[Derek D]

I'm about to begin recapping 2 Philco 620's. For the electrolytics, I was going to order a 10uF 500V and 20uF 500V. For all other caps I was planning on ordering all at 630V. Is this reasonable? I'm new to working on these old radios, and want to make sure I'm not missing anything.

Also, is it generally true that the mica caps will not need to be replaced? I'm placing an order and want to make sure it is complete.

Derek

[Ron Ramirez]

Hi Derek

You could use 450V electrolytics, but what you specified is just fine. Taking into consideration today's higher line voltage, the unfiltered DC from the rectifier tube will be around 350-375V.

Most of us use 600 or 630V metalized film capacitors, not only for the safety factor but for ease of stocking parts; you know, why bother with 200 or 400V units when 630V units will do, and are small enough to fit inside old cardboard tubular shells (if you restuff your caps)?

As for mica caps. For a long time, the universal school of thought was that micas were very stable and not prone to breakdown. This is no longer the case; as the original micas continue to age, even they are beginning to break down and require replacement. So, if you don't want to have to go back into your radio later on, you might wish to consider replacing the micas now, and be done with it.

[Derek D]

Thanks Ron.

If you don't mind, I have a few more questions regarding the caps.

1. Are the caps that are said to be part of another part replaceable( ie the compensating caps or the 1pF that is part of the tuning cap )?

2. What's the difference between a Bakelite block and a Twin Bakelite block?

3. Part 67 says it is an 8uF & 8uF Electrolytic. I take it that this is a multi-section cap. Do I need to replace with the same?

Thanks for all of the help. I'm just getting started in this, and need all the help I can get.

Derek

[Ron Ramirez]

Derek

1. No.

The 1 pF is, most likely, a wire "gimmick" which is run between the oscillator stator terminal and RF stator terminal of the tuning condenser, connected only at one end. The end that is not soldered is probably wrapped around the other terminal but not electrically connected. This is a "gimmick" - a twist of wire giving a very small, but necessary, capacity in the circuit.

2. A "twin bakelite block" is merely a bakelite block containing two capacitors of the same value.

3. Part (67) contains two 8 uF electrolytics in the same can. It may be replaced by two separate 10 uF, 450V electrolytics.

[Derek D]

Thank you Ron.

I have another question for you. I've been reading something about X/Y safety caps. If I understand it correctly, when these caps fail they fail open. Are you using these, and in what part of the circuit are these normally used?

If anyone has experience with these, I'm in need of education. Thank you all very much, this project would be much more difficult without the help of the people from this phorum.

Derek

[Ron Ramirez]

X/Y safety caps are discussed to some length in the "philco bakelite blocks" thread:
http://www.philcoradio.com/phorum/showth...hp?tid=121

Yes, they are designed to fail OPEN. They are designed to be used in line-to-ground or line-to-line applications. In other words, the only bakelite block you would put X/Y caps in would be the one where the AC cord is attached. This block has two capacitors, one leg of each connects to a leg of the AC line; the other end of each cap goes to ground via the grounding lug on the block.

Use conventional metalized film capacitors in the other blocks in your Model 620 sets.