Vintage HV Plate Xformer - HomeBrew Forum at eHam.net

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Vintage HV Plate Xformer	Reply
by W7NMD on October 27, 2009	Mail this to a friend!
I have a Chicago Transformer model number 72246. Primary is 115v 60 cycle and secondary is 2350v center tapped @ 750 ma. It is approximately 8" square and weighs 52 lbs. Any info would be appreciated.

RE: Vintage HV Plate Xformer	Reply
by W8JI on October 27, 2009	Mail this to a friend!
It probably isn't very good for a capacitor input supply. Short the primary and then ohm the secondary. Most transformers like that have too much secondary resistance to make good capacitor input transformers, and the apparent power factor will overheat them so you can't pull full rated current into a cap input supply. If you have a choke input it would do OK. Be sure you short the primary before ohming the secondary or you can zap your meter. Tom

RE: Vintage HV Plate Xformer	Reply
by WB5JEO on October 27, 2009	Mail this to a friend!
Here are some old Chicago catalogs. Don't know if they're the right era. http://www.bunkerofdoom.com/xfm/index.html

RE: Vintage HV Plate Xformer	Reply
by WX7G on October 27, 2009	Mail this to a friend!
W8JI: And the cap or no cap input filter resistance criterion is?

RE: Vintage HV Plate Xformer	Reply
by W7NMD on October 27, 2009	Mail this to a friend!
Primary resistance is 0.3 ohms. Secondary is 468 ohms. This calculates an impedance of 150 ohms +/-. Modeling the supply with psud2 shows an output of approx 2900 v at 200 ma idle and 2810v @ 1 amp peak ssb load. Big disadvantage is the 115v primary which will require at least a 30 amp circuit.

RE: Vintage HV Plate Xformer	Reply
by N2EY on October 27, 2009	Mail this to a friend!
Couple of things about that transformer: 1) From the secondary voltage, it was designed to provide 1000 volts DC in the full-wave center-tap rectifier configuration, with choke input filter and mercury-vapor or gas rectifiers. 2) Depending on the construction, it may or may not have been designed to be operated with the secondary center tap ungrounded. Using it in a bridge circuit may be asking for trouble if the center-tap isn't adequately insulated for ungrounded operation. 3) The effective transformer impedance may be high enough that regulation suffers when used with SS rectifiers and a capacitor filter. Simulation will tell you for sure. 73 de Jim, N2EY

RE: Vintage HV Plate Xformer	Reply
by W7NMD on October 27, 2009	Mail this to a friend!
The transformer has a fully floating secondary with thee one inch high porcelain insulated 1/4" terminals. Simulation run with Psud2 does not show any problems at 2.8 kvdc and 1.0 amp load. Diode bridge is 20 1N5408 with 49 ufd 4500 volt filter cap with an esr of 4.2 ohms. 73 Palmer W7NMD

RE: Vintage HV Plate Xformer	Reply
by WB2WIK on October 27, 2009	Mail this to a friend!
"Any info is appreciated." Sounds like you have all the info you need; what are you looking for?

RE: Vintage HV Plate Xformer	Reply
by W8JI on October 29, 2009	Mail this to a friend!
Palmer, Your numbers appear to be nonsense. Even a ten ohm ESR transformer has more FL voltage drop than that. These old transformers were pretty much designed to use in a choke input supply. The choke integrates the current loading over the whole AC cycle, rather than at peaks only like a capacitor. Here is how it would typically work: If the transformer has a 50+ ohm ESR, typical for an old medimum current HV transformer from that era, the rectifiers in a cap input supply would have a large dead zone. They would draw all of the current off a few degrees of the sine wave. The large hypersil in the AL1500 amp has a 12 ohm ESR and the voltage drops 10% at one ampere. With a transformer like this you would generally be lucky to make 20% regulation in a capacitor input supply. They are good with a choke input since power factor is corrected and peak current is greatly reduced. Using a 50 ohm ESR transformer PSU designer says 18% regulation at 1 amp on a capacitor input, and 2% regulation with a choke input of suitable design. These old transformers are great with choke input, because that is what was traditionally used back then. They are almost never good with capacitor input. Short the primary (for safety) and measure the secondary resistance with a meter, and we can roughly calculate the regulation. It generally won't be pretty for cap input. Tom

RE: Vintage HV Plate Xformer	Reply
by W7NMD on October 29, 2009	Mail this to a friend!
Tom, PSU designer shows a secondary impedance of approx 560 ohms. The measured dc secondary resistance seems to be very high. This limits the output voltage at full load to around 1600 vdc according to PSU. Ameritron sells the 1500 xformer for $400 which is not to bad. Have to check with Harbaugh today and see if they have something better. Back in the 1940-1950 time frame, there were all sorts of HV xformers at a very reasonable price, but no more. Palmer

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