H folks,
my son's got an used Engl Fireball 60 watts guitar head. It sounds quite good, but has a microphony issue: At Gain cranked fully up, the amp starts to squeak and howl when Ultra Gain is pushed and Master 2 is turned half way up.
This amp features four ECC83 (V1-4) and two 6L6GC (V5, V6) tubes. It came with two J/J ECC83S frame grid tubes as V1 and V3, and two ECC83 of unknown origin as V2 and V4, respectively. Swapping these four tubes lead to the same results, at the best, but those of unknown origin gave more noise and more microphonics at V1 (first tube) position. Replacing V1 by one of all the other ECC83's, or 12AX7's, or E83CC's that I have laying around, didn't solve the problem, even a military grade SYLVANIA JAN12AX7WA was even worse (very much noise and microphony). What's the fault with this amp?
Best regards!
my son's got an used Engl Fireball 60 watts guitar head. It sounds quite good, but has a microphony issue: At Gain cranked fully up, the amp starts to squeak and howl when Ultra Gain is pushed and Master 2 is turned half way up.
This amp features four ECC83 (V1-4) and two 6L6GC (V5, V6) tubes. It came with two J/J ECC83S frame grid tubes as V1 and V3, and two ECC83 of unknown origin as V2 and V4, respectively. Swapping these four tubes lead to the same results, at the best, but those of unknown origin gave more noise and more microphonics at V1 (first tube) position. Replacing V1 by one of all the other ECC83's, or 12AX7's, or E83CC's that I have laying around, didn't solve the problem, even a military grade SYLVANIA JAN12AX7WA was even worse (very much noise and microphony). What's the fault with this amp?
Best regards!
For general tube guitar amp repair read Tube Amplifier Debugging Page
squeal is item 4. Don't neglect to read the safety page about not killing yourself electrically.
squeal is item 4. Don't neglect to read the safety page about not killing yourself electrically.
It may be oscillating rather tham becoming microphonic. Something to consider.
But first, make it do it, now without touching the amp, turn the guitar volume to zero. Does it stop? Can you get it to do it with no guitar plugged in at all? Also, when it does this, does turning side to side - that is, facing the guitar diferent directions - change anything?
Another test, make it do it. Now while it is making the noise, reach in and firmly grasp each tube. If they are too hot for you, use a rag or a glove. If holding on to any one stops the noise, you have discovered a microphonic stage. Might be the tube, might be something about the socket.
But first, make it do it, now without touching the amp, turn the guitar volume to zero. Does it stop? Can you get it to do it with no guitar plugged in at all? Also, when it does this, does turning side to side - that is, facing the guitar diferent directions - change anything?
Another test, make it do it. Now while it is making the noise, reach in and firmly grasp each tube. If they are too hot for you, use a rag or a glove. If holding on to any one stops the noise, you have discovered a microphonic stage. Might be the tube, might be something about the socket.
might be a power supply issue. how old is it? may need a cap change. and if the valves are old, change them and have it re biased. I did experience a feedback problem when changing V1 for a sovtek and electro harmonix. my only guess is, the bigger plate picked up more from the out put transformer, if possible, try and get some shields for the valves.
The squeals occur even with no guitar plugged into the amp. And they start at higher Master 2 settings if I grasp the first tube. So I'm quite sure that this tube must be the cause of the trouble. But I'm irritated by the fact that literally each tube I plug into it's position leads to the same effect, at the best. Some of them are even more microphonic, some are noisier. The best tubes from my stock show the same amount of squealing as the original V1 tube does.
Best regards!
Best regards!
can you have a look at the tube socket,perhaps there is a bad soldering point or so what...........
Yes, I'm familiar with tube amps. Sometimes I build one myselves.
I've had the chassis dismounted from the case yet to get easier acces while swapping the ECC83's.
Best regards!
I've had the chassis dismounted from the case yet to get easier acces while swapping the ECC83's.
Best regards!
I would say check the voltage levels at all of the HT points, and it might not hurt to check the anode voltages to get an idea if any valves are off. also if you have an electro harmonix 12ax7 try it in V1 if you havnt already, that cleared up my problem which sounds very similar to yours.
other than that, it may be worth changing the filter capacitors in the power supply
other than that, it may be worth changing the filter capacitors in the power supply
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