Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: spacelabstudio on April 06, 2013, 11:57:36 am

Title: Using output transformer primary to separate plate and screens
Post by: spacelabstudio on April 06, 2013, 11:57:36 am

Hey all,

I was poking around on Google for some ideas for a 5902 amp I'm going to build as an MP3 player for my daughter.  I found two different schematics that both soom to be using nothing but the output transformer primary winding to separate the plates from the screens.  Have any of you guys played with this, know anything about it?  Here's the schematics:

(http://www.jogis-roehrenbude.de/Leserbriefe/Hermann-Mini-Amp/Schaltung.gif)

(http://www.pbpix.com/Radio/5902/pre-amp-copy.png)

Since the screen is fed from B+ before hitting the OP, I guess that ought the hold the voltage pretty steady.  It should only really be subject to PSU sag.  Does that give good, solid pentode operation, or does it wind up being kind of like ultralinear where it's a blend of pentode/triode characteristics?  Anyway, thought it was interesting.

Chris

Title: Re: Using output transformer primary to separate plate and screens
Post by: DummyLoad on April 06, 2013, 12:35:20 pm

i've run across a couple of mono phono players that did that. one was a motorola console, the other was a sears. i converted the motorola in to a guitar amp by adding another 6AV6 stage.

--pete

Title: Re: Using output transformer primary to separate plate and screens
Post by: tubeswell on April 06, 2013, 07:18:37 pm

Fender did it on some of their amps including the 5F2 http://www.thevintagesound.com/ffg/schem/princeton_5f2_schem.gif (http://www.thevintagesound.com/ffg/schem/princeton_5f2_schem.gif)

Title: Re: Using output transformer primary to separate plate and screens
Post by: PRR on April 06, 2013, 10:59:07 pm

> you guys played with this, know anything about it?

Quite normal.

Take your pick.

G2 needs better filtering than plate, so you put one step down the filter chain.

The difference is not that great, and often one big cap is cheaper than two, so you feed them the same.

5902? Why not use normal tubes? 25C5, 25L6, etc. The wire-end tubes won't save any space once you mount decent PT and OT.

Title: Re: Using output transformer primary to separate plate and screens
Post by: spacelabstudio on April 13, 2013, 02:07:33 pm

Quote from: PRR on April 06, 2013, 10:59:07 pm

> you guys played with this, know anything about it?

Quite normal.

Take your pick.

G2 needs better filtering than plate, so you put one step down the filter chain.

The difference is not that great, and often one big cap is cheaper than two, so you feed them the same.

5902? Why not use normal tubes? 25C5, 25L6, etc. The wire-end tubes won't save any space once you mount decent PT and OT.

I went a submini Ebay shopping spree a while back, so I got tubes burning a hole in my pocket.

Thanks for the responses.  FWIW, I enabled notifications for this thread but never got notified.  Something up with the board?