Got a call one day to look at an RCA radio. Seller decided to warm up the radio while I was driving over. This is what I saw when I got there. I ended up buying it for far less than he originally asked for.

I hope the power trans was ok! I'd leave the boric acid stain--it adds to it's heritage

A radio with a chimney .... just when you think you've seen it all ...

So was it in backward? I see those are the Miec brand. I always wondered if those were reliable?

Is this correct? if so, I had it backwards.

I have a Lafyette LSG-10 signal generator that I have used for many years with no problems. Last year it quit cold. When I opened it, there were 2 modern filter caps that had blown up. It seems the previous owner had mistakenly put 40 uF 10 WV ones in instead of 10uF 400 WV. How it worked that long is a mystery.

Dennis

Actually, the way you have it marked IS backwards.

The center tap of the HV winding is negative, the filament of the 80 is positive.

Even if you had it correct, sometimes there is more than 450 volts right at the first filter cap between the CT and rectifier.
That will indeed push the cap past its limit.

-Steve

Then I had it right and it popped anyway. Because, I had it opposite of the drawing above when it popped. Should I get a 600 volt cap?

Hi Kevin,

The WVDC rating of a capacitor is the DC voltage PLUS the peak ripple voltage. For the cap at the rectifier cathode, the ripple voltage may be quite significant. You can measure it with a peak-reading AC voltmeter.

- Leigh

Yes, i would reccomend a 600 volter there. 4 uf is small enough you could easily find a mylar or poly cap.
https://www.tubesandmore.com/products/c ... ylene-fast
The 4.7 uf is $5.10.

Or put two 2.2 uf 630V yellow ones in parallel with each other. Ends up being about the same price.

http://www.radiodaze.com/axial-film-2-2mf-630v/

-Steve

i use sprague atom capacitors they have never gave me a problem.

I got new capacitors is their a negative side to these caps?

perhaps are they not electrolytics and they are film caps ?

to me, they look like film caps, but then again, i could be wrong.

look where the leads come out of the top and bottom of the cylinder. is one surface a different color than the other ?

if so, do tell.

steve

Same color on both ends. I bought what Steve told me to buy

https://www.tubesandmore.com/products/c ... ylene-fast

Nope, it doesn't matter which end is used as positive or negative.

-Steve

Thanks Steve just wanted to make sure

A type 80 rectifier has a directly heated cathode and will have electron flow long before the other tubes in that radio begin to draw current and load the supply voltage (20-30 seconds.) A C-L-C input filter requires a minimum load, or the voltage will be quite higher than the operating voltage. Thus, after a few seconds after turn on, that capacitor may be seeing a higher than expected voltage until the rest of the set "warms up." Besides ripple rating, many of those older caps had a surge voltage rating just for that purpose. A 600 volt cap would be a good investment. Or you could use two 450 volt caps in series, with twice the capacitance value and equalizing resistors, to be even more conservative. It may be cheaper as well.

Pete

-or- install a CL-90 on the mains in.

i had to do that with two of my restored RCA-86K7 radios, plus i used 500 volt capacitors for the electros as i do on any transformered set.

both fully restored sets would hit over 500 volts at turn on with the directly heated 5W4. i also tend to believe that the input resistance/impedance was high as well to create such a surge before the rest of the radio started to conduct.

using a 5Z4 (i think) instead of the 5W4 solved the turn on surge problem since it was indrectly heated. the B+ slowly, safely, and climbed up nicely, but one of the offsets was a higher B+ which was not a big issue. that could have been lived with.

the second offset was that the 5Z4 (i think) that i installed drew 500 more mA on the filaments than a 5W4. i did not want to put an extra 500 mA on an eighty year old transformer.

between the 500 volt capacitors and the CL-90, the startup is very nice.

steve

What is a CL-90

https://www.ametherm.com/inrush-current/

steve