My new filiment PS for Push Pull GM70

[djn]

A friend just gave this to me. 2 channles of 24volt, 6 amp DC power. I think it would be a great filiment PS for a push pull GM70 amp. The GM70 needs 20v, 3a. It weights 38lbs!!! Talk about a boat anchor....and that is just a fraction of the whole amp. I think it will do nicely.

 

[Bandersnatch]

hey-Hey!!!,
For PP Dh amps I have not found DC heating required...at least not with 10V 813's. 5V tubes absolutely not, and 2.5V tubes...not even close.
cheers,
Douglas

 

[djn]

Hey D, sorry we missed you yesterday. I know this might be over kill and I still have three amp projects on the bench, but what the hey! George asked me if I wanted it, so what the heck.

 

[Bandersnatch]

Hey D, sorry we missed you yesterday. I know this might be over kill and I still have three amp projects on the bench, but what the hey! George asked me if I wanted it, so what the heck.

That's mighty strange, I've never known you to go in for 'overkill'...LOL

Douglas

 

[djn]

Bad habits die hard

 

[kevinkr]

hey-Hey!!!,
For PP Dh amps I have not found DC heating required...at least not with 10V 813's. 5V tubes absolutely not, and 2.5V tubes...not even close.
cheers,
Douglas

These are 20V tubes and DC is advisable if you need really low hum even in PP. I found with 300B PP amps driving very efficient speakers (>100dB) that DC was also advisable, although not strictly required if you can live with a mVrms or so of hum/buzz on the output..

 

[djn]

I agree Kevin. I generally run compression drivers that are 115db eff. and any hum is audable. Besides that, it is a simple one piece unit that just needs wire hooked up. no muss, no fuss.

 

[radiostar]

Good starting point and good luck with new project djn!!!

GM70 PP would be a beast ...

 

[djn]

Thanks Radio. I have three other amps on the bench but getting ready to move, so I dont think this one will be up and running any time soon, but that only means I have time to collect parts. Should do well with 800v B+. I don't know how to figure what the WPC will be but I'm sure it will be more than my GM70 SET.

 

[Bandersnatch]

These are 20V tubes and DC is advisable if you need really low hum even in PP. I found with 300B PP amps driving very efficient speakers (>100dB) that DC was also advisable, although not strictly required if you can live with a mVrms or so of hum/buzz on the output..

I have 813's on AC with horn-loaded EV DL10x and don't hear anything unless I stick my shoulders into the horn. I can live with that. Individual coils for each tube and their own hum pot. Variac on the primary to dial in exactly 10V, though it seems to be quite happy with 10.2-10.5V on them.
cheers,
Douglas

 

[djn]

If I get tight for space, it is still a great transformer to use without all the other stuff. You're right Douglas, I've heard your system and there is no hum.

 

[djn]

What happens when I run a gm70 or any tube for that fact with higher than called for fill voltage? Does it change the sound or just shorten the life of the tube?

 

[quikie22]

What happens when I run a gm70 or any tube for that fact with higher than called for fill voltage? Does it change the sound or just shorten the life of the tube?

Tried that with some Russkie 6SN7 (6N8S) tubes out of curiosity (adjusted between 8-12V).... no audible difference. But the tubes started popping/became noisy after about 50 hrs of the increased voltage.

** Tried this because was wondering if the increased fil Voltage would lead to a hotter cathode and thus higher emissions with a positive effect on sound. Turns out the tube life was drastically shortened.

 

[djn]

Thanks quikie, I thought that would be the case. Geeez, running the GM70 at 20v 3a gives off the same amount to light at the 60w light bulb. This thing (when ever it gets built) will heat the house. I guess it will be a winter/spring/fall amp.