revox b77

[stevevdb]

Hi

I have several revox tape recorders at home and I was wondering if there are some other revox guys out there.

repairs: just fire your questions, revox are quite simple to repair.

My revox collection
revox b77 mkI 2 track Normal Speed
revox b77 mkI 4 track Normal Speed
revox b77 mkII 2 track Normal Speed
revox b77 mkII 4 track Normal Speed
revox b77 mkI 2 track High Speed
revox a77 mkIV 2 track
revox a77 mkIV 4 track
revox a77 mkIV 2 track Dolby
revox pr99 mkIII (with butterfly heads)
revox b750 mkII
revox b760
revox B710 mkII
revox b780
revox b790
revox a76
revox a78 mkII

 

[trisho0]

Hello to all the AK community, I am new here.
I have the Revox B77 MKII and I wonder where is the 6dB from VU-Meters.
Trying to adjust the Overload Indicators but I don't see 6dB
The Service Manual says: 6.4.6 Checking the overload indicators. When raising the signal by more than 6 dB, the overload indicators in the VU-meters must become illuminated. No visible 6 dB from my VU-meters.
Also, what signal can I inject into RCA Inputs for overload lights adjustments?

 

[bobschneider]

Hello to all the AK community, I am new here.
I have the Revox B77 MKII and I wonder where is the 6dB from VU-Meters.
Trying to adjust the Overload Indicators but I don't see 6dB
The Service Manual says: 6.4.6 Checking the overload indicators. When raising the signal by more than 6 dB, the overload indicators in the VU-meters must become illuminated. No visible 6 dB from my VU-meters.
Also, what signal can I inject into RCA Inputs for overload lights adjustments?

The service manual is widely available on the net, including at HiFi Engine. But it looks like the official Studer Revox service manual download site has gone away, unfortunately.

 

[trisho0]

The service manual is widely available on the net, including at HiFi Engine. But it looks like the official Studer Revox service manual download site has gone away, unfortunately.

I said the service manual says: 6.4.6 Checking ……. meaning I have the Service Manual.
I injected 775 Hz on AUX inputs with the Input Level knobs at full clockwise (position 10 max). I was be able to send the 775HZ sine tone slowly and the VU meters went to 3 dB (end red zone) without any Overload lights yet. So, I increased more the signal source of 775 Hz and the VU needles after passed over the red zone of 3 dB then the Overload indicators worked. So, I am assuming the needles were at 6 dB (invisible obviously).
So, I guess both channels did overload lights as expected. Is my procedure wrong?

 

[Tinman]

You would also use an external millivolt meter to verify that you are ACTUALLY injecting +6db into the deck. Which is also how you adjust the meters. With a KNOWN reference LEVEL, not just a tone.

 

[trisho0]

You would also use an external millivolt meter to verify that you are ACTUALLY injecting +6db into the deck. Which is also how you adjust the meters. With a KNOWN reference LEVEL, not just a tone.

I appreciate your help so much. I have the FLUKE 77 Multimeter tool will work? I have no other electronic tools at home.
Since the B77 sometimes the Left Channel and VU meter needle drops suddenly I think the machine has an intermittent problem. An hour later I power the unit back On and the left channel and VU meter needle come back to normal and working just fine. Next day the B77 gets the same problem again. Next day is fine.
But I am taking care of the Overload indicators for now.

 

[Tinman]

A Fluke 77 is not an RMS meter, but at 400Hz it'll be ok. Good enough, anyway.
A Fluke 87, if you can pick up a used one at some point will do that just fine. A worthwhile upgrade.

 

[trisho0]

Next week I take take a look at my Preamplifier and to hook outputs cables from the preamp Output 2 to find if the Output 1 is the issue. It looks like the Revox B77 is OK so far for now.

 

[twiiii]

I have a B-77 HS 2 trk with a 4th head for 1/4 trk stereo play back. Its a great machine but it handle the dynamics that my AG 500-2/4, AG 350-2, AG 440 C and 300-4 and 300-2 could put on MAxell Low noise high output tape. I only have my Ag 500 and the Revox now.

 

[trisho0]

I found the B77 is adjusted properly and I thought it was faulty because of differences by looking at the VU-Meters. My unit McIntosh C22-CE preamp is configured with audio cables from the Outputs 1 and 2 to Inputs of Revox B77 tape deck and Revox B710 cassette deck. After powered On the system all signal appears just as normal by looking at the VU-Meters as well. After around 30 minutes idling the B77 drops the signal on the Left channel and it stays almost dead while B710 still up normal both channels. Then, I replaced twice the audio cables for B77 and it still exactly the same issue.
I think if both tape recording decks showed the dropped signal from the same Left channel I would replace tubes from the preamplifier C22-CE and also I think both preamp Outputs is sharing the tube.
But, as the Left signal dropped on one Tape Deck only then what can be the next step to give a try?

 

[perryinva]

On that series it is almost always the Tape/Source switch (assuming all capacitors have been replaced (see the B710 thread above)). When the left channel drops out, play with the Tape/Source switch and see if it comes back to life, even intermittently.

 

[trisho0]

On that series it is almost always the Tape/Source switch (assuming all capacitors have been replaced (see the B710 thread above)). When the left channel drops out, play with the Tape/Source switch and see if it comes back to life, even intermittently.

Flipping Tape/Source didn't make differences. That's weird, after 30min idling the signal drops or it becomes very weak and sometimes after 6 hours the issue is present again. I guess if any component is faulty then it can't be the problem in random time. It doesn't make sense. Right now I changed cables from the preamp Outputs and see what happen.

