Line 6 Bogner Spider Valve Fault - Dying tubes?

[pdf64]

Have you tried the new power valves yet? Sorry, I’ve tried going back through the thread but can’t find whether that had been done.

[Sosijdog]

No not yet, that may well be the next step as every other thing seems to check out ok....

I did a few tests previously that i thought did not point to a single tube. The interference was on both outputs from the power tubes. I thought it would be unlikely to have the same failure at the exact same time. But again perhaps my flawed thinking has steered me down a road to nowhere.

I will try and replace the tubes and take it from there. That would also rule out tube faults.

[maxkracht]

Not sure what the mechanism would be for your problem, but any time I see tubes mounted on a PCB and an intermittent problem, I reflow the solder on at least the power tube sockets. Chopsticking or wiggling the tube will not always point out a cold joint or hairline crack. Might be worth sucking out all the solder and starting fresh if it is lead free and your joints come out gray and dull. Use plenty of flux and be careful not to lift traces. Keep a lookout before and after for hairline cracks where the solder pad meets the trace/soldermask.

[Phil_S]

I do however have the fault at both pins 1 & 6 even with the PI tube pulled.

Progress! As I read the schematic, this suggests the problem is coming from V_B+E. That goes back to the filter caps at the upper right of page 9. These should be relatively cheap to replace. You might just reflow the solder on them. FWIW, I like what pdf64 and Max say. Both of them know more than I do. I'm also curious to see what you find at TV4 and TV5.

[pdf64]

Right, when I first heard it I thought it most likely to be a bad power valve, replacing those would be my first move

[Sosijdog]

Thanks again guys for all your input.
The first thing i did was to resolder the tube sockets but with no improvement.

As for the V-B+E Phil, i have already probed to the B+ side of the resistors and there was no interference there... I was on the same train of thought as you but, with absence of interference on that line and good ESR readings, i kind of ruled it out.

I guess i will try the new tubes and see what happens. If nothing changes then nothing is lost, just another part of the diagnosis steps checked off. If it works then great. Loads of experience gained AND a working amp.

I will give it a go tonight.

[Sosijdog]

Well after weeks of testing and chasing a fault the amp is finally fixed!
The new tubes have solved the issue.
The only terrible noise coming out of it now is when i play through it!

I really should have taken heed of my gut instinct. I suspected the tubes initially and its even in the title of this thread!

I wanted to test to make sure it was the tubes but then got myself into believing it wasnt a tube fault due to the interference on both tube outputs.

The tube is the weak link and i know they are prone to go faulty. Even striking the top of the amp cured the fault - like a bad connection...

Anyway- the amp is fixed! Thanks to all you guys who commented to try and steer me in the right direction, even though i was going wrong.

But i hope this thread may be useful to someone else who has a similar issue.

Thanks again.
Stevo