B&W 5100 Plate xfmr

[W4RFM]

Does anyone know the voltage of the secondary of the 5100 plate transformer?  I just blew up my Triplett VOM trying to read half of it!
(And that my son is why you need to keep an early version of a Simpson 260 around with a 5KV A C scale on it.)
Thanks
Bob

[w4bfs]

I believe if it is a pair of 6146 finals then 600 VDC would be target ... the EFJ Viking II is similar and it is about 850 - 900 Vac each side of ct ...hope this helps ...73...John

[WQ9E]

Bob,

I believe you end up with around 680V DC for the HV and the 5100 uses a full wave grounded center-tap circuit with choke input so allowing for some drop in the 5R4's and a choke input filter the transformer is going to be somewhere around 750 to 800 volts AC each side of center or 1,500-1,600 volts AC across the entire secondary which is probably about twice what your DMM was rated to take.

If you measure the resistance be aware that the collapsing magnetic field will cause a nice high voltage kick when you remove the meter probes so watch out for that.  It is typical to measure slightly more resistance in one side of the center tap since many transformers are wound with one side of center tap on top of the first winding which requires more wire and results in a slightly higher resistance.  Thus don't use a slightly different resistance as evidence of transformer damage.

Rodger WQ9E

[W4RFM]

Thanks folks, the color had faded so badly on the leads, I may have gotten across the full secondary! I smoked a resistor and a fuse in the Trip! Too lazy to pull out my home made variac/AC meter box and do some math.  That'll teach me.  Thanks again.

[W1EUJ]

Laziness is infrequently rewarded with failure.

[Jim, W5JO]

If you will notice that the terminal strip on the back of the 5100 has a couple of jumpers.  One is the HV and the other is something else (I don't remember at the moment).  You can read the HV on the jumper. 

Given the HV is around 600-650 volts, how did you blow your DMM?  Did you try to read the final voltage at the top of the plate RF choke?

[W4RFM]

The way the rectifier and choke act on the secondary, the operating voltage is way less than the secondary rms voltage total.  For example, a Heathkit Apache has a plate transformer secondary of 1830 volts, yet the voltage to the same 6146's is about 700 vdc.  A Johnson Viking II has a secondary of 1730 volts, yet again a pair of 6146's get a little over 600 volts.  See what I mean?
I was reading the actual A C secondary with the transformer removed from the circuit. I apparently got across the full sec instead of the center tap and one high side.

[KG6UTS]

"If you will notice that the terminal strip on the back of the 5100 has a couple of jumpers.  One is the HV and the other is something else (I don't remember at the moment). "

  The jumpers allow the 5100 to be an exciter and audio driver for a lager final and modulator. John WA6JUS uses a B&W5100 just that way.

[Jim, W5JO]

"If you will notice that the terminal strip on the back of the 5100 has a couple of jumpers.  One is the HV and the other is something else (I don't remember at the moment). "

  The jumpers allow the 5100 to be an exciter and audio driver for a lager final and modulator. John WA6JUS uses a B&W5100 just that way.

The plate voltage is also comes out on one terminal and is jumpered to another on that strip.  The audio is also there for it to be used as a driver.