Revox B77 Reel-to-Reel

[Arkless Electronics]

@337alant, since my knowledge of capacitors is limited to a few types used in vintage loudspeakers, I'd be grateful for a recommendation on a replacement for the Rifa X2 that's across the power supply. A link to where I can order it from would be even better.

X2 IS a safety spec for this type of cap. Any of similar value and with the X2 rating on it should be fine. It will make bugger all difference to just not fit one really...

 

[ToTo Man]

Some tentative initial testing this afternoon has revealed the following issues: -

- Left and right Record lights don't light up when I flick the Rec toggle switches. Is this normal?

- Playback is intermittent in channels. 9 times out of 10 it's only coming out of left channel. If I flick Source/Monitor a dozen times I'll get output in right channel but not the left! A further 40 or so flicks and I get both channels, but one more flick and I'll lose one channel again! So it looks like a severe case of pot oxidisation that'll need addressing at some point.

- Playback operation is quiet, speed is steady and sound is good from what I can tell from the cheap Behringer headphones I plugged into the deck. I replayed a test tape I recorded on the B77 I bought and subsequently returned for a refund a few years ago. I recorded those test tones at 0dB according to that B77's VU meters, but this B77's VU meters are showing +3dB on those recordings.

- Rewind function seemed OK. Smooth and quiet but not super fast. I don't know if it was foolish of me to stop the rewind a few times as it was getting near to the start of the tape, but I didn't want it to come off the take-up spool and have to re-thread it. The last interruption appears to have stretched the tape where it joins the leader tape (see pic below). Is this indicative of an issue with the brakes or was it my own fault for pressing stop?

 

[Jonathan]

From a safety POV does it matter which orientation the power cable is inserted? It appears to fit both ways and there's nothing to indicate which one is correct? I've inserted it so that the cable is travelling across the fuse holder.

doesn't matter - and the X2 cap can be replaced by pretty much anything - they are a bugger to get out though from behind the cover in the back ...

 

[Jonathan]

Some tentative initial testing this afternoon has revealed the following issues: -

- Left and right Record lights don't light up when I flick the Rec toggle switches. Is this normal?

- Playback is intermittent in channels. 9 times out of 10 it's only coming out of left channel. If I flick Source/Monitor a dozen times I'll get output in right channel but not the left! A further 40 or so flicks and I get both channels, but one more flick and I'll lose one channel again! So it looks like a severe case of pot oxidisation that'll need addressing at some point.

- Playback operation is quiet, speed is steady and sound is good from what I can tell from the cheap Behringer headphones I plugged into the deck. I replayed a test tape I recorded on the B77 I bought and subsequently returned for a refund a few years ago. I recorded those test tones at 0dB according to that B77's VU meters, but this B77's VU meters are showing +3dB on those recordings.

- Rewind function seemed OK. Smooth and quiet but not super fast. I don't know if it was foolish of me to stop the rewind a few times as it was getting near to the start of the tape, but I didn't want it to come off the take-up spool and have to re-thread it. The last interruption appears to have stretched the tape where it joins the leader tape (see pic below). Is this indicative of an issue with the brakes or was it my own fault for pressing stop?

gah! needs some adjustment methinks. sounds like it could do with an overall pot cleaning and electrical/mechanical calibration (tension check etc etc) ... take it to a reputable shop or tackle it yourself via the service manual. I had the same problem on mine with one of the record lights - tracked it down to a bad transistor on the sync card

 

[ToTo Man]

doesn't matter - and the X2 cap can be replaced by pretty much anything - they are a bugger to get out though from behind the cover in the back ...

I managed to snip it out from the side using a pair of scissors. Not sure how I'll get a soldering iron in there when fitting the new cap though?!

