Brenell Mk 5 restoration - UK Vintage Radio Repair and Restoration Discussion Forum

steve83 · 23rd Jun 2020, 10:08 am

Hi all - I have been restoring a Brenell Mk 5 reel to reel and have almost finished it, there are just a few final things left to do and I hoped someone here might be able to offer some advice:

1. I am having problems finding a suitable replacement material for the counter belt, I have tried fabric-lined elastic (the type you'd find in a craft shop) and it either slips, or puts too much tension on the take up motor and leads to unstable operation. What is recommended to use? I'd considered just a standard rubber band but can't imagine it lasting very long as they seem to degrade fairly quickly.

2. I was experiencing a faint burning smell on playback which I tracked down to the feed motor. I rebuilt it and it tested fine hooked up to mains out of the machine but when wired back in (and on playback) there would be a faint burning smell after a few minutes which I found strange as the motor is not energised in this mode of operation. The problem has since gone away and so am tempted to put it down to some residual dust which has gone, but have noticed there is a small amount of voltage present (<5vac rms)after the suppression cap. Could this be/have been the culprit? By my calculations the corner frequency of the .01uF / 220R suppressor acting as a HPF should be approx 72Khz so I'd imagine if properly operational there should be no voltage at all getting through! Are suppressor units still available to buy with resistance included or do people tend to buy a .01uF X2 cap and a series resistor?

3. Should the take up and feed motors read the same resistance across their windings? (i.e are they identical units?) One reads approx 230 ohms, the other approx 120 ohms (measurements taken out of circuit)

4. Lastly - is there a recommended procedure for dialling in the correct bias and adjusting the record level meter (this unit has the VU meter rather than the 'magic eye' valve)?

Thanks very much in advance!

barrymagrec · 23rd Jun 2020, 2:19 pm

I`ve had only passing dealings with the Brenell but those suppressors tend to be quite dodgy, particularly at such advanced age.

I`m pretty sure the feed and take-up motors are identical so different resistance readings doesn`t bode well - shorted turns could explain your burning smell.

The set up for the meter should be in the manual, I think it is a peak reading type, not a VU.

steve83 · 23rd Jun 2020, 2:46 pm

Thanks for the reply Barry - the thing that was confusing me is that the feed motor shouldn't be energised when in playback mode according to the schematic - could it be a combination of shorted turns and a leaky suppressor? It also didn't emit any burning odour after I'd rebuilt it and tested it out of the unit straight into mains (without suppressors connected).

Is it still possible to get suppressors with series resistance built in, or should I just use 0.01uF X2 caps with 220 ohm 2W resistors installed in series?

The service manual I have (titled "Brenell Mark 5 Tape Deck: Installation, Operating and Servicing Instructions") unfortunately doesn't have any information about adjustments for the magic eye or meter. If anyone has any info regarding setting this up, and also adjusting the bias (i.e. what voltages to aim for) that would be great!

barrymagrec · 23rd Jun 2020, 3:14 pm

The mark 5 type M is different to the magic eye version, it has separate record / play heads and amplifiers, you need the correct information.

You can still get suppressor blocks, they may not be exactly the same value but will do the job, equally using discrete components is also fine, so long as they are safely mounted, this of course is the advantage of the blocks.

There is more than one type of spool motor fitted to various ages of mark 5, have you checked the motor caps - if fitted?

stacman · 23rd Jun 2020, 3:23 pm

Hi Steve, Re the belting, I bought some round drive belting off ebay, you can buy it in different diameters, I bought 2mm, just buy a metre of it, it ‘melts’ together with a knife blade, used it on a tape recorder counter belt, seems to work, youtube has videos of how it melts together, takes a bit of practice, but ok for applications like counter belts,
I have no affiliation with the ebay link, for illustration only,
Regards, Alan.
https://www.ebay.co.uk/itm/1-2-5M-PU...YAAOSwcp9e4fEb

steve83 · 23rd Jun 2020, 3:38 pm

The unit I have here has one record / play head and an erase head, it's the gold / mushroom beige version. The schematic I have checks out OK compared to the circuit in the unit apart from the meter circuit.

The take up and feed motors don't have any caps (pic attached), the capstan motor does have a 1.5uF cap and I have replaced that.

I've been searching for the suppressor blocks on Mouser but can't see anything listed - do they come under any other name, or is there a specialist company it's best to order from (I'm UK-based)?

