Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: chip on April 10, 2010, 05:25:25 pm

Title: Standby switch needed? (Placement)
Post by: chip on April 10, 2010, 05:25:25 pm

This is my first try at a solid state rectifier amp.  Just a few questions on the standby switch:
Push Pull,   2X6L6GC,   4X12AX7,   Fixed Bias
1)   Do I really need a standby switch for this amp?
2)   If I do need a standby switch, is this location a good one?
3)   If I put the standby switch in the location shown does it have to be rated for at least 500-700V?
4)   Where can I find a switch that is rated for this high a voltage?

Title: Re: Standby switch needed? (Placement)
Post by: tubesornothing on April 10, 2010, 05:36:21 pm

A whole article on standby and power switches:

http://www.freewebs.com/valvewizard1/standby.html

Title: Re: Standby switch needed? (Placement)
Post by: JayB on April 10, 2010, 05:48:45 pm

I prefer the switching before the diodes. Safer that way.

Title: Re: Standby switch needed? (Placement)
Post by: kagliostro on April 11, 2010, 05:53:12 am

+ 1 for standby BEFORE diodes

I like to have a doubled switch

one for each branch of the transformer

Kagliostro

Title: Re: Standby switch needed? (Placement)
Post by: LooseChange on April 11, 2010, 06:35:20 am

IMO switch before the rectifiers is overkill.
Fender put them after the rectifiers and the first PS filter stage with no problems.

Title: Re: Standby switch needed? (Placement)
Post by: chip on April 11, 2010, 07:20:49 am

If I leave out the standby switch, what are the risks?

Title: Re: Standby switch needed? (Placement)
Post by: sluckey on April 11, 2010, 07:51:38 am

I don't see any risks on a 2x6L6 amp. The STBY is more of a convenience (I like it) for a 40 watt amp.

Title: Re: Standby switch needed? (Placement)
Post by: tubesornothing on April 11, 2010, 08:49:00 am

Man its tradition, ya dont buck tradition.  Just follow it, dont ask questions...

 :wink:

Title: Re: Standby switch needed? (Placement)
Post by: Fresh_Start on April 11, 2010, 01:07:14 pm

Would a 3-watt 220K "bleeder resistor" somewhere between the power rail and ground help limit the initial voltage surge in an amp without a standby switch? 

Don't know where I got that I idea.  I've also seen those bleeder resistors located at the reservoir cap (1st after PT) and at the last (preamp) end of the power rail.

I see the two pairs of 220K resistors in series on both sides of the Standby switch in the OP's schematic (R26, 27, 28 & 29).  Obviously those serve as "bleeder resistors" even though they are there for another purpose. BTW what is the wattage rating on those resistors going to be? 

Chip