5f6a loud pop switching on

[sapi]

My tech has finished my Fender Bassman RI LTD conversion to Hoffman board ptp and MM op tranny.

I got a chance to try it out today and it sounds great. Notes seem to bloom better, there's no harshness on the highs and it's warmer/sweeter, more 'vintage'. It's also louder and i could get some nice feedback.

The problem: a 'pop' sound switching on from standby. It's loud and annoying. It is only there the first time the amp is switched on. If it's switched off and on again (from standby) it won't do it. Lowering the volume is no help.

Also noticed there's a slight delay from the time you flick the switch on and the pop. Just slight but noticeable. The old cap board has some resistors on it, maybe they were there for the same reason?

The wiring has been checked and re-checked and the grounds are properly separated at their respective points on the board, 3 points if i remember well. The bias is 35mA.

Do you think a suppressor on the standby switch would help? My other slight concern is a blue-ish glow on one of the tubes. It flares up when the amp is turned on from standby. The op tubes are very good quality Jan Philips 6L6's from Watford, less than a year old.

I'm not an amp tech myself, i have a tech background, i'm just trying to find out.
Any help would be greatly appreciated. Thanks in advance,
jo

[MWJB]

Firstly, the blue glow is nothing to be concerned about.

"The old cap board has some resistors on it, maybe they were there for the same reason?" These are the smoothing resistors for the totem pole filter caps at the main B+ & screen supply...there should still be 2 of these bypassing the series main B+ filter caps? The screen supply may be handled by just one 500v cap and may not feature the 220K resistors.

How loud is it...as loud as a note at gig volume, or just loud enough to annoy you?

If the main filters have been wired to the rectifier side of the standby switch, then a pop on turn on is common. Wiring tham like this gives the rectifier an easier life.

Does the standby have the 0.046/630v cap from rectifier side to ground?

Tried a new switch?

[sapi]

Firstly, the blue glow is nothing to be concerned about.

"The old cap board has some resistors on it, maybe they were there for the same reason?" These are the smoothing resistors for the totem pole filter caps at the main B+ & screen supply...there should still be 2 of these bypassing the series main B+ filter caps? The screen supply may be handled by just one 500v cap and may not feature the 220K resistors.

How loud is it...as loud as a note at gig volume, or just loud enough to annoy you?

If the main filters have been wired to the rectifier side of the standby switch, then a pop on turn on is common. Wiring tham like this gives the rectifier an easier life.

Does the standby have the 0.046/630v cap from rectifier side to ground?

Tried a new switch?

Thanks MWJB ;-) My tech had already tried a .047uF from standby to ground and it did not help so he took it off.

Now what happened...

Yesterday i tried to give the amp a burn in of some sort, if that makes any sense. When i came back from rehearsals i put it on again.

GUESS WHAT? No pop. I tried again several times. Nothing. Today, hardly noticeable. One tube flares a bit blue-ish on switch on, but i don't think that should be worrying. Maybe the filter caps needed settling in? I'll keep my fingers crossed.
Cheers,
jo

[sapi]

Unfortunately the amp developed a new symptom.

It started like this: When i switched on the standby there was a crackling noise. Then when i plugged and played, the same. It was a crackling, hissing noise, a distortion on top, so when i hit a note you hear the note and the crackling and then decayed into a distortion superimposed on that note.

The tubes are good quality from Watford and not even a year old. Anyway I replaced all of them to check, and all it did was remind me how crappy sounding the stock ones were! So the tubes are ok.

The amp has been running for quite a while now and quiet. But just before that, playing a low bass note induced the crackling. I played around with the knobs while that was going on and it did nothing, except for the vol controls, which made the noise louder/more pronounced.
It's like something is shorting out. At times the noise was there even without playing. Actually i noticed it's more liable to do it on start up, or playing that bassy note. The volume has to be turned up to hear the noise, so it seems the problem may be in the pre amp stage, not the op?
Any help would be greatly appreciated.
Thank you,
jo

[tubeswell]

Hmmm.... crackling, hissing and popping can be symptoms of bad output tubes. Does it go away if you swap the output tubes?

[sapi]

No, i put the stock ones and it didn't help.

[Enzo]

Did you PAY for this conversion? The amp was rewired, and now that you have it home, it has issues and is not 100%. Take it back to the tech, tell him the tone is now great, but the amp is not quite right, would be straighten it out please. Give him a detailed description of any issues the amp has now or did have.

[sapi]

I could not believe it. But at least a happy ending ;-) my tech shortened the wires as much as he could and the amp has been running fine now, and no 'pop' at all

[Bruce / Mission Amps]

I could not believe it. But at least a happy ending ;-) my tech shortened the wires as much as he could and the amp has been running fine now, and no 'pop' at all

And probably now soldered where they weren't!

[capnjuan]

... and maybe cleaned the tube sockets ...

[sapi]

... and maybe cleaned the tube sockets ...

er... no i had taken care of that personally ;-) and new amp anyways

[capnjuan]

Glad it's working well!