Restoration Commences on 1947 RCA Victor 721TCS

[Penthode]

Just an update after 4 1/2 years of regular use. Only problem in the last 4 1/2 years was the KRK2 fine tuning shaft. I made a new one out of brass riveted to the original fine tuning disc.

Still using all of the original chassis mount electrolytics. 78 years and still fine. The restoration entailed only replacing the wax caps that needed replacing eg subject to a a large DC across them. A three resistors had drifted affecting operation. Tested transconductance on all tubes and replace a few with original period NOS RCA tubes.

The main point is the originality of the electrolytics. They survived because the set was not plugged in after the set sat unpowered for over 50 years. Slowly reformed the capacitor dielectrics and they are all still fine. One axial lead electrolytic was bad and was replaced.

Here are a couple of snapshots off air made this afternoon. Can you name the film?

[Penthode]

Thought I should resurrect this old thread considering the significance of the originality of my 1947 721TS. I resuscitated this set nearly 5 1/2 years ago and this was to be an experiment to see if a fairly well preserved set could be reliably operated replacing parts only what were absolutely necessary.

In the resuscitation of this set, it retains all but two of it's carbon resistors. About 95% of the paper dielectric capacitors were changed. The ones that were retained were shunted by resistances which swamped the leakage resistance of the capacitors. It retains some of its original tubes. I carefully selected RCA period tube for replacement so it is a fully RCA tubed set. When I received the set 10 years ago, it had sat in a heated attic in a house near Schenectady for just over 50 years. Upon pulling it apart I found a small mouse nest under the chassis and fortunately it caused almost no damage. The set was not powered from the early 1960's until after it's resuscitation in 2020.

However, of major consideration is this set retains all of it's original electrolytic capacitors. This thread describes the extra effort I took to preserve the capacitors. I am not averse to changing the electrolytic ic they test bad. But slowly reforming the dielectric on each electrolytic in this set brought them all back with very low leakage.

So the bet was on as to how long they would last? I power the set on average once a week and let it run for a couple of hours. I decided to check the capacitors this evening and can report that they all appear fine.

Here after 5 1/2 years, after the careful reforming of all the original electrolytic cans, are some off air shots. (I did replace the original 40uF axial lead electrolytic but all the chassis mounted cans are now 78 years old.

[old_tv_nut]

Gorgeous pics!

[Penthode]

Thanks.