From: "Gerry" 
Subject: RE: [drakelist] Drake 2-C hum follow-up


The Drake 2-C +12V power supply is about as basic as it gets. A simple full
wave rectifier and 0.82 Ohm and a pair of 1,000uf capacitors doing the
"filtering". This type of supply is by no means hum free and offers no line
noise isolation. If there is sufficient hum to be heard then the frequency
must be 120hz and not 60hz. I've only caught your most recent posting so I
don't know if you did measure the so-called +12V to see what it reads.
Whatever AC voltage is read between the 2 blue wires on the secondary, the
DC voltage would be approximately 1.414 times the AC voltage times
approximately .9 for loading, divided by 2. For example, assuming 20VAC: 10
x 1.414= 28.28 x .9= 25.452 / 2=12.73 volts DC. Be sure to check your
primary line voltage as well because there is no regulation here. If the
so-called +12V supply is much lower than that, then suspect one of the
diodes is bad or something else is loading the power supply to excess.
Excessive loading would tend to explain the excessive hum you say you're
hearing. I would also be tempted to temporarily pull out the last IF tube,
V5, and see if the hum is still there. Maybe one of your tubes is bad. In
any tube-type gear, I always try a new tube because experience has shown
that this is a likely problem, though it doesn't always work out that way.
Also the audio stage in the 2-C is the same as the R-4C so don't expect
great sounding stuff to come out of it. Don't get me wrong, it's not bad but
just don't compare it to more modern equipment because there is no
comparison. I had a 2-C and it was a great little receiver. It had very much
the same feel, if not the same good audio, as the R-4B. If you have the 2-CQ
Q multiplier, it's a better CW receiver than the R-4B because you can really
make the selectivity razor sharp to the point it almost sounds like a bell
with each CW character.

-----Original Message-----
From: owner-drakelist{at}www.zerobeat.net
[mailto:owner-drakelist{at}www.zerobeat.net] On Behalf Of Casey
Sent: Sunday, December 14, 2003 3:28 PM
To: drakelist{at}www.zerobeat.net
Subject: [drakelist] Drake 2-C hum follow-up


Thought I'd share my investigations and seek advice on next steps.

First off, with my headphones I don't have to adjust the AF gain from what I
use for the speaker. So, I think the 100 ohm resistor theory probably won't
help, but I admit I didn't try that yet.

As for filter caps, there are a pair of 1000 uF discretes on a separate
board along with an 8 uF one, plus a can that is labelled 60-40-20 uF, all
at 150V ratings. I found that my two schematics differed on how many 1000 uF
caps there are, but I can't find any 60 or 40 in the diagrams, just 50, 20,
and 10 uF at 150V. That aside, it should not be too difficult to replace the
1000 uF caps provided I can detach the board far enough to get my iron in
there. I think I may leave the "can" alone for the time being.

Should I also replace the power line bypass caps (.001)? Won't a failure of
those introduce some ripple as well?

73,

Casey, KS7J
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