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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 31st Oct 2020, 1:41 pm   #101
DMcMahon
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Default Re: Brenell Purchases

Photos for Post 98.
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Old 31st Oct 2020, 1:53 pm   #102
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Default Re: Brenell Purchases

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Mk. 5 Series 2 Update.


Have previously planned to replace the 2 capacitors with a new twin can 50uF 500V with a very local collection (to save postage) but currently they have gone out of stock.
Dual can 50uF/500V capacitor (with local collection) now back in stock but found out from measurement that they are too high/long to fit into available space in the Series 2.

But have ordered 2, one for the Mk. 5 which has plenty of space and most likely will benefit from old dual can being replaced and one for the Series 2, am hoping may be able to make more space by relocating one of the motor run capacitors that is currently in the way.
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Old 31st Oct 2020, 2:52 pm   #103
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Default Re: Brenell Purchases

Ring a tuner if you've one locally - they'll have various suitable offcuts. Our fabric shop also has a variety of wool felts in various thicknesses. I haven't investigated them for pressure pad use though.
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Old 1st Nov 2020, 11:22 am   #104
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Arrow Re: Brenell Purchases

Using a Scholl foam based footcare product made replacement pressure pads for the Erase and PB/Record heads, so far they are working well. The tape is now firmly held against the erase head and erase is now fully erasing recordings. Playback is still working well.

Did a quick test microphone recording with good signal level at the EM 87 but playback was weak (volume wise), increasing volume setting to hear it better also made the hum signal very noticeably. Will have to see what Line recording is like.

Hum level in Amplifier mode is greatly reduced compared to Playback mode.

Tried to track down source of the hum with scope but looks like it will be difficult. Hum can be just be herd at volume level 3 and increases as volume level is increased.

Can see a definite hum signal (maybe a composite 50/100Hz ripple/noise signal) at the input to the second stage (pin 2) of the ECC 83 which is fed from the volume control but minimal hum from the EF 86 & ECC 83 first stage. Removing the EF 86 somewhat reduces the hum signal, removing the ECC 83 results in there being no sound at all.

Intermittently when the volume control is set to high level ( 8 or above) the amplifier breaks into loud oscillation (Playback mode but not in Amplifier mode) a large very clean stable sinewave of period around 115uS, i.e. frequency around 8.7kHz

Tried to check source of the oscillation but when present just the act of connecting the scope lead can stop the oscillation so making it very difficult to trace further.

Am wondering about the second shorter spring in the attached photos, one end end connects to the mounting pin for the L2 pressure pad arm and the other end connects to a small lug on the pressure pad operating lever.

This spring is not shown in the Series 2 Operating Instructions manual head layout sketch (see attached Fig 1) and does not appear to be fitted to the Mk 5 (Series 1). I am wondering if it is a standard fit on the Series 2 ?

It stops the pressure pad operating lever from relaxing/moving when in Playback mode and maybe puts a little more pressure on the pressure pads on the heads but the long spring seems to apply plenty of pressure on its own even if the shorter spring is not fitted.
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Old 1st Nov 2020, 11:32 am   #105
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Default Re: Brenell Purchases

I have just noticed in Fig 2 from above that as well as the shorter spring not being shown the lug that the left hand end of the shorter spring fits onto, is also not shown.

The lug is present on the Mk. 5
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Old 1st Nov 2020, 11:36 am   #106
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Default Re: Brenell Purchases

Mk. 5 Series 2 Update.

Fitting the metal screening cans to the EF 86 and ECC 83 valves made no difference to the hum noise issue.
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Old 1st Nov 2020, 3:11 pm   #107
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Default Re: Brenell Purchases

Quote:
Originally Posted by DMcMahon View Post
Am wondering about the second shorter spring in the attached photos, one end end connects to the mounting pin for the L2 pressure pad arm and the other end connects to a small lug on the pressure pad operating lever.

This spring is not shown in the Series 2 Operating Instructions manual head layout sketch (see attached Fig 1) and does not appear to be fitted to the Mk 5 (Series 1). I am wondering if it is a standard fit on the Series 2 ?

It stops the pressure pad operating lever from relaxing/moving when in Playback mode and maybe puts a little more pressure on the pressure pads on the heads but the long spring seems to apply plenty of pressure on its own even if the shorter spring is not fitted.
The pressure-pad springs’ arrangement also baffled me back in the 1970s, when I got my new “bare” Brennel deck and came to fit the heads - trying to work out the intended spring configuration on a three-head deck. There was no manual provided with the deck (and no internet back then to find one), and it almost seemed as though it was arbitrary, that Brennel hadn’t bothered to work it out, and that they thought it didn’t matter whether the pressure on the pads was doubled or halved by the springs. It was just one of the things that made me think that Brennel had just lost the plot when you compared them with, e.g, the “new” Revox decks. I dropped in at their Islington factory in the early 1970s to get some spares, and definitely got the impression of a tech. company that didn’t know where it was going (at least in its domestic/semi-professional market - which is where I was).

Mike
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Old 1st Nov 2020, 4:04 pm   #108
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Default Re: Brenell Purchases

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It was just one of the things that made me think that Brennel had just lost the plot when you compared them with, e.g, the “new” Revox decks. I dropped in at their Islington factory in the early 1970s to get some spares, and definitely got the impression of a tech. company that didn’t know where it was going (at least in its domestic/semi-professional market - which is where I was).

