OK- I found one of these out of Luxembourg for (relative) sparrow-feed, listed as 'not working' that I snagged the other day. Although it has not yet arrived I am preparing for the restoration. Some history:

This will be my second A722. The first is now residing happily (and heavily) used with my 13 YO grand-daughter paired with the A720 and Piccolo speakers. That one was 'working' when it came into my hands via Denmark, needing only a few caps, lamps and a bit of cleaning. Although compact inside, they are assembled logically and every part can be reached. The intention here is that this unit will join my other A720 in the other all-Revox system that includes the various moving parts - RtR, CD, Cassette and TT.

I have a good, clean copy of the shop manual & schematics. I have a good 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 filters (4), but I have identified good sources with quick delivery (including Amazon of all places). '

In any case, has anyone here ever dived into this amp? Any suggestions? Otherwise, I will start at one end and work my way across to the other.

http://www.reeltoreel.de/worldwide/A722.htm is a link to the device.

Thanks in advance!

Peter Wieck
Melrose Park, PA

On Wednesday, December 14, 2016 at 10:22:03 AM UTC-5, wrote:
OK- I found one of these out of Luxembourg for (relative) sparrow-feed, listed as 'not working' that I snagged the other day. Although it has not yet arrived I am preparing for the restoration. Some history:

This will be my second A722. The first is now residing happily (and heavily) used with my 13 YO grand-daughter paired with the A720 and Piccolo speakers. That one was 'working' when it came into my hands via Denmark, needing only a few caps, lamps and a bit of cleaning. Although compact inside, they are assembled logically and every part can be reached. The intention here is that this unit will join my other A720 in the other all-Revox system that includes the various moving parts - RtR, CD, Cassette and TT.

I have a good, clean copy of the shop manual & schematics. I have a good 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 filters (4), but I have identified good sources with quick delivery (including Amazon of all places). '

In any case, has anyone here ever dived into this amp? Any suggestions? Otherwise, I will start at one end and work my way across to the other.

http://www.reeltoreel.de/worldwide/A722.htm is a link to the device.

Thanks in advance!

Peter Wieck
Melrose Park, PA


I'm not a fan of wholesale recapping quality equipment if said equipment has no history of needing them. A lot of stuff made in the early to late 2000s (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 that 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 worked perfectly until I unloaded it a couple of years ago. Hopefully someone with extensive knowledge of your model can give you more specific advice.

On 14/12/2016 15:21, wrote:
OK- I found one of these out of Luxembourg for (relative) sparrow-feed, listed as 'not working' that I snagged the other day. Although it has not yet arrived I am preparing for the restoration. Some history:

This will be my second A722. The first is now residing happily (and heavily) used with my 13 YO grand-daughter paired with the A720 and Piccolo speakers. That one was 'working' when it came into my hands via Denmark, needing only a few caps, lamps and a bit of cleaning. Although compact inside, they are assembled logically and every part can be reached. The intention here is that this unit will join my other A720 in the other all-Revox system that includes the various moving parts - RtR, CD, Cassette and TT.

I have a good, clean copy of the shop manual & schematics. I have a good 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 filters (4), but I have identified good sources with quick delivery (including Amazon of all places). '

In any case, has anyone here ever dived into this amp? Any suggestions? Otherwise, I will start at one end and work my way across to the other.

http://www.reeltoreel.de/worldwide/A722.htm is a link to the device.

Thanks in advance!

Peter Wieck
Melrose Park, PA


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, wrote:

I'm not a fan of wholesale recapping quality equipment if said equipment has no history of needing them. A lot of stuff made in the early to late 2000s (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 that 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 worked 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 working 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

On Wednesday, December 14, 2016 at 3:14:31 PM UTC-5, N_Cook wrote:

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

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 me in any case. They are readily available from several sellers in the US and elsewhere.
c) The Revox Cassette drive is considered the most reliable drive, ever. Favorably compared to the Nakamichi Dragon - which does use belts in its secondary functions.
d) The same may be written of my A77 road deck and B225 CD player. This last I have had to recap on the audio board (quite convenient to do, by the way) 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 - direct 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 grommets.

