View Full Version : Changing Capacitor values?


twist72
11-29-2007, 10:19 PM
Hi Y'all,

I'm in the process of refurbishing a Heathkit AA-1214 and my next step is replacing all the electrolytics as well as the cheap polypros. I am having difficulties locating exact values and need some guidance. BTW almost all the caps are TEMPLE brand if that means anything to ya. I can't find my camera so I am unable to take any pictures at the moment.

The PS Caps are 5000uf 30v. Can I go ahead and use 10000uf Nichicon Muse KG series caps?

Also there is another radial capacitor next to the two 5000uf filter caps rated at 500uf 50v. I cannot for the life of me find a radial 500uf cap anywhere. I see LOTS of 470uf caps of various quality. would it be ok to use this slightly smaller size, as it will still be within the originals +/- 20% range?

For all the small value radial caps (.22uf) I have located a source of the ELNA Cerafine series.

For the remaining axial caps, I plan to use the either the 5% or 1% Dayton polpros from partsexpress.com or perhaps Sprague orange drops.

jrsh92
11-29-2007, 10:49 PM
The 10,000 uf will be fine in the power supply. They will give tighter bass because they store more power, and they will make less background noise because they filter the power supply better.
As for the 470 vs. 500, I suspect you will be fine. At that large value (and being radial) I seriously doubt it's a signal path cap. It's probably more power supply filtering. Therefore, you could probably jump to almost any value without a problem (within reason), so you could use 680 uf or 470 uf and you wouldn't notice a difference. If you were really neurotic you could get a small 30 uf and put it on the other side of the circuit board, in parallel, so they add to 500 uf. But judging by the huge tolerance range (20% is a lot, that cap could be as little as 400 uf or as much as 600 uf) it isn't absolutely vital to the operation of the amp that it's perfect. I'd toss in a 680 personally just because when it comes to power supply filtering, the bigger the better.
Again, within reason-- if you have a whole farad in any of these places, it will seem like a short to the power transformer for so long that the thing would burn up. Charging a filter cap isn't easy on the transformer but at stock values or even twice that it just doesn't take long enough to do any damage.

twist72
11-30-2007, 12:07 AM
Thanks for the reply. I forgot to mention there are two PS caps but I figure you new that anyways. I don't know where I got 20% from but I rechecked the caps and there is no mention of their tolerance. I'm going to have to put this off till I can get the manual and a camera.

I got the amp for 15 bucks and its my "test subject". I hope to learn a little about audio circuits during the project. Up to now most of my repair work on the amp has been mechanical issues like switches going out as well as some resoldering of some wires that popped loose and replacement of blown fuses.
The amp sounds pretty good. The bass is kinda "punchy" but lacking in the lower frequencies. The highs are pretty harsh and seem to roll off pretty quickly. The midrange seems a bit veiled as well but all in all it sounds about on par with my Accurian with a little more ass behind it. BTW I'm running a pair of restored "New Advents" which I used the above mentioned Dayton 5% Polypropylenes with satisfactory results.

jrsh92
11-30-2007, 01:18 AM
You probably got 20% from the Partsexpress caps you are likely looking at as replacements.

mhardy6647
11-30-2007, 08:25 AM
As you noted the tolerance values for vintage caps, especially electrolytics, were very loose. Generally "close enough for Government work" is fine for caps... except in contour networks or in tuned (resonant) circuits. In the latter case, though, re-alignment of the receiver/tuner will usually get things back in tune.

One exception is that one should not use too much capacitance for the first filter cap in a tube-based high voltage rectifier circuit (at least if its a C-R-C type filter). If the first filter was, say, 40 uF, don't put 200 uF in there.

markamerica
11-30-2007, 08:40 AM
Twist,

Check tedss.com for the spec caps. I think you'll find what you're looking for there.

Mark

Fred Longworth
12-01-2007, 06:03 AM
For coupling and "emitter bypass" capacitors in amplifier circuits in solid-state units, I generally do NOT recommend film caps. The reason for this is that the comparatively large size of the devices makes them unduly susceptible to hum pickup.

Several years ago, a fellow brought a Sansui integrated amp into my shop for standard cleaning of switches and controls. He had "upgraded" all the coupling and emitter-bypass electrolytics on the preamp card with film devices. Lots of 2.2uF, 4.7uF, 10uF caps, for example, at 100v or more. These were huge. Not only did they pick up massive amounts of hum (or any other proximal electro-magnetic field), their huge mass put horrible strain on the foil traces to which they were soldered.

The amp sounded terrible. After considerable discussion, he finally agreed to have the unit returned to "stock." I installed a population of Xicon 105-degree devices.

* * * * *

When you jack up the main power supply electrolytics substantially, you correspondingly increase the time domains of the turn-on surge. This can stress the power supply rectifiers, so you may need to upgrade one notch as far as the rectifier bridge.

* * * * *

Better to go up from 500uF to 680uF, than to go down to 470uF.

Best,

Fred

Paul C
12-02-2007, 12:01 AM
When you jack up the main power supply electrolytics substantially, you correspondingly increase the time domains of the turn-on surge. This can stress the power supply rectifiers, so you may need to upgrade one notch as far as the rectifier bridge.

* * * * *

Better to go up from 500uF to 680uF, than to go down to 470uF.

Best,

Fred

Thanks, Fred... two great points!

:thmbsp:

twist72
12-02-2007, 05:40 PM
Mark:

Thanks for the link! I've decided to put off recapping the Heathkit till I can round up a manual. But I have decided to change out the electrolytics in my VM 1428. Its a PP EL84 integrated amp from 1964. The caps appear to be Oil and Paper and show signs of leaking. The Sprague Atoms that tedss.com has are perfect matches for replacement. I plan to leave the Ceramics as they generally do not go bad and the amp sounds fantastic as is, much better than any of my SS stuff.

Fred:

Thanks for the heads up. I realized later that the film caps would be way to big to fit on the board. I think I will just replace the Electrolytics on the heath and leave all the poly caps alone. I still need to round up a manual first befor the heath gets an overhaul. BTW it looks like the diodes near the PS caps are showing signs of excess current. The leads are black and from what I understand about this is that it indicates weak PS caps.

I just found my camera this morning and will post some pics of both the Heath and the VM as soon as I get through the final weeks of this semester. I have so much crap to do its almost overwhelming.

Laters