Thanks for your help!

steve83 · 23rd Jun 2020, 3:39 pm

Quote:

Originally Posted by stacman

Hi Steve, Re the belting, I bought some round drive belting off ebay, you can buy it in different diameters, I bought 2mm, just buy a metre of it, it ‘melts’ together with a knife blade, used it on a tape recorder counter belt, seems to work, youtube has videos of how it melts together, takes a bit of practice, but ok for applications like counter belts,
I have no affiliation with the ebay link, for illustration only,
Regards, Alan.
https://www.ebay.co.uk/itm/1-2-5M-PU...YAAOSwcp9e4fEb

Thanks Alan that's great! Much appreciated

wd40addict · 23rd Jun 2020, 6:36 pm

Here's a snubber at Mouser https://www.mouser.co.uk/ProductDeta...%2FNCjp4qXg%3D

I fitted similar from RS years ago to my Brenell. The smell of leaking suppressors is very distinctive and it's a Brenell stock fault.

IIRC the motors are different ratiings because punters back in the day wanted fast rewind. Fast forward wasn't considered so important and maybe a smaller motor was better for even take up?

If your motors work OK with new suppressors fitted they probably are OK.The motors themselves get very hot in use and Brenell warn of this in the manual.

steve83 · 23rd Jun 2020, 7:34 pm

Quote:

Originally Posted by wd40addict

Here's a snubber at Mouser https://www.mouser.co.uk/ProductDeta...%2FNCjp4qXg%3D

I fitted similar from RS years ago to my Brenell. The smell of leaking suppressors is very distinctive and it's a Brenell stock fault.

IIRC the motors are different ratiings because punters back in the day wanted fast rewind. Fast forward wasn't considered so important and maybe a smaller motor was better for even take up?

If your motors work OK with new suppressors fitted they probably are OK.The motors themselves get very hot in use and Brenell warn of this in the manual.

Thanks very much for the link! I'll order some of those.

Yes I wondered if the speed difference was intentional but they look physically identical so wasn't sure if this was the case - they seem to function fine at the moment, and as I say the smell has gone away! I'll fit the snubbers and give it a thorough test.

Thanks again!

If anyone does have any links to manuals / instructions specific to this model with setup info regarding the record level meter circuit that would be great

wd40addict · 24th Jun 2020, 10:45 am

Also be aware that the wiring to the motors can get very crinkly due to the heat. I had to change mine last year as insulation was starting to fall off!

I have never seen any instructions on how to set up the meter, what makes you think it's wrong?

If you really really had to do it then the best I could suggest would be:

1) Set bias up for chosen tape.
2) Record 1kHz tone, adjust level to achieve 3% THD off tape.
3) Set meter to read 0dBm

Hartley118 · 24th Jun 2020, 12:26 pm

Quote:

Originally Posted by barrymagrec

I`ve had only passing dealings with the Brenell but those suppressors tend to be quite dodgy, particularly at such advanced age.

I had to replace all the suppressors on my Brenell Mk5, so it's not surprising that you've found yours faulty.

Martin

steve83 · 24th Jun 2020, 5:03 pm

Quote:

Originally Posted by wd40addict

Also be aware that the wiring to the motors can get very crinkly due to the heat. I had to change mine last year as insulation was starting to fall off!

I have never seen any instructions on how to set up the meter, what makes you think it's wrong?

If you really really had to do it then the best I could suggest would be:

1) Set bias up for chosen tape.
2) Record 1kHz tone, adjust level to achieve 3% THD off tape.
3) Set meter to read 0dBm

Ah thanks that's useful! The reason I asked is that the pot that's wired across the meter needed some attention, and in putting it back together it's now almost certainly in a different position! It seems to record and play back fine but I wondered if there's a way of setting it up optimally. With the pot being accessible from the front panel it seems like it would have been intended for the user to adjust it themselves? I don't know enough about the way that part of the circuit operates to know for sure what the pot is supposed to do. The RV2 "Pre-set" looks like an adjustment for amount of signal being sent to the grid of ECC83a.

RE: tape - I only have experience with 2" tape and usually use RTM SM 900 / SM911 - I've seen they do something called LPR 90 in 1/4" with same formula as SM 900...is this well regarded for this type of machine? Are there any other alternatives people would recommend?

wd40addict · 24th Jun 2020, 8:46 pm

Ah, if it's just the front panel control follow the manual:

"On some models a meter is used in lieu of the magic eye. This meter should
be adjusted by means of the " Meter Zero " control to read " 0 " in the record position of the amplifier (volume control to minimum) before recording commences. Peak recording level will be indicated when the needle rises to " 7" on the scale."

steve83 · 25th Jun 2020, 10:51 pm

Thanks! I seem to have a different manual here, it's a pdf of "Installation, Operating and Service Instructions" that has what looks like a couple of magazine journal technical articles with advice on servicing included at the end.

