Ideas for a Conn Caprice conversion

[Pdavis68]

So today I bought a 1959 Conn Caprice 426M in good condition. I paid $30 for this baby. Let my daughter and nephew play it in the driveway for the neighborhood for a bit and then pulled out leaf blower and the electric screwdriver and got to work.

It's got 2 channels (power amps) which does nothing for me, so I'm going to pull out one of the output transformers for something else and just do a single power amp with this. I've been wanting to do an amp with a 6SJ7 preamp, so I could use one of the extra octal slots for that. As you can see from the photo of the tube layout, it has some 12V6s, a couple 12AX7s, a 12BH7 and a 5U4. There's also an OA3 which I don't see much use for (saw a suggestion that it would make a good nightlight. Looks cool, for sure).

So really, I'm looking for ideas. I'm assuming 12V6s sound like 6V6s? So I was thinking maybe a 6SJ7 preamp into a 12AX7 driver into 12AX7 PI into dual 12V6 power amp. Does that sound like a decent way to go? Anyone have other ideas?

Oh, and the tone generator, as you can see, was loaded with 12AU7s. 44 of them... I'll see what I can get for them on ebay... Surely I can make my money back and then some. There are also a gazillion caps in the tone generator, all over the spectrum at 200V and 400V.

The 12" speaker is a Magnavox (I was really hoping for a Jensen). Is that going to sound terrible with a guitar?

This probably won't be my next project, but I'd like to be thinking about it.

[olddawg]

I doubt that speaker was made by Magnavox. I pulled a pair of 12" speakers out of a huge Magnavox console stereo once and they were mid 60s square magnet CTS like we're used in Ampegs. Not sure if I would use the 12V6s. Depending on the B+ a SS rectifies simplifies things and improves reliability.

[Pdavis68]

I've attached shots of the numbering on the speakers. If I'm not mistaken, the EIA codes are 232, which is Magnavox. I've also read elsewhere that Magnavox also stamped their speakers with the 583xxx numbers as well (in a posting by someone who was into Magnavox consoles). I could be wrong, though.

Why wouldn't you use the 12V6s? I've got 4 of them now (and they seem to be working fine). I don't have a huge selection of power tubes and a lot of the ones I have are singles, so if I want to do an AB amp, it's going to be 12V6s, EL84s, 7868s, or buy new power tubes...

[DRH1958]

The 12v6 is the exact same tube as the 6V6 except for the heater being 12 volt in stead of 6v. http://www.tubebooks.org/tubedata/HB..._2/12V6-GT.PDF They should be fine. And 232 is Magnavox's EIA code.

[Pdavis68]

That's what I thought. I only have one 6V6 and I'd love a 6V6 class AB amp, so this should be close enough. Thanks D.

I'm about half way through stripping the tone generators (except for tube sockets which I'm going to do separately). I've salvaged about 80 caps. About 50 of them 200V and the others 400V. I've tested all of them. Not including the oil and paper (all of which have drifted significantly), I'm averaging about a 97% good rate with these (within 10%). I did keep 2 that were right at about 11%. I figured that was close enough for my needs. But given that I had about a dozen HV caps before this expedition began, this is really going to get me in good shape. I'm also recovering a bunch of resistors (though I haven't tested those yet and figure I'll test them as I pull them out to use them).

The way things are laid out, the leads tend to be generously long. I've tossed out a few resistors with leads that were too short and a few caps that had glue covering the labels so I couldn't verify the values (there are 6 caps per tube in the tone generator and they're glued together in groups of 3. A small screwdriver readily separates them without damage.)

This is just turning into a great source of parts for me.

6 sections of the tone generator were inside a long metal chassis which I'm pretty sure I can cut up into 3 chassis big enough for a guitar amp. And I've recovered enough wire to keep me from needing to buy wire, probably ever again... I just keep getting happier with my purchase...

[Pdavis68]

Just finished stripping the tone generators of caps. By my calculations, I got a bit over 300 caps out of the deal. About 65% 200V and 35% 400V. 3 got tossed because the leads were too short. 2 got tossed because I couldn't read the actual values they were supposed to be and about 6 were out of tolerance. I'm really surprised by the condition of the caps. This doesn't include the PIO caps (there were only 3 in the tone generator). There was a transformer in the tone generator (PN 56274). Can't find specs on it yet, though.

Needless to say, I'm good for caps for quite some time. Lots of 400V ones in the .008-.015 range, so I'm good for coupling caps. I've got a mountain of 100K and 1M resistors, so I'm good for plate load and grid leaks. There were some other values as well, but 100Ks and 1Ms more than anything.

So, if anyone needs to stock up on parts, I can highly recommend the Conn Caprice as a good source.

As I said before, because of the way it's laid out, almost all the leads were long enough (some quite long) to work with.

[Enzo]

About those 56 year old caps. You are testing them by measuring their value, but that is not the major issue. You need to test them for leakage at voltage. Your meter measures caps with just a volt or so. A cap that tests fine at a volt or so may well leak like a screen door at 50-100-200-400 volts. You need to set up a high voltage power supply and a couple resistors so you can put the rated voltage across a cap and see if any DC leaks through. When I restore old amps, I am not replacing caps due to value shift, I am doing it for leakage.