 

[Jonathan]

I managed to snip it out from the side using a pair of scissors. Not sure how I'll get a soldering iron in there when fitting the new cap though?!

you should really do it 'properly' and remove the two screws fastening the shell (housing) to the frame (WAYYY DOWN INSIDE) and remove the assembly so you can make a clean job of it - working like that will only introduce problems or worse - danger or faults

i wouldn't have removed it personally if in good condition - you can usually tell by the amount of cracking going on in the shell .... from what i understand anyway

 

[ToTo Man]

you should really do it 'properly' and remove the two screws fastening the shell (housing) to the frame (WAYYY DOWN INSIDE) and remove the assembly so you can make a clean job of it - working like that will only introduce problems or worse - danger or faults

i wouldn't have removed it personally if in good condition - you can usually tell by the amount of cracking going on in the shell .... from what i understand anyway

It was already exploded when I got the deck so thought it was safer just to remove it (see post #9).

 

[337alant]

Some tentative initial testing this afternoon has revealed the following issues: -

- Left and right Record lights don't light up when I flick the Rec toggle switches. Is this normal?

- Playback is intermittent in channels. 9 times out of 10 it's only coming out of left channel. If I flick Source/Monitor a dozen times I'll get output in right channel but not the left! A further 40 or so flicks and I get both channels, but one more flick and I'll lose one channel again! So it looks like a severe case of pot oxidisation that'll need addressing at some point.

- Playback operation is quiet, speed is steady and sound is good from what I can tell from the cheap Behringer headphones I plugged into the deck. I replayed a test tape I recorded on the B77 I bought and subsequently returned for a refund a few years ago. I recorded those test tones at 0dB according to that B77's VU meters, but this B77's VU meters are showing +3dB on those recordings.

- Rewind function seemed OK. Smooth and quiet but not super fast. I don't know if it was foolish of me to stop the rewind a few times as it was getting near to the start of the tape, but I didn't want it to come off the take-up spool and have to re-thread it. The last interruption appears to have stretched the tape where it joins the leader tape (see pic below). Is this indicative of an issue with the brakes or was it my own fault for pressing stop?

As others have said the deck will work without the X2 cap across the mains but I all ways replace them with a new one even a new rifa, here is a non Rife version https://www.cricklewoodelectronics....j_ctjbMesMFYKqYUoIL4IXAhmKiwB_T8aApatEALw_wcB

If the red light dont come on after you press record + Play it could be that the LEDs are wired wrong or have failed or the relays on the oscillator board are defective, do you get a record signal even though the lights dont come on?

Intermittent playback is normally the main switchboard switches and selectors need cleaning, can also be the output relays

To check the play back frequency response you will need a calibration tape
To check the Record / Playback response you will need a sign wave signal generator with a output level of 0.775VAC plu a analogue AC voltmeter to check the output levels, at a pinch you can use the VU meters if you know they are accurate dont use a DVM as the majority are not accurate above 1k
but before you do this you should have calibrated the deck

stretching the tape on RW is probably that the supply reel brake is not functioning but the take up reel is

Alan

 

[ToTo Man]

If the red light dont come on after you press record + Play it could be that the LEDs are wired wrong or have failed or the relays on the oscillator board are defective, do you get a record signal even though the lights dont come on?

I didn't get as far as pressing REC+PLAY as the tape had stretched at that point and I didn't proceed any further as I assumed pressing these would start the tape rolling. Will the VU meters still show an input signal if the REC+PLAY buttons aren't engaged?

stretching the tape on RW is probably that the supply reel brake is not functioning but the take up reel is

Makes sense. Until it's sorted I presume I should just let it fully rewind and let the leader tape whip out of the take-up reel?

 

[337alant]

I didn't get as far as pressing REC+PLAY as the tape had stretched at that point and I didn't proceed any further as I assumed pressing these would start the tape rolling. Will the VU meters still show an input signal if the REC+PLAY buttons aren't engaged

Put the Tape monitor switch to Monitor tape and Pressing Rec/Play will start the tape rolling, you should also hear the sound and see the VU meters going and red lights come on
To listen to the source and set your recording levels before you are recording, put the tape monitor switch to Input
For the stretched tape just cut that section out and splice the leader back on

Alan

 

[ToTo Man]

It turns out my Apogee Duet FW Soundcard wasn't passing a signal to the B77 (I haven't used the Apogee since upgrading to El Capitan and apparently it isn't supported under this OS!). I'm now using my Mac's built-in audio output and the B77's VU meters are now responding to the input signal when I set the MONITOR toggle to INPUT.