Going to try some LPR 90 - what are people's recommended methods for setting up bias? I've been googling around and it seems like there's a few different approaches. I've attached the specs from the datasheet - planning on running it at 15ips (managed to find a 1" capstan sleeve!).

jamesperrett · 26th Jun 2020, 12:02 am

The data sheet holds the clue - the first line tells you the sensitivity drop for the recommended bias setting so on a 3 head machine the proceedure would be to reduce the bias level, start recording a 10kHz tone and then gradually increase the bias level while watching the output level meters. The level will increase to a maximum and then start reducing again. When it has reduced by 3dB you've reached the optimum bias level and you can now start on the other record eq adjustments.

With a 2 head machine this all becomes more convoluted as you have to keep rewinding and replaying each section to take a measurement.

wd40addict · 26th Jun 2020, 8:40 am

At 15ips my Brenell was like an open window to the source - very impressive! At lower speeds it was nothing special, presumably the heads were past their best.

Note that when the speed control is set to the 15 position the take-up series resistor is bypassed and the motor is stalled direct on the mains. This could be another reason why this motor is lower rated than its rewind brother.

Bias can also be set by ear: too trebly = not enough.

ricard · 27th Jun 2020, 5:20 am

Quote:

Originally Posted by jamesperrett

With a 2 head machine this all becomes more convoluted as you have to keep rewinding and replaying each section to take a measurement.

I've been thinking, a lot of folks here have more than one recorder. If so, one could set up a second recorder, and feed the tape directly from the one whose bias is being adjusted, to the other one, set up as a playback machine. We now have a three head arrangement, albeit with two machines, and a rather large delay between the record and playback heads. Even if the equalization or azimuth isn't correct on the second machine, it should still be possible to observe relative changes in signal level.

This is assuming the playback machine is not the slower of the two, as then a loop will start to form between the two machines.

steve83 · 16th Jul 2020, 8:59 pm

Hi everyone - I’ve been working away trying to finish off this Brenell! I’ve replaced the suppressors, made up some tape counter band from the ebay link above, swapped out the last few out of tolerance resistors in the amp and cleaned all the tracks in the switches. The amp/deck sounds great, there’s just a few remaining niggles:

- When in amplifier mode the tone control responds as expected monitoring through the ‘monitor’ output (brighter as the dial goes CW, although most of the action happens in the last quarter of travel!) but through the internal speaker the opposite happens and the treble rolls off. I can’t figure out what’s going on. Is this normal because of where in the circuit the monitor feed is taken?
- The feed motor sometimes need a bit of a ‘nudge’ on rewind with a nearly-full feed spool, is this to be expected? Playback and record are both fine with no wow/flutter.
- I’m getting popping when switching between record/playback/amp. I’m guessing there’s DC on the switches somewhere - again, is this normal or should it be silent?

I’m struggling to pin down the electrical issues without the correct schematic - I have the one for the magic eye version and its pretty similar but the switching seems different...does anyone have a correct version? It’s the mushroom/beige mark 5 with VU meter. I’ve traced out the VU section but would be good to be able to verify this too!

Thanks!

23rd Jun 2020, 10:08 am	#1
steve83 Triode Join Date: Dec 2017 Location: London, UK. Posts: 23	Brenell Mk 5 restoration Hi all - I have been restoring a Brenell Mk 5 reel to reel and have almost finished it, there are just a few final things left to do and I hoped someone here might be able to offer some advice: 1. I am having problems finding a suitable replacement material for the counter belt, I have tried fabric-lined elastic (the type you'd find in a craft shop) and it either slips, or puts too much tension on the take up motor and leads to unstable operation. What is recommended to use? I'd considered just a standard rubber band but can't imagine it lasting very long as they seem to degrade fairly quickly. 2. I was experiencing a faint burning smell on playback which I tracked down to the feed motor. I rebuilt it and it tested fine hooked up to mains out of the machine but when wired back in (and on playback) there would be a faint burning smell after a few minutes which I found strange as the motor is not energised in this mode of operation. The problem has since gone away and so am tempted to put it down to some residual dust which has gone, but have noticed there is a small amount of voltage present (<5vac rms)after the suppression cap. Could this be/have been the culprit? By my calculations the corner frequency of the .01uF / 220R suppressor acting as a HPF should be approx 72Khz so I'd imagine if properly operational there should be no voltage at all getting through! Are suppressor units still available to buy with resistance included or do people tend to buy a .01uF X2 cap and a series resistor? 3. Should the take up and feed motors read the same resistance across their windings? (i.e are they identical units?) One reads approx 230 ohms, the other approx 120 ohms (measurements taken out of circuit) 4. Lastly - is there a recommended procedure for dialling in the correct bias and adjusting the record level meter (this unit has the VU meter rather than the 'magic eye' valve)? Thanks very much in advance!

