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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 25th Jul 2021, 7:32 pm   #1
DMcMahon
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Default Baird TR1 Reel to Reel Coil Connections

Does anybody have any information on where the 2 wires of this coil connect to ?

It is fitted to the left of the erase head and I assume it is for hum bucking.

The 2 wires seem to be too short to connect anywhere, I have yet to locate a schematic, let alone a service manual.

David
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Old 25th Jul 2021, 11:26 pm   #2
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Default Re: Baird TR1 Reel to Reel Coil Connections

My memory has returned, I do have the schematic

https://www.google.com/url?client=in...Ivz1vfpWPwZSpM

David
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Old 27th Jul 2021, 11:27 pm   #3
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Default Re: Baird TR1 Reel to Reel Coil Connections

Later saw that there is another one of these coils on the right hand side, this was previously not visible as I had perched the removed top panel on the right hand side of the unit. This one looks to have longer wires that disappear inside.

Looking at the schematic I think these coils must be L1 and L3 which are in series with L2 and L4 (the upper and lower record/replay heads respectively).

Been trying to get the recorder out of its box so as to see where the right hand coil wires physically connect to, so as to work out where they go for the disconnected left coil but struggling at the moment to get any movement on it.

David
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Old 30th Jul 2021, 12:10 am   #4
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Default Re: Baird TR1 Reel to Reel Coil Connections

I’ve got one of these machines complete and working if you need any further references or photos
Regards
Chris
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Old 30th Jul 2021, 9:29 am   #5
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Default Re: Baird TR1 Reel to Reel Coil Connections

Thank you Chris, I may come back to you later.

David
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Old 24th Aug 2021, 11:13 pm   #6
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Default Re: Baird TR1 Reel to Reel Coil Connections

After quite some struggling managed to get the recorder out of its wooden case.

Think I can see the 2 wires for the left hum bucking coil, they have broken from the topside wires.

Looks like this may be yet another R2R that has suffered abuse during shipping, a cross member piece on the plywood top panel has partially broken with result that the left hand side of the tape chassis sits low and there is a noticeable gap on the right hand side of the control panel. this probably also explains the broken hum coil wires. Can see that a metal piece below the broken plywood is also dented down so maybe the unit was dropped during shipping and the weight (very heavy unit) of it bore down and broke/cracked the cross member.

Will have to try and straighten the cross member and maybe if space add a bracing/strengthening piece of wood or metal on the underside.

David
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Old 25th Aug 2021, 1:41 pm   #7
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Default Re: Baird TR1 Reel to Reel Coil Connections

Having great trouble getting the cross member straightened, is is strongly bowed downwards. Have glued and clamped the crack damage but do not think it will have any effect on the bowing.

No real room underneath to try and fix a bracing batten, will try and find a suitable metal piece that can be fitted underneath to the crossmember but think it still will be difficult to straighten.

The Power On indicator will not be difficult to see, although I think the bulb may have blown.

David
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Old 25th Aug 2021, 7:35 pm   #8
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Default Re: Baird TR1 Reel to Reel Coil Connections

Removed the power supply and output module to be able to access & remove seized screw and nut for one of the rubber feet, the rubber foot is missing so will fit a new one.

Gave the module a good clean, there are 2 capacitors that could do with replacing, a 25uF 25V Plessey electrolytic (C25 cathode bypass for V4 Output Pentode) and a 0.002uF 1,000VDC waxy paper (C24 phase correction across the output transformer primary).

On the schematic C24 appears to be clearly incorrectly shown as 0.002pF which by my calculation would be 2 fF (2 femto Farads).

David
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Old 25th Aug 2021, 7:46 pm   #9
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Default Re: Baird TR1 Reel to Reel Coil Connections

Hi David
these are decent enough machines and funny enough i've got one here myself. what intrigues me is your machine uses a 15w pigmy lamp to light up the control panel / graduated dials . My one uses 4 x 6.3V mes dial lamps . otherwise the set up is the same. Heat issue perhaps or a cost cutter?
whats the serial number on yours?


I dont know why but I have always had a soft spot for the transciptor deck!

regards


Terry
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Old 25th Aug 2021, 11:06 pm   #10
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Default Re: Baird TR1 Reel to Reel Coil Connections

Terry the serial number is 02114.

