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Old 5th Dec 2021, 1:56 am   #41
Join Date: Apr 2017
Location: Buderim, Queensland, Australia.
Posts: 428
Default Re: Taylor 65B Sig Generator: Dodgy Waveform

Gday HB

I don't have a Taylor 65B.
I am only an innocent antipodean bystander.

In my post #33, I was attempting to test the emission capability of rectifier V1 with Volts across R1 to ground.
And the CRO test would show up other rectification issues.
All the above assumed full wave operation as per circuit.

In your last post you have measured the total current drawn by V2 and V3 in normal service, which is different.

So.... aware of your posts to date, and the circuit variations which appear to be bubbling up, you are now in a situation where you may not know if your beast is ex factory, or modified later, to make the best of a faulty transformer?
I would think that it is unlikely that, the factory would install a full wave type transformer and only use half of it, even though later models may have used half wave.

We cannot see the beast, and you will have to tell us what you think has happened to your specific unit.

If you get 190 volts at V1 cathode, that should be enough, provided hum on the HT is not a problem.

If you are considering actually using this unit, as distinct from a nostalgic resto, then you may have to put up with it as it is.
You will have some hum, probably, mod distortion probably, and some free FM, probably.
But for rough tests on BC receivers, it may be just useable.

If it were me, and if I was going to use it, and one side of the power trans is crook, I would use a bridge rectifier across the good winding, and plonk in some extra filter capacitors.
This is to reduce hum, and a higher anode voltage may make V3 operate in a more linear fashion as modulated oscillator.

May have to raise R1 up to 7K5 or even 10K.

I still think that optimisation of the mod is possible without being too quixotic.

Does that modulated RF distortion reduce as you reduce the RF level?
I wonder if the grid circuit is loaded too much by the RF level control and ladder attenuator?
Taking the RF output from the oscillator grid circuit is perhaps not the best design idea.
But it works.

Good luck.
Radio1950 is offline   Reply With Quote