[vydram]

I figured out the replacements for all of my other paper condenser except this one?  What do I replace this one with - I have tried all morning to decipher it.  The photos are of the same part - just different angle.  Its the largest condenser in these types of radios.  2 wires on one end; one on the other.

THANK YOU!
MV

[GarySP]

Welcome to the Phorum,MV! What you have is a dual 20 MFD 'condenser' with a common negative. If you are looking to repack the paper cap you could use 22 MFD electrolytics (for size issues). Pay close attention to wiring them common negative. I would also bump the volts to at least 250 v. I know just enough to be dangerous at my stage in the hobby. There are other sage minds here to help with a lot more expertise. All you need do is ask. Take care and BE HEALTHY! Gary

[RodB]

Hi and welcome to the Phorum. You can replace the dual 20mfd cap with 2 - 22mfd 160 volt aluminum electrolytic caps. Tie the common negative leads together and you have the same as the original, but smaller. Like Gary mentioned, you can remove the guts of the old one and insert the new parts. Use a black wire for the common and red for the positive leads. Fill the ends with hot glue.

Some will mount the caps on a terminal strip and run the wires to the strip terminals.

[klondike98]

Welcome to the Phorum!


As the guys have mentioned, you can replace with two 22uF caps with their negative lead connected together.  Here's an example of a similar (although this one had 3 caps instead of 2) situation where the new electrolytics are inserted into the gutted paper tube.  usually some warming of the old capacitor with a heat gun and then some pulling and digging will get the guts extracted.  See: https://philcoradio.com/phorum/showthrea...8#pid35928

The new electrolytics were pushed further into the tube than you see in the photo and then sealed with hot glue. the three positive leads are not shown but exit from the top side of the tube.

[vydram]

Thank you to everyone, I had to keep looking at the pictures and found the new caps on-line and I see it now - written in PLAIN sight   !.  One question - why boost to 250V?

Thanks all!
MV

[MrFixr55]

Hi Vydram,
I, too, wonder why 250V for the filter caps. Read on:
The TH4 is a variant of that is known in the hobby as an "AA5" Radio, a Superheterodyne using a Pentagrid Converter, Pentode IF amplifier, Duo Diode - Triode as Detector ad 1st AF Amp and a Beam Power Output Tube. The B+ on this radio is typically between 100 and 135V.

For non-electrolytic caps (capacitors) it is good to use as high a voltage rating as possible. the old paper / wax caps used in these radios typically had a maximum voltage rating between 200 and 400V. Current mylar and poly caps used by the hobby are typically rated at 630V.

However, for electrolytic caps, there is a difference. Electrolytics are rated (or used to be rated) in "Working Volts". this is because the cap is designed to work at a specific voltage. Back when I was a kid and learned this (50 years ago), if you used a cap with too high a working voltage, the capacity of the cap would drop. This may or may not be the case with current electrolytic technology.

The Working Voltage of the cap affects size and price. The 160V caps should be fine in this radio. Go to 200 if you have concerns.

Experts, please comment yay or nay to what I posted here.

[David]

In North Florida the line voltage runs between 119-125 VAC. 125 divided by .707 gives a peak voltage of 176.8 this is why I go with 220V-250V caps for a AC/DC set.

[vydram]

Thanks everyone! I will do some more research based on these responses... they all make sense to me.

[GarySP]

Electrolytics rated to handle the line voltage will do the job. I like to build a little 'buffer' zone into the circuit if I can. I've seen spikes on our Michigan grid hit way above suggested line voltage. I like to build a little insurance in if I can. I have not seen issues with increasing working voltage to double live voltage on sets I've replaced them on. Not saying it can't happen, just hasn't with me. Since you're replacing 20MFD caps with 22MFD caps the drop should still keep the value near 20MFD +/- 20 percent. That's my story, and I'm sticking with it! Please correct me if my reasoning is in error... that's how I learn! Take care and BE HEALTHY! Gary