BRC 4012 lives again!

[pye mozart]

I do repair work for a shop called "Retro Reproduction" and although I try to lessen my work with the owner he still manages to persuade me to take on things, (they are never as straight forward as he imagines!). This record player via some old volumes of R & TV Servicing, the interweb and searching conversations on this lovely site soon revealed itself to be a "deathtrap", "biggest load of crap ever" etc it was in rather nice condition for c1960 though. It actually closely relates to the BRC 3019, a 1962 facelift, and uses a push-pull output stage via UCL83's.

The customer said it hummed and wasn't very loud. Voltage checks revealed an HT at about 70V lower than specified so the rectifier was checked, changed for a silicon diode and a power resistor put in series to bring it back to the correct voltage. So far so good, the valves were tested and looked to be half way through their life, some new stylii from The Stylus Lady and we we're back in action.

The deathtrap comes from it being a mains dropper resistor circuit with the deck being tied to Mains Neutral. In the event of some wiring error the deck could be wired to the mains Live and the thing would still work. Touch the deck whilst holding a radiator and place your bets! I isolated the deck and fitted a 3 core mains lead earthing this and the signal screen surrounding the pick-up wires, the controls shielding was also tied to earth.

Hum wasnt too bad, it is a half wave PSU and the audio wiring isnt exactly hifi. It says output power is approx 5W but these valves can give about 4.5W each so in PP it is pretty loud and maybe about 7-9W with no real distortion.

We now have a safe record player that would probably pass a PAT Test. Why did they use mains droppers anyway, are transformers more expensive than life was in 1960?

['LIVEWIRE?']

One answer to your last question is that radios such as this were made for use on either AC or DC mains, although the many record players, such as yours, would, because of the motor, only work on AC, so no doubt it did come down to the relative cost of droppers vs. transformers. Slightly OT, I know, but, AFAIK, all TV sets were 'live chassis' in those days

[Herald1360]

Originally Posted by pye mozart

Why did they use mains droppers anyway, are transformers more expensive than life was in 1960?

No, but definitely more expensive than resistors.

Then some bright spark thought about tapping the motor winding- even cheaper and less heat dissipation as a bonus!

The "death trap" nature of this beast smells of poor design (or perhaps just incorrect assembly- one can but hope...)

As you found, it is perfectly possible to make the things safe for the end user- the service engineer was expected to understand the risks and take the appropriate precautions

[julie_m]

"Is it very heavy?"
"Not if you wire it up wrong, it's just a killer gram!"

(Sorry .....)

[Fidelity Fan]

Hi,

Is this fitted with the same amp as the BRC 2014, mounted on a PCB? https://www.vintage-radio.net/forum/...d.php?p=275104

I once owned a 2014, which developed leaky coupling capacitors. Half way through a 45RPM record, the amp would start buzzing and get progressively worse.

The half wave metal rectifier was easy to catch with the cover removed. Even with the player disconnected from the mains supply for a while, the unwary could get a nasty shock if the rectifier was touched due to the charge in the HT smoothing capacitors. Isolating this and bypassing it with a diode is a good idea.


I

[Nicklyons2]

I know many readers of this will know already but I just want to mention that replacing valve rectifiers with silicon ones places extra stress on the circuit powered. Although putting a series resistor, as dropper, to compenste for the rectifier valve's dynamic resistance is fine on load but, on switch on, with no HT current drawn, the poor old smoothing electrolytics and cold valves can be sat there with rectified mains (circa 330 VD.C.) sat on them for 20 or 30 secs which they might not be amused by.

[Paul Stenning]

I wonder whether it's been "got at" in the past?

Normally the decks were left floating or only connected to neutral through a small capacitor, not connected directly to neutral. Even the cartridge was normally connected through small capacitors to isolate it.

Also normally the heaters would be run from a tapping on the motor winding (using it as an autotransformer), and not a separate dropper resistor.

See the circuit diagram in the thread linked above for example of all this.

I suspect the deck has been replaced in your example at some point, and whoever did it added the dropper resistor (because there was no tapping on the new motor) and didn't consider the mains isolation. The deck probably came from a different piece of equipment that was isolated, possibly transistor era. A dangerous bodge job!

The way you have done it now is much better.