On the 2 schematics I have seen (which look identical but from different sources) they only show 1 lamp.

While cleaning the top panel found there is a nasty crack on the left middle side. The hole just below the crack is where the securing screw fixes down into the cross member and the crack is directly below this so the panel damage maybe occurred at same time as the cross member damage.

I have put a heavy recorder (Grundig TK 820) on top of the glue repaired cross member in the hope that it might help to straighten out the bowed cross member but not confident it will.

Plenty of capacitor candidates for checking/replacing inside the pre-amp module but will check them out when unit is powered up.

David
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Old 26th Aug 2021, 8:26 am   #11
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Default Re: Baird TR1 Reel to Reel Coil Connections

Re the cracked plywood, is there room to fit a piece of L-section aluminium as a straightener? Something like 1" x 1" x 1/8" thick. One flange bolted or screwed to the plywood, the other flange pointing downwards, clear of the metalwork underneath. Easier to use bolts than screws, but you would either have to accept bolt heads showing, or use countersunk bolts, filler over the heads, and paint to match existing finish. Just a thought.

Les.
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Old 26th Aug 2021, 9:12 am   #12
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Default Re: Baird TR1 Reel to Reel Coil Connections

Les thankyou for the good suggestion, I assume you are suggesting L section because it will be stronger/less likely to flex/bend than a flat piece of metal. There may be space, I need to temporarily fit the plywood piece to the deck and check for space/clearance. Not sure if it needs to be in the case to do this which then makes it very difficult to see the area.

I was thinking of trying a flat piece of steel plate (just need to find something suitable) screwed on from the underside, bolts would be stronger and do a better job of pulling the piece straight but extra work as would not want the bolts showing.

David
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Old 26th Aug 2021, 9:36 am   #13
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Default Re: Baird TR1 Reel to Reel Coil Connections

I did not start this Thread with the usual brief description of the recorder (because the Thread was a specific question) so:-

A late 1950's 2 track, 3 speed (including 15 ips), valve mono recorder, one of a small handful of recorders that Baird produced, documentation is thin on the ground, still trying to locate a service manual. Large and very heavy. Uses a Collaro Transcriptor tape deck, maybe Mk. 4 ?

David
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Old 29th Aug 2021, 5:16 pm   #14
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Default Re: Baird TR1 Reel to Reel Coil Connections

[QUOTE=DMcMahon;1401319
Gave the module a good clean, there are 2 capacitors that could do with replacing, a 25uF 25V Plessey electrolytic (C25 cathode bypass for V4 Output Pentode) and a 0.002uF 1,000VDC waxy paper (C24 phase correction across the output transformer primary).
David[/QUOTE]

Replaced C24 & C25.

Replaced C28 & C29 horrible sticky waxy 0.1uF at the Bias Oscillator with NOS 0.1uF Green Mustard (ones I had got through the Forum which have come in very handy). C29 on the schematic is shown as 1uF, which I think must be a mistake. The sticky waxy 3,500pF 750V C31 at the Bias oscillator tested OK.

There is a 4th capacitor C30 (0.01uF) shown at the Bias Oscillator, this was physically on the underside of the preamp module and when tested was very bad so replaced.

Replaced grid coupling capacitors C9, C11 & C23, also replaced coupling/decoupling capacitors C5, C7, C18 & C21. All capacitors had high to very high capacitance and very low insulation resistance on on Megger checks so very leaky. Actually C9 was totally open circuit. Several small Hunts still to change possibly around the tone controls.

Replaced cathode bypass capacitors (50uF 12V) C4, C10 & C16, they had quite high capacitance and fairly high ESR.

While changing all these various capacitors found 2 small mods/circuit differences:-

1. V2a ECC83 cathode resistor R11 is shown as 1.8kOhm whereas there are 2 resistors fitted in parallel namely what looks like from the colour codes 6.8k and 4.7k which calculates to 2.779k and actually measures around 2.7k

2. The positions of C7 in series with paralleled C16/R10 is interchanged, i.e. C7 connects directly to the Radio connector not C16/R10 as shown on the schematic.

