Primary switch soft start DPST wiring

[aumamps]

I have a Carling DPST and I'd like to try Merlin Blencowes Primary soft start (instead of the usual secondary stand by)
I was curious if that's possible with this switch. I feel like if I jumper the mains wiring, the resistor will always be in series.

[sluckey]

That switch will work. You just need to understand how it works. Look at my AC-15 Standby Plus switch. I'm switching B+ but the idea is the same. Just put line hot on the left and PT primary on the right.

http://sluckeyamps.com/VAC15/Vox_AC15_mods.pdf

[aumamps]

Ah! I see how you jumpered that resistor. Thank You. I get dyslexic with switches.

[Roe]

another option is just to use an ordinary dpdt on/off switch with a termistor in series

[pjd3]

I'm building an amp now (modded 2204) and came upon the "47K resistor across the standby switch". I thought this in itself was offering a reasonable soft start condition when powered on with STBY switched open.

The voltage to the first cap raised to 35 volts the first second, about 70 volts after 2 seconds, and may around 130 or so after 3 seconds. I took that as a really good sign that my PT HV/diodes and any other part of the amp wasn't being stressed at all as compared to the first capacitor looking like a dead short the first moments of turn on. I may have lost a bit of a total "Mute" but, I was very willing to give that up for the nice advantage of a nice slow rising power up. Plus, knowing that the cathodes are never baking away with no current was another added nice feature, should it be true that its bad for cathodes.

I also placed another diode after the "standby become soft start" switch to keep the switch in a more AC environment than a constant DC. Statistically, it looked as thought the switch wouldn't be arcing as heavy every time. Better switch life and quality over time.

Just my 2 cents.

Phil D

[TUBEDUDE]

I agree that this is reducing the stress on supply components, but don't worry about cathode stripping, that occurs at much higher voltages.

[dorrisant]

Cathode stripping only occurs in transmission tubes, not receiving tubes.

Since we generally never see transmission tubes in a guitar related tube amp, we shouldn't worry at all.

Your parents or grandparents probably had an old console stereo... tube based, right? You would turn it on and sound would slowly ramp up after 30-40 seconds. There was no standby involved. Now, think of how long all of those tubes lasted. We still find these units pushed outside for heavy trash pickup and I can't help myself to stop and pull the chassis and if not the chassis, at least some of the tubes that I can quickly grab. My experience is that most all of the tubes I pull from these units have plenty of good life left in them and sometimes you just know that they are the original tubes... not that hard to determine. If cathode stripping of receiving tubes was really a thing, most of these tubes would be stripped, right?

[pjd3]

Thanks guys,

You've done well to educate me on that. I won't worry about cathode stripping in my guitar tube amps.

Thank you for the information!

Best,

PJD3

[xtian]

And then there is cathode POISONING, which, and I'm parroting info I've heard before, can degrade your tubes if left in standby for long periods of time.

[pjd3]

Thanks Xtian,

Perhaps it is that that I heard about. It never became clear to me either way but, on the chance that this occurs, it felt all warm and fuzzy to think that even a bit of plate current when in "47K ohm standby trickle mode" may serve to thwart that ugly sounding situation away.

Best,

Phil D,

[aumamps]

I appreciate the comments on this one.
I probably could have learned a few Van Halen solos in the amount of time I've spent reading about these debates. Merlin's book really covered good ground on this.

I already have the switch and the resistors. I don't want to buy more stuff after doing several orders for sourcing this build.

I've thought about even giving way to a standby in general (none of my tweed style builds have a standby. I just wait half a minute before playing)

This scenario looked like a good compromise.

[dorrisant]

And then there is cathode POISONING, which, and I'm parroting info I've heard before, can degrade your tubes if left in standby for long periods of time.

Yes, you are right. I will edit my post above so as not to confuse anyone.