Revox A722

isted as 'not working' that I snagged the other day. Although it has not ye t arrived I am preparing for the restoration. Some history:

ly) used with my 13 YO grand-daughter paired with the A720 and Piccolo spea kers. That one was 'working' when it came into my hands via Denmark, needin g only a few caps, lamps and a bit of cleaning. Although compact inside, th ey are assembled logically and every part can be reached. The intention her e is that this unit will join my other A720 in the other all-Revox system t hat includes the various moving parts - RtR, CD, Cassette and TT.

stock of compatible transistors and the means to match them if needed, most of the caps (I will have to acquire the correct 10,000uF @ 63V main filter s (4), but I have identified good sources with quick delivery (including Am azon of all places). '

therwise, I will start at one end and work my way across to the other.

I'm not a fan of wholesale recapping quality equipment if said equipment ha s no history of needing them. A lot of stuff made in the early to late 2000 s (and beyond really) are electrolytic killers and that's a different issue .

If you were rebuilding it to send to Mars where it could never be serviced, then go through it top to bottom and left to right. Otherwise, I'll bet t hat it's got a problem that you'll fix, and you'll find it will work as it' s supposed to and just like the other one.

My experience with ReVox is limited to a 70s tuner that I had, and it worke d perfectly until I unloaded it a couple of years ago. Hopefully someone w ith extensive knowledge of your model can give you more specific advice.

How do you deal with rubber bits? its awkward enough keeping cassette decks going well past they're sell-by date

On Wednesday, December 14, 2016 at 3:04:58 PM UTC-5, snipped-for-privacy@gmail.com wrote :

has no history of needing them. A lot of stuff made in the early to late 20

00s (and beyond really) are electrolytic killers and that's a different iss ue.

d, then go through it top to bottom and left to right. Otherwise, I'll bet that it's got a problem that you'll fix, and you'll find it will work as i t's supposed to and just like the other one.

ked perfectly until I unloaded it a couple of years ago. Hopefully someone with extensive knowledge of your model can give you more specific advice.

Thanks for this. I have yet to determine why it is represented as "not work ing other than there is no fuse-holder (or fuse) cap in place. I should be so lucky. But, I promise to report my findings.

Peter Wieck Melrose Park, PA

A few things:

a) Revox is direct-drive, dual capstan, three-head. So no belts anywhere. b) The pinch-roller is new, and of an exotic material that should outlast m e in any case. They are readily available from several sellers in the US an d elsewhere. c) The Revox Cassette drive is considered the most reliable drive, ever. Fa vorably compared to the Nakamichi Dragon - which does use belts in its seco ndary functions. d) The same may be written of my A77 road deck and B225 CD player. This las t I have had to recap on the audio board (quite convenient to do, by the wa y) and also re-set the pot-metal frame due to decayed grommets. THAT was a PITA, but well worth it. I used silicon grommets for the replacements - dir ect from my local plumbing supply house at $0.10 each.

As an aside, I also keep an HK2000 that has more belts than Brooks Brothers . Also mostly replaced from an O-Ring kit from the same source as the gromm ets.

g

The B215 has Dolby B & C on board as well. And at over 20 pounds, no lightw eight. US$1,400 in 1985.

Peter Wieck Melrose Park, PA

The only reoccurring problem I saw with the B215 back in the 80s was that the screws that attached the reel tables to the drive motors would loosen and the deck would intermittently stop during play. A CEO of a major hair care company bought one from us and it had this problem. He got all ragey like because any deck this expensive should never fail. Guess he didn't own any European luxury automobiles.

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The tiniest bit of the wife's clear fingernail polish eliminated that issue without causing future servicing issues. I purchased my unit in nearly unu sed condition for very little as the owner was upset with it for just that reason. US$100 in 2001. It was on a local for-sale bulletin board where I w orked. I offered to fix it for him, but he was done with cassettes by then.

Peter Wieck Melrose Park, PA

Revox came out with a service bulletin about a year later to inform service centers that they had a more reliable reel table. We recalled all that we sold and replaced the tables.

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Update: The unit arrived with a thoroughly cooked power transformer - not one coil intact. Happily, I do not need an international transformer as a r eplacement, I can stick with 120V on the primary side. However, the rest of the unit, including the main amplifier boards test fine.

I have put out feelers to the usual suspects, Hammond et.al. as well as a c ouple of custom winders I have used in the past. Revox wants US$400 FOB Mel rose Park. I think not.

I will report results.

Peter Wieck Melrose Park, PA

:

t one coil intact. Happily, I do not need an international transformer as a replacement, I can stick with 120V on the primary side. However, the rest of the unit, including the main amplifier boards test fine.

couple of custom winders I have used in the past. Revox wants US$400 FOB M elrose Park. I think not.

If it's packed tightly, it could be a problem doing a retrofit if you don't mind not looking original. If it's got room, there are tons of options in cluding using a XFR from a typical Japanese receiver (I might have some don ors if you need one). You can split it up by putting in a trans for the po wer amp and a smaller one for the low voltage control voltages.

