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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 23rd Apr 2012, 3:58 pm   #1
mark pirate
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Default Jvc ja-s71 (1976)

I bought this amp second hand over 25 years ago to use as the heart of my secondary system. It was regularly in use until it started to intermittently lose one channel about 5 years ago, when it was replaced by a Quad 33/303 amp.

So I decided it was about time to get it on the bench, it certainly is a heavy old beast!

I blew away 36 years of dust, connected it up to my workshop speakers and CD player and powered up. I was greeted by music from the left channel only, the balance control was very scratchy so this was given a dose of Servisol, along with the tone controls and this sorted that problem. Wiggling the tape monitor switch bought back operation of the right channel, but the only way to get some Servisol into it was via the front of the switch with the amp tilted upwards.

With the amp now working as it should, I left it playing while I went in for a cuppa. On my return the right channel had gone off again

After some closer inspection, the problem turned out to be some dry joints on the preamp board beneath the muting switch!

I left the amp on all evening with no further problems, so it was given a good clean externally. I then decided to try it out in place of the Quad.

Wow what a revelation!
Connected to my Marantz CD73 and my Tannoy 638's and it blew the Quad into the weeds. The sound quality is simply stunning, far better than I remember, so it is now back in its rightful place.

Amps like these should be cherished, you would have to pay a fortune to match both its build and sound quality.

As can be seen in the photos it has four output trannies on a massive heatsink for each channel, two massive caps and huge transformer.

They just don't make them like this anymore!

Mark
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Old 23rd Apr 2012, 4:30 pm   #2
robjkmannering
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Default Re: Jvc ja-s71 (1976)

Nice looking amp Stand, is it Phillips or crosshead?
Nice looking amp too.
Rob
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Old 23rd Apr 2012, 5:12 pm   #3
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Default Re: Jvc ja-s71 (1976)

That amp is a beast! I've got a JVC JA-S22 amp and a JL-A1 turntable. They sound better than anything I've ever heard. Now I just need some speakers for it
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Old 23rd Apr 2012, 6:11 pm   #4
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Default Re: Jvc ja-s71 (1976)

Rob, it is a crosshead It was very useful in keeping the Servisol from running on to the front panel!

Yampy, it is certainly a beast. The power reserves are very impressive, as is the build quality.

I have been listening to it all afternoon and it has not missed a beat and was very pleased that there were no real faults with it. It has never seen any repairs until last week, a real testament to the quality of its components.

Even at full volume with no signal, there is no noise or hum at all.

I really love equipment of this era, it looks great and I am sure it will go on for another 36 years.

Mark
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Old 23rd Apr 2012, 6:58 pm   #5
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Default Re: Jvc ja-s71 (1976)

Wonderful amp. I love that mains transformer!

JVC made several similar-looking units, but not all were created equal. One very popular model has a much smaller transformer and STK-series "slab" output ICs giving an output of something like 25W x2. Very nice, but not in the same league as yours.

Nick.
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Old 24th Apr 2012, 7:39 am   #6
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Default Re: Jvc ja-s71 (1976)

Hi Nick, this was JVC's flagship model, a quick look on the web revealed the spec.

http://www.radiomuseum.org/r/jvc_ja_s71.html


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Old 24th Apr 2012, 9:51 pm   #7
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Default Re: Jvc ja-s71 (1976)

Quote:
Originally Posted by robjkmannering View Post
Nice looking Amp Stand, is it Phillips or cross head?
Quote:
Originally Posted by mark pirate View Post
Rob, it is a crosshead
Err, a Phillips screwdriver is a crosshead type screwdriver, bit like a Biro is a ballpoint pen.

Judging by the colour of the handle, it's probably Pozidriv. ISTR in that style, Phillips had red handles.
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Old 25th Apr 2012, 7:43 am   #8
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Default Re: Jvc ja-s71 (1976)

Thanks for pointing that out Chris, I was trying (and failing) to be humerous. Phillips because the amp was made by JVC and crosshead because anything supporting that load would probably get cross.
No, it doesn't sound any better trying to explain it!

Rob
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Old 25th Apr 2012, 12:03 pm   #9
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Default Re: Jvc ja-s71 (1976)

Well, you just tickled my funnybone, sort of



Back with the amplifier- the RM spec is rather vague.... 260W output. Did you get any decent info with it?

I see they went for wirewrap in some of the power supply stuff at least. I guess that's typical of the period. Hopefully it will live up to the claims made for its longterm reliability as a connection method.
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Old 25th Apr 2012, 1:03 pm   #10
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Default Re: Jvc ja-s71 (1976)

Quote:
260W output. Did you get any decent info with it?
Looking elsewhere on the web, it appears to be rated at 80 watts per channel.
As for reliability, this has been the first time any attention has been needed. I was relieved that it was only a couple of dry joints and dirty switches and crackly pots and not as I had feared, the output stages.

I have certainly given it a lot of use over the years, it even got pressed in to use as a disco power amp back in the 90's.

Mark
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Old 29th Apr 2012, 11:43 pm   #11
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Default Re: Jvc ja-s71 (1976)

What are the markings on the power transistors?
They look like Hitachi MOSFETs.
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Old 30th Apr 2012, 7:15 am   #12
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Default Re: Jvc ja-s71 (1976)

There are 2 x 2SA753V and 2 x 2SC898V transistors per channel, so the rating of 80 WPC looks correct. It certainly delivers more power than I will ever need!

Mark
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Old 9th May 2012, 3:49 pm   #13
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Default Re: Jvc ja-s71 (1976)

Mark,

Nice amp and no doubt nice sound.
Here are the spec's.
They came from the full service-manual. PM me for more if you need it.

rgds,

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Old 13th May 2012, 1:39 pm   #14
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Default Re: Jvc ja-s71 (1976)

Nice looking amp. I love Jap equipment from the 70s/early 80s. Used to have a Luxman amp and then a Yamaha CR600, both completely blew away any more modern IC amps I have heard.

Nice to see someone else with some decent 'speakers (Tannoys) too
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