[Jamesm]

I have been reading on a few sites that some people replace the filter capacitors with the 630v poly/foil caps ( non electrolytic) Is this a good idea or not?

[Phlogiston]

I think it is a good idea, if you can get them into the original cans (restuff). The physical size limit for this is about 10mf and they cost about $6 - $8 each. Sometimes you can stack them for 20mf. It takes a little practice restuffing caps especially the copper Mershons.

[Jamesm]

It should not be a problem re stuffing them into a can. They only call for 1.0 and 1.5mfd.
What is the benefit in using non electrolytic ? I think that's really what I am trying to find out.
Thanks phlogiston

[Mondial]

The small value electrolytics like 1 or 2 uF sold today are not rated for the amount of ripple current they will be subjected to in a vintage radio power supply. They are physically tiny and cannot dissipate the heat created by the charge and discharge currents flowing through their high effective series resistance. In use they will overheat and eventually fail.

A film cap has a very low ESR and will not have this problem. The original caps were paper and more closely resembled a film cap than an electrolytic.

The best choice for replacing these low value paper filter caps is a metallized film style cap. They are cheap enough and will last almost forever, so practically speaking you will never need to replace them again.

[GarySP]

Hello. The only reason I can see for using electrolytics is when space is an issue, as they are smaller. However, in the case of the model 20 the filter caps are in the large can next to the transformer. Empty out the old caps in the can, and you'll have enough room to hear an echo in there! The can isn't that hard to rebuild, and is touched on in other threads in this forum. I used poly-film non polarized caps with no problem. Go with 630v caps. Take care, Gary

[Jamesm]

Ok so I should use the 630v caps at the value as described by the schematic correct? The radio would not benefit from having slightly larger values? I will be changing them out this week.
Thank you all for your help. I am fairly new to old radios, I love them
. I have taken courses in digital circuits in school but these are completely different.

[morzh]

Obviously your course of digital circuitry was short on teaching the history of digital circuitry. The first flip-flop was using tubes, and the computers in Blatchley Park were tube-based.

But if you really look at the element-based schematics you will see that a transistor and tube flops or multivibrators are very much the same.

The single difference is the size (and, of course, the size dictates the speed).

[GarySP]

I personally went with original value 630v caps when I rebuilt mine, with one exception. One cap was rated .13 mfd, and not easily available in that value. I went with a .15 mfd cap there with no issues. Take care, Gary

[morzh]

Gary

if you means the 0.13uF across the filter choke, it needs not to be anywhere near 630V. 100V is good enough and 200V is an overkill.

[Jamesm]

If you need a .13uf and you can't find one of that value, can you not just connect them in parallel? So have a .10 and a .03 ?
Also is there a problem with going too high on the voltage rating?

[jerryhawthorne]

For low value caps in the power supply I have found that in my experience the " solen fast caps" from AES are just fine and high quality. The first cap on my Scott 800B power supply was 4mfd. Lot of voltage and current. E-cap just got hot and then shorted. Not fun. Non polarized fast cap ran cool. Just my experience. I used them on my 1929 Fada, lots of room inside the giant tar filled block. I'm a fan of these caps for high voltage and low mfd values on old radios. A little pricey but you only need a couple. May not fit well in a "standard" cap can for your radio but if they are single or perhaps a double I suspect you can stuff.
Regards, Jerry

A link to 4 of them installed after removing a lot of ugly tar. As I recall 3 of the 2 or 3mfd and a 1mfd.
http://antiqueradios.com/forums/viewtopi...6&start=80

[morzh]

You do not necessarily need 0.13uF cap - you will do just fine with 0.15uF. remember, most these caps are themselves of 20% tolerance.

[Jamesm]

So really, in radios the only reason why electrolytic caps are used is because of their small size?

[morzh]

Well, more or less, yes. At the tme of invention, same as today, the electrolytic cap provides the highest per unit of volume capacitive density.
As your load increases, using smaller values no longer provides adequate filtering, and using lots and lots of film or tubular paper caps is size- and cost- prohibitive.

However where one needs a low capacitance, often times a film cap will do.

Also electrolytics have poor frequency response so if one needs low ESR/ESL and good frequency characteristics this is where other types like ceramics come in.

[GarySP]

Morzh, at the time I didn,t know I could get away with a lower voltage rating cap for the across the filter choke. I was a newbie just getting started on my first radio, and the electronic store near me had all the caps in stock in 630v rating. Overkill...yes. Functional... also yes, and not all that expensive anyway. Take care,Gary