1.0uF 150V capacitor for Pye 121.

[Herald1360]

I wonder what the designer of that was smoking? He seems to favour biassing each stage from the emitter circuit of the previous one at any rate. It seems to be consciously trying to avoid using a circuit that resembles any of the more common designs for this sort of 4-transistor amplifier.

I would expect "slight" distortion to be the order of the day- certainly if the output pair are mismatched at all. C5 seems to be there to smooth out the worst of the HF distortion.

The general description shouts "marginal design" I particularly liked the warning about fluff on the stylus affecting the turntable speed!

[G8UWM-MildMartin]

A couple of trivial thoughts, before actually starting to fault-find on it:
Is there a stray component lead shorting to the junction of the afore-mentioned 1K resistors, or does it just miss? (Wouldn't do any harm to trim it anyway.)
Does the amplifier work OK with an audio signal input rather than the possibly suspect cartrides?

[Radio Wrangler]

The scheme of biassing from the emitter of each previous stage might just save two resistors! But it will save a few mA out of the battery. It's a bit of interesting cleverness.

Around that time this was all new stuff and designers were dancing around each other's patents.

One big big drawback to this arrangement is, I think, that it makes the whole thing more unstable in terms of bias versus temperature. This is certainly a contributor to the reputation of germanium transistors for thermal runaway. As temperature increases, vbe drops in each transistor, and the poor old output pair don't just get the effect of their own Vbe reduction, but the sums of those of the two preceding transistors. Ooops.

You see why it didn't become a standard configuration.

David

[astro63]

Cheers guys, some really interesting info you're giving me. I think I'll replace C5 as I had removed that and make sure I get the correct part this time.

My new stylus have arrived and I will see how it sounds after it's put in.

Oh and if you think the circuit board is crude, the 3 speed mechanism is just as bad.

[Herald1360]

Not exactly crude- if anything too clever for its own good as David said.

If originality is less of an issue than usefulness, I'd leave the old electronics as is in situ disconnected and just plonk in a little audio amp kit from Vellemann or the like.

[Glowing Bits!]

Originally Posted by Herald1360

Not exactly crude- if anything too clever for its own good as David said.

If originality is less of an issue than usefulness, I'd leave the old electronics as is in situ disconnected and just plonk in a little audio amp kit from Vellemann or the like.

That's a sin!
Saying that though, a new amp is likely to be a better idea than using the original one.
On the other hand, the O/P will learn nothing about electronics with shop-bought pre-fabricated amps.

[astro63]

well, ( i thought i had posted this reply ) haha done a check on circuit board and found 2 pins with wires which go to different terminals on the on/off vol switch looked rather close ( touching ) seperated them and the fuzzy distortion has almost gone, well sounds as good as it did before, so hoping its sorted, i have on order the replacement 0.47uf 160v capacitor, as i had removed the old one then refitted it and even thou i used a heat shield i think its best to put a new one in.
so big thanks to everyone and sorry it was likely down to me removing the deck etc in the first place causing the 2 pins to touch

[Herald1360]

Ah, sounds like the fuzzy distortion may have been mains pickup between a switch wire and a signal wire, then.

Well spotted and happy it nows sounds fine!