Howard 437 A - Revisited

[David Franklin]

Fellow BA enthusiasts,

Thought I would follow up on my last post on the above receiver with the
smoked  power transformer.  You may remember that the Xfmr smoked after
cleaning the chassis even though I took pains to dry it off at low
temperature in the oven.

I took resistance readings on the windings.  The secondary measured 92 ohms
from one side to the center tap and 148 ohms from the other. So I took the
transformer apart and unwound the windings to see what had occurred. The HV
windings were burned. The damage looked as if it had happened over a long
period of time not just on one power up.  Also, after reading another post
here about an imbalance in the power XFMR causing hum in the audio, I
suspect that it was unbalanced before it smoked.  The radio had a hum in it
from the begining and I had checked all of the capacitors and they measured
OK.

I bought a Hammond replacement XFMR from Antique Radio.  It was not a phsyical
match (vertical instead of horizontal mount) and was higher rated on
current. The the B+ voltage was a little high.  It fit on the chassis OK
and I put a 500 ohm resistor in series and the B+ voltage and current came
into normal range.
The hum was gone.

After alignment, the radio plays fine.  It does not win any selectivity awards
or exibit much dial accuracy but it sounds good to be 60+ years old.  It is
just great to have it working again.

I hosed off my HQ-170 last Saturday.  This time I covered the transformers
underneath the chassis to prevent the water from getting in to the windings.
Boy! does it look good inside and out.  Hope to have it up and running next
weekend.

Thanks for the bandwidth,
Dave

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