[Boatanchors] RCA 811K

[Dan Gutowski]

Hi Bob,
I'm a long time RCA collector, and have restored several 811K consoles for
myself and others. After re-capping each one, I was presented with a unique
set of circumstances for each one, including what you have described. Don't
have a definitive answer for each unique situation, but here's what I found.
and by taking the extra time, this cleared up any issues I ever had. First,
I found these circumstances in all 7 radios I had worked on.
1. Nearly all of the original carbon resistors had a measured value that was
double to even 3 times higher than the indicated value. The larger 1-2 watt
resistors don't seem to be as adverse. I now check and relace all resistors
that are out of spec.
2. Years ago, I would leave in mice capacitors, since they typically were
good. Today, I find more trouble with ones that are inermittent. Now I
replace any mica capacitor that has a circuit voltage over say 50 volts, and
any that is used in a coupling situation.
3. Double check the polarity of the cathode bypass capacitor on thr output
tube, since many have the + side to chassis. Can't recall off hand if this
set in particular has one, but the 813K and 816K I recall do.
4. Don't overlook the block assembly located on the chassis that connects to
the tone switch. This a a constant source of distortion, inside is a network
of resistors and capacitors inside it these days are almost always bad and
need replacing.
5. Be sure you replaced every paper/wax and electrolytic, it's always those
1 or 2 hard to get at ones that end up causing troubles
ultimately.....Here's a couple things to keep an "origianl" look. The
original caps have a tubular carboard shell. What I do is, with an awl, I
take the point of it and use it to lift the knurled carboard end of the
capacitor, then with a pair of pliers, pull the capacitor out of the shell
and place the new one inside, using beeswax to fill the void. The ends of
the original caps have "covers" on each end with a hole for the leads, that
I reuse. The end result looks like the original. If you want to keep the
original appearrance for the resistors, here's a trick. If the resistor in
question is good, but the value is too high, then add a new resistor in
parallel to with it, as to bring the value lower to its proper level, and
solder it in to the underside of the original, as to conceal it for the most
part. (of course, you will need to do a proper calculation of the resister
you add underneath).
6. I've seen many distortion issues traced to the metal 6F6 tubes that have
a tendancy to develop grid leakage, so I typically add NOS 6F6's to any of
these I work one. The metal ones haven't gotten too pricely, versus the G or
GT versions.

Hope this was of help, or of interest to you and the group.

Best Wishes,
Dan
AB8VM

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
[mailto:boatanchors-bounces at mailman.qth.net]On Behalf Of Bob Young
Sent: Sunday, January 25, 2009 1:06 AM
To: boatanchors at mailman.qth.net
Subject: [Boatanchors] RCA 811K



I brought up an RCA 811K console that I've had for a few years on a Variac
tonight. I know it needs to be recapped, it use to hum pretty loud which is
why I shut it off until I had the time to recap it which is now. Anyway the
radio did not hum tonight but worked much better at approx 75 V than at 115,
it got progressively more distorted, softer in volume and less sensitive
when brought up to 115, when brought back down to about 75 it performed much
better. (it did hum at first until I switched a bandswitch knob, the hum
went away
as did the background receiver noise) Does this indicate that perhaps an
electrolytic has shorted out? I didn't keep it on for too long, the power
trannsformer was still cold along two of the cans, one was warm. I am going
to replace all three but just thought I'd ask the group what it thought. I
haven't pulled it apart yet, I'll also be replacing all paper caps and/or
BB's.

Bob Young
Analog, MA
KB1OKL

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