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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 27th Oct 2020, 1:51 pm   #81
DMcMahon
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Default Re: Brenell Purchases

Thank you for your inputs, from various previous measurements I think the answer to A & B most likely is No, but would not discount anything at this stage.

I will certainly check out the transformer as you suggest but in-situ, especially as early on I found out that the primary winding wire colours were somewhat different to the schematic, although at the time resistance checks of the primary winding taps made sense even though some of the wire colours were different.

I am also bearing in mind that from day 1 after replacing the 50uF dual can reservoir/filter capacitor (that had little capacitance resulting in very high mains ripple) the HT voltage has apparently been high (compared to schematic values) and also the output winding voltage, even more recently when measured using Avo.

David
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Old 27th Oct 2020, 5:10 pm   #82
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Default Re: Brenell Purchases

Mk. 5 Series 2 Update.

Did a barrage of resistance, insulation resistance and voltage tests, will not bore you with the fine details, but everything checked out OK.

Too difficult to remove the mains transformer, using Variac adjusted to suit, set the mains voltage selection switch to the 3 settings of 110V, 220 & 240 volt and got the expected outputs. The primary winding tap various resistances also made sense.

Measured the white/pink wire using Avo wrt to both ends of the output winding and only got a few volts at most, so this result supporting strongly Lawrence's suggestion that it most likely is a transformer screen wire and the DVM high voltage readings were due to capacitive coupling effect.

The blue wire (the actual output winding centre tap) measured correct voltage wrt to both ends of the output winding using DVM & Avo.

Had a look at the Mk.5 power supply for comparison. First time I have inspected this power supply, it is a right mess, everything is very sticky and dirty covered in dead insects etc, especially the cables. Been spoilt by the Series 2 which by comparison was relatively clean.

Very similar power supply with subtle differences. The primary winding taps wire colours agree with the Series 2 schematic, the primary winding tap resistances are very similar to the Series 2, so definitely the mains transformer on the Series 2 is different from the Mk. 5, at least in terms of wire colours, with the Series 2 schematic reflecting the Mk. 5 transformer wire colours.

By resistance measurement the Mk. 5 output winding centre tap is a black wire and it correctly goes to the input side of the 47 Ohm resistor (as per schematic) with the output side connecting to earth. Just these 2 wires connecting to the 47 Ohm on the MK.5

Could not tell if there might be a transformer screen wire on the Mk. 5

Had fun and games putting the Mk. 5 Tape deck back in, it sits on 3 loose rubberised metal spacer mounts (should be 4 but 1 appears missing) and found it very difficult to get the deck in position without the mounts falling inside the case.

Now need to put everything back together on the Series 2, replacing the 470 Ohm resistor and two capacitors and correcting the wiring to the 47 Ohm, nothing so far really explains why the 470 Ohm burnt up ?
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Old 27th Oct 2020, 5:48 pm   #83
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Default Re: Brenell Purchases

If it's burnt up violently I would check for intermittent dead short in the wiring/interconnect plugs and sockets/function switch, a whisker of wire or small blob of solder can sometimes wreak havoc on an intermittent basis.

Lawrence.
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Old 27th Oct 2020, 6:34 pm   #84
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Default Re: Brenell Purchases

When it occurred there was zero current/voltage monitored at the HT connection into the amplifier, which seems odd. This is the only connector really involved, have already closely inspected that connector/pins with nothing untoward seen. I felt (with my finger) the two 10k resistors (including the one that previously got a bit cooked) which connect directly off the HT input to the amplifier and they were cold, that still leaves the direct HT connection to the output transformer circuitry but because there was no voltage/current seen think more likely the issue was at the power supply end.

Seems very strange even if the fault occurred at the power supply end, would have thought would have seen some voltage at the amplifier HT input.

Have visually inspected the wires in the cables from the power supply to the amplifier connector all look good, at both ends at least, will have to meggar them.

David
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Old 27th Oct 2020, 11:36 pm   #85
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Default Re: Brenell Purchases

Mk. 5 Series 2 Update.

