Tube AMP problem! Please help me.

  • Thread starter Thread starter AngeloG.
  • Start date Start date
I'll throw this in 'cause no one has said it yet:

You mentioned you removed a circuit board. That means you are inside the chasis... BE AWARE THAT THERE ARE LETHAL VOLTAGES IN THERE. LIKE IN THE NEIGHBORHOOD OF 400V!!! You say you study electronics, so if you know what you're doing, fine. If not, you're messing with dangerous stuff. Just 'cause it's turned off, or even unplugged does not necessarily mean the dangerous voltages are gone depending on the design of the power supply. Be very, very careful!
 
Thanks for the warning man, I was pretty careful. I tried what I could, I am going to replace every tube on the amp, then if nothing works, I will try to look for cold joints. Oh, and the noise didn't stop after 1 hour of working, I don't know if it needs more. The room was at ~15C when I turned it on, I don't know if that's enough..
 
I will try that arcaxis, and I will report back. I also happen to have the schematics, thank you very much :)
 
I removed all the tubes and powered it on. No sound-hiss is coming out. Does that mean anything? Also, running a cable from "Send" to another amp makes no noise. I will now try to place back the tubes and plugging a cable on the return one.

EDIT: Okay, verdict.

Tubes off, no cables = No noise or sound.
Tubes off, cable on send = No noise or sound.
Tubes off, cable on return = No noise or sound.

Tubes on, no cables = Noise & sound.
Tubes on, cable on send = Noise & sound on both the main and the secondary amp.
Tubes on, cable on return = Noise & sound remain.
 
Last edited:
EDIT: Ooops, mis-read...

Sound like you've isolated it to the preamp section.

Try gently tapping the preamp tubes and see fi that has any affect.
 
LDS said:
EDIT: Ooops, mis-read...

Sound like you've isolated it to the preamp section.

Try gently tapping the preamp tubes and see fi that has any affect.
Click to expand...

I will try that right now.
 
No variation on the sound tapping either on the preamps or the poweramp tubes.
 
Man, you are taking the long road around on this thing.You really shouldve checked the tubes first because almost without fail a microphonic preamp tube will be the cause of any strange new noise you may encounter.Very easy to check for.
With all tubes in and nothing plugged into the amp turn the amp on and turn the volume up.With a pencil or light wooden dowl gently tap each tube(power tubes as well).If you can hear the tap amplified through the speaker then the tube is microphonic and should be replaced.This may or may not be your problem but it is the best place to start your search.
Sheppard
 
Just replace the damn tubes already! If you don't know what you're doing you can actually cause the tubes to fail by tapping on them.
 
SHEPPARDB. said:
Man, you are taking the long road around on this thing.You really shouldve checked the tubes first because almost without fail a microphonic preamp tube will be the cause of any strange new noise you may encounter.Very easy to check for.
With all tubes in and nothing plugged into the amp turn the amp on and turn the volume up.With a pencil or light wooden dowl gently tap each tube(power tubes as well).If you can hear the tap amplified through the speaker then the tube is microphonic and should be replaced.This may or may not be your problem but it is the best place to start your search.
Sheppard
Click to expand...
Noted, I will try it.
ocnor said:
Just replace the damn tubes already! If you don't know what you're doing you can actually cause the tubes to fail by tapping on them.
Click to expand...

Eeeeasy there, I'm in no rush. No one is forcing you to wait ;) I don't have 100$ to spare for something I'm not sure. Thanks.
 
Tapping on the tubes does not change anything to my experience.
 
I bought one new pre-amp tube, swapped it with all the 3, nothing changes.
 
No difference with gain knob at 0, it's so annoying! I will take another look on the pcb and I will post again.
 
Behold..After scrubbing for a couple of hours, I found out the source of the noise was a cable being a bit bigger than the contacts and making sparks. I feel so stupid. And lucky.
 
Cable going from the power tubes to the main board! Glad you helped me! Big thanks.
 
I have the same amp and had a similar problem. What I discovered was the ground to the high gain input jack had a cracked connection and was intermittent. I opened the amp up and cleaned up the old solder and resoldered all of the input connections.
These are a China built amp with the connections all on circuit boards-vibrations from the speaker had eventually cracked loose the connections. If you have any more trouble you may as well look into this as well.
 
AngeloG. said:
Cable going from the power tubes to the main board! Glad you helped me! Big thanks.
Click to expand...
great ..... that's good news.

BTW
Lt. Bob said:
they have multi connectors between circuit boards inside the amp. Those connectors get flexed by the weight of the cables bouncing around as you move the amp.

..... any of those connectors inside the amp could concievably just need reseating. You unplug them ..... maybe use a little DeOxit to clean them and replug them.

.
Click to expand...

:D
 
Anfontan said:
I have the same amp and had a similar problem. What I discovered was the ground to the high gain input jack had a cracked connection and was intermittent. I opened the amp up and cleaned up the old solder and resoldered all of the input connections.
These are a China built amp with the connections all on circuit boards-vibrations from the speaker had eventually cracked loose the connections. If you have any more trouble you may as well look into this as well.
Click to expand...

Yes, it's funny because the sound the connector made with the contacts when you jiggle it a bit was exactly the same even without any power running through it, that's how I found it. Hehe!
Lt. Bob said:
great ..... that's good news.

BTW

:D
Click to expand...

Hehehe you had the right idea all along! REP ;) Thanks all.
 
arcaxis said:
Yup, Lt. Bob is the winner on this one :D

Different subject...... have you changed the speaker in that amp? I have the same amp and I've thought about swapping the speaker out for something else. Just not sure what I might try.
Click to expand...

I haven't changed the speaker, but sure, I've thought about it. What kept me back is what would I look for on a new speaker? I have no experience in amp speakers so I wouldn't know the difference. Anyone here has an idea what a speaker would change, and how much?
 
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