Many thanks to long-time RF Cafe visitor Bob Davis for submitting this article on his restoration
of an RCA 86T antique radio. Bob is an RF engineer who works in the remote utility meter reading
field. He is an avid collector and refurbisher of antique radio equipment in his spare time. You
can see some of his radios on the
Radio & Electronics Restoration
Projects page. You are welcome to submit photos of your own projects for publishing.
Here are Bob's restoration stories for his
shortwave radio, his RCA 86T, and a few other
radio restoration projects.
I bought this RCA 86T radio from a garage sale, the cabinet was in pretty good shape and I
needed a winter project.
RCS 86T Antique Radio
Putting the radio on my dim bulb test rig showed no horrible shorts, so I went for it and brought
it up using a variac. The old girl came to life with substantial hum but brought in WWL on the
AM band (I live close to New Orleans).
Removing the chassis from the cabinet, several hours of cleaning took 70 years of dust and
grime off if it. I removed all the tubes, which luckily all tested well, cleaned them, wrapped
them in paper towels, and stored them safely until the chassis was rebuilt.
Inspection of the wiring in the chassis found many rubber insulation covered wires where the
insulation was crumbling requiring replacement of the wires. This is a step sometimes missed by
amateurs rebuilding such sets and is an important one if one doesn’t want the house burning down.
A few pictures follow showing some of the bad wiring and some dubious repairs made to the set
over it’s 70+ year lifetime.
Brittle Wire Insulation
Crappy Tape Repair, Frayed Wire
Brittle Insulation Near Tube Pin
Further inspection showed the culprit for all the hum when I turned the radio on. All the larger
electrolytic capacitors had dried up and were ready to short their center pins to the ground system
of the radio. One example is below.
Dried Out Old Filter Capacitor
Taking a few digital pictures before I started the re-wiring process was in order as one is
worth a thousand words as they say. I also hand sketched several areas of the wiring for further
reference as the point to point wiring of the chassis in places was complex.
I then researched the radio on the internet and was lucky enough to find an original RCA service
manual for the set containing detailed chassis wiring drawings and service information. The Nostalgia
Air web site was then visited allowing me to download the Rider’s manuals for the set (if you
use this site, send the webmaster a few bucks, donations keep this site up for us all).
Where does one start with a project like this, I figured work from one side to the other. The
cap below the volume control looked like a good place to start. Taking the volume control off
also allowed me to clean it up with some DeOxIt.
Let the carnage begin!
The black parts are all mica capacitors that didn’t need to be replaced. Note the amount of
disassembly needed to get to the old wax paper caps to replace them.
A few notes.
- As you replace the wires, try to keep them the same length and routing as the originals.
Sometimes these wires are in the tuning sections of the radios (as the green and yellow ones
are above) and paying attention allows you to re-tune the radio easily without producing feedback
paths that may take considerable time to trace and fix.
- Be gentle with de-soldering parts, old carbon composition resistors are delicate and if
you heat them up too much, their values could change to a point where they need to be replaced.
- Grab your VOM (or more modern DMM) and measure resistance values as you go along.
Since “you’re here” it only takes a few minutes and restoring the resistors to the original
values the set’s designers specified will reap benefits after you play your restored treasure
a few hours.
The pictures that follow show some of the restoration of the radio’s wiring, replacement of the
wax paper caps, and the addition of a few terminal strips to hold the point to point wiring that
was accomplished using the terminals of the old electrolytic caps. It’s always a good idea to
disconnect those caps terminals from the circuit (i.e. don’t just slap the replacement caps across
the old terminals). This takes a little time, but you’ll be rewarded for it later, and it’s imperative
The volume control areas shown above after re-work. Note the replacement cloth covered wiring
just to “make it pretty”.
All Spiffed Up with New Components
The power supply side of the chassis. Note the terminal strips installed to attach the point
to point wiring parts that used to be connected to the electrolytic capacitors. Note also that
the transformer wires were covered with heat shrink tubing as needed for safety.
New Wiring & Capacitors
Safety first, the following pictures show the detail of the additional terminal strips added.
A Safer Radio
Point-to-Point Wiring (the good old days?)
This radio had a very dangerously wired (and strain relieved) AC power cord connection. The
addition of a terminal strip and proper strain relieving under the chassis makes it safe for the
next 70 years. I like to dress the AC input cord away from the hot portions of the radio like
the dropping resistor network used for this radios B+ voltage generation. See picture below.
Modern Wire Substituted for the Old Crusty Stuff
One more shot of the completed build point to point wiring (I like to use quality parts). I
had a lot of time in this radio when I was finished, but I don’t rebuild these to make a buck,
I do it because I like to!
A View Only the True Aficionado Can Appreciate!
A little hint, order some Teflon coated wire and strip off the insulation as needed for spaghetti
insulation. It works great and won’t melt on you! Note the reproduction cloth wire used in the
picture above, Radio Daze is a great source for the wire.
All done, time to put the final polish on the chassis, and string the new dial cord. I used
a dial belt for this one as it worked better. You can buy a kit from Radio Daze that works great
The old speaker shown in the picture has had a few tears over the years that were repaired.
I did a few myself, it sounded OK when I finished, I’ll leave a re-cone of that to the person
who buys my estate stash some day ;-).
Note the Belt-Driven Dial Pointer (dial missing)
Time to install all the tubes, do one more check of the wiring, hook it up to the Variac and
cross my fingers. Fired right up! Here she is all done with a clean chassis with the tubes lit
A Bird's Eye View - Born Again!
I connected an antenna to the radio and all bands played well. No hum heard at all thanks to
the new electrolytic caps. Note that I left the old electrolytic cans in place to maintain the
look of the top of the chassis.
A few hours with my trusty old HP 8640B signal generator, HP 8614 Network Analyzer, and R&S
FSP spec an and she tuned up beautifully (hey, I AM an RF guy by day).
Back in the chassis with a reproduction cloth covered AC cord just for looks.
I took the
liberty of signing my work, what the heck?
A Bob Davis Restoration Original
All done, polished up, ready to play for another 70 years, if they keep the shortwave band
active for that long! I’ll leave the cabinet alone, I hope I only have a scratch or two on me
after 70 years, and I’m an RF guy and not a woodworker ;-)
RCA 86T Antique Radio
There you have it, an old radio, over 100 hours of fun and toil, and another one comes back
from the grave. I want to get an RCA reproduction logo from Radio Daze to finish the front panel
to ice the cake!
Before I close, let me say that safely rebuilding these old sets takes a little time, but is
worth it for the peace of mind one gets by switching them on and knowing that you won’t be calling
State Farm for a fire claim. Be careful of sets you buy off the internet, at junk shops, or for
that matter by some who claim to have restored them. Inspect them well and err on the side of
caution if you are unsure of their safety. Have a pro look them over before you plug them in if
you can, or buy one from a pro in the first place and save all the trouble unless you like to
rebuild them yourself and have the proper tools. A good site that has several talented professionals
who restore radios is http://www.radioattic.com.
I suggest if you do buy a set off the internet ask the seller for credentials or references, the
pros will always be happy to supply them (and should warrant their work!).
Rebuilding old radios is a fun and rewarding hobby. If you want to learn more, this site has
many good articles and several rebuilds such as this chronicled. I’m sure Phil won’t mind me sending
you to him. He really knows what he’s doing, you can learn a lot from him.