2nd Generation ODS first power up issue! (Resolved)

[Guitarman18]

Having just completed my first new build in 5 years ( I've been tweaking my 6 other ODS's in that time), I noticed something unusual on first power up and was hoping that someone might know what is going on and help me find a cure.

I should point out first that all voltages are within ball park and it works, except;

When switching from clean to OD there is sometimes a loss of power- it sort of fades out a little/a lot. What concerns me though, is that when I put probe between V1b plate and the coupling cap, there is a pop (as expected) but it seems to 'clear' the fade out. The sound comes back to full strength and works as I would expect again.

It feels as though there is a charge buildup somewhere. Some DC leaking maybe?

Has anyone had a similar experience and if so where should I start looking.

As always, any help would be greatly appreciated.

Cheers,

Paul.

[xtian]

This sounds like a preamp grid that is not referenced to ground. Missing or incorrect grid leak resistor. The triode will work for a while, sometimes, and then it will float away, and stop working.

[Guitarman18]

Thanks for the suggestions xtian.

I have gone through the preamp and reflowed all the solder joints, hoping that might solve the issue, but it hasn't sorted it out.

As far as I can see the grids are referenced to ground. Could it be an internal pot issue, where the wiper is not making secure contact?

The issue only seems to show up when switching channels, sometimes.

I'll have another look tomorrow.

Cheers,

Paul.

[Structo]

Double check pot values total and sweep.
Not a bad idea to inspect all values unless you do that pre assembly.

I had a NOS 1M Allen Bradley pot that was defective.
Probably the only part I didn't meter out.

[Duble]

This sounds like the grid on one of the (3rd?) triodes is getting too much signal. It will make the signal fade in and out. Is the clean working properly? Does this do this no matter what you're on? Maybe post a pic and someone here can help?

[Guitarman18]

Hi Tom,

I hope you are well!

Like you, I try to check each component before installing, but something may have slipped through the net on this occasion.

I will check the pots to see if they give me a full sweep.

Duble,

Thanks for the suggestion. That could explain why the issue only appears when switching channels. If left in clean mode it seems to be perfectly happy, but when switching the 4th or 5th time back and forth leaves the clean and or OD signal weak. It's a sudden drop, rather than a gradual change, until I put a probe on V1b plate/CC junction to clear it. If that doesn't work, then V1b's cathode ground point works instead. Very curious.

I'll post some pics later.

Cheers,

Paul.

[Guitarman18]

Some photos (Updated Photos-better quality!)

[Guitarman18]

Thanks for all responses. It seems as though the issue is now resolved.

I'm not absolutely sure which single remedy solved the problem, but I did notice that one of the wires from PI tube socket to grid resistors' solder joint had too much sleeve attached, which may have caused a less than perfect connection.

Also, removing some more paint off the chassis, around the MV pot seems to have fully resolved the problem.

Once again thanks for all the help.

Cheers,

Paul.

[M Fowler]

It is a great looking build

[Guitarman18]

Thanks M Fowler,

I'm really liking the new tones available from this 2nd Gen build. I particularly like the transition from clean to OD. It's basically the same tone, but with more 'hair'. Nice!

Cheers, Paul.