Everything connected back up with new 470 Ohm 2 Watt resistor (original had gone open circuit) and two new 47uF 350 volts axials (originals measured OK) temporarily mounted on topside of the power supply.

Reconnected the output winding centre tap (green wire) to correct side of the 47 Ohm resistor and the white/pink wire (thought to be the screen of the mains transformer) to the other side (earthed side) of the 47 Ohm.

Rechecked all connections/wires looking for anything that might potentially intermittently short down but all checked out OK.

Powered up and all measurement as before, left running for well over an hour with no change, the various HT resistors were barely warm to the touch at the end.

Tomorrow will reconnect the tape deck and hopefully will be able to do more operational checks.
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Old 29th Oct 2020, 12:42 am   #86
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Default Re: Brenell Purchases

Mk. 5 Series 2 Update:-

Rear cover to humdinger pot (150 Ohm wirewound Linear Egen Type 126) refitted, as had previously fallen out).

Cleaned up heavy tape oxide deposits off the 15 ips capstan shaft sleeve. Cleaned up the pinch roller, there was a felt ring on the underside recess, assume for oil reservoir so added a little oil. Cleaned the the top panel mask.

Replaced a small black plastic P clip that clamped down (at power supply) the sleeved cables going from the power supply to the amplifier with a larger P clip. The black P clip was too small and was tightly crimping down the sleeving, checked wires in the sleeving but not damaged.

Checked Erase operation by selecting Record but recording on tape was not erased. Scope checked and getting good erase and bias signals going to the heads. One strange thing only get the bias and record signals when the tape deck is set to record (amplifier has to be set to record as well). Must be missing something obvious, but cannot see anything on the schematic that explains why the tape deck has to be switched to Record ?

Found 2 reasons why Record setting was not erasing the tape.

1. The tape release pin was fouling the upper head cover, so the L1 pressure pad arm was not not allowing the arm to reach the erase head (cover re-adjusted to clear).

2. The tape is not contacting the erase had due to the L1 pressure pad felt having previously fallen off. By manually pushing the tape to contact the erase head, the recording is then erased.

Cannot currently find the pressure pad, may have to find something suitable to make a new one, the felt pad on the L2 arm (PB/Record head ) is also not in good condition.

Tested recording using a microphone, got good record signal on the EM 87 Magic Eye and could see the record signal modulating the bias signal going to the PB/Record head, but the microphone recording did not play back. The recording may have been masked by the existing recordings, need to try again once erase is working properly.

Exercised fast wind more, sometimes did experience some tape spillage (mainly on rewind) so tried the fast switching to opposite fast wind function before going to stop procedure, probably need to get the technique/timing of this better as it did not always help when there was a spillage.

Also experienced that when the Take Up spool is at least 50% loaded with tape that Fast Forward often fails to start, can get it going quite easily by manually turning either spool. Fast forwarding works fine end to end as long as there is approximately less than 50% of the tape on the take up spool when fast forward is selected. Have read this is quite common with these Brenells.

Using a microphone checked out the straight through amplifier function all OK.

Have now changed over to non back coated 7" tape. Still to find 8 1/4" tape, I did offer up a 8 3/4" tape (which I easily found) but of course it was too large.
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Last edited by DMcMahon; 29th Oct 2020 at 12:49 am.
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Old 29th Oct 2020, 1:44 pm   #87
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Default Re: Brenell Purchases

Do not recall if it the machine manages to play back a tape that has something recorded on it already? If it does then that rules out Open Circuit Head which the Bogen heads are prone to.

Just checking the obvious and of course your troubles will help me with the repairs I have to do on my Brenell Tape machines.

If it is this much trouble I can not say with confidence that I look forward to repairing my Mk5's or MK5M and even worse double trouble STB-1 & STB-2. I have Brenell valve tape link plus a Jason Valve tape link as well.