One often overlooked resource in an old unit like this is the wire. TONS of insulated hookup wire in various colors. Have you priced buying wire recently?

[Pdavis68]

Enzo, thanks for the info. As always, you have great information to share. I will set up a circuit to test for leakage. Is there a level of leakage that's acceptable?

I did save the wire. There was even about 10-12' of insulated wire (though I already had a bunch of 6-8" pieces that I had salvaged from a television). Yes, I don't think I'll need to be buying wire anytime soon.

[olddawg]

I've attached shots of the numbering on the speakers. If I'm not mistaken, the EIA codes are 232, which is Magnavox. I've also read elsewhere that Magnavox also stamped their speakers with the 583xxx numbers as well (in a posting by someone who was into Magnavox consoles). I could be wrong, though.

Why wouldn't you use the 12V6s? I've got 4 of them now (and they seem to be working fine). I don't have a huge selection of power tubes and a lot of the ones I have are singles, so if I want to do an AB amp, it's going to be 12V6s, EL84s, 7868s, or buy new power tubes...

The only reason I wouldn't use 12v6s is if they were tired and was considering replacement in the future. I assumed they aren't that common. If they are easily sourced for a decent price, why not.... The Magnavox number may be an in house number. The speaker may have been made for them by a different manufacturer. Just a thought.

At $6.25 each I guess it isn't a big deal: https://www.tubesandmore.com/products/T-12V6GT

[Pdavis68]

About those 56 year old caps. You are testing them by measuring their value, but that is not the major issue. You need to test them for leakage at voltage. Your meter measures caps with just a volt or so. A cap that tests fine at a volt or so may well leak like a screen door at 50-100-200-400 volts. You need to set up a high voltage power supply and a couple resistors so you can put the rated voltage across a cap and see if any DC leaks through. When I restore old amps, I am not replacing caps due to value shift, I am doing it for leakage.

One often overlooked resource in an old unit like this is the wire. TONS of insulated hookup wire in various colors. Have you priced buying wire recently?

I have this 230V transformer, so I can get about 320V DC out of it. Would that be sufficient for testing the 400V caps? I could wire it up for 460V CT, but then we're getting up to 640V DC and I start getting pretty nervous.

[Enzo]

It ain't rocket science, 300v is better than 2v, eh?

How much? I don't really want to see more than millivolts.


We all start somewhere, and beginners often have more time than money. When I was a kid learning electronics in the 1950s, I would go down the road to a local TV repair shop, and I'd find dead TVs out back that they were tossing out. I'd take the chassis from a dead TV, bring it home, and strip it for parts. This was before circuit boards came to consumer goods. SO I had many resistors and caps with snipped leads or twisted leads. Today I buy new resistors in bulk - they only cost a penny that way. I toss them in the drawers. But I never went through and fished out all those old used resistors. SO in many of my drawers, there are still some old resistors mixed in with the new...with their twisted or short leads and all. These 60 years later, I don't know how many of them are even close to value, but now and them I remember where a certain bit came from.

[bluto]

The only reason I wouldn't use 12v6s is if they were tired and was considering replacement in the future. I assumed they aren't that common. If they are easily sourced for a decent price, why not.... The Magnavox number may be an in house number. The speaker may have been made for them by a different manufacturer. Just a thought.

At $6.25 each I guess it isn't a big deal: https://www.tubesandmore.com/products/T-12V6GT

FWIW 12V6's are common and easy to find NOS from various makers because they were used in a LOT of tube auto radios back in the day. I've built a couple of amps with them, using a cheap 12V filament transformer from radio shack and a separate low cost 230V xfrmr for B+. Anyway, this worked out well, my beat up breadboard amp is currently a parallel SE Gibson GA-9 using two 12V6's.

[olddawg]

For a new build, I wouldn't use any old resistors, capacitor, diodes, or tube sockets. They are dirt cheap online and it will save you a world of headaches in the future by not reusing them. New ceramic tube sockets takes away the possibility of a lot of possible intermitancies. I would even be leery of the hookup wire because 50 year old vinyl (or whatever petroleum product they used, they all outgas) gets brittle and cracks.

[Pdavis68]

This hobby is already expensive enough. If I intend to pursue it at all, I'm going to have to cut some corners and that's probably going to mean reusing parts. I'm not out to build works of art and at the moment, I'm not even out to build the most amazing amp. Right now, I'm largely interested in learning more and getting a better handle on amp design and amp building. If a 50 year old resistor or capacitor (which has been in an organ that's been used for 50 years, not sitting in a garage) is still within specs, I don't see any reason not to use it. Seems like it's probably a pretty reliable component if it's gone that long.

[olddawg]

Suit yourself.. Resistors are pennies, new ceramic tube sockets are around a dollar each, caps are cheap as well except power supply filter caps that you will want to replace anyway. What's your time worth?