troubleshooting bought trainwreck clone

[eleanor296]

hey there!
Been lurking for a while over here, but been pretty active on SEwatt.com (Dana might maybe know me from over there?).
Anyway, I just acquired an Express clone that's been built from a Ceriatone kit. The previous owner said that Moose wired it up for him 2 years ago.
The problem I have is a very, very noticeable hiss, becoming louder when I turn up the volume. Another symptom is that the hiss disappears and turns into a hum when I turn the guitar volume all the way down.
The amp itself sounds from very ok to great (haven't had a chance to blast it through a nice cab yet).
Sorry, I can't supply pics right now, but I will try to get a camera early this afternoon.
Any pointers though as of right now?
My un-experience tells me that it's probably a grounding issue? (probably not hehe). Maybe this project is just a little over my head, but it'd be nice if you guys could help me out. After all I didn't know the amp was humming/hissing at the time *sigh*

Thanks already guys!
~Andy

[eleanor296]

I tried replacing all the preamp tubes, still nothing changes.
The noise seems to vary as the volume is turned up, about 1/3 up I get a high frequency noise, and there seems to be a lot going on in the high frequency range anyway (sounds like a tv turned on, only higher pitched and much much louder, though almost inaudible if that makes sense.... a lot of pressure on the eardrums.)
Weird... *sigh*
Guess I'ma see if I can get my money back

[Phil_S]

It is not unusual for the guitar to introduce hum to an amp. That is guitar related (or pickup related) and not amp related. A pretty sure way to establish this is to reposition the guitar in relation to the amp to find a spot where it doesn't hum. Just stand up holding the guitar and slowly rotate yourself in a circle. See if you can find the "spot".

Does it hum when you have nothing plugged in?

Hiss is common in high gain amps like the Express. Sometimes, they just seem to work out that way. Other times, you can find a way to reduce the hiss.

For starters, let's try to establish if the amp is responsible for the hum. If it's not then we have one less problem to address.

I suspect you are confused. Hiss and hum are typically two different kinds of problems.

[eleanor296]

The amp *hums* when the guitar volume is all the way down.
The other noise occurs when the guitar volume isn't closed.
I "hear" the presence control being turned.
TMB doesn't make any noise except that the buzz/high frequency noise gets louder.
The guitar is ok. Tried it with both my strat and Schecter. Same thing. Tried different outlets in different rooms. Same thing.
The higher I turn the volume the louder the noise gets and it seems like more "frequencies" are added if that makes sense.
Could it be that one of my EL34s is bad?
I noticed that, the further I turn up the volume , the brighter the inside (filament?) of one of them gets. It's not orange like the other one, but almost yellow in the middle.
The other one stays the same color.
Guess I'll have to get a set of EL34s?
Thoughts?
It seems like that should be it... never noticed anything like it.

[CaseyJones]

Chopsticks... they're not just for Chinese take-out anymore!

They're also useful for Malaysian amps...

The amp *hums* when the guitar volume is all the way down.

Is there a 1 meg grid leak from the V1 grid to ground? If not stick one in there. Without a point of reference (the 1 meg resistor) the first preamp stage will amplifiy whatever noise and hum is available.

Real Trainwrecks don't use a grid blocker although a 33k between the input and the preamp grid can eliminate a lot of noise on an otherwise troublesome clone.

The other noise occurs when the guitar volume isn't closed.
I "hear" the presence control being turned.
TMB doesn't make any noise except that the buzz/high frequency noise gets louder.
The guitar is ok. Tried it with both my strat and Schecter. Same thing. Tried different outlets in different rooms. Same thing.
The higher I turn the volume the louder the noise gets and it seems like more "frequencies" are added if that makes sense.

Your amp is oscillatiing. It's easy to see on a 'scope, poke your probe in a number of insertion points and there wil be "hash" there. Your amp is acting more like an oscillator and less like an amplifier although obviously it will do both, they're very similar circuits.

Simply put an oscillator is an amplifier with positive feedback

Changing your tone controls changes the tuning (resonant frequency) of the oscillator.

It's a matter of figuring out what is crosstalking (your positive feedback. Regenerative oscillation) and moving those wires so it doesn't crosstalk. That's why "they" say this design is "on the edge".

Could it be that one of my EL34s is bad?
I noticed that, the further I turn up the volume , the brighter the inside (filament?) of one of them gets. It's not orange like the other one, but almost yellow in the middle.

It may not be bad yet but it will be if you let the amp keep doin' what it's doin'. Worst case scenario... the amp is oscillating wildly. It likely will oscillate at a supersonic frequency, that means you won't hear it. You're probably seein' your screen grids lighting up. If it was just a little worse the tubes might red plate.

Guess I'll have to get a set of EL34s?

Not yet. Sort out the other problems before you cook a fresh set of tubes.

Thoughts?

You got 'em!

It seems like that should be it... never noticed anything like it.

Yeah but... I think you're seein' the symptoms not the problem. Fix the problem and the symptoms go away.

[eleanor296]

okie dokie then
chopsticking it is.
Arrrgh...
first timer for me.
I'll report back on how it goes.
It's just weird cause the owner said the amp was working fine before he shipped it.
So I figured it was the tubes.
Especially seeing as to how he told me the amp was wired by Moose.

See you guys soon with results!

~Andy

[C Moore]

We have 25-30 amps. Our "TW Clone" was the only one that ever gave us any of these kinds of problems. It was rather amusing to our amp techs. We could not afford their shop time to fix such a time consuming problem. But with their guidance this is what I did.
Played around with all the heater wires and whatever other kind of wire runs between the pre tubes. Up, down, in, out and I just kind of magically got rid of all the noise that might be called hum or hiss.
Speaking of pre tubes, V1=5751 V2=12AX7 V3=12AT7.
Changed the input resistor to 69K.
The presence knob was a complete F'ing, oscillating nightmare. I wanted to beat it to death with a hammer (some say I have a temper). Took off whatever cap was there and put in a 0.68uf. The previous sound of a pig screaming for mercy completely vanished.
I am nowhere near being an amp tech. I have given the best and most accurate description as I know how. What amazes me is that I have seen MANY of the same amp that had either NO problems; or amps with the same problems that were cured with VERY different changes.
I no longer envision Ken Fischer as an amp tech. More like the guy from a 1920's tent show that was somehow able to wrestle alligators and keep wild beasts at bey with a whip and a chair.
Good Luck

[tubetek]

"I no longer envision Ken Fischer as an amp tech. More like the guy from a 1920's tent show..."
Or Nikola Tesla; a true wizard able to do things people still can't figure out even long after his "departure from this plane"

[CaseyJones]

More like the guy from a 1920's tent show that was somehow able to wrestle alligators and keep wild beasts at bey with a whip and a chair.

Ooh, so close. Try a preacher from a tent revival or a medicine show. White shirt, string tie, Apache arrowhead tie clip. Able to heal with the laying on of hands. 'Course first you're gonna have to roll around in the dirt speakin' in tongues!

[Lonely Raven]

Or Nikola Tesla; a true wizard able to do things people still can't figure out even long after his "departure from this plane"

He's my Hero...true story.