When I output a -10dB pink noise signal from my Mac (and I'm not exactly sure what the max RMS voltage output of the Mac is, but I doubt it's more than 1.5Vrms), the B77's Input Level knobs need to be set to approximately half (5/10) to read -10dB on the VU meters.

This happens when both REC toggles are in the OFF or ON position. However, if only one REC toggle is in the ON position, both VU meters read -3dB instead of -10dB and the signal that's being outputted from the B77 into my computer becomes +7dB louder on both channels. Is there a known reason for this as it seems rather odd to me?

 

[Arkless Electronics]

As others have said the deck will work without the X2 cap across the mains but I all ways replace them with a new one even a new rifa, here is a non Rife version https://www.cricklewoodelectronics....j_ctjbMesMFYKqYUoIL4IXAhmKiwB_T8aApatEALw_wcB

If the red light dont come on after you press record + Play it could be that the LEDs are wired wrong or have failed or the relays on the oscillator board are defective, do you get a record signal even though the lights dont come on?

Intermittent playback is normally the main switchboard switches and selectors need cleaning, can also be the output relays

To check the play back frequency response you will need a calibration tape
To check the Record / Playback response you will need a sign wave signal generator with a output level of 0.775VAC plu a analogue AC voltmeter to check the output levels, at a pinch you can use the VU meters if you know they are accurate dont use a DVM as the majority are not accurate above 1k
but before you do this you should have calibrated the deck

stretching the tape on RW is probably that the supply reel brake is not functioning but the take up reel is

Alan

You really need an AC millivolt meter or an old valve voltmeter or something similar for this as most passive analogue meters also are inaccurate at 1KHz. A 'scope will obviously be fine. One of the main reasons I choose the Metrix MX56C DMM I use is that it is designed for audio and AC use and flat to 50KHz....

Meters vary hugely in AC accuracy at frequencies above 400Hz (many are designed to be accurate at 400Hz as it's the AC frequency in aircraft). Some will be fine at 1KHz and even 10KHz but more will not be and so it's best to use a proper AC millivoltmeter. Many have dB scaling as well which can be very useful. My 60's valve hybrid Marconi Instruments TF2604 goes up to 1500MHz!! These and similar even older ones still come up cheaply now and then on ebay etc and later solid state meters from Goodwill Instruments, Trio and others should be pretty cheap.

 

[ToTo Man]

Some more info I'd like to note down in case I forget at a later date:

- VU meter sensitivities don't match. When I set recording levels so that the L&R input meters in Audacity are perfectly matched, the B77's L VU meter reads -10dB and the R VU meter reads -7dB.

- Record level knobs don't match. For equal L&R channel input levels in Audacity, the B77's R Record knob has to be set slightly higher than Left. Not a big issue really as long as you remember to compensate.

- When I output -10dBFS Pink Noise from the computer into the B77, the B77's Record Level needs to be set to 5/10 for -10dB on VU meters. When I loop this signal back into Audacity and set the computer's Line In gain to 0dB (i.e. unity gain), Audacity records the input at -6dBFS.

- When I output -10dBFS White Noise from the computer into the B77, the B77's Record Level needs to be set to 3/10 for -10dB on VU meters. When I loop this signal back into Audacity and set the computer's Line In gain to 0dB (i.e. unity gain), Audacity records the input at approx -9.7dBFS, which almost perfectly matches the -10dBFS level of the signal I originally output from the computer, - perhaps just coincidence?!

- When I output 100Hz, 1kHz and 10kHz tones from the computer into the B77, the B77's Record Level needs to be set to 2.75/10 for -10dB on VU meters. When I loop this signal back into Audacity and set the computer's Line In gain to 0dB (i.e. unity gain), Audacity records the input at -17dBFS.

Note: All of the above applies to the B77 with the MONITOR switch set to SOURCE.