 

[paul bi]

I have a B-77 HS 2 trk with a 4th head for 1/4 trk stereo play back. Its a great machine but it handle the dynamics that my AG 500-2/4, AG 350-2, AG 440 C and 300-4 and 300-2 could put on MAxell Low noise high output tape. I only have my Ag 500 and the Revox now.

Hi regarding your B-77 HS 2 trk with a 4th head for 1/4 trk stereo play back.

I intend doing the same modification do you have any pictures as I am particularly interested in the ¼ track head used how it is mounted also how you have configured the electronics my thought is to put another play back circuit board in
Regards Paul located UK

 

[radiokom]

Hi regarding your B-77 HS 2 trk with a 4th head for 1/4 trk stereo play back.

I intend doing the same modification do you have any pictures as I am particularly interested in the ¼ track head used how it is mounted also how you have configured the electronics my thought is to put another play back circuit board in
Regards Paul located UK

In my opinion 4 tracks at 15 ips is something strange. There is nothing important to replace 2 track heads with 4 track (they are direct replacement, mounting is the same) and some minor changes in circuit (possibly), but why? 15ips is for 2 track. And what is wrong, in your opinion, with original Revox circuit boards? Why you want to change them? Recap original boards. Now it is time to replace even blue tantalum capacitors (not only red devils). I replace them with new tantalum capacitors. Yes, I know there are several opinions about replacing them with common electrolytic caps, but for me original design is the best. I do not think I am better engineer as Studer engineers. And I do not trust if someone claims he is better I do not talk about Studer/Revox cassette decks. There are some well known issues and solutions for them.

 

[paul bi]

I do not think you have understood what we are talking about
Firstly I have a B77 half track slow speed 3 ¾ and 7 ½
There is a position for a forth head this was used as a pilot track for controlling a slide projector
So I assume the person I was asking has put a ¼ track head as the 4 th head

This would require switching between the original ½ track head to the new ¼ track head
Switching audio signals requires some thought as you cannot just use a relay
and is best done with higher levels rather than those that come from a head
So my thought is to have another replay PCB for the new head and do the switching at a higher level

Regards Paul

 

[radiokom]

I do not think you have understood what we are talking about
Firstly I have a B77 half track slow speed 3 ¾ and 7 ½
There is a position for a forth head this was used as a pilot track for controlling a slide projector
So I assume the person I was asking has put a ¼ track head as the 4 th head

This would require switching between the original ½ track head to the new ¼ track head
Switching audio signals requires some thought as you cannot just use a relay
and is best done with higher levels rather than those that come from a head
So my thought is to have another replay PCB for the new head and do the switching at a higher level

Regards Paul

HS means "Hi speed", what is 7,5/15ips version. Anyway, Why? Why you want to make Dr. Frankenstein's son? Buy another machine for 4 track. If you have not enough space (I know this is a problem in UK, all premises are like a matchbox), buy a larger house before (as I did). But I am not in UK. Anyway, you always can change a country, if nothing helps to find appropriate space in UK (maybe Cornwall as last try?).

 

[paul bi]

Dear radiokom

I wrote a robust reply to you last posting but unfortunately I am too much of an Englishman to post it but to say I find your posting offensive and irrelevant to the topic

 

[radiokom]

Dear radiokom

I wrote a robust reply to you last posting but unfortunately I am too much of an Englishman to post it but to say I find your posting offensive and irrelevant to the topic

Taking in account your sense of humor, you could be German What I want to say - it is nearly impossible to modify B77 the way you imagine without losing performance. There are 2 track recorders with 4 track playback head originally (Otari MX 55, 5050 for example, Technics is another story) But even with them are 2 problems - there are no scrape flutter roller and if you have 2 in 1, there is unnecesary head wear so better is to have 2 and 4 track head blocks (what I have for my A80s and Otari MTR-15). So what you can do with B77 - restore it carefully. If you want another modification - sell this one and buy another or keep both. There are models for all your needs. Modifications should be done if you want IEC 1 (CCIR) 70µs @ 7,5ips instead of IEC-2 (NAB) 50+3180µs time constants, because B77 3 ¾ and 7 ½ originally is NAB. 3 ¾ is the same for CCIR and NAB 90+3180µs. HS are available CCIR and NAB.

 

[paul bi]

Taking in account your sense of humor, you could be German What I want to say - it is nearly impossible to modify B77 the way you imagine without losing performance. There are 2 track recorders with 4 track playback head originally (Otari MX 55, 5050 for example, Technics is another story) But even with them are 2 problems - there are no scrape flutter roller and if you have 2 in 1, there is unnecesary head wear so better is to have 2 and 4 track head blocks (what I have for my A80s and Otari MTR-15). So what you can do with B77 - restore it carefully. If you want another modification - sell this one and buy another or keep both. There are models for all your needs. Modifications should be done if you want IEC 1 (CCIR) 70µs @ 7,5ips instead of IEC-2 (NAB) 50+3180µs time constants, because B77 3 ¾ and 7 ½ originally is NAB. 3 ¾ is the same for CCIR and NAB 90+3180µs. HS are available CCIR and NAB.

Hi no problem hear actually I spend a lot of time in Cornwall on the lizard and have my Owen room their
My preferred format is 1/2 track at 7 1/2 but having a forth head for 1/4 track means I can play back 1/4 track tapes
Hence making the deck more valuable
Paul south coast UK

 

[Paul Hurst]

Hi Steve - I have an old A77 and it isn't working. Last time I turned it on, VU meters went to mid-scale after power on. Motors operate.
Do you think it is likely a 'replace all electrolytic caps' issue?

I have the manual, but I haven't had the time to try a repair in the past. Now retired, time is on my side.

Very well built machine, and the removable boards make it pretty easy to work on (I have repaired it a few times, decades ago)

thanks
Paul