7800µ/100V cap can for Acoustic 370

[PRNDL]

I've been fixing an Acoustic 370 and it sounds great after replacing about 20 parts that fried.

The owner, however, states the amp sounds funny at high volume with the 80/100 Hz EQ sliders up. I'm thinking that the power supply electrolytic cap is going bad, and causing excess ripple.

It's a very big 7800µ/100V cap can (after a diode bridge).

Any ideas on where to find a replacement, or a modern equivalent (from Mouser)?

Would these be suitable?

8,000µF 100vdc Can KS-19830L,7 3-5/16" x 5-7/16"

7,700µF 200v (250v Surge) Can Aero M CGS DC9316, 85ºC, 3" x 6"

http://www.surplussales.com/Capacito...F-99999uF.html



Thanks!!

[drewl]

I found one in an old piece of HP test equipment, but you might try getting a couple 3000-4000uf caps and wiring them in parallel.

[Robert M. Martinelli]

Yeah, the value's not critical, as most electrolytic can be up to 20 percent over or under the specified value.....I' d go paralleling a 3300 and a 4700 Microfarad / 100 V, or even a couple of 4700 Microfarad /100V to improve filtering.
Regards
Bob

[Enzo]

It is a large can cap, clamped in, I would stick with a single cap, but the value doesn;t matter. 8000 or better 10,000 would be easy to find in a 100v cap. When buying large caps, ALWAYS check the dimensions..You won;t feel so smart when that new cap is a half inch taller than the amp chassis.

Mouser sells a screw terminal 8200/100v cap for $22.13 and a snap-in of same rating for $15. You'd have to make solder connections to save the $7.

But before you order up a huge cap, why not make sure instead of guessing? Slam a heavy signal into it and put it on loads or speaker, then SCOPE the power rails. Arre they sagging hard? Is there excess ripple? Are signal peaks lumpy? Is the amp clipping on one or both polarities? is the signal coming out the preamp clean? I'd hate to order an expensive cap to find out the graphic itelf is the problem. Or a loss of preamp node decoupling. And how do you know it is the filter cap instead of the speaker cap?

But you still think it might be that one large filter? Tack some parallel capacitance across it with clip wires.

[PRNDL]

Thanks Enzo

I now have an ESR meter (BK Precision 830) and plan on testing all three.

I found these three on Mouser
(the trick seems to be using their web search instead of flipping through the catalog).

8200uF 100v -- 75-36DY822F100BL2A
Vishay/Sprague Large Can Computer Grade Capacitors 100V 8200u $22.13
Dimensions: 51 mm Dia. x 92 mm L

3900uF 80v
661-EKMH800VNN392MA Page: 721 United Chemi-Con
Mini Radial Aluminum Electrolytic Capacitors - 105 Degree 3900uF 80volts 20% $4.58

1000uF 75V -- 539-CG102U075R3C
Mallory Screw Terminal, Computer Grade Electrolytic Capacitors 1000uF 75V $13.54
1.375 in Dia. x 3.125 in L

The Mini Cap 3900uF/80V is very small, and I wonder if it might be better to use a larger value (this is for the output).

I'm also thinking that these new caps might be preferred over NOS cap cans, especially since they're not exact replacements. The total price is similar.

[52 Bill]

I'm also thinking that these new caps might be preferred over NOS cap cans, especially since they're not exact replacements. The total price is similar.

Unless there is a real need for vintage correct parts, my vote would be for the new caps. At least you know they are fresh and will work for the next 10 years.

[gbono]

370 caps

I have purchased capacitors (Al electrolytics) from surplus sales and the parts had +10 year old date codes. You will find that new electrolytics are smaller and will not fit the original clamps.

I made up some PCBs that fit the hole pattern of the clamp hardware. You can easily double the capacity using modern PCB mountable capacitors and this mod is much cheaper than a can.

Did you replace the PA output and driver stage transistors?

[PRNDL]

Did you replace the PA output and driver stage transistors?

Yes.