UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Success Stories

Notices

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!

Reply
 
Thread Tools
Old 23rd Apr 2012, 3:58 pm   #1
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 4,503
Default JVC JA-S71 amplifier (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
Attached Thumbnails
Click image for larger version

Name:	amp1.jpg
Views:	1211
Size:	90.6 KB
ID:	65582   Click image for larger version

Name:	amp2.jpg
Views:	1828
Size:	121.6 KB
ID:	65583   Click image for larger version

Name:	amp3.jpg
Views:	954
Size:	135.9 KB
ID:	65584   Click image for larger version

Name:	amp4.jpg
Views:	1251
Size:	136.1 KB
ID:	65585   Click image for larger version

Name:	amp5.jpg
Views:	1981
Size:	136.1 KB
ID:	65586  

mark pirate is offline   Reply With Quote
Old 23rd Apr 2012, 4:30 pm   #2
robjkmannering
Heptode
 
robjkmannering's Avatar
 
Join Date: May 2009
Location: Norwich, Norfolk, UK.
Posts: 716
Default Re: Jvc ja-s71 (1976)

Nice looking amp Stand, is it Phillips or crosshead?
Nice looking amp too.
Rob
__________________
AF117's are worth their weight in scrap.....
robjkmannering is offline   Reply With Quote
Old 23rd Apr 2012, 5:12 pm   #3
yampy187
Pentode
 
yampy187's Avatar
 
Join Date: May 2010
Location: Coventry, Warwickshire, UK
Posts: 226
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
yampy187 is offline   Reply With Quote
Old 23rd Apr 2012, 6:11 pm   #4
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 4,503
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
mark pirate is offline   Reply With Quote
Old 23rd Apr 2012, 6:58 pm   #5
Nickthedentist
Dekatron
 
Nickthedentist's Avatar
 
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 12,200
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.
Nickthedentist is offline   Reply With Quote
Old 24th Apr 2012, 7:39 am   #6
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 4,503
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


Mark
mark pirate is offline   Reply With Quote
Old 24th Apr 2012, 9:51 pm   #7
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Witney, Oxfordshire, UK.
Posts: 9,626
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.
__________________
.........._______
.....___/|__|__|\____
.=.( _---\__|___|_---_)
.........O...Chris....O
Herald1360 is offline   Reply With Quote
Old 25th Apr 2012, 7:43 am   #8
robjkmannering
Heptode
 
robjkmannering's Avatar
 
Join Date: May 2009
Location: Norwich, Norfolk, UK.
Posts: 716
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
__________________
AF117's are worth their weight in scrap.....
robjkmannering is offline   Reply With Quote
Old 25th Apr 2012, 12:03 pm   #9
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Witney, Oxfordshire, UK.
Posts: 9,626
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.
__________________
.........._______
.....___/|__|__|\____
.=.( _---\__|___|_---_)
.........O...Chris....O
Herald1360 is offline   Reply With Quote
Old 25th Apr 2012, 1:03 pm   #10
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 4,503
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
mark pirate is offline   Reply With Quote
Old 29th Apr 2012, 11:43 pm   #11
Silicon
Heptode
 
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 602
Default Re: Jvc ja-s71 (1976)

What are the markings on the power transistors?
They look like Hitachi MOSFETs.
Silicon is offline   Reply With Quote
Old 30th Apr 2012, 7:15 am   #12
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 4,503
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
mark pirate is offline   Reply With Quote
Old 9th May 2012, 3:49 pm   #13
tri-comp
Heptode
 
Join Date: Oct 2008
Location: Aalborg, Denmark
Posts: 616
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,

/tri-comp
Attached Files
File Type: pdf JA-S71_specs.pdf (185.0 KB, 337 views)

Last edited by tri-comp; 9th May 2012 at 3:55 pm.
tri-comp is offline   Reply With Quote
Old 13th May 2012, 1:39 pm   #14
JoshWard
Octode
 
JoshWard's Avatar
 
Join Date: Dec 2005
Location: Near Stowmarket, Suffolk, UK.
Posts: 1,777
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
JoshWard is offline   Reply With Quote
Old 13th May 2016, 6:42 pm   #15
bgood2bme
Diode
 
Join Date: May 2016
Location: Scott City, Kansas, USA.
Posts: 1
Default Re: Jvc ja-s71 (1976)

Hi all, wonderful reading in here. I just bought a JVC JA-S71 for 80 dollars. The ad says no power up, should get it from UPS in a few days. Are there any fuses that would cause this unit to be completely dead?
bgood2bme is offline   Reply With Quote
Old 15th May 2016, 7:20 pm   #16
Ted Kendall
Heptode
 
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 520
Default Re: JVC JA-S71 amplifier (1976)

If it blew a 33/303 into the weeds, methinks the Quad is next in line for the bench...
Ted Kendall is offline   Reply With Quote
Old 15th May 2016, 7:53 pm   #17
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 6,779
Default Re: JVC JA-S71 amplifier (1976)

The reputation of the 33/303 is somewhat larger than the reality. It was probably the first transistor amplifier which overcame thermal instability and reliability issues. Back in the day it was a very desirable amplifier indeed, but it pre-dates the fixing of a few problems created by peaks in music.

I did a serious revamp job on one a few years ago and tried it out into my big transmission line speakers and I found it generally disappointing compared to their usual driver, but then it's a substantially lower power unit and the coupling capacitors in the outputs create a roll off which can be detected with these speakers.

So I'm not surprised that one of the Japanese monster amplifiers from the period before they went mad on STK modules, comes out well in comparison. They were very good amplifiers and were designed after a few limitations had been recognised and overcome. I find it a bit amusing that they can be picked up for a better price than the Quads, but then hifi is all about brand worship anyway. I'm also somewhat amused by the Japanese liking for sticking the heatsinks on the inside of the cabinets.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 15th May 2016, 9:10 pm   #18
mark pirate
Dekatron
 
mark pirate's Avatar
 
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 4,503
Default Re: JVC JA-S71 amplifier (1976)

Quote:
The reputation of the 33/303 is somewhat larger than the reality.
I agree, IMHO the power amp never sounded as good as my Quad II's (which I will never part with).

The JVC does sound better than the 33/303, it really makes my Tannoys sing
There is a wonderful clarity and depth from the JVC that the Quad just could not match, it has not missed a beat since I serviced it four years ago, no doubt it will outlast me!

The 33/303 was swapped for a Leak stereo 50 last year, another restoration project awaiting attention...

Mark
mark pirate is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 3:57 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at http://www.vintage-radio.net.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Copyright ©2002 - 2016, Paul Stenning.