recapping ampex 440 cards?

[dynomike]

Hey all,

I have an ampex 440b-4. Two of the electronics channels make noise (at around -60db.. still annoying though) and the other two seem to drift out of 'stereo alignment' with each other. In fact, one of them seems to limit the peaks more than the other two. Obviously, this is a big pain for recording stereo tracks. I'm just using the line amps for their xfmr color / compression characteristics. I've taken a look at the cards and they look really easy to work on. I have the manual...

So, where to begin? I know lots of people have done this but besides building a few hamptone kits, etc, I don't know much about the DIY tech business. Any little guides you know of on recapping ampex cards?

-Mike

[honkyjonk]

I would definitely recap the electrolytics, if you haven't already done that. They're 50uF/50V's I believe. I think a 47uF/50 Volt cap will work. That's what I used in my cards. In retrospect, I probably should have used Nichicon HE 56uF/50V radials, and just put some tubing on the legs. I used some other Nichicon axial caps that aren't rated at 105 degrees.

As for the tants, my 440 cards always seem off in some sort of way, and I suspect these tants. Folks say you don't need to replace them, but I'm sort of wondering. There is a parts list for all the cards in the full 440 manual, so it's easy to find the correct values for each cap. It's hard to tell by looking at the tants.

Anyway, I bet Brian Roth will reply to this. He always does when there is a 440 question. Thanks Brian.

There is one tant in the record card, now I can't remember which, but I can look when I have a chance, that, if it goes bad it can take your record head with it. It's been recommended by a number of folks to replace it with a lytic.

The other tants are also replacable with lytics, but it'll no doubt change the sound a bit. I think I was able to find all the proper tant values in Kemet tants for replacements. I just havn't replaced them yet. Don't know if I will. They're just sitting there like my 440 waiting for me to finish 25 other things first.

[brianroth]

I need to drag-out my 440 manuals to revisit all of the possible "recapping issues"....

In the original question, apparently the machinery is NOT being used as a true tape recorder (did I read the orignal post correctly??), but instead as an in-line "signal processor", via the line in/line out pathway with the electronics set up for "feed-through". (IE, monitoring mode set for "input").

If I am correct, then there aren't all that many caps in the signal pathway.

Bad caps seldom (if ever) cause noise to be introduced, although I also believe that "anything is possible" .

Noise (hiss? crackles?) is more likely due to a faulty transistor, or perhaps a faulty resistor. Crappy connections (edge connector, etc) is another possibility, especially if the noise is more of a "crackle" than a "hiss".

On a 440, one Weak Link is the electrolytic capacitor (220 uF/50V...IIRC) which is hard-mounted (on terminal strips) on one of the side panels within the audio electronics chassis rack-mounted assemblies. That cap couples the audio from the line amplifier (located on the repro plug-in card) to the output transformer.

Sidebar...some folks seem to believe that re-capping will cure all sorts of problems...noise, warts, etc <G>. Sometimes re-capping WILL fix problems, but not always.

Bri







.

[dynomike]

I need to drag-out my 440 manuals to revisit all of the possible "recapping issues"....

In the original question, apparently the machinery is NOT being used as a true tape recorder (did I read the orignal post correctly??), but instead as an in-line "signal processor", via the line in/line out pathway with the electronics set up for "feed-through". (IE, monitoring mode set for "input").

Correct. I plan to get the whole thing operational eventually, but it needs a new supply motor and master bias oscillator, apparently.

I will try to replace those electrolytic caps the two of you mentioned, as well as the input level pots, which are scratchy and sensitive, and might be causing some of the level drift problems too.

Where is a good place to get these parts, ideally in Toronto? (but I can of course mail order if need be) Do I need to look for anything special, or will anything that matches the values work?

Thanks for your help thus far,
Mike

[brianroth]

Hmmmm....I order from Digikey or Mouser here in the USA....no suggestions for Canada.

Digikey does stock PEI pots (made in Canada!) which are modern day dead-ringers for the original Allen Bradley pots that Ampex used. Of course, one can also argue that conductive plastic pots are better than the olde style carbon track pots, but finding audio taper pots can be a bit tricky.

Bri

[jefe]

I just recapped my 440b-4 based on the info on this page:

http://www.analogrules.com/badcap01.html

I ordered all the axial electrolytics from Allied.

Before recapping, I was getting intermittent low-level popping when recording on channel 3, which has disappeared.