sound comes back for a moment after standby turned off

[matt h]

(deleted)

[pdf64]

My theory is that this is simply the amp draining the filter caps, all of which are located after the standby switch

I don't think it's good practice to arrange a standby switch so that a capacitive load can be connected to a hot tube rectifier, as the switch on current surge may exceed Iap (750mA) http://www.mif.pg.gda.pl/homepages/fran ... g/GZ34.pdf

Regarding the quirky sound level fade, it may be to do with the ratio of cap values for the bias supply, plate B+ node and screen grid B+ node.

[Reeltarded]

^^^^^ that first point.

[Stevem]

In a build with a recto tube I much prefer to have the standby switch after the first filter node as this greatly limits the shock of UF load that the recto see`s when the switch is thrown and the other nodes get powered up.

[SilverFox]

What about a Semiconductor Diode. I wired my standby between the first node and the HV so there is nothing on the caps when in Standby Mode. It seems as though this will result in a max inrush but that's not supposed to be an issue with semiconductors?

Silverfox.

[pops]

When you turn on your amp you turn on the on switch then the standby, when you turn off your amp do the same the on switch first then wait the same 30 seconds or so to turn off your standby, it will bleed the caps. That is the way i learned to turn the amp on and off.

[pdf64]

The best use for a standby switch is not to use it!

[TUBEDUDE]

+1 on the no standby switch!

[hans-jörg]

Hi,
I have my STB switch always with DPDT in front of the (tube)rectifier and switch both AC lines. I think its a save way to use such a switch.

Best

Hans-Jörg

[pdf64]

I have my STB switch always with DPDT in front of the (tube)rectifier and switch both AC lines. I think its a save way to use such a switch

It's safe, as there's little risk of personal injury.
There's an advantage of switching ac, there's less chance of an arc being sustained as the switch is opened, as it will tend to self extinguish.

But that arrangement still results in hot switching of a capacitive load (bear in mind that it's the same current either side of the rectifier).
And the switch is probably being exposed to voltages significantly above its spec.
My understanding is that the surge currents standby causes are stressful to HT fuses, Si rectifiers and the B+ caps, eg 1 amp diodes in a FWB arrangement occasionally fail in higher voltage amps with big reservoir caps.
I think that standby was introduced in late tweed era with the larger 5F* amps, so it got cloned by Marshall.
Maybe time in military service exposed guys to radio transmitters etc with standby, so the feature got copied over, perhaps to provide a warm fuzzy feeling of mil standard quality.
I guess that the mute function that standby provided was handy, and once the switch-on ritual (as described above) became ingrained, standby has become a user expectation.

[Structo]

When you turn on your amp you turn on the on switch then the standby, when you turn off your amp do the same the on switch first then wait the same 30 seconds or so to turn off your standby, it will bleed the caps. That is the way i learned to turn the amp on and off.

I do it similarly.

I turn on the power, the the standby switch after about ten seconds.

When I turn off the amp, I simply turn the power switch off.
That way the standby switch only sees high DC voltage when switched to play.

So half the DC power cycles are eliminated.

Also having the balancing or bleeder resistors on the first filter caps, helps things as well.

I like the Dumble method of putting the standby switch after the first reservoir caps (Main B+ supply caps)
Puts a bit less stress on the amp when turning on.

[Merlinb]

My theory is that this is simply the amp draining the filter caps, all of which are located after the standby switch.

My guess is it is caused by a difference in the rate at which the bias supply voltage collapses, compared with the HT voltages.

[Reeltarded]

I bet this amp gets louder if you slam a chord and pull the plug too.

[TUBEDUDE]

If extra switches give a sense of relief, joy or safety, rock on. Even though they are as necessary as the plastic Jesus sittin' on the dashboard of my car.

[Gaz]

My theory is that this is simply the amp draining the filter caps, all of which are located after the standby switch.

My guess is it is caused by a difference in the rate at which the bias supply voltage collapses, compared with the HT voltages.

Anything that can be done to alleviate this?