BSR UA6 Autochanger Queries

['LIVEWIRE?']

In another thread I am discussing dismantling and repair of a Westminster Bureau style Radiogram from the mid 1950's. This is fitted with a BSR UA6 Autochanger, which appears to be in good condition. My question concerns the 4-pole Motor, it's supply and switching. I've downloaded the service sheets from the Instant Download data, but neither the Manufacturer's sheet nor the ERT one shows the circuit. This, admittedly is simple, but I'd like some clarification as to how the motor is switched. As many members will know, the 240V only version of the motor has 4 wires, brown and black leads which go to the mains supply, plus yellow and green leads which go to the single pole motor switch. So far, so good, however there is no resistance reading (i.e. an open circuit) between the brown and black lead, and about 230 ohms between the black and yellow wires. Obviously when the motor switch is closed the green & yellow leads will be common, but how is the circuit completed? The brown lead goes to the common point of the voltage selector on the radio chassis, and the black lead to the mains neutral. I've never opened a UA6 motor so expected it to be a shaded pole type similar to those used in later BSR (and Garrard) decks. Maybe it isn't that type, but I was expecting to read resistance between the two pairs of wires. Perhaps someone more familiar with this motor can explain how it works?

[TonyDuell]

What resistance do you measure between the brown and green leads of the motor?

My guess is that the 2 motor windings and the switch are all in series across the mains. Live is the common point on the voltage selector, neutral you've found). So if brown and green is one winding and black and yellow the other, then the circuit would be mains live -> brown -> winding -> green -> switch -> yellow -> winding -> black -> mains neutral.

['LIVEWIRE?']

The way you describe the circuit makes sense, Tony, but there is definitely no reading between the brown and green wires. The motor switch is, at best, intermittent, but when it does make contact the yellow & green leads are common. Only way to prove it is to connect the motor to 240VAC via the brown & black leads and see if it runs (or open up the motor and check inside it first!)

['LIVEWIRE?']

I've just removed the bottom bearing from the motor, and, hey presto!-both windings read about 230 ohms., brown to green and black to yellow. The motor switch effectively connects the two coils in series when it's operated, so the motor should run once the switch problem is sorted.

['LIVEWIRE?']

Having (hopefully) sorted out the motor, the next problem may be the cartridge. According to the data in the ERT service sheet for the UA6, the (mono) cartridge fitted has an o/p of 750mV @ 1Khz, with a frequency range of 25Hz-10Khz into a 2Meg load (btw I was going to put that info in the 'sticky' thread about Crystal & Ceramic Cartridges, but the thread is Closed-why?) If, as is like ly, the cartridge needs replacing, what more modern, stereo-compatible type would members recommend? The Chinese cartridges lower o/p would almost certainly mean that a preamp is needed, which I would like to avoid if possible, and the deck may also be used to play 78s (It's not my Radiogram, so I'll have to check with the owner on that point)

[Edward Huggins]

There are very few ceramic cartridges today that can give the eqivalent output of an old crystal type. What is the input sensitivity of the ampliiier? Currently available mono stereo-compatible or stereo ceramic cartridges can give between 150mV to 350mV depending on type. Be aware, UA6 tone arm was not really designed for such (relatively) high-compliance cartridges.

['LIVEWIRE?']

I'm not sure what the input sensitivity of the amplifier (which is part of a mid-1950s Westminster radiogram, btw,), but it's no doubt typical of 'gram inputs in radios of that era. I cannot find any data on the chassis, but it's a typical valve circuit. When I checked it there was no sound from it at all, and I've yet to find out why.

[Edward Huggins]

If this is a standard 5 valve AC superhet of the period, the input sensitivity for the PU input is likely to be c.250mV. In that case a cartridge giving around that value or slightly less should be OK. This suggests, say, a stereo BSR SC11M (bridged for mono) with LPS/78 stylus if one is needed. If you can get a BSR X5M all the better, but they are nearly all gone now.

['LIVEWIRE?']

Edward, it is a standard superhet of that era, using ECH81, EF89, EABC80, EL84, & EZ80, wth, AFAIK, an ECC85 as the VHFMixer. There is an RC Network on a tagstrip between the pickup o/p and the amp i/p, presumably to reduce the level from the 750mV pick-uo o/p to around 200-250mV.

[Edward Huggins]

Thanks for this detail. If a new replacement ceramic cartridge is used, then that RC network should be removed - otherwise the sound level on Gram will be too low/mismatched.

['LIVEWIRE?']

I did think that would be the case, Edward.