[Heathkit] GR-91 SWL Radio - on to the q-multipler

[Charles Yahrling]

the new electrolytics changed the hum to more staccato, but no louder.
however when I plug in the q-multiplier (on input side of 1st LC
circuit in 1st IF stage) hum drops sharply.  that's not new, tho.  I'm
thinking this means the hum is coming from upstream. I checked all the
components incl the new caps in the gr-91 but did not find anything
amiss.  also pulled tubes and tested all pins from filament pins with
no shorts.  maybe it's "old tube" disease. have a set of brand new
tubes on the way.  maybe a full wave bridge would help. would you a
have a diode recommendation for those?

You mentioned replacing the diode if it's selenium.  GR-91 is not but
there's a selenium diode rectifier in the q-multiplier, marked Model
10. 3/8" diameter x 1/2" long. no other specs in the manual or
schematic. should I replace that as well (unrelated to hum, just PM)?
if so can you recommend a replacement part?

also ordering the 2 20mf ps filter electrolytics for q-mult. while I'm at it.

tks!

chuck

On Mon, Feb 11, 2013 at 12:37 PM, Charles Yahrling
<cfytech24x7 at gmail.com> wrote:
> excellent. another responder suggesting checking the DC power
> resistors, so I'll pull all the tubes and check the resistors and
> report back FYI.
>
> tks again
>
> On Mon, Feb 11, 2013 at 11:33 AM, Brian Harris <cosmophone at yahoo.com> wrote:
>> With half wave you'll have 60 Hz.  There would be no leakage of any
>> significance with a silicon diode.  They either work or they don't (30 years
>> experience in semiconductors talking).
>>
>>