Author Topic: Revox B750 all mine!  (Read 8930 times)

Offline Steerpike

Revox B750 all mine!
« on: August 02, 2012, 08:51:49 PM »
No section for classic transistor amplifiers?
This arrived in the post today, with its cassette sibling, Thank you Kent K and Wessel.

The B750 is one I've been after for a while - it was my teenage dream, but at R900 it was too expensive. Typical 2x50W Japanese amps were under R300, and amplifiers were not something my parents thought was a worthwhile expenditure!

It's a 'late' Mk1, having the "phono or aux" option on the 4th input, but it still has the 'low' power output. Apparently that can be a blessing, as the Mk2 runs hot.
Also interesting is that it has Siemens capacitors - not the deadly Frakos. Still a few of those nasy yellow Rifas.

Outside its moderately scraped, but that can be re-surfaced. The Nextel has been removed by a previous owner. Happily the face plate has barely any marks.
Interior looks all original, though it has been opened up and reassembled at some stage. Certainly it can not work as is - things like mica washers missing, but nothing looks electrically damaged.

A nice addition it will be!

---

Offline GECO

Re: Revox B750 all mine!
« Reply #1 on: August 02, 2012, 08:55:25 PM »
Wow. what a nice find.

show BWS that transformer

Offline WD

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Re: Revox B750 all mine!
« Reply #2 on: August 02, 2012, 09:07:48 PM »
Hmm, mid-engined, wonder if it is quite agile? ;D

Offline SeanS

Re: Revox B750 all mine!
« Reply #3 on: August 02, 2012, 09:10:04 PM »
I like the "presence" function.... makes me think you can make someone "appear" in the room at the twist of a button...

Offline Kent Kassler

Re: Revox B750 all mine!
« Reply #4 on: August 02, 2012, 09:39:49 PM »
..glad it got to you safely Steerpike,that package was close on 30 kilo's and I was nervous...can't wait to see those beaut's up and running...all the best.
Audiophile Sound Sommelier Extraordinaire....aka Manic Depressive Temporary Void Filler Deluxe.

Online Family_Dog

Re: Revox B750 all mine!
« Reply #5 on: August 02, 2012, 09:44:38 PM »
Nice one!!


-F_D



-Eric

That Guy in South Africa...
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Offline Tachyon

Re: Revox B750 all mine!
« Reply #6 on: August 02, 2012, 10:32:12 PM »
Soon it'll be time to build an extension to your Revox museum  ;D
« Last Edit: August 02, 2012, 10:38:35 PM by Tachyon »
After silence, that which comes nearest to expressing the inexpressible is music - Aldous Huxley

Offline Steerpike

Re: Revox B750 all mine!
« Reply #7 on: August 02, 2012, 10:46:28 PM »
..glad it got to you safely Steerpike,that package was close on 30 kilo's and I was nervous...

I was too! And as I said to you privately, when I said to the P.O. woman that I wanted to check the contents "because I saw how you were throwing it around", she told me "We were not throwing it around! We were rolling it. It's heavy".

The rolling of eyes is now appropriate.

Thank <your favourite deity> that it was not a turntable!

It has the much maligned DIN 2-pin "speaker B" sockets. But there is also plenty of space behind the transformer to add bananna-socket-binding posts on the back panel if desired. I'm not convinced that properly cleaned DIN plugs are so bad anyway.

The two vertical PCBs in the back right corner are the two RIAA phono amps, each one stereo - nice that they use TWO phono pre-amps and don't do any low-level switching on the phono signal. So it's an ideal candidate for an MC upgrade/modification, though MC was never a factory option on this model.
The Tape Rec output on the front panel could also be turned into an input for a portable MP3 player!
« Last Edit: August 02, 2012, 10:56:15 PM by Steerpike »

Offline fdlsys

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Re: Revox B750 all mine!
« Reply #8 on: August 02, 2012, 11:35:59 PM »
The two vertical PCBs in the back right corner are the two RIAA phono amps, each one stereo - nice that they use TWO phono pre-amps and don't do any low-level switching on the phono signal. So it's an ideal candidate for an MC upgrade/modification, though MC was never a factory option on this model.
The Tape Rec output on the front panel could also be turned into an input for a portable MP3 player!
Massive  :clap: :clap: to that!!!

I see it has all switch levers intact, so no need for Steerpike's special lever-graft - good! Knobs all look good and unscraped - a really nice find!
What's the cassette deck like?