The electronics are very repairable and usually other than the electrolytic or coupling capacitors should present no real problems. Hence why I am following your trials so closely.
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Old 29th Oct 2020, 2:13 pm   #88
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Default Re: Brenell Purchases

Yes it plays back recorded tapes very well.

David
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Old 29th Oct 2020, 2:18 pm   #89
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Default Re: Brenell Purchases

Quote:
Originally Posted by DMcMahon View Post

Have visually inspected the wires in the cables from the power supply to the amplifier connector all look good, at both ends at least, will have to meggar them.

David
Above from Post # 84, cables were later Meggared for isolation resistance to earth and each other, all OK.
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Old 29th Oct 2020, 2:27 pm   #90
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Default Re: Brenell Purchases

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Cleaned up the burred shaft of the Fast wind control. Found several potential donor grub screws to replace the broken grub screw in the Fast wind control knob, but all fractionally wrong size/incorrect thread, so borrowed the control knob from the Mk. 5
Utilised suitable grub screw taken from the 0.5" Capstan sleeve (sleeve not being used) to replenish the damaged one.
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Old 29th Oct 2020, 2:30 pm   #91
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Quote:
Originally Posted by Stevie342000 View Post

If it is this much trouble I can not say with confidence that I look forward to repairing my Mk5's or MK5M and even worse double trouble STB-1 & STB-2. I have Brenell valve tape link plus a Jason Valve tape link as well.
Am I correct in thinking that the standard STB1/STB2 do not have any internal power amps and speakers, is that what the tape links provide ?

David
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Old 29th Oct 2020, 4:00 pm   #92
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Default Re: Brenell Purchases

The STB1 did not have any internal power amps or speakers. The 2 might have but I only owner a couple of the STB1's. Mine were 10.5" models.
Re the poor wind/rewind - I see you have the fixed guide on the wind side and that was later changed to a rotating guide which helped the fast winding. Also note that the guides near the heads need to be clean and smooth - you can loosed the fixing screws and turn them to an unworn part.
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Old 29th Oct 2020, 4:11 pm   #93
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Default Re: Brenell Purchases

Thank you vidjoman for your inputs. I can imagine that that the wind side later rotating guide could help, presumably very difficult to find spares of them.

The guides near the heads are clean, need to recheck their wear, I do not think bad but will see if can rotate to less worn section.

Talking about guides what is the function of the pin with domed head on the tape guide as per photo ?

David
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Old 29th Oct 2020, 4:39 pm   #94
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The pin was to stop the tape dropping below the guide when the tape stops. I can see the wear to the guide as someone has already turned the guide. You can probably take the guide off and fit the pin in a different position by drilling another hole and tapping a thread in it.

My machines had a lot of use and I replaced the guides when worn - winding/rewinding 10.5" spools used to cause quite a lot of wear to the guides. But that was about 55/60 years ago when the parts were available.
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Old 29th Oct 2020, 8:06 pm   #95
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Quote:
Originally Posted by vidjoman View Post
The STB1 did not have any internal power amps or speakers. The 2 might have but I only owner a couple of the STB1's. Mine were 10.5" models.
Re the poor wind/rewind - I see you have the fixed guide on the wind side and that was later changed to a rotating guide which helped the fast winding. Also note that the guides near the heads need to be clean and smooth - you can loosed the fixing screws and turn them to an unworn part.
Correct the STB-1 does not have power amps in it but my STB-2 does have the power amps and internal speakers (if I recall correctly awhile since I looked inside) the power amps cost an additional 25. My 10.5" Brenell Mk5 is of the grey crinkle top plate type.

The tape links are what the STB-1 & STB-2 electronics is based on, the STB-2 has additional input mixing and optional power amps.

The Jason is the same as a Brenell tape link (as far as I can tell)it can be found as build in Radio Constructor about 1961 it predates the Tape link.

I suspect Brenell bought that design as I suspect Jason went out of business about the the time the STB-1 came out in 1963/64. The Radio Constructor articles can be found on American Broadcast History Website.

