Re: 20-50H choke@800volts

[k4kyv]

I would like a choke to drive the finals in a Viking 2 with a External amp.Thanx,Lee,N2udf.

It's not clear exactly what you are looking for or what you plan to do.

What current rating do you need for the choke?

How would you "drive" the finals in a Viking 2 with a choke?  Do you mean a modulation reactor to MODULATE the Viking 2 with an external modulator?

Or are you seeking a filter choke to use in the power supply for an external linear amp that will be driven BY the Viking 2?  In that case you would need something more than 800 volts on the plate if you are using normal tubes, since, to gain any advantage over the full power Viking 2 standing alone you would need an amplifier capable of running close to a KW DC input at 100% duty cycle and dissipating over 600 watts of that power in the plates continuously.  Most tubes I can think of would need 1500 to 3000 volts to do the job, not 800v, unless you plan to build one of those CB style "leen-yars" with a dozen or two small tubes (sweep tubes for example) in parallel. Those things are rarely worth the effort, and usually make a more spectacular fireworks display than rf power amplifier.

[N2udf]

I hope top drive the finals of a Viking 2 with a PAamplifier.People have told me to use a choke as sort of heising modulation.THanks for your interest.....Lee,N2UDF

[k4kyv]

I see.  There was some  confusion regarding terminology.

You drive the finals with whatever the rig uses for an rf driver.  A 5763, 6AG7 or 12BY7 maybe?  You modulate the final with the PA audio amplifier.

Besides the Heising choke (the one you mentioned should do fine, as long as the current is rated to carry the full rf final amplifier plate current), you will need another transformer to step the low-Z output from the PA amp up to the modulating impedance of the Viking final. A similar transformer to the output transformer in the PA amp, wired back-to-back via the low-Z secondary windings of both transformers would do.

[KE6DF]

You would need more than 800v rating if you are using the choke as a heising reactor. Something like 3 times the plate voltage or more since 100% modulation would drive the voltage up to 2x.

[N2udf]

Thank you for your input.I have the output transformer.I will look for the choke(or chokes).....Lee

[W2VW]

You drive the finals with whatever the rig uses for an rf driver.  A 5763, 6AG7 or 12BY7 maybe?  You modulate the final with the PA audio amplifier.

Hopefully.

[k4kyv]

You would need more than 800v rating if you are using the choke as a heising reactor. Something like 3 times the plate voltage or more since 100% modulation would drive the voltage up to 2x.

If the voltage rating of the Heising choke is questionable, float it on insulators.  Usually, the breakdown occurs between the winding and the core, or to the case of the choke.  High voltage stress between the coil and core is unnecessary, since grounding the core serves no useful purpose other than making sure the whole thing isn't live with HV should the insulation fail.  Mount the choke on stand-off insulators, and for safety's sake, treat the body of the choke the same as you would the plate caps on the modulator tubes. If the choke is to be outboard, enclose it in some kind of box or cage to prevent inquisitive hands or animals from contacting it.

With the choke floating as described above, the only stress on the insulation comes from the audio voltage that appears at the output of the modulator.

I float my modulation transformer, modulation reactor and power supply filter chokes.