Bush SRP31D

[ppppenguin]

I've just been given a Bush SRP31D which should end up in one of the period living rooms we're planning at the Broadcast Engineering Museum. The non-technical donor said it wasn't working and it doesn't need to work but I'm curious.

The SRP31 data is in R&TVS 1959-60. A pair of ECL83 pentodes in push-pull with the triodes acting as pre-amp and phase splitter. A note in R&TVS 1961-62 says the SRP31C adds a facility to connect and external amp for stereo which I can also see on my SRP31D. The Radiomuseum site says that the SRP31D uses a pair of ECL86. I can't see the SRP31D data in R&TVS or Trader but guess that the circuit is very similar but beefed up for the extra power. I hope that the ECL86s are OK as they're a bit scarce and expensive these days. The get-out is a pair of PCL86 (I have several NOS) and a small heater transformer.

Does this model have an electrostatic tweeter which I guess is unlikely to work any more?

I haven't touched a gram like this in many years so any helpful hints please. The amp looks easy enough. Bring it up on a lamp limiter and change the coupling caps to the output stage regardless. Buzz test at the input.

[ppppenguin]

Not sure when I'll have to time to look at properly but I opened it up this morning. Most of the caps are ceramic, including the ones to the output valves, so that gives the valves and transformers a good chance. One black horror in what looks like a non-critical position. Two "red and black" 50uF electrolytics as cathode decouplers. To be changed on sight. Looks like the original rectifier has been replaced, very neatly, by a silicon diode and a Radiospares 39R WW resistor.

There's a fuse that looks like and MES lamp. I've never seen one before. Slightly surprised to see half-wave rectification in a slightly up-market product. I noticed that the SRP30 (on the same page in R&TVS) used an EZ80 with both halves in parallel to do halfwave. Buch must also have had a surplus of EBC81s as they used the triode section of that in the SRP30, with the diode anodes grounded.

[Mike Watterson]

I've had to replace the cartridge on a UA16 player. Decent ceramic ones are easy to find, but most only have LP stylus. I managed to get a couple with LP/78 flip-over stylus and one is on one of those cheap modern suitcase record players as the LP stylus is useless for 78s. There may have been a special stylus profile for microgroove and 78, but the cheap modern players and replacement cartridges don't have it.

Sometimes the "idler" wheel is degraded. Or whatever it's called.

Most of the transportable players with valves used U series and "live" chassis. Is the heater supply a tap on the motor?

[ppppenguin]

Apart from the half-wave rectifier this is pretty well engineered. Earthed chassis, a pair of ECL86 in push-pull and separate electrostatic tweeter. Separate bass and treble controls. Looks like enough gain to work with a relatively low output ceramic cartridge.

[Mike Watterson]

Certainly a more deluxe example of the genre. Some had only a single pentode.

[ppppenguin]

Almost up there with the Hackers of the same period. Way above the UY85 and UL84 jobs with a TC8H cartridge.

[ppppenguin]

Had a chance to power it up. I used the lamp limiter and all seems happy enough. Good buzz from the pickup input and noises if I touch the stylus. not sure if the tweeter's OK but that really doesn't matter. The turntable doesn't rotate so next step is to see if the motor is getting power and then if it turns at all.

[Mike Watterson]

Seized grease on turntable.
Roller disk jammed and spring not pulling it into spindle + turntable.
Failed / misaligned auto on-off switch.
I've had all of those, but never a failed motor except on a 1935, where fortunately the lead-out wire had only parted company with enamelled wire of winding. Those have a worm-drive gear box too, which was seized grease. The UA16 is straightforward. I might even have a spare motor in the very unlikely event it's needed.