Looking forward to your aesthetics refurbishment details; you know I'll have to go thorough the same process, right?
The four building blocks of the universe are fire, water, gravel and vinyl. Dave Barry
Come back when you’ve lived a little. Miles Davis

Offline Steerpike

Re: Revox B750 all mine!
« Reply #9 on: August 03, 2012, 11:39:58 AM »
What's the cassette deck like?

Outside cabinet also scratched and previously de-Nextelled. But no real damage. The cassette well frame (the metal casting) is a little oxidized, same material as the B77 headblock cover, and this cannot be polished or sandblasted because it is plated - the metal is a copper colour underneath. but it's not a bad corrosion. A good wash will help a lot. Inside.... not looked yet! The back panel is missing, but it is cosmetic - the sockets are still present & mounted as should be.
This one has the transport with the tiny pinch rollers and the separate Sony heads. The small pinch rollers are harder to replace than the big ones used in later models, but the Sony heads are a plus.

Did you 'debug' your B77 yet?

Offline fdlsys

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Re: Revox B750 all mine!
« Reply #10 on: August 03, 2012, 11:49:04 AM »
Did you 'debug' your B77 yet?
Nope, days (and nights) were busy this week :(
But starting today, after work... vac & wash. Should I really attempt to hose it down? I did read some of yours & Ghostie's instructions - bath tub, water and detergent... brrr... to say I'm a little afraid of that would be a serious understatement. Isn't calcium from the water going to leave (hard!) marks on slide-guides/rollers/shafts and other bits where you wouldn't really want any deposits? Or did I take the whole wash process a bit too literally?
The four building blocks of the universe are fire, water, gravel and vinyl. Dave Barry
Come back when you’ve lived a little. Miles Davis

Offline Steerpike

Re: Revox B750 all mine!
« Reply #11 on: August 03, 2012, 03:38:19 PM »
Should I really attempt to hose it down? .... Or did I take the whole wash process a bit too literally?

No, and yes, in that order!
Do not wash it in water in its entirety!
Certain parts can be washed like dishes - the circuit boards that DO NOT CONTAIN transformers, relays or inductors, the case, face plates etc.
DO NOT WASH with water, any wound components (inductors, coils, transformers, relays, recording heads and motors and VU meters).
Motors can be disassembled, and the NON-BEARING bits washed in turpentine. Ball race bearings can be re-greased, they generally do not wear out since the forces and speeds in a tape recorder are so low. Sintered bronze bearings can be wiped briefly with alcohol, never soak them in anything.

The ball races can be opened up, old grease washed out (turpentine) & new grease put in - nimble fingers are required. I think Only the capstan motor has bronze bearings. The reel motors are ball races, as is the left side tape guide.

 :teach: DO NOT USE WD40 or Q20 ANYWHERE AT ALL ON A TAPE RECORDER!!!! :teach:

Don't wash the interconnect PCB with the switches attached to it, until you have removed the switches. A careful wipe with acetone will restore the gold-flashed contact foils.

The chassis parts can all be washed in water & detergent. If you want to remove all the Nextel for re-finishing, purple methylated spirits disssolves it.



The B710 cassette deck, opened it up to look. Hasn't had any of the factory-derived updates (changes to component values) so it is all very original inside. It has the IR-remote receiver option installed too, which is rare and nice. The reel motors feel good to the finger test - a good sign since the bearings here wear quite badly sometimes and new motors are about R1500 each!
« Last Edit: August 03, 2012, 03:50:14 PM by Steerpike »

Offline Steerpike

Re: Revox B750 all mine!
« Reply #12 on: August 11, 2012, 12:25:19 AM »
The A750 inside in a good state. No nasties like the A722's unknown 'repairer'. A few very leaky TO3 and TO220 transistors in the B750. The idle curent trimmers have been changed - for ones that don't fit the PCB, and being horizontal mounting, you couldn't set the idle current with the amp assembled. Luckily I have some original big ceramic 1W Ruwidos from the 1970s!



New 4-pin electrolytics already on their way from RS Europe!
And that Rifa class X has to go! It's 'only' the Zobel network, but still it must be cast out into the Gadarene Swine!
« Last Edit: August 11, 2012, 12:30:25 AM by Steerpike »

Offline fdlsys

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Re: Revox B750 all mine!
« Reply #13 on: August 11, 2012, 01:23:32 AM »
My precioussssss....  :Whoohoo:
The four building blocks of the universe are fire, water, gravel and vinyl. Dave Barry
Come back when you’ve lived a little. Miles Davis

Online Family_Dog

Re: Revox B750 all mine!
« Reply #14 on: August 11, 2012, 09:57:32 AM »
Still very clean! Are the caps still OK?


-F_D



-Eric

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