My Grandpa's Old Radio: It's time I got her going

[sluckey]

Why aren't we using Field Coil speakers anymore?

Same reason we aren't still driving a Model T.

[martin manning]

I think I'll put some CR2032 batteries in their place...

That's a 3V Li cell. I would choose a 1.5V alkaline.

What should I expect the result to be to the radio when they are dead?

The bias would be off. Interesting that some recommended just switching to grid leak bias using a large grid leak resistor.

[bcmatt]

That's a 3V Li cell. I would choose a 1.5V alkaline.

Whoops! Weird that someone on that thread uses them. Any reason not to use a Li cell if I can find one between 1-1.5V?

The bias would be off. Interesting that some recommended just switching to grid leak bias using a large grid leak resistor.

Ya, that idea was tempting, but looking at my schematic, I got confused about how I would implement that method. Do you think that B.C.1 is for biasing the 84M?
What would you do, Martin?

[martin manning]

Li chemistry produces 3V. I'm basing my recommendation on the assumption that the original cells produced around 1.2V. There are also zinc-air batteries that might work.

Do you think that B.C.1 is for biasing the 84M?

Looks like it does.

[bcmatt]

I'll have to measure the actual dimensions. Maybe something like this:
4Pcs Rechargeable Battery, 2/3AA Size 1.2V 650mAh Solar Light Battery https://a.co/d/7T9h4qq

[martin manning]

I'd go with this: https://data.energizer.com/pdfs/395-399z.pdf or this: https://data.energizer.com/pdfs/a76z-.pdf
Alkaline seems to have a slower voltage roll off, so maybe that would be the better choice. A76 is a bit bigger too.

More background info: https://antiqradio.com/post_mallory-bias-cells.html

[bcmatt]

I'd go with this: https://data.energizer.com/pdfs/395-399z.pdf or this: https://data.energizer.com/pdfs/a76z-.pdf
Alkaline seems to have a slower voltage roll off, so maybe that would be the better choice. A76 is a bit bigger too.

Oh ya, I was looking at the A76s because I have a couple of old film cameras that require those batteries as well.

[bcmatt]

The cap cans in the schematic are 25uF and 60uF. Not quite wired in parallel?

Cap Cans.jpg

I see that in actuality they are currently 30uF and 40uF 500V respectively.

20230904_152429.jpg

20230904_152558.jpg

I actually have several electrolytics that were almost or very temporarily used in other projects:

20230907_071903.jpg

Any thoughts on whether I should replace with what's on the schematic, or what they actually were? Would I even notice a difference?
I'm thinking maybe of using an F&T 30uF for the smaller one,
but trying to decide whether to use the JJ 2x 32uF can for the one labelled as 60 on the schematic, or just use a Sprague 40uF to replace it with the same as what is actually being used.
Do you think it is more about which I can get to fit easier?

[bcmatt]

I don't know if maybe the cap cans were replaced once already, but they are even further from the schematic than I thought. The 30uF can is in the place where there should be a 60uF capacitor on the schematic and the 40uF can is in the place of the 25uF capacitor on the schematic.

Cap Cans.jpeg

[martin manning]

I'd follow the schematic using values as close as you can get. Maybe 68u for the 60u, and either 22u or 33u for the 25u.

[bcmatt]

I'd follow the schematic using values as close as you can get. Maybe 68u for the 60u, and either 22u or 33u for the 25u.

Ok, cool. Thanks. That's pretty much what I'm doing. Good to know I'm not wrong to err on the side of the schematic.
I replaced this 40uF can that's supposed to by 25uF with a 30uF axial cap and left the can in place to keep it's hole plugged. I felt I needed to replace the red rubber insulated wire with some blue cloth stuff because it was looking rough.

25uf can.jpg

30uF Can.jpg

This 30uF can that is supposed to be 60uF I pulled out because I need the space to mount this 2x32uf can inside the chassis.

30not60.jpg

2x32.jpg

I'll wait to mount it so I have room to work pulling all the wax covered caps out.

[martin manning]

I'll wait to mount it so I have room to work pulling all the wax covered caps out.

I'd recommend doing those one or two a a time, and take pictures before clipping the old ones out. Mark the outer foil leads of the new ones, and match them to the originals. Interestingly, the old caps have both a printed band and a red paint dot, which are not always the same.

[bcmatt]

I'd recommend doing those one or two a a time, and take pictures before clipping the old ones out. Mark the outer foil leads of the new ones, and match them to the originals. Interestingly, the old caps have both a printed band and a red paint dot, which are not always the same.

The old caps seem to have the outer foil pretty clearly marked but the my new ones I have on hand are not so clear... is there a way to tell?

20230909_210952 (1).jpg

(I know I have to ground that cap can and there is a third larger (2uf) cap to add on the top left that is parallel to one of the partially connected new ones.)

I feel like I vaguely remember someone had a way to test for where the outer foil is with noise or headphones or something....

look at all the pretty tubes this thing uses:

20230909_192142.jpg

[martin manning]

I feel like I vaguely remember someone had a way to test for where the outer foil is with noise or headphones or something....

A couple of ways of finding the outer foil lead are described here: https://ampgarage.com/forum/viewtopic.php?f=6&t=30459

[bcmatt]

A couple of ways of finding the outer foil lead are described here: https://ampgarage.com/forum/viewtopic.php?f=6&t=30459

Thanks Martin. I'll check all the rest that go in... as well as the ones that I can take back out easily enough.