The Jason Tape Link was available from about 1959, I have a Shirley TWA1515D tape amplifier as well spec'd for Ferrograph or Brenell or Bradmatic. Yet another rebuild project, thankfully for a lot of us guys/gals with being locked down at home we can get more of the projects off the list and into working order.
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Old 30th Oct 2020, 10:42 am   #96
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Default Re: Brenell Purchases

Answers to the above are in the Brenell book. The Tape Link was for any deck. The STB-2 was certainly available with a power amp and speakers - mine is transistorised - it helps explain why the STB2 case is longer.

Jason and Lorlin tape decks were tied-up; Jason closed in 1962 but I'm not aware of any Brenell connection/link.
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Old 31st Oct 2020, 9:43 am   #97
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Default Re: Brenell Purchases

Mk. 5 Series 2 Update:-

Thoroughly cleaned again the complete tape path including tape guides, no change to fast winding to stop tape spillage and fast forward winding reluctance when tape on take up spool > 50%

Tried rotating the right hand tape guide near the PB/Record head to several positions but no change to tape spillage/winding symptoms. Guide only slightly worn compared to the left hand guide.

Rotated the left hand tape guide 180 degrees to move the worn area away from tape contact. The domed pin is now at around 1 O'clock. Do not think it has helped tape spillage, but it has made a big improvement to fast forwarding, now can start fast forward with any amount of tape on the take up spool and the fast wind starts OK.

If I can remove the domed pin will try and determine its thread size/type and see if I can source correct tap to be able to drill/tap another hole/thread to reposition pin.

In playback mode with no tape playing there is noticeable hum from the speaker when the volume is increased above around a 1/3 max. Hum not noticeable when tape playing music (maybe is on very quiet music).

As well as the valves being originally missing the metal screening cans for the EF 86 & ECC 83 valves were also missing, so wondered if fitting cans might reduce the hum level. Remembered that the Mk. 5 unit (which also has missing valves) had the 2 cans fitted, so have taken the cans from the MK. 5 to fit into the Series 2 (not yet fitted).

Need to replace the missing felt pressure pad for the erase head and the worn felt pressure pad for the PB/Record. Found some felt at home but too thin and maybe too soft. Most of my pressure pads on various machines are hard/very firm, I assume when new the felt pads would be somewhat less firm/softer.

Had read on the Forum that hat felt was good but tried a couple of charity shops but no felt hats. Also read many reports of footcare products such as Dr. Scholl doing some suitable pad material. I checked out numerous footcare products but nothing really suitable. I did buy one Dr. Scholl product but it was just foam which I think may not be suitable. Also brought a Tesco footcare product that is foam but has thin front face of a felt type material which might be suitable. Have also just seen that B & Q do various sized/shaped furniture protector felt pads.
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Old 31st Oct 2020, 9:55 am   #98
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Default Re: Brenell Purchases

Mk. 5 Update:-

While removing the valve screening cans as above noticed that the front panel tone control has an on/off mains switch, which I believe is not standard build. There also is a 6 way chocolate strip terminal block near the tone control where various wires from the tone control go to (mains cable and screened cables I think). The cabling from the terminal strip go into the back of the unit, the mains cable presumably to wire into the standard mains on/off switch circuit on the power supply but no idea where the other cables would go to.

I cannot see any of this on the Mk. 5 schematic, so guess it is a modification.

Some of the cabling is in a poor state with rubber insulation decomposing so will probably remove (once I check out exactly what it is) all this cabling once I start looking at the Mk. 5
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Old 31st Oct 2020, 11:26 am   #99
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Default Re: Brenell Purchases

Isn't piano felt the go-to?

If you want a variety of grades, I use RH Nuttall for the felt I'm using for my windows. They'll send you a free sample, I'm sure, and have many different grades.
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Old 31st Oct 2020, 1:30 pm   #100
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Yes had also read that piano felt was good but have no idea where one could easily obtain some.

Thank you for the Nuttall info, looks a good site.

David
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