EDIT - Having inspected the waveforms of the signals being output from my computer, the white noise signal is clearly louder (i.e. spends more time at peak output) than the pink noise and the sine tones are even louder again, despite them all peaking at -10dB. The B77's VU meters therefore aren't reflecting the peaks of the pink noise signal, hence why I'm getting a higher level of input going back into my computer.

 

[337alant]

Don't worry about all that, its pretty typical of most B77s due to leaky caps dirty switches and trimpots that are falling apart
After servicing the deck all levels will be sorted during the calibration
Alan

 

[337alant]

You really need an AC millivolt meter or an old valve voltmeter or something similar for this as most passive analogue meters also are inaccurate at 1KHz. A 'scope will obviously be fine. One of the main reasons I choose the Metrix MX56C DMM I use is that it is designed for audio and AC use and flat to 50KHz....

Meters vary hugely in AC accuracy at frequencies above 400Hz (many are designed to be accurate at 400Hz as it's the AC frequency in aircraft). Some will be fine at 1KHz and even 10KHz but more will not be and so it's best to use a proper AC millivoltmeter. Many have dB scaling as well which can be very useful. My 60's valve hybrid Marconi Instruments TF2604 goes up to 1500MHz!! These and similar even older ones still come up cheaply now and then on ebay etc and later solid state meters from Goodwill Instruments, Trio and others should be pretty cheap.

Jez
I like the spec on those metrix meters, got my eye on one of these https://www.tester.co.uk/chauvin-ar...TiQi7CwZBgXncdmgl9sDBl50YFm9-_IhoCPpoQAvD_BwE

Alan

 

[Arkless Electronics]

Jez
I like the spec on those metrix meters, got my eye on one of these https://www.tester.co.uk/chauvin-ar...TiQi7CwZBgXncdmgl9sDBl50YFm9-_IhoCPpoQAvD_BwE

Alan

Some odd specs to that one... don't know if typo's but says it only goes down to 600R on resistance and down to 60mV on Volts! A useful 20KHz bandwidth though.
You could prob get one like mine S/H for £150 these days... It was advertised as designed for people working in audio and AC work etc hence the unusual 50KHz bandwidth. It does some neat tricks like you can set your 0.775V you are measuring as "0 dB" at the press of a button and it will display 0 dB. You can then read directly in dB and show the +/- 3dB points. Nice! No doubt very useful for setting up R2R's! You can also do things like cancelling the resistance of the test leads and then measure down to like 0.02 Ohms or whatever. Does loads of other stuff like storing data to be downloaded to PC later.
In my last job as R & D engineer before going self employed I was allowed to spec and choose a DMM for my personal use and after a lot of comparisons with others and reading up on what was available this is what I selected. I was VERY impressed with it and when I left the company I missed it so much I bought one with my own money (FFS I must have liked it!). About £350 in 2005 from RS. They no longer make them unfortunately.

 

[ToTo Man]

My B77 is now in the safe hands of Alan for a full service and also some additional performance upgrades.

As I await its return, I am working out how I am going to permanently accommodate it my 4.2m x 3.8m listening room, along with my Teac A3440 that I've also been itching to put back on display.

From an aesthetics POV it would look great having one deck sat on top each downfiring subwoofer either side of my rack, but I'm assuming this is a big no-no in terms of being too close to too many magnetic fields (that of the sub, that of the Tannoy and that of the Ditton 66).

The only other free space I have that would not require me running ridiculously long interconnects is an area of sidewall to the left of the left Tannoy, which would put the tape decks around 75cm away from the nearest speaker magnet. Is this far enough away?

 

[337alant]

Richard
Measuring with a gauss meter if you go 300-400 to the side of a speaker or behind in the middle of the speaker's there is Zero reading
In front of the speakers there is a strong +ve reading close up that fades after 1.5-2m
On top of a speaker there is a strong -Ve reading
Stand the R2R on a strong table 300-400mm to the side would be OK


Alan

 

[337alant]

Video

https://youtu.be/cADGy-_UJmY

Alan

 

[ToTo Man]

Video

https://youtu.be/cADGy-_UJmY

Alan

That video illustrates it perfectly. I must get myself one of those gadgets!...