Filter Caps for Sho-bud Amp

Larry Robinson · From: Peachtree City, Georgia, USA

Does anyone know of a source for 4000ufd, 60V caps or replacements used in Show-bud "Christmas tree" amp? I've tried several parts supply houses here in Atlanta area and none have a source or anything usable. The physical dimensions for the caps in the amp now are 1 3/8" in diameter and approx 3" long cannisters. They are leaking and need replacing. I'm repairing this amp for a fellow musician who is a steel player and forum member. Any help locating these parts appreciated.

Regards,
Larry Robinson

David Mullis · From: Rock Hill, SC

Hopefully Mike Bagwell will see this. He replaced the caps in a Christmas Tree amp that I bought from him. The caps were a lot shorter that the originals, but the values were the same.

John Floyd · From: R.I.P.

I'm having similar problems with some 30 year old military equipment finding Electrolytic filter caps that are the same size as the originals. Seems capacitor Technology has advanced and downsized most everything in the Electrolytic Cap field.

As long as it meets the same Value and Working Voltage requirements, it shouldn't be a problem, except for mounting in the chassis.

[This message was edited by John Floyd on 10 January 2004 at 06:56 AM.]

Brad Sarno · From: St. Louis, MO USA

Digi-Key (www.digikey.com) or Mouser (www.mouser.com) carry these caps. I recently re-capped an old Gretsch amp which like the Sho-Bud single channel. The replacement cap's were about 1/3rd the size of the originals but value was the same. I like to use that Goop glue to hold them in place since the old clamps were too large.

Brad Sarno

Blake Hawkins · From: Florida

John, When you want to preserve the original appearance of the chassis and get it working, you can use this old radio restorer's trick which I have done many times.
Carefully take the original part apart, then
insert the modern component and reassemble.

Electrolytics can be cut with a fine saw, or the end carefully drilled out, the internal
parts pulled out and discarded then the new component or components inserted and the assembly resealed.

The same technique can be used on old tubular caps, electrolytics, and multicomponent assemblies.

It just requires a lot of skill and care.
Open it in such a way that you relieve any internal pressure safely.

Blake

Brad Sarno · From: St. Louis, MO USA

Blake, another way to preserve the original look is to just leave the old capacitors there, in their clips but disconnect them and use new ones inside the chassis. Modern electrolytics are so small that they can usually fit inside with no problem.

Brad Sarno

Mike Bagwell · From: Greenville, SC, USA

I used replacement caps from peavey, same as used on yhe old session 400. They are much shorter, but have the same diameter as to fit in the existing bracket. They do not have the screw terminals like the mallorys, so I just soldered them in. Its a bit of work, but the results are fine.

Mike

John Floyd · From: R.I.P.

Larry
When You Install Those new caps in the Shobud amp, you may want to reform them, by slowly bringing them up to their rated working voltage with a current limiting power supply, the current limit should be set at 100MA or less and wait until the voltage rises to the rated working Voltage. this may take some time. THe Voltage control should be set open circuit first with the current limit disabled and then connect it to the cap bring the current slowly up to 100 MA limited, You will see the Voltage slowly rise to its preset value.Which should be the working Volatge of the cap.
Not all new Electrolytic caps can be used right out of the box. I have seen instances where the new cap would appear shorted and blow fuses if not reformed properly.

Blake
I (my employer) was just awarded an overhaul Contract with the US navy that calls for for Strict MilSpec/ Mil Standard Parts. I doubt if the inspectors would pass something like you described and it involves replacing twenty 12,800 mfd 100 wvdc caps in one particular assembly. We may be able to get a waiver to modify the mounting scheme, but to do this it is our responsibility to provide new drawings with new part numbers.

I would be afraid to make mods like this, this beast provides 80 Volts DC at 3,375 amps to Sonar Transmitters. I have a healthy respect for its ability to kill me, I have been involved with this system for over 27 years and Those 27 years are a testament to my respect for it. You only have to see one person killed with this monster and you never forget. You don't call the EMT's or undertaker, You sweep up the victim in a dustpan.
Thanks
John

[This message was edited by John Floyd on 10 January 2004 at 12:40 PM.]

Larry Robinson · From: Peachtree City, Georgia, USA

Thanks for the input. I"ll probably get caps from Peavey.
Please close the thread.
Regards,

Larry

Blake Hawkins · From: Florida

John,
Sorry, I didn't know you were a high echelon repair depot.
My concept of repiring and restoring military equipment is of WW II machines in the hands of collectors.

Of course you must do it to mil spec.

I'm a retired Television Engineer and would never think of any off the wall work in a Television or Radar Transmitter which has high voltage and high current and must be used 24/7 with the maximum MTBF.
Never worked on a Sonar Transmitter but it sounds like fun.

Brad, Thanks, I've done that too. Lots of old radios with cans on the top of the chassis and plenty of room underneath.
Many of the old tube type "3 Way" portables
use a large can electrolytic on the top of the chassis, and the cap lugs are tie points for the circuit. No room for any extra components. Most of those have a cardboard sleeve on the cap which can be replaced after repair and everything looks as it was.

I've done some pre 1940 guitar amps in which the electrolytic caps are in wax impregnated, cardboard boxes. These are easy to do and your collector amp looks original inside and out.
Blake

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