Mike
That was about the time that a colleague went to the Brenell place for a job interview - he came away less than impressed, given that they were supposed to be trying to get into the professional market at the time.

I don`t know if he was offered the job but if so he didn`t take it.
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Old 1st Nov 2020, 11:09 pm   #109
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Default Re: Brenell Purchases

Had a quick look at the modified mains wiring around the tone control. A 3 core (red, black & green) screened mains cable taps into the mains cable connections at the back of the machine and connects to the on/off switch on the tone control.

The switched output side of the switch connects to a lamp (neon I assume) that has been added to the amplifier front panel (to indicate power/mains on) and the green core of the cable is used as a switched neutral from the switch back to the rear panel mains wiring and a coaxial cable is used to feed back the switched live back to rear mains connections. Have not conclusively proven it yet but strongly believe that both the power supply mains on/off switch and the added on/off switch on the tone control both have to be switched on for power to reach the power supply.

It is a right mess, I will remove the added cabling and put it back to standard, may possibly later add an LED power on indicator to the amplifier front panel in the hole where the neon indicator presently is.
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Old 2nd Nov 2020, 11:11 pm   #110
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Default Re: Brenell Purchases

Mk. 5 Update.

Am collecting the new dual 50uF 500V can capacitors tomorrow, so have removed the old can from the Mk.5

It turned out to be a triple 50uF can but only 2 are used. Capacitance and ESR measurement wise it was not bad (unlike the Series 2 dual can) but still will replace it and keep the old can as an emergency spare.

Gave the power supply a good clean, it was really greasy. Also cleaned out the case.
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Old 2nd Nov 2020, 11:40 pm   #111
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Default Re: Brenell Purchases

Mk. 5 Update.

Checked out the modified mains wiring more. Yesterday thought that the extra on/off switch on the tone control may have been in series with the mains on/off switch on the back of the power supply, but the switches are in parallel across the switched side of the power supply switch. So either switch could switch the unit on, but both would have to be off for the unit not to be powered.

Did anybody notice the 2 yellow twisted together wires in the first photo in Post #109.

These are a ground connection, one end connecting to a ground busbar and the other end connecting to the added 6 way terminal strip connecting the screen of the 3 core mains cable and the screen of the co-ax/screened cable (inner core carrying the switched live back to the power supply), this ground/screen connection connecting back to the power supply ground/earth connection.

Because the 3 core mains cable and co-ax cable carrying the switched live are screened presumably screened cables are being used to reduce any noise/hum etc pickup at the amplifier. I have seen twisted wire connections before for ground connections, is this for common mode noise/hum reduction ? although I thought that was more for twin signal twisted pairs like differential signals.

Found that the unit was not connected to mains earth as it had a 2 round pin mains plug with the earth wire hiding inside. I will fit a new 3 core cable/3 pin plug and connect earth to the ground connection.

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Old 4th Nov 2020, 7:51 pm   #112
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Default Re: Brenell Purchases

Mk. 5 Update.

Fitted new 3 core mains cable and 3 pin plug.

Checked the mains transformer winding resistances.

Primary :- 110 volt = 18.1 Ohm, 210 volt = 44.8 Ohm & 240 volt = 52.7 Ohm

Secondary:- Heaters = 0.6 Ohm, EZ80 heater = 0.4 Ohm, EZ80 anode to anode = 837 Ohms, Anode 1 to centre tap = 426 Ohms, Anode 2 to centre tap = 411 Ohms

Checked insulation resistance of all windings (Meggered) all OK.

Secondary voltages (DVM) :- Amplifier heater = 6.9VAC, EZ80 heater = 6.92VAC, EZ80 anode to anode = 645 VAC, Anode 1 to centre to 321 VAC, Anode 2 to centre tape = 321 VAC.

Checked that the secondary centre tape connected to correct side of the 47 Ohm current limiting resistor, which it did (the Series 2 connected to the incorrect/earth side).

As far as I could see there is no transformer screen wire connection, the Series 2 had a thin white/pink wire that was believed to be a transformer screen. The Mk. 5 does have a thicker pink wire (same as Series 2) which is the low end (0V) of the primary winding. On the Mk. 5 the mains cable red wire connected to the primary pink wire so technically live connection (as opposed to neutral) but as the mains connector was 2 pin then depending upon how the 2 pin connector would have been fitted then either Live or Neutral would have connected to the primary pink wire.

I would say normally Live/Neutral connection polarity to primary winding would not make any difference, although I have seen a few references to swapping over live and neutral when hum is a problem.

Fitted new dual can 50uF/500V reservoir/filter capacitor and associated 470 Ohm resistor.

Next to check out main components on the amplifier particularly the grid coupling paper capacitors then to connect the amplifier to the power supply and power up.
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Old 4th Nov 2020, 10:45 pm   #113
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Default Re: Brenell Purchases

Hi D, I really appreciate the insight into your methods for revamping these old treasures!

Out of interest, what is your source for can caps?
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Old 5th Nov 2020, 12:17 am   #114
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Default Re: Brenell Purchases

I do not normally replace can caps, for this one source was eBay.

David
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