Re: Push-pull interstage xfmr

"exray" <radioexray@[EMAIL PROTECTED]
> wrote in message 
news:6cc5f$482768b9$22289@[EMAIL PROTECTED]
> I'm working on a new project...an audio amp similar to the Western 
> Electric 7A.
> http://www.nutshellhifi.com/library/7Apix.jpg
>
> Having trouble with the PP output stage....apparently overlooking 
> something butt-simple.
>
> In trouble shooting I came across something I find strange.  I'm using a

> single ended stage feeding into the PP grids using a Hammond 124A xfmr. 
> With both of the PP output tubes pulled and using high z fones to
'listen' 
> at the grid pin on the socket the volume/tone is drastically different 
> between the two.  The xfmr ohms out at 840 and 720 ohms from each end to

> CT which doesn't seem unreasonable.
>
> I also note that with one of the PP tubes in place and listening to the 
> grid on the empty socket I'm getting some gain.  If I put the tube in
the 
> other socket I get an oscillation.  Wiring is somewhat symmetrical and
if 
> I switch the grid wires the symptom follows to the other socket.
>
> Whats going on here?  Do I have a bad xfmr?  Anybody have a 124A xfmr 
> handy to confirm the resistance readings?
>
> TIA,
> Bill
> ** Posted from http://www.teranews.com
**


Those resistances are fairly close.  Are the plate voltages similar on
each 
tube?

BH