[AMRadio] Want Ranger pwr xfmr


Larry Szendrei ne1s at neandertech.com
Fri Nov 25 15:37:25 EST 2005


Hi John,

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.
> 
>   Ok.
> 
>   So I restored the original circuit - there is a definite 'under-load' 
> short from the HV rect fils to the HV winding.
> 
>   Ok..
> 
>  Disconnected all that - the LV side works fine, Osc runs, buffer runs - 
> can 'zero-beat' to a receiver, frequency of VFO seems accurate.
> 
>  Ok...
> 
>  Tansformer voltage and resistance checks are within 10% of spec.
> 
> Ok....
> 
> 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.
> 
> Ok.......!
> 
>   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???
> 
> 
> Cheers
> 
> John  KB6SCO
> 
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