Looking for advice on replacing coupling capacitors in this circa 1964 N.Y. built amp. I picked it up some 20 years ago in a pile of stuff and it worked when I tried it, but my son wants to use it with a turntable and she barely makes a peep now. I found a whole batch of 4uf W.German electros totally inert, and need to replace them. I'll need at least 15 but don't want to break the bank on an amplifier of dubious value, particularly since it's all germanium and some blown outputs would probably end it's useful life. My son loves it because of it's looks, and it is very well made otherwise.

So instead of putting electrolytics back in, I was thinking of putting in some film caps. Is there a relatively cheap film cap or should I just stay with electrolytics, and if so, which? I found these on DigiKey which are reasonable:

http://www.digikey.com/product-detai...511-ND/4833337

Another anomaly is that while the schematic calls out mostly 4uf caps, this particular unit has two locations that have 10uf installed on each preamp board, everything is the same as the schematic. Strangely, although they're the same 10uf value and voltage, the two locations have two different manufacturers. The other twin preamp board has the same exact two caps in the same exact spot, as if they were selected for voicing reasons. Service manual he

http://www.fisherconsoles.com/non%20...10000%20sm.pdf

And since 4uf caps are pretty much made of unobtainium, should I go to 4.7 or 3.3, or should I cobble some together?

On Saturday, April 9, 2016 at 5:51:09 PM UTC-4, wrote:

A few things:

a) After a certain basic level of quality construction, a cap is a cap is a cap. So, within the universe of film caps, after that level, there is effectively nothing to choose between brands. Similarly within the universe of electrolytic caps.

b) at less than 5uF, moving from electrolytic caps to film caps is generally a good thing. Keep in mind that a typical electrolytic cap has a tolerance of -20% to +100% unless screened. The typical film cap (these days) is usually within 5% or less. So, a film cap will be far closer ab initio, and also stay that way. Above 5%, you may run into real-estate problems, so make sure the film cap will fit before making a purchase.

c) Voicing Reasons: Not really. Supply availability is far more likely and/or actual tolerance.

d) Better to 4.7 than 3.3. The 3.3 is at the bottom end of the electrolytic tolerance scale, 4.7 is close enough on the upper end.

e) Make your voltage *AT LEAST* 20% higher than OEM. Try to be "not more" than 100% if possible. Much more an issue with electrolytic than with film caps. I stock film caps in 200 (anything less than 100V) and 600/650V (anything above to 550V).

Enjoy! That is a fine unit! Fisher iron is legendary.

Digikey is a fine source, also Mouser and Newark. All three will sell you quality goods.

Peter Wieck
Melrose Park, PA

wrote:



And since 4uf caps are pretty much made of unobtainium, should I go
to 4.7 or 3.3, or should I cobble some together?



** Just use any brand name 4.7uF, 63V electros.

Panasonic, Nippon-Chemicon etc.

IMO, 1960s Germanium transistor amplifiers are the "missing link" between tube and modern solid state - and they should stay missing.



..... Phil


..... Phil

On Sunday, April 10, 2016 at 2:12:28 AM UTC-4, Phil Allison wrote:

IMO, 1960s Germanium transistor amplifiers are the "missing link" between tube and modern solid state - and they should stay missing.

OK - a valid opinion. On the other hand, this particular unit does use transistors that are still readily available, so a worthwhile bit of history for all that.

Peter Wieck
Melrose Park, PA

wrote:

Phil Allison wrote:

IMO, 1960s Germanium transistor amplifiers are the "missing link"
between tube and modern solid state - and they should stay missing.

OK - a valid opinion. On the other hand, this particular unit does use
transistors that are still readily available, so a worthwhile bit of
history for all that.


** You must have a different idea of "readily available" to mine.

The original RCA 35144s PNP outputs are not easy to find ( no listings on Ebay) and the only similar type I can find from a dealer is the AD149.


http://www.transparentsound.com/tran.../AD149M-0A.JPG


.... Phil

On Sunday, April 10, 2016 at 11:25:43 PM UTC-4, Phil Allison wrote:
wrote:

Phil Allison wrote:

IMO, 1960s Germanium transistor amplifiers are the "missing link"
between tube and modern solid state - and they should stay missing.

OK - a valid opinion. On the other hand, this particular unit does use
transistors that are still readily available, so a worthwhile bit of
history for all that.


** You must have a different idea of "readily available" to mine.

The original RCA 35144s PNP outputs are not easy to find ( no listings on Ebay) and the only similar type I can find from a dealer is the AD149.


http://www.transparentsound.com/tran.../AD149M-0A.JPG


... Phil

Didn't suggest they were cheap, just readily available.

https://octopart.com/nte179-nte+electronics-22547

The NTE (by direct experience) is a drop-in replacement for the OEM in actual function. Or so it worked for me on a vintage KLH product back in the day. That amp is still working, as it happens.

I also agree that in the US, we have access to a much greater array of relatively local (2 days by cheap mail) suppliers than many other parts of the world.

Would I spend US$100 restoring this amp? Not for me, but given the cult status of vintage Fisher in the US, perhaps for that market.

Peter Wieck
Melrose Park, PA

wrote:


** You must have a different idea of "readily available" to mine.

The original RCA 35144s PNP outputs are not easy to find ( no listings
on Ebay) and the only similar type I can find from a dealer is the AD149.


http://www.transparentsound.com/tran.../AD149M-0A.JPG




Didn't suggest they were cheap, just readily available.


** Then you are wrong on both counts.


https://octopart.com/nte179-nte+electronics-22547


** The NTE179 is nothing like the original RCA part and is very expensive.

OTOH, the AD149 is very close as sells for under US$10 on Ebay or just over A$5 from the store I usually frequent here in Sydney.



..... Phil

On Sunday, April 10, 2016 at 2:12:28 AM UTC-4, Phil Allison wrote:
wrote:



And since 4uf caps are pretty much made of unobtainium, should I go
to 4.7 or 3.3, or should I cobble some together?



** Just use any brand name 4.7uF, 63V electros.

Panasonic, Nippon-Chemicon etc.

IMO, 1960s Germanium transistor amplifiers are the "missing link" between tube and modern solid state - and they should stay missing.



.... Phil

Heheh... funny.

Phil: is your objection to 60s germanium amplifiers their performance, quirkiness, or parts availability (or all three).

Peter: none of the outputs are blown, so I don't need to acquire any ge for now, although I wouldn't mind picking up a set just to have. It is a very handsome and flexible amplifier if nothing else.

After doing some resistance checks around the output transistor, it's surprising that the outputs didn't blow. The bias controls read between 15 and 20 ohms before I marked their exact position and cleaned them. Once cleaned, lubed, and put back on the spot, they averaged about 6 ohms (and they're shunted by 22 ohm resistors). In the manual I have, there is a note about replacing the 22 ohm resistors with 10 ohm ones. Apparently, the bias pots may have been problematic from early on. The note also said to replace all four pots if suspect. Since the manual is of the same year as the amp, it tells me something about them. Perhaps those inert coupling caps prevented the output stage from blowing.