23rd Jun 2020, 2:19 pm	#2
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,562	Re: Brenell Mk 5 restoration I`ve had only passing dealings with the Brenell but those suppressors tend to be quite dodgy, particularly at such advanced age. I`m pretty sure the feed and take-up motors are identical so different resistance readings doesn`t bode well - shorted turns could explain your burning smell. The set up for the meter should be in the manual, I think it is a peak reading type, not a VU.

23rd Jun 2020, 2:46 pm	#3
steve83 Triode Join Date: Dec 2017 Location: London, UK. Posts: 23	Re: Brenell Mk 5 restoration Thanks for the reply Barry - the thing that was confusing me is that the feed motor shouldn't be energised when in playback mode according to the schematic - could it be a combination of shorted turns and a leaky suppressor? It also didn't emit any burning odour after I'd rebuilt it and tested it out of the unit straight into mains (without suppressors connected). Is it still possible to get suppressors with series resistance built in, or should I just use 0.01uF X2 caps with 220 ohm 2W resistors installed in series? The service manual I have (titled "Brenell Mark 5 Tape Deck: Installation, Operating and Servicing Instructions") unfortunately doesn't have any information about adjustments for the magic eye or meter. If anyone has any info regarding setting this up, and also adjusting the bias (i.e. what voltages to aim for) that would be great!

23rd Jun 2020, 3:14 pm	#4
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,562	Re: Brenell Mk 5 restoration The mark 5 type M is different to the magic eye version, it has separate record / play heads and amplifiers, you need the correct information. You can still get suppressor blocks, they may not be exactly the same value but will do the job, equally using discrete components is also fine, so long as they are safely mounted, this of course is the advantage of the blocks. There is more than one type of spool motor fitted to various ages of mark 5, have you checked the motor caps - if fitted?

23rd Jun 2020, 3:23 pm	#5
stacman Hexode Join Date: Nov 2010 Location: Sheffield, South Yorkshire, UK. Posts: 278	Re: Brenell Mk 5 restoration Hi Steve, Re the belting, I bought some round drive belting off ebay, you can buy it in different diameters, I bought 2mm, just buy a metre of it, it ‘melts’ together with a knife blade, used it on a tape recorder counter belt, seems to work, youtube has videos of how it melts together, takes a bit of practice, but ok for applications like counter belts, I have no affiliation with the ebay link, for illustration only, Regards, Alan. https://www.ebay.co.uk/itm/1-2-5M-PU...YAAOSwcp9e4fEb Attached Thumbnails

23rd Jun 2020, 3:38 pm	#6
steve83 Triode Join Date: Dec 2017 Location: London, UK. Posts: 23	Re: Brenell Mk 5 restoration The unit I have here has one record / play head and an erase head, it's the gold / mushroom beige version. The schematic I have checks out OK compared to the circuit in the unit apart from the meter circuit. The take up and feed motors don't have any caps (pic attached), the capstan motor does have a 1.5uF cap and I have replaced that. I've been searching for the suppressor blocks on Mouser but can't see anything listed - do they come under any other name, or is there a specialist company it's best to order from (I'm UK-based)? Thanks for your help! Attached Thumbnails

23rd Jun 2020, 6:36 pm	#8
wd40addict Octode Join Date: May 2009 Location: Stevenage, Herts. UK. Posts: 1,518	Re: Brenell Mk 5 restoration Here's a snubber at Mouser https://www.mouser.co.uk/ProductDeta...%2FNCjp4qXg%3D I fitted similar from RS years ago to my Brenell. The smell of leaking suppressors is very distinctive and it's a Brenell stock fault. IIRC the motors are different ratiings because punters back in the day wanted fast rewind. Fast forward wasn't considered so important and maybe a smaller motor was better for even take up? If your motors work OK with new suppressors fitted they probably are OK.The motors themselves get very hot in use and Brenell warn of this in the manual.

