PART ID PLEASE

[Ronald Carlson]

Al,

If the specifica transformer can't be found then some estimates can be done to get a transformer that will get the unit working again.  From the schematic I would spec this transformer as:

Primary 110VAC
Filament secondary 6.3VAC 500mA (315mA calculated load)
Plate voltage secondary winding 150 to 177 VAC calculating ideal half wave output with no drop through the two series resistors.  Given the inefficiency of a half-wave and filtering something like 175VAC should work.  100mA ought to be sufficient..

If the existing transformer is bad due to an open winding the turns ratio can be measured between the other two.  If the primary or filament is open then you can measure the turns ration using an audio oscillator to drive one winding and read the no-load output on the other winding.  If the H.V winding is good then this will provide a fairly accurate measurement of the H.V. winding RMS output.
Since the filament winding's current and thus wattage requirement is a fixed amount based on the 6C4 and #47 bulb the wattage and thus current of the H.V can be estimated based on the transformer's dimensions.  Lamination size and stack thickness.  The amount of steel is a direct function of the wattage transferred.  Given this is the 1950's one would expect an ordinary lamination steel.  Then one can back into the rated output of the two secondaries from this info.

Another way is empirical - use a variac on a isolation transformer and feed the selenium with AC until the plate voltage reads just below 80 volts DC.  The variac output is the winding voltage needed.

In a worst case scenario, just to get functionality out of the unit separate transformers could be used for the filament and H.V.

Those selenium rectifiers are not too reliable either...

regards, Ron




________________________________
From: k2sse <k2sse at EMBARQMAIL.COM>
To: HEATH at LISTS.TEMPE.GOV
Sent: Saturday, August 8, 2009 9:51:34 AM
Subject: PART ID PLEASE

Have a Sig Gen model SG 7 with bad Power Transformer Heath part 
54-2 circa 1953 or so.
Can anyone give me specs on this Transformer?

Thank you
Al

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