http://images43.fotki.com/v61/photos...ansport-vi.jpg

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

Peter Wieck
Melrose Park, PA

On Wed, 14 Dec 2016 12:44:03 -0800 (PST), "
wrote:

On Wednesday, December 14, 2016 at 3:14:31 PM UTC-5, N_Cook wrote:

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

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 me in any case. They are readily available from several sellers in the US and elsewhere.
c) The Revox Cassette drive is considered the most reliable drive, ever. Favorably compared to the Nakamichi Dragon - which does use belts in its secondary functions.
d) The same may be written of my A77 road deck and B225 CD player. This last I have had to recap on the audio board (quite convenient to do, by the way) 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 - direct 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 grommets.

http://images43.fotki.com/v61/photos...ansport-vi.jpg

The B215 has Dolby B & C on board as well. And at over 20 pounds, no lightweight. 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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On Thursday, December 15, 2016 at 9:27:12 AM UTC-5, Chuck wrote:
Snippage
\
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 unused 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 worked. I offered to fix it for him, but he was done with cassettes by then.

Peter Wieck
Melrose Park, PA

On Thu, 15 Dec 2016 06:49:59 -0800 (PST), "
wrote:

On Thursday, December 15, 2016 at 9:27:12 AM UTC-5, Chuck wrote:
Snippage
\
He got all ragey like because any deck this expensive should
never fail. Guess he didn't own any European luxury automobiles.

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

The tiniest bit of the wife's clear fingernail polish eliminated that issue without causing future servicing issues. I purchased my unit in nearly unused 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 worked. 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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On Wednesday, December 14, 2016 at 10:22:03 AM UTC-5, wrote:

Update: The unit arrived with a thoroughly cooked power transformer - not 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.

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

I will report results.

Peter Wieck
Melrose Park, PA

On Monday, December 19, 2016 at 8:46:33 AM UTC-5, wrote:
On Wednesday, December 14, 2016 at 10:22:03 AM UTC-5, wrote:

Update: The unit arrived with a thoroughly cooked power transformer - not 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.

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

I will report results.

Peter Wieck
Melrose Park, PA


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 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 the power 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.

On Monday, December 19, 2016 at 11:15:20 AM UTC-5, wrote:


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 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 the power amp and a smaller one for the low voltage control voltages.
SNIPPAGE

I have a good deal of room. I need four (4) secondary windings.

ftp://ftp.studer.ch/Public/Products/...A722_Diagr.pdf

Per the schematic. 26V, 24V, and two @ 63V. I DO NOT need more than one primary voltage (120V). If you do have a transformer that has those secondaries, I am interested at any reasonable price. I should have enough room, but I can also send dimensions if needed.

I suspect that the failure was due to someone putting in a massively over-large fuse as the burn extends all the way to the MV switch.

Thanks in advance!

Peter Wieck
Melrose Park, PA

wrote:


I have a good deal of room. I need four (4) secondary windings.

ftp://ftp.studer.ch/Public/Products/...A722_Diagr.pdf

Per the schematic. 26V, 24V, and two @ 63V. I DO NOT need more
than one primary voltage (120V). If you do have a transformer
that has those secondaries, I am interested at any reasonable
price. I should have enough room, but I can also send dimensions
if needed.



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


I suspect that the failure was due to someone putting in a
massively over-large fuse as the burn extends all the way to the MV switch.


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

That triac may well be cooked too.


...... Phil

On Monday, December 19, 2016 at 3:34:56 PM UTC-5, Phil Allison wrote:

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


I suspect that the failure was due to someone putting in a
massively over-large fuse as the burn extends all the way to the MV switch.


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

That triac may well be cooked too.

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

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

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

Peter Wieck
Melrose Park, PA

On Monday, December 19, 2016 at 3:20:39 PM UTC-5, wrote:
On Monday, December 19, 2016 at 11:15:20 AM UTC-5, wrote:


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 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 the power amp and a smaller one for the low voltage control voltages.
SNIPPAGE

I have a good deal of room. I need four (4) secondary windings.

ftp://ftp.studer.ch/Public/Products/...A722_Diagr.pdf

Per the schematic. 26V, 24V, and two @ 63V. I DO NOT need more than one primary voltage (120V). If you do have a transformer that has those secondaries, I am interested at any reasonable price. I should have enough room, but I can also send dimensions if needed.