David
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Old 29th Aug 2021, 10:55 pm   #15
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Default Re: Baird TR1 Reel to Reel Coil Connections

Found a mystery component that looks like an overheated resistor on the floor just under the Baird TR1 work area, do not recognize it and am sure have not removed it.

Resistance wise on DMM measures around 5 to 10MOhm but component tester sees it as a 230uF capacitor with 0.14k ESR which it obviously is not.

David
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Old 30th Aug 2021, 8:21 pm   #16
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Default Re: Baird TR1 Reel to Reel Coil Connections

Believe have solved the mystery component, think it must the resistor for the failed snubber from my Murphy TR1. Had previously thrown the snubber away in a waste bin that was very close to where I found the resistor on the floor.

The resistor has the same characteristic burnt smell as the snubber. I retrieved the snubber from the waste bin and removed the potted outer shell, which was easy as it was crumbling apart anyway. No sign of a resistor inside just the foil capacitor and some internal connection wires.

Replaced the old 3 core mains cable. Replaced missing rubber foot. Started various general cleaning including removing the loudspeaker which had lots of trapped fluff behind.

David
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Old 30th Aug 2021, 10:29 pm   #17
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Default Re: Baird TR1 Reel to Reel Coil Connections

Powered up for the first time. As expected the 15 watt pygmy power on/control panel bulb has blown, somewhere I have some pygmy lamps but cannot find, so temporarily have fitted a 25 watt LED bulb.

Main HT voltage very low at around 120 volts. The TR1 schematic unhelpfully does not show any circuit voltages, but the main HT should be at least 250 volts, so need to check out the power supply to see why the voltage is so low.

David
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Old 30th Aug 2021, 10:46 pm   #18
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Default Re: Baird TR1 Reel to Reel Coil Connections

Bad memory again, Attachment 2 of Post 2 in the linked Thread at Post 2 above lists the valve electrode voltages

David
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Old 31st Aug 2021, 5:36 pm   #19
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Default Re: Baird TR1 Reel to Reel Coil Connections

Checked out the power supply.

Mains transformer primary winding (set to 245 Volts on voltage selector) measured 61 Ohms from Live and Neutral of mains plug (via On/Off switch and Octal connector) so good, schematic lists it (L9) as 56 Ohms. Mains 240 volts measured reaching the winding OK.

Mains transformer 2 x valve heater windings measured OK around 6.3 volts

Mains transformer main secondary winding connecting to the EZ80 rectifier anodes good at 620 volts. Winding centre tape correctly grounded.

No shorts or low resistance to earth on the live and neutral connections and also the HT supplies.

Powered up with just the EL84 output pentode as load, all good with around 300V at the reservoir capacitor and around 270V at main HT (HT +1 designation).

Fitted the EF86, ECC83 & EL84 (Bias Oscillator) one at a time and everything stayed good/stayed basically the same.

Reservoir (C26) = 300V, HT +1 (C27) = 273V, HT+2 (C22) = 238V, HT+3 (C1) = 223V, HT+ 4 (C2) = 202V

Replaced coupling capacitor C15 (0.003uF).

So now all looks good, do not know why originally only had 120 volts HT. At the time the Variac current was > 0.3A (which was noticeably higher than most recorders) now it is 0.15A (mains to tape deck not yet connected).

Wonder if the can capacitors reformed ? during the earlier investigations.

At times was getting a noticeable hum from the speaker it would come and go depending upon the positions of the units, the pre-amp is very sensitive, do not think it is a fault, will see what it is like when screening cover fitted to the pre-amp.

Next to power up the tape deck, first will clean the tape heads and tape path as pretty dirty.

David
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Old 31st Aug 2021, 8:31 pm   #20
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Default Re: Baird TR1 Reel to Reel Coil Connections

Been having a fairly close look at the broken wires on the underside of the tape deck that I think connect to the broken wires on the hum bucking coil on the top left side of the deck.

The wires have the same same white and black sleeving over enameled wire, will clean off the enamel (hopefully) from the ends of the 4 wires and rejoin them. As per Post 2 I think the hum bucking coils are L1 & L3 shown in series with L2 & L4 (the upper and lower record/replay heads respectively).

The broken wires underneath connect onto the LHS tape transport switches, i.e. not direct to the head, maybe these switch connections are just connection points rather than switch contact connections, need to look more closely.

David
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