24th Jun 2020, 10:45 am	#10
wd40addict Octode Join Date: May 2009 Location: Stevenage, Herts. UK. Posts: 1,518	Re: Brenell Mk 5 restoration Also be aware that the wiring to the motors can get very crinkly due to the heat. I had to change mine last year as insulation was starting to fall off! I have never seen any instructions on how to set up the meter, what makes you think it's wrong? If you really really had to do it then the best I could suggest would be: 1) Set bias up for chosen tape. 2) Record 1kHz tone, adjust level to achieve 3% THD off tape. 3) Set meter to read 0dBm

24th Jun 2020, 8:46 pm	#13
wd40addict Octode Join Date: May 2009 Location: Stevenage, Herts. UK. Posts: 1,518	Re: Brenell Mk 5 restoration Ah, if it's just the front panel control follow the manual: "On some models a meter is used in lieu of the magic eye. This meter should be adjusted by means of the " Meter Zero " control to read " 0 " in the record position of the amplifier (volume control to minimum) before recording commences. Peak recording level will be indicated when the needle rises to " 7" on the scale."

25th Jun 2020, 10:51 pm	#14
steve83 Triode Join Date: Dec 2017 Location: London, UK. Posts: 23	Re: Brenell Mk 5 restoration Thanks! I seem to have a different manual here, it's a pdf of "Installation, Operating and Service Instructions" that has what looks like a couple of magazine journal technical articles with advice on servicing included at the end. Going to try some LPR 90 - what are people's recommended methods for setting up bias? I've been googling around and it seems like there's a few different approaches. I've attached the specs from the datasheet - planning on running it at 15ips (managed to find a 1" capstan sleeve!). Attached Thumbnails

26th Jun 2020, 12:02 am	#15
jamesperrett Octode Join Date: May 2007 Location: Liss, Hampshire, UK. Posts: 1,876	Re: Brenell Mk 5 restoration The data sheet holds the clue - the first line tells you the sensitivity drop for the recommended bias setting so on a 3 head machine the proceedure would be to reduce the bias level, start recording a 10kHz tone and then gradually increase the bias level while watching the output level meters. The level will increase to a maximum and then start reducing again. When it has reduced by 3dB you've reached the optimum bias level and you can now start on the other record eq adjustments. With a 2 head machine this all becomes more convoluted as you have to keep rewinding and replaying each section to take a measurement.

26th Jun 2020, 8:40 am	#16
wd40addict Octode Join Date: May 2009 Location: Stevenage, Herts. UK. Posts: 1,518	Re: Brenell Mk 5 restoration At 15ips my Brenell was like an open window to the source - very impressive! At lower speeds it was nothing special, presumably the heads were past their best. Note that when the speed control is set to the 15 position the take-up series resistor is bypassed and the motor is stalled direct on the mains. This could be another reason why this motor is lower rated than its rewind brother. Bias can also be set by ear: too trebly = not enough.

16th Jul 2020, 8:59 pm	#18
steve83 Triode Join Date: Dec 2017 Location: London, UK. Posts: 23	Re: Brenell Mk 5 restoration Hi everyone - I’ve been working away trying to finish off this Brenell! I’ve replaced the suppressors, made up some tape counter band from the ebay link above, swapped out the last few out of tolerance resistors in the amp and cleaned all the tracks in the switches. The amp/deck sounds great, there’s just a few remaining niggles: - When in amplifier mode the tone control responds as expected monitoring through the ‘monitor’ output (brighter as the dial goes CW, although most of the action happens in the last quarter of travel!) but through the internal speaker the opposite happens and the treble rolls off. I can’t figure out what’s going on. Is this normal because of where in the circuit the monitor feed is taken? - The feed motor sometimes need a bit of a ‘nudge’ on rewind with a nearly-full feed spool, is this to be expected? Playback and record are both fine with no wow/flutter. - I’m getting popping when switching between record/playback/amp. I’m guessing there’s DC on the switches somewhere - again, is this normal or should it be silent? I’m struggling to pin down the electrical issues without the correct schematic - I have the one for the magic eye version and its pretty similar but the switching seems different...does anyone have a correct version? It’s the mushroom/beige mark 5 with VU meter. I’ve traced out the VU section but would be good to be able to verify this too! Thanks!