[R-390] Ballast Tubes (no, not the dead horse!)

[Paul Galpin]

Hi all,

I recently got two 390As, one working, one not. Both were fitted with 3TF7
ballasts. Hooray, original, great! I thought.

Then I measured the voltages, 25 Vac in, 15 Vac out. Correct tubes in BFO
and PTO.

So at the correct current, they are not dropping the specified voltage.

No problem, I put in the 42R resistor.


What I want to know is - is this a common failure mode? If so, why?

Paul Galpin
ZS2PG


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