Transformer failures are so uncommon these days in big ampifiers. I have a

70s Heathkit AR1500 with a bad transformer. Pretty sure it's the only one I've ever seen in a relatively modern stereo system.

't mind not looking original. If it's got room, there are tons of options including using a XFR from a typical Japanese receiver (I might have some d onors if you need one). You can split it up by putting in a trans for the power amp and a smaller one for the low voltage control voltages.

** I see a triac "soft start" circuit hiding in there.

** Very likely the voltage selector was set wrongly for use in Europe.

That triac may well be cooked too.

..... Phil

tch.

Assuming I find a suitable power-transformer, I will behave as if the entir e power-supply from the rectifier board and beyond is cooked. Happily, most of the interior parts are of common types and voltages such that replaceme nts and appropriate upgrades will be simple and not unusually costly. And d espite being of Swiss design, Revox was not big on relabeled, proprietary p arts on this amp.

When I received it (from Luxembourg), the MV switch was set to 240V. For wh at that is worth.

My existing very well behaved unit will be my comparison device if I can ge t it away from my granddaughter long enough.

Peter Wieck Melrose Park, PA

:

on't mind not looking original. If it's got room, there are tons of option s including using a XFR from a typical Japanese receiver (I might have some donors if you need one). You can split it up by putting in a trans for th e power amp and a smaller one for the low voltage control voltages.

rimary voltage (120V). If you do have a transformer that has those secondar ies, I am interested at any reasonable price. I should have enough room, bu t I can also send dimensions if needed.

-large fuse as the burn extends all the way to the MV switch.

What's your time frame Peter? I am way above the top of my heinie with pro blems this week. Next week should be much easier for me.

I'll dig through my pile of yet to be scrapped stereo receivers and see wha t I have that will work. If I have something you can use, it's yours for t he asking. It will do my heart good to see someone have use out of stuff t hat's been under foot for too long a time.

** It's really a remote on/off switch.

BTW:

What the heck are 82kohm resistors R1 and R2 doing in the power amp circuit ?

Even if they are 1% precision types, they can only creates a DC offset that is not desirable.

.... Phil

it ?

Even if they are 1% precision types, they can only creates a DC offset that is not desirable."

If the open loop gain is high enough it doesn't matter. Plus they got R4 in there which should bias the thing.

Possibly it is a method to keep DC offset from happening with highly non-si nosodial waves with extreme second harmonic distortion (such as the human v oice) so that when it loaded one side of the power supply the imbalance wou ld cancel out.

Revox is a weird company like that. I got the print of an FM tuner I can't even follow. They got more transistors in there than, well, anything. Ceram ic filters all over the place n shit. Seriously ridiculous. And I mean to t he point where I consider it severely overdesigned. On FM they transmit up to 15 KHz, it is not worth ten grand to receive. But this thing by golly ca n receive, I am sure of that. I'll have to see if I can find the model numb er, the print will make you drink. I can imagine it on paper, each of a ton of pages would be bigger than almost any desk, and some rooms.

I am not saying their stuff is not good, I just think they go too far somet imes.

You need two supplies for an amp, a low and a high. If you want, have a boo sted supply like Pioneer et alii did years ago to run the drivers and smoot h out the linearity when you got to the rails. That's three. This amp does not do that.

The only other thing those 82Ks might do it stabilise it during power up an d power down. Remember the discussion about the QSC circuit with no center tap on the transformer ? Well they have to manage that DC from power up til l power down. But this amp is not like that.

Really, those 82Ks are working into an 18K, so just how much can they do ?

Weird company, engineers probably get better drugs than anyone.

My best guess at the moment.

roblems this week. Next week should be much easier for me.

hat I have that will work. If I have something you can use, it's yours for the asking. It will do my heart good to see someone have use out of stuff that's been under foot for too long a time.

I have enough projects in the queue such that June, 2022 would be OK. So, n o rush whatsoever. And your efforts are much appreciated!

Take care!

Peter Wieck Melrose Park, PA

Maybe I'm getting dense with old age but you said ALL the windings are open? Both primary and secondary or just the multiple ones on the primary side?

Unless that thing caught fire and cooked for a while, I really can't see how those secondaries opened, if that is the case.

Two observational things, unless my eyesight is failing, those two secondaries are 53V not 63 and I don't see any indication what the current rating is.

It's one thing looking for a transformer with 53V @ 2A secondaries and one that is 53V @ 10A.

-bruce snipped-for-privacy@ripco.com

Correct - 53VAC - I linked the clear schematic, while still looking at the blurry one.

I have come to find out from further discussions (all pleasant) with the seller that his source left it on overnight with a 10A automotive-type fuse in it and found it dead the next morning.

So, yes, 'cooked for a while' about covers it. No single winding is intact. Some are open, some are dead-shorted to each other and internally. The clear plastic wrap around the transformer is also mostly melted.

I paid little enough that I am sure I could recover everything, and more, in parting the remaining bits out. But I choose to accept the challenge and bring it back to life.

Peter Wieck Melrose Park, PA

** So it is a toroidal type ???

Should be easy enough to get one made that is near identical.

.... Phil