Standby

[Super_Reverb]

Read some info on R. Kuehnel's site regarding standby switches being glorified mute switches. His claim is they are not really needed in tube guitar amps, that they have been copied ever since Adam and Eve discovered thermionic emission and built the first amp, and essentially poo-pooed the idea that standby mode is needed to allow heaters to bring cathode up to temp prior to application of plate voltage.

So... Whaddu you think?

Personally, I like the standby option. He also had some good circuit ideas. One idea I liked was half wave rectifying the heaters (h/c Si diode in series with heater winding) in standby. His claim was extended tube life resulting from lower filament current. So, the standby switch would need to be double pole in order to connect rectifier(s) to the 1st filter cap and also to short out the series diode in heater circuit.

cheers,

rob

[Structo]

Interesting.

Is this what you are talking about?

That does seem like a good idea.

Also if your heater voltage is a bit high you can drop it by .7v with a single diode in series with the heater wiring.

[M Fowler]

From what I have read the standby switch is not needed and I would really like to stop putting them in my amps.

[Alexo]

I happily don't use 'em.

Besides, if you're using certain rectifiers (GZ34, for one) they won't hit your tubes with high voltage until after they've warmed up.

...the one exception where I do want a SB switch is in an amp with a very high B+, and you may not want to hit your caps with it before your tubes heat up enough to draw your voltages down -- but then you (and by you, I mean me) should really just use higher rated caps..

...or an SS rectified amp with a giant filter cap, several hundred UF - I prefer to run a 220K or so R across the SB switch to let the caps charge up a little bit to lessen the short circuit effect of charging them up all at once.

...plus if you omit one, you'll get people who know less than you but think they know more than you tell you you're doing things wrong.

[KellyBass]

Also if your heater voltage is a bit high you can drop it by .7v with a single diode in series with the heater wiring.

Thank you for reminding me of this trick, Tom! I had forgotten all about it and have an amp that I can use this on. The heaters are running about 7.1v with full current draw. Will a 1n4007 work for a .7 drop?

[Super_Reverb]

To get a 0.7v drop, you'll need to connect a pair of parallel diodes, wired anode to cathode - in series with heater or else you'll only be using half the heater sine wave.

rob

[Alexo]

..I might opt for a 1N5408, heater current being what it is... but I'm not sure what the voltage drop is on those.

You can buy .47 or 1 ohm 2 Watt R's and just parallel them and lay them in series with one leg of the heater line and achieve the same goal without getting your hands dirty touching solid state components.

[selloutrr]

I still use the standby switch.
I can hear a difference in an amp that is warmed up and one that is warming up. esp.. in the compression and highs when it's driven hard.
I leave amps powered up for hours in the studio keeping them warm while other amps are used for a certain track then back to another for layers, etc. I usually have 3-4 amps setup at a time. I'd hate to have the speaker active in the room for a recording even if it's just that low "on" sound.

[Alexo]

I still use the standby switch.
I can hear a difference in an amp that is warmed up and one that is warming up. esp.. in the compression and highs when it's driven hard.
I leave amps powered up for hours in the studio keeping them warm while other amps are used for a certain track then back to another for layers, etc. I usually have 3-4 amps setup at a time. I'd hate to have the speaker active in the room for a recording even if it's just that low "on" sound.

Hey sellout, fyi, this can be very hard on the tubes if there is no voltage present on the plates, etc.. If you don't already do this, you might want to tie a 470K 2 watt R across the pins of the SB switch, just to let enough current trickle through that you avoid cathode poisoning.

...your argument really favors a "mute" switch over a standby switch that interrupts the B+. There are several ways to do this, inserting a a 10 or 20K 5 Watt R in series with the power tube cathodes comes to mind.

[selloutrr]

I've tried the mute switching. It still trickles a faint "noise" to the speaker. I'm not to concerned with tube life, they are covered by the amp rental / record label. I pull tubes at 80% for studio work, unless the artist request different. It's wasteful but all about the tone. Variacs and Power brakes don't help tube life.

I'd be interested in something I could plug into the front pre the amps or post the amp pre speaker. But I'm not to excited about modding vintage collector amps. It would be nice to have something I can also use when artists bring in amplifiers that I don't supply.

[Alexo]

You could just build a dummy load box with a bypass switch, but of course, it wouldn't do much good for an amp where the speaker's hardwired to the OT.

...I think you are right on about letting the amp warm up to get the best sounds out of it, but in that case, it makes more sense to give the tubes HT and let them really warm up - a 6L6 that's only got it's filament glowing is barely warmed up compared to one that's dissipating 21 watts on the plate.

[Firestorm]

I'd be interested in something I could plug into the front pre the amps or post the amp pre speaker.

You could try a 50W or 100W pad between the output and the speaker. But I've always had good luck with a thing called a "Volume Knob."

[Structo]

To get a 0.7v drop, you'll need to connect a pair of parallel diodes, wired anode to cathode - in series with heater or else you'll only be using half the heater sine wave.

rob

Thanks for the reminder of this.

[ampdoc1]

I haven't used standby switches since I read this several years ago! Also a lot of other good info on his web site.

ampdoc1

[Reeltarded]

My tech told me forever ago to standby Marshalls, and turn down Voxes.

I do that.

Umm.. this cathode stripping stuff.. please, show me cathode stripping.

I run amps at the bare minimum voltage to keep the light on OFTEN. I have never experienced this cathode stripping. I know it must exist, I just never created the condition in the prescribed ways.