Combined Plate Fil Transformer Standby

[KB3DKS]

  I have this nice 1500vac ct with 10v ct power transformer from an old Quack Med RF device. It used a pair of 311s (211 ind.) tubes wired as an about 13mhz 300W rated power osc terminated into a patient fixture.
 The power switch just turned the transformer on Fil and Plate together of course.
The center taps are not common so if I lifted the hi volt ct would that be safe for standby in a modulator application using a pair of 211s or 814s?
 Has anyone used this method with a relay?
 Have seen many audio amps using that method with dc voltages of at least 700v.
Filament current of a 211 is 3.25 per tube so the 814s would work also but not 813s.
Bill

[w4bfs]

 I have this nice 1500vac ct with 10v ct power transformer from an old Quack Med RF device. It used a pair of 311s (211 ind.) tubes wired as an about 13mhz 300W rated power osc terminated into a patient fixture.
 The power switch just turned the transformer on Fil and Plate together of course.
The center taps are not common so if I lifted the hi volt ct would that be safe for standby in a modulator application using a pair of 211s or 814s?
 Has anyone used this method with a relay?
 Have seen many audio amps using that method with dc voltages of at least 700v.
Filament current of a 211 is 3.25 per tube so the 814s would work also but not 813s.
Bill

take a look at K1JJ dual 813 transmitter in an older thread ... he placed the modulator tubes in standby with a 10 to 50 kOhm from the filiament ct to ground and shorted it out with ptt relay to tx ... it is not necessary to turn B+ on and off

[WQ9E]

Go with Beefus's suggestion or some other method of biasing the modulator into standby.  In many HV transformers it is assumed the center tap will always be grounded and the transformer will be damaged if the center tap is not grounded.  Many transformers must be used as designed with a full wave rectifier secondary and grounded center tap.  Attempts to use these transformers with a full wave bridge or even putting the filter choke between the center tap and ground (as recommended in many ARRL handbooks which puts the center tap at ripple above ground) will cause flash over inside the transformer.  Orr warned about these issues in some of the "West coast" handbooks.

I definitely wouldn't experiment like this with a vintage transformer because it is very likely to ruin an otherwise good transformer.

[KB3DKS]

Thanks Guys,
 The original circuit was the two 311s configured as a PP oscillator without any DC filtering or rectification. The tank circuit was a coil and fixed cap with a small value trimmer to peak resonance. There was no loading cap so whatever the patient connection produced was it.
 The center taps were connected and designated as the patient ground connection. Floating from earth, two wire AC power in a wooden cabinet. Must have been a great RFI generator.
  Since it wasn't meant for continuous duty I will set it up and do load testing before committing to a build. Would like to see what the actual filtered and loaded DC would be anyway. Also a Variac would be needed to get the 10v filament right on since the primary is probably 110-115vac.   
 I have a copy of the K1JJ 813 rig on file and will look at that modulator.
It would be handy to have a somewhat universal modulator using this transformer and a UTC S-22 or a multitap Thordarson of similar power rating I have.
Bill, KB3DKS

[W7TFO]

I'd wager it was not a quack device, rather an early diathermy generator.

They seem to like RF around 15 MHz.

Lots of SS ones in use today by docs the world over.

73DG

[W2PFY]

hey seem to like RF around 15 MHz.

Most of the units I knew about were on the CB band. I think it was in the early fifty's that the FFCC outlawed them. My grandfather had one that he had for his wife. When they received the notice, they discontinued to use it. I remember them hooking the thing up so we all could feel the heat it put out. He gave it to me around 1955 and I quickly tore it apart to build something out of it.

Later in life around 1967, a doctor I was using used his on me for a back problem and it was very much like the one my grandfather had, no shielding etc. They are still used to this day for certain medical conditions.
QUACK QUACK 

[kb3ouk]

Yea, most of them I saw were around 27 mhz and used a self-rectifying oscillator.