burns orbit 2 tremolo issue

[Arbutt]

They were new old stock. Made no difference. I did keep the legs long.
Thanks for the info I will try that with the 220r and lowing the value of r31

Thanks again

[Helmholtz]

For lowering R31 in small steps just wire a larger value resistor in parallel, e.g. 100k or 68k.

[Arbutt]

good morning
I tried what you said. Fitted back the 220R and lowering the value of R31, by parallel 100k/82k.68k made no difference.
With the 220R in the hiss was much less but tremolo was very weak
Tried a few lower values of the 220R down to 150R and 100R this brought the tremolo back to a better level and reduced the hiss , But didn't make it correct

leaving the 220R in place and increasing the 4.7k up to as high as 8.2k with the 100Uf has reduced the hiss too what i would believe is an exceptable level and made the tremolo better too

Do you see anything wrong in increasing R31.?
By increasing or decreasing the value of the 100uf cap

Thank you for the help so far you have been very helpful. I just don't know enough sometimes

Arbutt

[Helmholtz]

good morning
I tried what you said. Fitted back the 220R and lowering the value of R31, by parallel 100k/82k.68k made no difference.
With the 220R in the hiss was much less but tremolo was very weak
Tried a few lower values of the 220R down to 150R and 100R this brought the tremolo back to a better level and reduced the hiss , But didn't make it correct

leaving the 220R in place and increasing the 4.7k up to as high as 8.2k with the 100Uf has reduced the hiss too what i would believe is an exceptable level and made the tremolo better too

Do you see anything wrong in increasing R31.?

I understood you needed to remove the 220R to make the circuit work with the replacement transistor. That's why I proposed to decrease R31 a bit to compensate.

Increasing R31 lowers collector current and changes transistor voltages. But if it works and sounds good I see no problem.
Transistor noise depends on collector current, so that might explain the improvement.

It seems obvious to me that your replacement transistors don't perform the same as the original one. As Germanium transistors had a lot of parameter variation, it's likely that originals were selected.

By increasing or decreasing the value of the 100uf cap

As long as the 100µ cap is good regarding capacitance and leakage, I don't see a sense in changing the value.


You should also make sure that C22 is not leaky. To test, lift one end and see if TR3 collector voltage changes.

[Arbutt]

Thanks all caps are new. The replacement transistor was new but old stock. I have left the 220r in place and played around with r31 decreasing it seem to do nothing. But increasing it reduced the hiss and gave it an ever better tremelo.

I will play with a few values to see what's best

Thanks again for all the help. I think it's done. All I've got to do is tidy up. As it looks like a dogs dinner at present.

I've learnt my lesson on this on. Next time do more notes and pictures
Arbutt

[Helmholtz]

The replacement transistor was new but old stock.

Yes, I thought so. Because NKT transistors were only made by a single UK company. NKT means Newmarket Transistors/Suffolk. Shut down production in the early 60s.
But as you needed to mod circuit values, these are obviously not identical to the original one(s).
As said, Germanium transistors of same type varied a lot and often required selection.

These days some dealers even sell factory rejects as NOS.