Drake 2-B - Audio Oscillation

[Mike Langner]

Hello !

Any chance the primary (or the secondary) of the output transformer has had
the Plate and the B+ leads reversed?

This will cause positive feedback instead of negative feedback, and the
system will oscillate.

I once fixed a hi-fi amplifier kit that someone built who had reversed the
"polarity" of one winding on the output transformer.

If you hooked up the feedback, the oscillation was terrible!!

I sent this to the list 'cause someone else may run into the same/similar
problem.

It can be a head-scratcher!

Good luck!

Mike
K5MGR
______________________________________________________

-----Original Message-----
From: Boat Anchor Owners and Collectors List
[mailto:BOATANCHORS at LISTSERV.TEMPE.GOV]On Behalf Of joe sloss
Sent: Wednesday, March 15, 2006 3:50 PM
To: BOATANCHORS at LISTSERV.TEMPE.GOV
Subject: Drake 2-B - Audio Oscillation


Helping a ham restore his 2-B and am having problems with audio feedback in
the negative feed back circuit which is a 150 ohm resistor between the
cathode of the 8BN8 audio amp. and the secondary of the output transformer.
Lift one end of the resistor and the oscillation stops.  Resistor is correct
value; filter caps are OK, tube OK, etc.  Chassis grounds have been checked.

Any ideas?

Thanks,

Joe k7mks

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