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20/10/10 cap can for Supro 1624

Tone Meister

Member
Messages
3,266
Have a bone stock 1962 Supro Model 1624 and am trying to source a direct replacement for the stock Mallory 20/10/10 @ 450 cap can. There really isn't all that much room inside the chassis to put a terminal strip and individual caps.

The problem I'm running into is the diameter of the can. The stock can is 1" in diameter and the replacements I'm finding are all 1 3/8" and I am dead set against making the hole larger to accommodate the currently available cap cans. The amp has never been touched and all it needs is the replacement cap can and the two 35/50s.

Open to any ideas that'll help preserve this beauty the way it is now.






 

EFK

Silver Supporting Member
Messages
1,115
You won't find one. You can buy a CE Dist 20/20/10/10 can, or a 20/10/10/10, and use two wafers to make an adapter. You take one wafer and cut off the screw tabs - this goes against the can, as a spacer. Then you take the second wafer and redrill for the smaller screw centers. Take two 6/32 screws and grind the heads down fairly flat. Stick them through the redrilled 2nd wafer, and the spacer (cut off wafer) gives them clearance. Now the larger can will fit. You fold over two ground tabs to hold the whole package together, and put washers in between the assembly and the chassis so that the folded ground tabs don't touch the chassis (thus maintaining the original ground scheme). The other two ground tabs are bent in slightly so they don;t touch the sides of the smaller chassis hole (use a little insulating varnish if necessary).

Hope this makes sense. I've probably done it a hundred times, literally. Alternately, I've seen people take the larger cans and fold over the ground tabs inside the hole and solder to the chassis (the ground tabs will just clear the hole, without enlarging it), like a brown princeton, it will work but I don;t personally like to do this. No wafer in other words.

Either way you are using only 3 of the 4 tabs in the cap can. DO NOT use more than 10 uf on the screens - that sag is necessary to keep the tubes from completely self destructing at their 100% plus bias and only a 1K dropper.
 

wyatt

Member
Messages
4,169
What is the diameter of the hole in the chassis? Spacing of the mounting screws? Can diameter is less important.

Oh, EFK beat me to it.
 

EFK

Silver Supporting Member
Messages
1,115
A dual 20, with 20 on the screens, will eat those tubes in very short order as the plate current will run away when the amp is 'dimed' - which it inevitably will be, as that's the only reason people love these amps!

There's a very practical reason that Valco consistently used very low screen capacitance on all their amps.
 
Messages
1,657
Richey Golds makes a dual section 10uf/10uf @ 500v that is 1" wide (and 1-5/8" tall) and mounts with a screw-on clamp, which is perfect for your Supro, considering the old "can cap" is already mounted with screws.

I installed one of these in my 1959 Gretsch (Valco) 6163 when faced with the same 20/10/10 dilemma. The Richey Golds 10/10 @ 500v caps can be had for about $10.

Then you'll have to put a 20uf cap inside the chassis. I've worked on hi-fidelity tube receivers, and a chassis can get MUCH more cramped than that Supro... so believe me, you won't have a problem squeezing in a 20uf @ 450v cap.
 

Tone Meister

Member
Messages
3,266
What is the diameter of the hole in the chassis? Spacing of the mounting screws? Can diameter is less important.

Oh, EFK beat me to it.
The diameter of that hole is also 1" and we're hoping to preserve the original appearance as much as possible.

A dual 20, with 20 on the screens, will eat those tubes in very short order as the plate current will run away when the amp is 'dimed' - which it inevitably will be, as that's the only reason people love these amps!

There's a very practical reason that Valco consistently used very low screen capacitance on all their amps.
Yep, I have been told this several times already, so I am certainly gonna keep it in mind. Great info EFK

Richey Golds makes a dual section 10uf/10uf @ 500v that is 1" wide (and 1-5/8" tall) and mounts with a screw-on clamp, which is perfect for your Supro, considering the old "can cap" is already mounted with screws.

I installed one of these in my 1959 Gretsch (Valco) 6163 when faced with the same 20/10/10 dilemma. The Richey Golds 10/10 @ 500v caps can be had for about $10.

Then you'll have to put a 20uf cap inside the chassis. I've worked on hi-fidelity tube receivers, and a chassis can get MUCH more cramped than that Supro... so believe me, you won't have a problem squeezing in a 20uf @ 450v cap.

Heading there now to find it. Thanks everyone for the in depth info. I'll report back here with the solution we choose.
 

EFK

Silver Supporting Member
Messages
1,115
After a bunch of messages with CE Dist and some pestering by other folks as well, CE Dist now makes a 20/10/10 at 450V which is the same form factor as the old Mallorys. They have it listed with their can caps but the picture is incorrect - the photo is of a 4-tab cap, but the piece they make IS the correct 3-tab form factor to fit all the old Valcos. They just used the wrong photo. However, the piece they are making uses PCB type ground lugs instead of the wider twist lock lugs, but it works easily enough and FINALLY there is something that fits the 3-tab form as a replacement without having to mod a chassis or spend a lot of time coming up with adapters.
 
Messages
1,657
After a bunch of messages with CE Dist and some pestering by other folks as well, CE Dist now makes a 20/10/10 at 450V which is the same form factor as the old Mallorys. They have it listed with their can caps but the picture is incorrect - the photo is of a 4-tab cap, but the piece they make IS the correct 3-tab form factor to fit all the old Valcos. They just used the wrong photo. However, the piece they are making uses PCB type ground lugs instead of the wider twist lock lugs, but it works easily enough and FINALLY there is something that fits the 3-tab form as a replacement without having to mod a chassis or spend a lot of time coming up with adapters.
Well, that's good news, but I'm sure 50% of buyers would be getting it for a Valco resto (in fact, before they discontinued it, I recall the original description for this type to mentioning "for Supro replacement")... so why in the world would they put PC-mount tabs on it? That's pretty ridiculous.

I remember when they discontinued them. I had my Gretsch 6163 waiting for a restoration, I saved the 20/10/10 in my shopping cart... came back about a month later, and it was discontinued.

I may pick one up... but since I've already had to swap out the awful old wax caps, what's the point of looking original?
 

EFK

Silver Supporting Member
Messages
1,115
Baxtercat - that is very, very kind of you. Thank you so much - I hope it's not interpreted as spam.

DT - I don't know why they put those stupid PCB tabs on it either but it does seem like a silly move. How many people are using these in conjunction with PCBs? My guess is that they had something else on hand already that they could just set up as 20/10/10 so it was the cheapest way for them to make them.
 






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