Standby to Operate...thunk and blue flash?

[Normster]

All of my builds to date have always exhibited the same "thunk" and blue flash in the power tubes when switching from standby to operate. I never gave it a second thought since everything seems to works as intended. However, I noticed that a friend's Fuchs-modded Bassman doesn't do this so now I'm wondering, do I have a problem?

[ElectronAvalanche]

Hi Normster,

does your amp do this with different tubes? The blue light in the tubes is normally a sign of gas inside the tube. Once you apply the B+, the gas starts to glow (short explanantion).

Do you have a small cap across your Standby-switch (say 0.01 uF/1000V cap). This will get rid of the "thunk".

Do you have the Standby before or after the first filter section?

Cheers,

Electron

[Normster]

I have the standby switch between the rectifier and the first filter stage. (Same as every Dumble schematic I've ever seen.) I'm not really worried if it's normal. It just seemed odd that the Fuchs doesn't behave the same way as every other amp I've ever built. I checked the Fuchs wiring and it's identical to mine. Maybe Andy knows a few things that I don't.

[Bob-I]

I have the standby switch between the rectifier and the first filter stage. (Same as every Dumble schematic I've ever seen.) I'm not really worried if it's normal. It just seemed odd that the Fuchs doesn't behave the same way as every other amp I've ever built. I checked the Fuchs wiring and it's identical to mine. Maybe Andy knows a few things that I don't.

You might want to put the rectifier directly to the first filters, then the SB next. A .047uF 600V to ground from the rectifier may also help.

[ElectronAvalanche]

Sometimes the Standby switch has dirt inside and this will make a sound.

I built a Fender Vibroclone once and the Stdby would pop. After flicking the switch for a couple of the times the pop was gone.

Do you have a cap across the switch?

I do not think that the Fuchs has some mojo working. It is either your switch, maybe your tubes?

Does your amp do this with different tubes as well?

Electron

[dogears]

Ahhh.... But maybe it does!!! Maybe someone lovingly caressed and modified the circuit through and through......

I do not think that the Fuchs has some mojo working.
Electron

[ElectronAvalanche]

Heya Scott,

of course the audio ckt of a Fuchs has a lot of Mojo going on!

I only meant the Standbye-switch Mojo!

Cheers,

Electron

[Normster]

Thanks for all of the replies. As I said, EVERY amp I build seems to do this. Definately a design thing rather than a bad component. It's not a popping noise as much as a soft "whoomp." As I said, it doesn't really bother me, I just thought it was odd that the Fuchs didn't do this. I'm pretty sure it's just the cap voltage slamming into the power tubes for the first time.

[glasman]

Thanks for all of the replies. As I said, EVERY amp I build seems to do this. Definately a design thing rather than a bad component. It's not a popping noise as much as a soft "whoomp." As I said, it doesn't really bother me, I just thought it was odd that the Fuchs didn't do this. I'm pretty sure it's just the cap voltage slamming into the power tubes for the first time.

I agree with Electron, a small cap across the standby should fix the problem. I had to do this with my personal amp.

Gary

[dogears]

Hehe... I was just sayin' that the mod spent some time in the 'doghouse' for some hand tuning! LOL

Heya Scott,

of course the audio ckt of a Fuchs has a lot of Mojo going on!

I only meant the Standbye-switch Mojo!

Cheers,

Electron

[v00d00blues79]

Heh... My '65 Bandmaster does the same thing when its taken off of stand-by... I never even gave it a thought... =)

[Normster]

I'll give the cap a try. And I guess I forgot to mention the Fuchs was tuned by Dogears. (Killer sounding amp, BTW.)