Recapping Old Hammond Power Amp

[Asa]

Hey, I'm in the process of replacing some blown caps in the power amp of my Hammond X5, I've identified the ones that need replacing - however, they're about 3 times the size of the new ones (same spec), so I was wondering if anyone with experience recapping old gear had any tips on how to fit the new caps in place of the old?

 

Here's a photograph of one of the new caps next to the old ones - they're secured in place by a clamp-like mechanism, with the connections to the PCB soldered at the top.

 

http://i.imgur.com/4cBfq3ul.jpg

[BlueAndGreen]

I would solder the new caps on some "perf" Board

perf board

 

and then solder the heavy wires to the board, not to the caps, and them mount the board with screws.

Make sure the new caps have at least the same voltage rating.

[WesG]

Lots of ways to do this... one thing to remember is that if there are small signal wires nearby that wire dress in the amp should not be altered, or you might wind up adding hum.

 

If I was going this, I would probably use one terminal of the old capacitor - the one with the long wire - as a mounting point for the new capacitor...providing I could figure out way to stabilize either the other lead or the body.

 

Perf board with stand-offs works, too, and has the advantage that you don't need to worry about lead vibration damaging the capacitor over tens of thousands of gigs.

 

Wes

[MIDI2XS]

It's amazing how much smaller those 3300µF 35V caps have gotten over the years. I see that you chose 105C rated replacements, which is a good idea since heat is an electrolytic cap's enemy.

 

My approach would be to start by cleaning the tops of the old caps. Then take a new cap, place it on the top of an old cap, lying perpendicular to the orientation of the old one, and positioned so there'll be no problem with getting things closed back up afterward. Solder the new cap's leads to the terminals of the old. Pay close attention to polarity, of course. Do the same with the remaining cap.

 

At that point, verify that the supply voltages are correct and the amp is operational. If all's OK, you could glue the new cap to the old one in each case with 100% silicone sealant (RTV).

 

If there's a concern that the old caps are (or might become) electrically leaky, clip off one terminal from each of the old caps, close to the top of the cap. I'd leave the common terminals (black wires) intact and snip the ones with the red (+Vcc) and blue (-Vcc) wires. Separate the clipped-off terminals a bit from the old cap, and use blobs of silicone sealant to prevent things from moving.

 

[Asa]

Thanks for all the suggestions - I ended up removing the old caps and fashioning some adaptors for the clamps out of rubber to hold the new ones.

 

Still hasn't fixed the problem (Leslie's recieving speed control messages but no audio), but they needed replacing anyway.

 

Next step is looking at the amp in the Leslie, testing yet more capacitors...

[mate stubb]

Make sure your leslie crossover isn't fried, before you dig into the amp.

[Asa]

It's an 820 (single rotor) so I'm assuming it doesn't have a crossover as far as I know.

[WesG]

Make sure audio is leaving the Leslie kit in your organ before you start digging in the amp, too!

 

It should be pretty hot, in the neighbourhood of 5-7VAC.

 

Wes