RCA 721TS restoration
 

Here's a closer look at the RCA 721TS I picked up along with a few other sets in Wisconsin a couple months ago. Three issues were quickly apparent. The back was missing, the channel plate was missing and the 10BP4 CRT was dead.

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Serial C0011703. I'm not sure how many were made, but I'm going to guess this is early.
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Electomagnet used for the ion trap.
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First a peek underneath. Man is this set heavy!
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I can only see one replacement Spraque cap in the upper left.
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Now the reason I took a break from other projects to poke around with this set, is that a potential replacement CRT just arrived :) Out of the blue I was contacted by an online friend that had an untested, unknown CRT and asked if I'd like to have it. I figured it must be a 10BP4 based on his photo so I said sure.

It was well packed and arrived intact. It sure is a 10BP4 and RCA Victor branded too.
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I crossed my fingers and fired it up. It tests like new :banana:
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Now how to install it ?
I removed the bolts from the chassis and started to slide it out of the cabinet. Huge mistake :no: Luckily, disaster was avoided as I noticed the heavy CRT front drop down and stopped before the neck snapped off in my face :yikes:

Just like in the 630TS, the CRT must be removed from the front as it's only supported by little brackets attached to the cabinet. I consulted the service info and discovered the trick to removing the front of the cabinet.
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It appears to be a replacement from 3-3-1948. I guess the original didn't last very long.
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I tried every trick I could think of to resurrect the open filament in the old 10BP4 with no luck. Very frustrating since the getters are nice and shinny and I can see the intact filament wires running down into the gun.
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Nice trick Bob,

I would have been one of the guys to pull the chassis before looking at my RCA book

My 721TS needs channel knobs, back cover, HV cage. 028580 is the serial number.

Here's a closer look at the chassis. This is the first time I've seen one close up. After poking around with the larger but similar RCA 630TS, it feels like stuff is missing :)
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Crusty, deteriorating focus coil.
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I hauled it up on the workbench to test the power transformer. I popped out the 5U4 rectifier, stuck my meter on the plate pins and fired it up with a fused variac.

The tubes all lit up and I have over 800VAC unloaded on the plates :thmbsp:
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Here's the new CRT installed. I'll worry about centering it properly when I do the restoration in earnest.
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I dug through my knobs stash and pulled out a channel plate :D
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Finally, I picked up a reproduction back from Amptech Systems.
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That's better :yes: For now it goes on the backburner though while I finish off a few outstanding projects.
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I'd replace all the micas in the horizontal sweep. They are frequently a problem in these early RCA sets.

I did that to my 721TS and 721TCS. Both had problems there. :smoke:

I have on in the shop awaiting my attention. Ive not even tested the CRT. All parts are accounted for. 1947 comes to mind. Someone put putty at the corners for the CRT. There is another only slightly newer keeping it company.

Hi All;
Cowboy, what is the Radio in the second Picture ??
THANK YOU Marty

Philco 90

Yup waitin it's turn also. A CL score, had all the knobs and such. Even a blind squirl finds a nut now and then.

I have the exact same model that I'm in the process of restoring. Problem I have is that as soon as I pulled the chassis, the CRT just hangs loose. My CRT checks very good on my Beltron, but how do I work on the chassis and keep the CRT in place so I can see whats going on, when I power it up. I'm really afraid of damaging the tube. Anyone have any suggestions.

Duct Tape

Or a box and some foam:

http://antiqueradio.org/art/RCA721TC...erAnimated.gif

Even better is a 5AXP4 test CRT:

http://antiqueradio.org/art/RCA721TCSAdjustments.jpg

Bob, if you had read my 721TCS article, you'd have been forewarned not to pull the chassis out the back before removing the CRT :)

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html