2204 clone gut job

fitz said:
Got it in the shell and put it through some paces.
Everything seems to be working the way I'd expect.
I hooked up the Boss board because it can be problematic with some amps, but it's working fine.

View attachment 112091

Even with the NS-2 off, the drive pedals out front & EQ in the loop aren't too bad with noise.
With the gate on, the whole set up is quiet.

View attachment 112092
Click to expand...
And it looks great!
 
fitz said:
Never had 3 preamp tubes fail simultaneously from sitting in a box for a week.
Last thing I would have suspected.
Click to expand...
Well, that was a helluva ride!! Frickn mind blowing too! I bet the feeling of relief is overwhelming. Hell… I’m going to have a beer in your honor… :cheers:

Just for clarification: Are we all sure that all three of the original preamp tubes are no bueno?
 
syscokid said:
Well, that was a helluva ride!! Frickn mind blowing too! I bet the feeling of relief is overwhelming. Hell… I’m going to have a beer in your honor… :cheers:

Just for clarification: Are we all sure that all three of the original preamp tubes are no bueno?
Click to expand...
Yes, I made sure.

After I put in the other 3 tubes and made sure everything was working, I swapped each of the 3 suspect tubes into V1 and confirmed that they are non- functional.
Those JJ 803S long plates are my favorite preamp tubes - I'm going to have to buy some more...

The thought of trying different tubes crossed my mind more than once.
I just kept telling myself, no way all 3 went toes up at the same time...
 
fitz said:
Yes, I made sure.

After I put in the other 3 tubes and made sure everything was working, I swapped each of the 3 suspect tubes into V1 and confirmed that they are non- functional.
Those JJ 803S long plates are my favorite preamp tubes - I'm going to have to buy some more...

The thought of trying different tubes crossed my mind more than once.
I just kept telling myself, no way all 3 went toes up at the same time...
Click to expand...

That's crazy. Do you think something that wasn't right before caused them to fail?
 
DirtySteve said:
That's crazy. Do you think something that wasn't right before caused them to fail?
Click to expand...

They almost undoubtably got taken out by a common cause. I speculated in post #75:

PelliX

Post in thread '2204 clone gut job'

67plexi said:
I will never use Belton tube sockets had the octal ark between the pins switched to mil spec ceramic tube sockets
that was a hard issue to troubleshoot
Click to expand...

I had to read that a couple of times to figure out the punctuation. What was the potential between the two affected contacts?

fitz said:
Perhaps they got fried the last time I tried to use the amp.
It was giving me trouble and doing strange things.
Click to expand...

... this would at least dovetail with what we're seeing here, yup. Potentially heater/cathode insulation (or other) breakdown on V2 leading to a condition taking out all preamp valve...
  • Like
  • Love

Either a breakdown in one of the preamp valves leading to a short which exposed the heater circuit to high voltage or an auxiliary factor causing pretty much the same. There's no heater elevation in this amp so the h/k insulation of V2 (cathode follower) gets stressed.

Pro-tip for those reading at home, you can check a valve filament with a regular multimeter. Set it to resistance (or continuity) and check that the heater pins all connect to each other. On a noval like these that's pins #4, #5 and #9. If those read open circuit, the filament is done for. This holds true for any 5 or 6.3V heated valve more or less.
 
Who knows right?
PelliX said:
Either a breakdown in one of the preamp valves leading to a short which exposed the heater circuit to high voltage or an auxiliary factor causing pretty much the same.
Click to expand...
It is such a weird failure to have all three preamp tube heaters open at the same moment, even the same moment is a guess.
It would be very hard to repeat.
 
Well, here's what we know; they seem to have all failed roughly at the same time when the amp was exhibiting problems. Given that the filaments are destroyed, there must have been excess voltage on the circuit. The output valves do not seem to be affected. I haven't tested this en masse but the filament of an EL34 or such is a little beefier - this might be why only the preamp valves failed. Maybe the fuse was just in time for the output valves but too slow for the lighter heaters in the preamp. The voltage has to come from somewhere, though it doesn't take much to destroy the unregulated filaments. Heater/cathode short seems a likely candidate, the cathode follower on V2b. That's my best shot based on what I know.
 
You must log in or register to reply here.
Back
Top