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Beginning a 37-620 Restoration - Printable Version

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RE: Beginning a 37-620 Restoration - morzh - 04-20-2026

I overcame my fear of dim bulb testers and watched.
Well, good, the radio works. Congrats!

But why are you playing it with the Dimwit Tester inline? If anything, it doesn't help at this point. Only makes it worse.

RE: Beginning a 37-620 Restoration - glyphmon - 04-20-2026

Just testing different configurations.  The only difference I really noticed was the dial lamp was not as bright on dim bulb.  Everything else seemed about the same.  60W bulb.  65W radio.  So I think it's pretty close to full-power.

Best wishes,
Roy

RE: Beginning a 37-620 Restoration - DaleHCook - 04-21-2026

glyphmon Wrote:  I've also been looking at some variacs online.

Note that Variac® is spelled with a capital "V" and is a registered trademark, originally of General Radio Company, and now of ISE, Inc. Any other brand is a variable autotranscormer and not a Variac®.

My Variac®is built into a custon cabinet with fused input and output, and a voltmeter and ammer on the output. I use it plugged into an RCA WP-26A Isotap isolation transformer.

RE: Beginning a 37-620 Restoration - morzh - 04-21-2026

Variac became what is known as "genericized trademark."

Those include (there are way more), or used to, those I will give below. Also in other countries.

Keds - sportswear of the fashion similar to what the first Keds looked like.
Frigidaire - people used to (not today) call refrigerators that name.
Jeep - in some countries any off-roader SUV (or sometimes just any SUV) is called Jeep.
Variac - variable autotransformer.
Aspirin - acetylsalicylic acid. The tradename is still own by Bayer.

Dry ice.
Escalator
Lanolin
Laundromat
Heroin (Bayer)
Zipper.

And so on.

RE: Beginning a 37-620 Restoration - morzh - 04-21-2026

Glyphmon

If I understood you correctly, the bulb is in series with the radio, burns at at least half-power and the input voltage to the whole circuit is 120 (110/115/117, whatever) volts?
If this is the case, out of interest, measure the input voltage across the radio plug.

RE: Beginning a 37-620 Restoration - DaleHCook - 04-21-2026

morzh Wrote:  Variac became what is known as "genericized trademark."

Just because a trademark is used incorrectly doesn't make it right. I own a number of variable autotransformers, and have worked with a few brands. Mine are all General Radio Variac®s, and I wouldn't own anything else.

RE: Beginning a 37-620 Restoration - radiorich - 04-21-2026

Hello Guys,
Yes, variac is a trade name like my Sencore is called a Powerite !
Few other's not to do with electronics is Sawzall and Skillsaw .

Sincerely Richard

RE: Beginning a 37-620 Restoration - DaleHCook - 04-21-2026

Sawzall is, of course, a brand of reciprocating saw. I own two reciprocating saws - an older corded Craftsman, and a newer cordless Kobalt which is the one I normally use.

Skillsaw is primarily a brand of hand-held circular saw. I own an older Craftsman.

One thing that has always bugged me is when people call a sabre saw a jig saw - I own both, and they are entirely different power tools. Just as bad is confusing a sabre saw with a reciprocating saw. My sabre saw is, once again, a vintage Craftsman. All of my Craftsman tools, both power and hand, are older examples made in the USA.

RE: Beginning a 37-620 Restoration - glyphmon - 04-21-2026

Mike,

Just so I'm clear on where you're curious about, I should check for AC voltage with my multimeter leads across the two power cord wires at the points where they are soldered inside the radio chassis while the dim bulb is in series, drawing power through my variable transformer (not a Variac®, Dale  Icon_biggrin )?  Just like to be sure I'm on the same page as I tend to be very literally minded.

Best wishes,
Roy

RE: Beginning a 37-620 Restoration - Joe Rossi - 04-21-2026

Dont forget "Xerox" copy and "Kleenex". Just sayin'... Joe

RE: Beginning a 37-620 Restoration - morzh - 04-21-2026

Roy

Again, if I understood you correctly (if not, correct me): your setup is kinda like this.

   

Your radio and the Dimbulb are serialized and then plugged into the Variac that is set at 117VAC. (OK, 110, 120, whatever).
So your V1 is 117V.
If this is the case, measure the V2 and V3. That is, across the lightbulb and across the radio plug (inside, outside, whatever is easier - they are the same)
`

RE: Beginning a 37-620 Restoration - RodB - 04-21-2026

That doesn't look like a 37-620. Icon_lol Icon_wtf

RE: Beginning a 37-620 Restoration - Arran - 04-21-2026

Mike;
I used to use a dim bulb setup, before I had a Variac, I always regarded them as a poor man's substitute. and I don't think that I have used one since I acquired a proper unit. The best thing I can say is that they offer a "cushion" should the device being powered up develop a dead short. The way I used to use them was to start off with a lower Wattage bulb, and work my way up to a higher Wattage one in stages, like I said a "poor man's Variac". I have heard mentioned though that if the intent is to reform the filter caps it would be beneficial to construct a solid state substitute for the rectifier tube, as the set often has to be cranked up to 60-70 volts or so before the tube rectifier starts to conduct, I'm not sure how much difference this would make, and since I usually replace the filter caps as the first order of business I haven't had much reason to worry about it.
Regards
Arran

RE: Beginning a 37-620 Restoration - morzh - 04-21-2026

Arran

This is exactly what I call it everywhere, "poor man's Variac".
It is a protection device, but not a troubleshooting/measurement equipment.

I use Variacs to slowly bring up the voltage while watching the secondaries rise.
Dim Wit Tester will tell you SOMETHING IS shorted. But that can be an honest short both before and after xfmr, could be a bad shorted rectifier tube or a capacitor, could be the xfmr itself.

Anywho, I am trying to understand why it is still in the picture, after we have established there is no short.

RE: Beginning a 37-620 Restoration - RodB - 04-21-2026

Here ya go Mike. Genuine 37-620.