Yes I do. As a teenager I was the proud owner of a Philips Electronic Engineer kit. It was a great introduction to a very fascinating hobby and a rewarding career.

 

Thank you everyone for your responses. I knew I came to the right place. I will order up that diode, and I will also replace the AC127 with a new one and get it installed the correct way round. Will report back with results.

What kind of effects would the AC127 being installed the wrong way round have on the circuit, or the transistor itself?

 

Are you really sure it is the wrong way round?
Apart from the wrong zener voltage that circuit seems to be working correctly.

 

I don't see that the AC127 would have been damaged.
If your DMM has diode test range, do a diode test on the transistor out of circuit.

There are 6 measurements to be made: 3 measurements in both directions.

1) B - E
2) E - B
3) B - C
4) C - B
5) C - E
6) E - C

 

Are you really sure it is the wrong way round?
Apart from the wrong zener voltage that circuit seems to be working correctly.

I'm fairly certain, as I've also been having another issue with the table, in which say 1 out of every 10 times I power up the table, the lights are very dim and the 9v rail would only be showing about 1.5v. Strangely though, if I tapped AC127 lightly with an insulated screwdriver it would "wake up" and the table would work perfectly (at 9.7v though of course). I initially thought this was the AC127 failing. I checked, then checked again to see which pin of the transistor was soldered where, and it was definitely incorrect. This evening I flipped the transistor around and I have yet to see it exhibit this behaviour again. 9v rail is still sitting at 9.7v.

I don't see that the AC127 would have been damaged.
If your DMM has diode test range, do a diode test on the transistor out of circuit.

There are 6 measurements to be made: 3 measurements in both directions.

1) B - E
2) E - B
3) B - C
4) C - B
5) C - E
6) E - C

Unfortunately I don't own a multimeter with this function... but I've resoldered the transistor the correct way round and it seems to be working fine. I have already ordered a replacement transistor (reason for which I've mentioned above) so I will change it anyways.

I've been curious, would it be worth modifying the circuit to change this transistor to silicon? As I doubt this germanium type will be available forever.

 

You can still use your DMM in resistance mode.

No, usually you cannot substitute a silicon BJT for a germanium one. The bias voltages are different.
It would depend on the function of the transistor, the circuit topology and how it is biased.

 

Transistors do work with the collector and emitter reversed. The gain will be much lower and the maximum voltage will be lower but, depending on the circuit, the transistor won't be damaged and the circuit may still work.

 

Pleased to report, that after installing a new BZX79C7V5 the voltage is now where it should be. I've adjusted R472 and it's now sitting at a very stable 9.00v.

Again, thank you everyone for your help with this.

 

Good.
Did you replace/switch round the AC172?

 

If you get stuck with the psu, you can replace it with a Lm7909 regulator, ..

 

Good.
Did you replace/switch round the AC172?

I put in a new and unused AC127 that I ordered previously. Turntable is working great, here's hoping it will last another 40 years.