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Old 22nd March 2013, 04:58 AM   #81
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OK Got the NTE's today. Put a pair in on the bad side, re-biased both sides; sounds good. Hum is actually about 95% gone, don't ask me why. As I'd mentioned it seemed to travel to the other side when I swapped the L & R pairs. Whereas before I could sit between the speakers, about 3' from each, and hear the low-level hum, now I have to put my ear right up to the speaker. Mind you my ears suck...

My last question is should I put the NTE's on the left side as well even though it has good original transistors, just for symmetry? I can't hear much of a difference between channels but I can't quite be sure they're the same, or whether any difference might be for this or other reasons. But seems maybe right to have both sides the same so that's what I'm leaning toward. One way or the other this thing's getting its cabinet back on tomorrow night and back to my friend. Phew!

It's actually a very nice sounding amp through the KEF's I just rebuilt...
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Old 23rd March 2013, 02:18 AM   #82
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Done and done, the cover's on.
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Old 23rd March 2013, 02:26 AM   #83
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And thanks Ian and all for the help and encouragement. My friend will be very happy. Now I just have to get back to my own receiver projects...
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Old 29th March 2013, 11:50 PM   #84
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Quote:
Originally Posted by mmmalmberg View Post
.....My last question is should I put the NTE's on the left side as well even though it has good original transistors, just for symmetry? I can't hear much of a difference between channels but I can't quite be sure they're the same, or whether any difference might be for this or other reasons. But seems maybe right to have both sides the same so that's what I'm leaning toward....
Hi, sorry to have missed your recent posts but pleased with your happy outcome.

As a matter of good procedure, you could match the replacements in each channel. However, I've different specs on datasheets apparently issued by NTE and I'm puzzled but one set looks identical to 2N3019 which should be a good substitute.

There was a fault there, which you may have eliminated by resoldering or just replacing a failing transistor but to be honest, I can't see that as likely, after all your previous work. Perhaps it is a matter of another faulty part waiting to show up again. Time will tell.

Personally, I would invite comment from your friend without prompting and gauge how happy he remains with the amp. Driver transistors don't have a lot of influence on the amplifier "sound" until the wick gets turned up and the current begins to stretch the linearity of the devices. If you ever have a failure or questions there, I would simply fit 4 x genuine 2N3019 from ST Micro (Mouser) and be done with it then. Parts like that possibly will remain in production for some time yet, owing to the tons of ancient high-rel. equipment still specified for hermetic steel cases.

Good work and tenacity has paid off. Congratulations.
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Old 30th March 2013, 01:35 AM   #85
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Hey there you are. Just finally got the amp to him last night, both of us have been busy. I'm anxious to hear what he has to say. I couldn't hear a difference sonically between the originals and the NTE's (I did replace all 4), but I don't have the golden ears (they worked great in my youth but now I have very rolled off highs). For how inexpensive they are, I may just put the 2N3019's on my next Mouser order and just have them or give them to him or put them in...

The other thing is I spent extremely little time listening to it after I got the NTE's in, being anxious to button it up and getting it back to him. I'm sure we'll get together for an evening of listening in the coming weeks and see what it really sounds like. I thought it a very sweet little receiver. I'm going through a similar process with my own shop receiver, a Harman Kardon 330A. It's sounding good but with some channel imbalance and possibly some distortion, but has all new caps and I think a bad volume pot. But I think the Fisher is just a bit more refined and balanced. Too may projects. After all that a Marantz 2230 that I really should just leave alone, it sounds great, and a Kenwood KA6000 integrated amp I'm picking up tomorrow with a dead channel. Hopefully something small, $45. for the amp. Too much fun & not enough time. Thanks again for all your help, love having this sort of dialog and support from as far away as we could be on the planet. Thanks.
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Old 31st March 2013, 04:48 AM   #86
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Default unobtanium

I see in your HK 330A thread, you have come to a difficult point of pot. replacement and other fixit threads here raise this same problem for the Marantz 2230. This has certainly become a popular amplifier but old 60's amps like the KA 6000 and early 70's models like the Marantz and HK 330 are chock full of caps that will be begging for replacement by now. This will be more expensive for the really ancient KA 6000, which is AC coupled (caps are used to couple the signal between the various stages of the amp and preamps).

