in article , Lynn Coffelt at
wrote on 6/6/06 12:48 PM:


"WDØHCO - Biz" wrote in message
...
Howdy - WDØHCO Biz here ...

I am working on a moldie oldie - an old SBE-33 - one of the first
transistor/hybrid tube rigs of the mid-60's. This rig was new when "I
Dream
of Jeannie" was broadcasted on NBC - 42 years ago I think.

Well anyway that's what I remembered - the rig is fixed and working
great -
but every now and then the "PA Load" cap shorts to ground and output goes
bye-bye.

Old Faust Gonset used a trimmer cap for the PA LOAD. It's an ARCO L305
compression trimmer type - no value on the schematic but I am assuming its
180 mfd by the size.

Question is... has anyone worked on this and I am thinkin of pulling the
whole thing out and putting a "REAL" variable cap in it's place.

Opinions Please... thanks - B

Two or three ideas.
The L305 has a capacitance range from 190 to 760pF (source
http://www.arco-electronics.com/prod...ductlineID=12&
productline_categoryID=1
) if you are considering a replacement. Not an entirely bad idea.
Those Arco's are not hard to repair if you can get it out in your hands
to work on it. Most shorts come from mica dielectric sheets between the
plates that have cracked, shifted, or were too thin for your RF voltages to
begin with. Old Arco's from the junk box (or your favorite Ham's junk box)
are a source for new mica sheets if you find one or two that need
replacement.
I like stuff relatively unmodified, but hey, whatever you choose!
Old Chief Lynn, W7LTQ




Lynn - YOUR THE MAN !!

I looked on Google for an hour and gave up and here your got the info right
there - Well anyway I was lazy and tried to order the cap - you know the
drill - gotta order through the distributors - called several - all say
minumum order required - 4 weeks delivery -

So I took your suggestion and tried rebuilding it - didn't have the exact
cap in the junkbox but had several that same physical size - the hardest
part was getting that little bugger out of the rig!

Took it apart and your right - there where several places where RF had punch
some holes in the Mica - pretty small but you could see it without a mag
glass - Replaced the sheets and borrowed a friends digital cap meter to
check out the range - re-installed and now it tunes correctly -

Interesting design - I wondered why they would use a padder cap for final
tune - guess it was the only way to get 700 pikes in such a small space so
you can tune a wide variety of ants - if you were going to use this with an
amp you could get away with a small vairable with 360 pikes or less.

Overall the whole TX side was designed for low level duty cycle - typical
SSB. If someone tried RTTY on this thing I have no doubts it would blow up
in 10 minutes - The design was ahead of its time in the early 60's. No way
this 42 year old radio can keep up with today's jap rigs - still it works
well enough to use everyday on 40 and 80.

The filament situation still bothers me - in the 60's tubes were 90 cents
each, gas was 35 cents a gallon and electricity was 2 cents a kwh. Ah the
good ol days!

Today, its different and I want those tubes OFF when I spend time listening
on the bands - but I'm like you Lynn, hate to drill holes and ruin a nice
piece of equipment.

Then it came to me - if I could find a 10k pot with a switch, I could
replace the Mic Gain pot and turn the Filaments ON/OFF with the Mic Gain
control. Only need Mic Gain when the transmitter is ON anyway so it makes
sense and I don't have to drill a hole for a toggle switch.

So that's the next project!

Thanks for all your help! - Biz WDØHCO