Ampex 440C parts list and schematics don't match actual values on audio cards

[Shawn sullivan]

Hi , so I am replacing all the old carbon comp resistors ( and most tantalum capacitors) with high quality metal films and elecctrlytics because I can't leave well enough alone, and I ran into a couple problems .

One problem is that some of the tantalum capacitor values that are physically on the audio cards (right now I'm working on the reproduce cards) don't match the values stated in the parts list . Specifically C 1, 2, 3, 5, 7, 11, 12,17, are all listed as 3.3 uf , in the build description, but the actual values physically on the pub are 50uf ! So now I'm not sure if I should continue and replace with the parts I ordered which are all from the build list , or order similar parts to watts actually on the pub currently. Also some resistor values are different , such as on the reproduce cards R3 is listed on the build sheet as 130K but actually is a 180K resistor on all the reproduce cards I have. My Ampex 440C manual and technicals docs are from 1975 April. Please advise. Should I leave most of those tantalums alone? any extra experience... do's and don'ts on this machine would be appreciated!

 

[Brian Roth]

In the 1970's I worked for a pro audio company which was an authorized Ampex dealer. But, it's been at least 10 years since I actually worked on any 440 series machines, so take my comments with a grain of (old) salt.

I wonder if this machine has been re-capped at some point. That is a HUGE jump in capacitor values. Any evidence of recapping? Typically that is a hack job and should be apparent by examining the solder side of the card.

Somewhere I may have a 440C manual...I'll see if I can find it and see where in the circuit those caps are located. Remind me if I forget to look for that blue binder! <g>

Bri

 

[Shawn sullivan]

Hi Brian, no evidence of recapping, it looks absolutely factory.

The caps and resisters I ordered are from the build sheet of my Ampex 440C 1976 manual blue binder parts list.

 

[Shawn sullivan]

In the 1970's I worked for a pro audio company which was an authorized Ampex dealer. But, it's been at least 10 years since I actually worked on any 440 series machines, so take my comments with a grain of (old) salt.

I wonder if this machine has been re-capped at some point. That is a HUGE jump in capacitor values. Any evidence of recapping? Typically that is a hack job and should be apparent by examining the solder side of the card.

Somewhere I may have a 440C manual...I'll see if I can find it and see where in the circuit those caps are located. Remind me if I forget to look for that blue binder! <g>

Bri

OK may have an answer, I just looked up the Ampex 440B reproduce electronics from about five years before (1970) and guess what? the caps on the reproduce boards where 50uf vs my spec'd 3.3 uf caps on the 440C . Like you said huge jump in values!

Now I'm really conflicted because I dont know which way to go on the values.

 

[gar381]

Check with the Guys on the Ampex mailing list.

Gary

 

[radeng]

When I acquired my 1967 440-4 about 30 years ago, the first thing I did was just what you are doing now. Even though mine is a 1/2" 4 channel I only updated 2 of them. So it was easy to compare the stock vs. the updated ones (when set up as a 1/4" two track). The difference was immediately apparent, not only did the updated ones sound more open and extended, they measured 3 db quieter than the stock ones. Definitely worth doing. Don't forget to replace the "hidden" cap in each rack chassis as well, the one that can kill a head if it shorts.

 

[gar381]

the one that can kill a head if it shorts.

C32 record card

see... Giving my old Ampex 440B warhorses a re-capping... 440C pcb are here