popping sound

[hartjr]

I have a 25 yr. old JMF Spectra tube amp that pops (quite loud) only when the standby switch is switched "on", but not when switched off. Otherwise it sounds great. It does "hum" a bit, don't know if that's related to the problem.
I've replaced all the electrolytic caps, swapped tubes and the switch, cleaned the sockets, but no change. Any ideas why it would pop when switched on to standby rather than off, when you would think there would be a power surge?

[imbuedblue]

In certain amps, some pop is normal when switching the standby on. This may be remedied by installing a snubber across the switch.

The pop can also be complicated by poor grounding or a bad solder joint somewhere. If you're hearing a low 60-cycle hum, there are most likely grounding issues.

[Paul P]

In certain amps, some pop is normal when switching the standby on. This may be remedied by installing a snubber across the switch.

My amp also pops quite loudly going in and out of standby (but not with
power on/off). I've been planning to add a .047uf cap to ground at the
standby switch like in a 5F6-A Bassman. Are you saying that I could add
a cap across the switch instead ? Same size cap ?

Paul P

[tubeswell]

My amp also pops quite loudly going in and out of standby (but not with
power on/off). I've been planning to add a .047uf cap to ground at the
standby switch like in a 5F6-A Bassman. Are you saying that I could add
a cap across the switch instead ? Same size cap ?

Paul P

Hi Paul P - I think its more like a 1M resistor

[imbuedblue]

By snubber I meant something like the Mallory Quencharc (Mouser carries these) which is a polyester cap with a built-in series resistor.

But a .047uF 600V cap across the switch should work fine. I've used them to quiet the pops on many old Fender amps.

[Paul P]

Thanks for the info. Here's a data sheet for Quencharcs :

http://www.paktron.com/pdf/Quencharc_QRL.pdf

Paul P

[hartjr]

[QUOTE=imbuedblue;65037]By snubber I meant something like the Mallory Quencharc (Mouser carries these) which is a polyester cap with a built-in series resistor.


Thanks for the suggestion. What size of "Quencharc" would you recommend?

[imbuedblue]

.1uF 47 Ohm 600V

[hartjr]

Thanks, I'll give that a try.