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Old 16th Sep 2021, 9:38 pm   #6
vintage_8bit
Heptode
 
Join Date: Feb 2013
Location: Rainham, Kent, UK.
Posts: 523
Default Re: Marconi TF1066B/1

Update
I found that an old fault had come back to haunt me, I had this in a previous Marconi genny, and it was conductive sleeving in the turret! I’ve now corrected that and also 3 of the plastic contact pin holders that had split.

I tried again. With the original valve. I now only have trouble with reduced amplitude on the 1st and 3rd ranges at the low end of the ranges.

Fitting in a new valve, a DET22 / CV273 I found the output amplitude increased slightly on the 1st two ranges up to 48MHz, but it refused to oscillate in places on the last two ranges between 110 to 470MHz.

As the original valve works reasonably well, I’m wondering if the valves as listed in the parts list are not suitable. Looking at the beginning of the manual it lists a TD03-10E / CV5458, not a TDO3-10 / CV273 as listed in the parts list, schematic & valve replacement data.? To confuse further the valve originally fitted was a CV354 So I’m now looking for a TD03-10E / CV5458 or CV354 as originally fitted to try.

I can fix the low output on the 3rd range by adjusting an s.o.t. resistor but on the 1st range this s.o.t. is shorted out. The s.o.t. resisters increase the H.T. to the output valve. The regulated H.T. is set to 280V, the regulated L.T. is set at 6.3V at the output valve heater contacts. There is a potential divider from the H.T. feeding the “set carrier” pot and these resistors are in tolerance.
As suggested above by Hugh, maybe the Marconi user group could help here. Colin.
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