|[AMRadio] Want Ranger pwr xfmr|
ne1s at neandertech.com
Fri Nov 25 15:37:25 EST 2005
Unless you really want to keep 'er totally original, there are several
xfmrs that would work using the "Economy Supply" hookup with solid-state
diodes. Use anything between a 275-CT-275 and a 375-CT-375 VAC winding
rated at a minimum of 150 mA, preferably more. I know 150 mA sounds
light for the application, and it is, but I've successfully used one in
my Ranger for years. You'll also need a nice hefty 6.3VAC winding for
the heaters. Just about any TV transformer salvaged from an earlier
vacuum tube-era set would work. Build a full-wave bridge around the
entire HV winding, ground the negative DC output of the bridge; positive
DC output is your HV B+ for the modulators and finals; winding
center-tap is your LV B+. Use the original filters on outputs.
John Lawson wrote:
> 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 (for once)
> NOW: Today I'll try and get the Valiant healthy.
> What else are 4-day weekends for???
> John KB6SCO
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