|[AMRadio] Want Ranger pwr xfmr|
jpl15 at panix.com
Fri Nov 25 12:36:33 EST 2005
Anyone happen to have a NOS or Good-Used Ranger power transformer for
sale? I need one - or a Good-Used Ranger - or, a new hobby... ;}
After several hours on the bench last night - it is apparent why this
old girl was shelved - it came to me with a 5R4 in the HV socket, but the
fils didn't light, tho the tube was good. So sure enough - someone had
tied the 5V fil lines back, and there was a 10-ohm 10W resistor in series
with the B+ lead.
I made a plug-in SS rectifier, installed it, switched the rig on - and
blew both diodes and both line fuses to little bits.
So I restored the original circuit - there is a definite 'under-load'
short from the HV rect fils to the HV winding.
Disconnected all that - the LV side works fine, Osc runs, buffer runs -
can 'zero-beat' to a receiver, frequency of VFO seems accurate.
Tansformer voltage and resistance checks are within 10% of spec.
Put new diodes in put a Variac and ac ammeter in the mains line, turned it
up slowly - POW. Actually, with the diodes in cicuit, it appears to the
Variac / AC Ammeter that the power transformer has a dead short. Having
replaced the filter caps, and checked the plate choke - it ain't them. The
B+ line resistance is slightly over 20K.
In this process the power transformer has begun to get slighly warm, so
I went back to checking the LV side - as I was testing, the transformer
started to arc internally - and resistance measurements now show the
fil-to-HV short. So: It's toast.
While working on it, I did get to listen to a wonderful, hours-long AM
QSO on 3.885 - altogether seven or eight stations from both coasts and the
midwest - nice loud sigs, band wide open and quiet - little QRN and no QRM
NOW: Today I'll try and get the Valiant healthy.
What else are 4-day weekends for???
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