson xla-1000 squealing

[scrimpus]

This amp came to me missing the O.T. so I wired up an old 40 watt O.T. and some old tubes I had pulled from an old organ and it seemed to work ok, so I order a marshall 100 O.T. from here and installed a set of new JJ tubes and now the amp shrieks and squeals and just goes crazy way before if ever gets close to being loud. I have swapped to power tube leads and re-routed the wiring countless times now. Any suggestions or maybe a schematic as i have been unable to find one. Oh, and without the MTA attenuator thingy engaged the amp is a totally useless screaming machine.

[sluckey]

I have swapped to power tube leads

Does this mean you swapped the transformer blue and brown leads? And nothing else?

[scrimpus]

Well the wires are red and brown on this transformer and I have re-routed all the other wiring as much as possible.

[Ritchie200]

When you swapped the red and brown was there any change? Better? Worse?

Jim

[scrimpus]

When you swapped the red and brown was there any change? Better? Worse?

Jim

Much worse if I swap the leads. motorboats like mad with all volumes at 0 with the MTA turned off.

[eleventeen]

It is not the red and brown which get swapped when trying to fix motorboating or shrieking [positive feedback] ...it is the blue and brown. Red gets the highest of the high B+ and that's the single and only place it goes. Blue and brown feed the plates. Blue and brown are either right or wrong. Swap or not.

[scrimpus]

It is not the red and brown which get swapped when trying to fix motorboating or shrieking [positive feedback] ...it is the blue and brown. Red gets the highest of the high B+ and that's the single and only place it goes. Blue and brown feed the plates. Blue and brown are either right or wrong. Swap or not.

Not according to specs given here where I purchased the transformer.
http://el34world.com/Transformers/marshall.htm

[scrimpus]

Well I put the old tubes I had first tested the amp with and it seems to be working pretty much as is should now. It barely functioned with that new set of matched JJ 6L6s but it sounds alright with some old wurlitzer tubes from 1959 so problem solved.sorta.

[eleventeen]

Sorry, you're right. Not the conventional color code.

[Ritchie200]

It came to you without a tranny. Odds are the problem(s) that toasted the original is still there.  Now its time to fill out the voltage chart and dig deeper.

Jim

[scrimpus]

It came to you without a tranny. Odds are the problem(s) that toasted the original is still there.  Now its time to fill out the voltage chart and dig deeper.

Jim

Yeah, I figured there was probably a reason the tranny was gone, voltages seem reasonable except for the bias is way cold, with the bias pot cranked I am getting about 13 watts per tube.

[scrimpus]

I got the tubes biased and its still just a squealing, farting disaster.

[shooter]

a squealing, farting disaster.

how many tubes, starting at V1, do you have to pull to make it quiet?

[scrimpus]

a squealing, farting disaster.

how many tubes, starting at V1, do you have to pull to make it quiet?

Just V1.

[scrimpus]

This thing is a nightmare, any idea where I can find a schematic?

[Ritchie200]

Scrimpus,

You can try to contact Lee for a schemo, but it does not appear he is very accommodating.  It should be pretty easy to sketch something out.  As I mentioned earlier, to help you we really need to see voltages at all the tubes.  You mentioned voltages looked good?  What does that mean?  Based on what?  This is the first step.

Jim

[sluckey]

Can you post some hi rez pics? And provide some background info on the amp. Is this your amp, or does it belong to a friend, or a customer? How long have you had it?

You say it gets quiet by pulling only V1. Have you taken a close look at V1 circuit?