I suspect that the failure was due to someone putting in a massively over-large fuse as the burn extends all the way to the MV switch.

Thanks in advance!

Peter Wieck
Melrose Park, PA

What's your time frame Peter? I am way above the top of my heinie with problems 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 what 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.

Phil Allison wrote:

wrote:


I have a good deal of room. I need four (4) secondary windings.

ftp://ftp.studer.ch/Public/Products/...A722_Diagr.pdf


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



** 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

"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."

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-sinosodial waves with extreme second harmonic distortion (such as the human voice) so that when it loaded one side of the power supply the imbalance would 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. Ceramic filters all over the place n ****. Seriously ridiculous. And I mean to the 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 can receive, I am sure of that. I'll have to see if I can find the model number, 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 sometimes.

You need two supplies for an amp, a low and a high. If you want, have a boosted supply like Pioneer et alii did years ago to run the drivers and smooth 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 and 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 till 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.

wrote:


"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."

If the open loop gain is high enough it doesn't matter.


** You really need to take MORE drugs.

Cos the ones you are taking now are not strong enough.

You still have a tenuous grasp on reality - but only just.



Plus they got R4 in there which should bias the thing.


** Posts the math anytime, in the next billion years, ****head.



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


** Plenty - you ****ing tenth witted prick.


Weird company, engineers probably get better drugs than anyone.


** ROTFL - says it all 'really.



..... Phil

On Monday, December 19, 2016 at 7:56:37 PM UTC-5, wrote:

What's your time frame Peter? I am way above the top of my heinie with problems 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 what 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, no rush whatsoever. And your efforts are much appreciated!

Take care!

Peter Wieck
Melrose Park, PA

wrote:

Per the schematic. 26V, 24V, and two @ 63V. I DO NOT need more than one
primary voltage (120V). If you do have a transformer that has those
secondaries, I am interested at any reasonable price. I should have enough
room, but I can also send dimensions if needed.

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

On Tuesday, December 20, 2016 at 7:40:25 AM UTC-5, Bruce Esquibel wrote:
wrote:

Per the schematic. 26V, 24V, and two @ 63V. I DO NOT need more than one
primary voltage (120V). If you do have a transformer that has those
secondaries, I am interested at any reasonable price. I should have enough
room, but I can also send dimensions if needed.

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


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

wrote:


The clear plastic wrap around the transformer is also mostly melted.




** So it is a toroidal type ???

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


..... Phil

wrote:

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

Ok, if this is a "for yourself" repair, I'd do what someone else suggested
and use multiple transformers. At least one for the low current pair and
the oddball for the dual 53V side.

One suggestion, you can probably find dual 48V ones without too many
problems, those had to have been used by the telcos for charging their
batteries when everything was copper based.

I really think the 5V difference is going to make little change, probably
cut a couple watts off peak output but should be totally safe to use.

At least you can see if the rest of it still works and if it does, just
leave it like that while in search of something closer to the original one.

-bruce

On Tuesday, December 20, 2016 at 7:04:33 PM UTC-5, Phil Allison wrote:
wrote:


The clear plastic wrap around the transformer is also mostly melted.




** So it is a toroidal type ???

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


.... Phil

Not a toroid. Remember, this is a Revox - never use one part when three-or-more will do better. There is a clear plastic clam shell over the windings but under the end bells. It is also a 'double C' core.

I am trying to avoid multiple transformers - the on/off switching scheme is complicated enough without introducing additional connections. But, if I must go that way eventually, I will.

Peter Wieck
Melrose Park, PA

wrote:




** So it is a toroidal type ???

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



Not a toroid. Remember, this is a Revox - never use one part when
three-or-more will do better. There is a clear plastic clam shell over the windings but under the end bells. It is also a 'double C' core.

I am trying to avoid multiple transformers -



** Then using a custom toroidal is the obvious way to go.

Are the no winders set up in your part of the world?




..... Phil

Many. Getting prices.

Peter Wieck
Melrose Park PA