Standby Switch for my Magnavox 9302

[byoung334]

I am interested in installing a standby switch in my Magnavox 9302 amp. Anyone have a schematic they can share?

Bill

 

[Tinkerbelle]

I think I have that, if that's the one with 6EU7s and 6BQ5s; can email a copy

 

[jaymanaa]

Does Magnavox have a schematic that includes a standby switch? I would think you would want to drop your heater voltage to about 1/2 in standby mode to prevent cathode poisoning.


Edit - Nice amp BTW if that's it in your Avatar.:thmbsp:

 

[markn2wae]

Does Magnavox have a schematic that includes a standby switch? I would think you would want to drop your heater voltage to about 1/2 in standby mode to prevent cathode poisoning.


Edit - Nice amp BTW if that's it in your Avatar.:thmbsp:

IMHO, "cathode poisoning" occurs because B+ is applied before the heaters are up to temp. (Perhaps I am thinking of "cathode stripping"?)

You could drop the heater Voltage, but not with the ability to have the heaters "up to heat" before applying B+ high Voltage.

Most amps I have seen only switch off the B+ for stand by, the heaters are kept on full.

Mark T.

 

[jaymanaa]

Yeh, you're thinking of stripping. Poisioning occurs from having heaters "full" on with no B+. I can't remember which one, but either Jones or Rozenblitz covers it pretty well in their books.:yes:

 

[wa2ise]

Yeh, you're thinking of stripping. Poisioning occurs from having heaters "full" on with no B+.

I've heard that you can avoid that by having a high resistance resistor across the B+ standby switch. something like 100K. The idea is that just drawing a few microamps from each cathode is enough to prevent poisioning.

 

[byoung334]

I got a schematic of a Fender Bassman amp, and it has an ON-OFF "standby" switch int the B+ high voltage coming off the rectifier tube.

My purpose in wanting to install one was to keep the heaters going if I have to interrupt my listening for 20 to 30 minutes. I wanted to keep the tubes warm for when I resume listening to the music.

BTW Jaymanaa yes that is the amp. I am gluing together an oak frame to drop it into. Then it will be stained and sealed. I have a old Magnavox Cosmopolitan brass badge that is going on the front.

 

[jaymanaa]

I'm not sure if 30 minutes would start poisining or not, of course, what if you're like me and forgot. I guess why I (we) would worry about it, is the quickly diminishing supply of NOS tubes. You have to realize that when the guit amp guys were doing standby, tubes were plentiful and affordable (not to mention they sold tubes). IMHO, if you're only talking 20 or 30 minutes, I'd just leave it "on".