The KA6000 would benefit from a larger output cap of up to 6,800uF but note that C172, 272 are only rated 50V when for safety, they should be audio quality, 100V rated ($$) to withstand the >80V across them in series with the loudspeaker. There are no safety relays and modern caps are not so generous with peak voltage ratings as some older types, so if the upper output transistor fails, the cap gets it. On the rare occasions it happens, it's not funny really - at best your ears ring for weeks from the explosion but foil fragments get blasted everywhere, even making a write-off of the electronics.

Here's a page of various pots that might suit your needs, if you haven't already found them together.
ALPS 50K STEREO LOUDNESS TAPPING VOLUME CONTROL POT | eBay
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Old 8th April 2013, 01:16 AM   #87
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Hi Ian. Funny I can't even find my KA-6000 thread right now. Another AK'r is sending me a couple of NOS pots so I should be set, if that takes care of the problem with the 330A. Re the KA-6000, do you mean the speaker coupling caps? I'll find my KA-6000 thread and finish that story there. Thanks
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Old 8th April 2013, 01:44 AM   #88
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Hi again
Yes, those are the output coupling caps and usually restorers want to fit so called "for audio" or some similar specialty caps there but i think that standard caps of good, long life (>3000 hour rating) quality will be fine. Even they will be expensive if over 63V rated so no need to go overboard with old designs that never used uber-quality parts in the first place.

'Nice to see things coming together for you. Good luck with this one too.
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Old 8th April 2013, 02:40 AM   #89
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Don't know if I had a thread here for the KA-6000 (found a thread I started on AK) but you picked up on it somewhere so... Anyway I bought one for $45. with a dead channel. Just picked it up last night and fired it up tonight. Can't find a thing wrong with it. It's like perfect, sounds excellent and even all the little lights work. So, yeah thinking maybe I'll replace all the coupling caps and p.s. caps, will definitely use nice ones all around. I have to look at the schematic again but I think there's a bunch of very small coupling caps throughout and wondering if I could use film caps there. Would I consider to be coupling caps any caps that are in series with the audio signal, like in front of a transistor base?
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Old 8th April 2013, 04:04 AM   #90
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Coupling caps over 1 uF value tend to be only electrolytic types because size becomes an issue with film caps which are almost always better performing but the size and cost increases dramatically as we go from polyester (MKT) to ultimate quality polypropylene types (MKP) and their film/foil equivalents at extraordinary boutique prices. Size is important because large parts are more vulnerable to noise pickup from RF, power supply and output circuits so the simple adage that super quality parts = super quality sound can be wrong. For large value coupling caps, Non-polarised electrolytics are often quite sufficient quality but Bipolar caps are back-to-back electros that whilst cheap, have some limitations as DC blocking devices for audio.

If you are tempted to use polyester, AKA mylar, MKT, MKS and other handle types, use a higher voltage rating type of >160V to avoid poor sound quality. This is my opinion based on old subjective experiences and there are plenty of naysayers so check this for yourself.

The principle of what type of electrolytic is best hangs on how much DC is present across it in the first place. If there is >2V or so, there is likely no improvement at low signal levels by using special non polarized types, whatever hype, mantras and parroting you typically read on the web. This a highly contentious subject with a lot of vested interests and indignance when some guys feel offended having just spent hundreds of dollars on their amp with no reality check on what it would have sounded like with more rational replacement parts. I don't like flaming so I'll leave it at that with the comment that the original, attractive sound quality of these amps never included super grade parts so upgrading will likely alter sound alright, but is that necessarily going to be good, long term? Some friends of mine do this fancy recapping routine regularly, rave about the results and compare notes for some time but then consign the amp to the cupboard or resell it at even a loss. If it remains in constant use, I then tend to think the mods may have actually been beneficial.
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