My yearly Altec 436C post

[Crash]

OK, in my once a year post about my cranky Altec 436C compressors, I have a new question. I re-capped C2, 3, 5 and 6 without issue. I used some Mojotone vitamin T's in those spots and everything seemed fine. When I replaced C4 (1mfd, 200v) with a Solen cap with the exact same specs I get a weird popping  oscillation type thing going on that I can control the speed of with release adjustments. Put the old Sprague cap back in and all is fine. Anyone got anything on that? It did this with both units, no matter of orientation of the cap... Maybe the Solen caps just suck? Does not seem very likely to me but Iam the village idiot with this stuff. The reason I am going for the recap is that the unit can get sort of farty sounding, especially on the leading edge of a signal and I have heard a re-cap is a good place to start. C4 seems to be "the" cap to get done and of course, that is the one giving me fits.

 

[mrphotodude]

well...i know alot of people use the large solen's in power supplies like the 47u@630....
i have a few 2.2, 4.7 's in 630 that whenever i tried them out, i did not like them at all.
Obviously they do sell...so they work out for some people.
Why do you need to change that cap? Just experimenting or is it leaky?

I don't think this is the issue..buuuuutttt...you could flip the cap around if it is non polarized metal film and see what happens.
Most tubular metal film caps have a lead that is attached to the inside foil, and one on the outside foil.
http://www.aikenamps.com/OutsideFoil.htm

I kinda like mallory 150m's... Depends what position on what device the cap is for though 

 

[Crash]

Why do you need to change that cap? Just experimenting or is it leaky?

I don't think this is the issue..buuuuutttt...you could flip the cap around if it is non polarized metal film and see what happens.

Thanks for your most speedy reply, I am trying to rid of some distortion issues and was told on this very forum that a recap couldn't hurt...so off I went. The only reason I went with the Solen was it was all I could find at the time. I replaced same for same in terms of specs (Solen had higher votage rating but that is it) so imagine my surprise when it didn't work. We tried the flipped polarity on the 2nd unit with the same results so that didn't fly either. I am considering going with like a Aricap in that position but I don't know after it all went to poop in a basket with the Solen cap.

I have been down the tube swap path on these issues too, to no avail just, so you know where I have been thus far.

I really should pull the compression tube and see if that clears anything up. I bet it does but I have been in and out of these things over quite a period of time and can't remember if I tried this trick yet. These seem to really not like low end, which is exactly what I am trying to use them for...bass gutiar.

Could really dirty pots cause any of these issues?...he says out loud to himself.

 

[emrr]

Simplistically, c4 controls the side chain timing.  Have you measured the old caps and the new caps to see if they are in spec?  I believe this compressor is known to have a 'farty' attack in the first place, and several experimenters here concluded the attack could not be made much faster without the unit freaking out.  Maybe the Solen value is off enough to speed up the unit into the freakout zone, even though at first think it doesn't seem like the whole story. 

 

[Crash]

Simplistically, c4 controls the side chain timing.  Have you measured the old caps and the new caps to see if they are in spec?   I believe this compressor is known to have a 'farty' attack in the first place, and several experimenters here concluded the attack could not be made much faster without the unit freaking out.   Maybe the Solen value is off enough to speed up the unit into the freakout zone, even though at first think it doesn't seem like the whole story. 

Thanks for your reply Doug. Maybe it is my imagination, or wishful thinking, but things seemed to improve some with the rest of the caps being replaced. The Solen (C4), other than voltage was spec'd the same as what was in there. I'll keep poking around in here and see what else I stumble upon.

 

[craptical]

I am trying to rid of some distortion issues...

Did you check out the supposed "EMI mods", i.e. balance trimming of pos/neg side of circuit (trimmer on 6BC8, tighter spec resistors IIRC)?

/Dave

 

[Crash]

I am trying to rid of some distortion issues...

Did you check out the supposed "EMI mods", i.e. balance trimming of pos/neg side of circuit (trimmer on 6BC8, tighter spec resistors IIRC)?

/Dave

I have yet to figure out what the real EMI mods are... I have seen various layouts that claim to be them with just as many people saying it just ain't so.