Desk Kilowatt

[K5OG]

Took my Desk Kilowatt out of service for about 3 months while some remodeling was going on.
Everything is hooked back up and it works fine in AM Low.
However, when you transmit in AM High (high tap) there is a low pitch sound and vibration and immediately the breaker in the breaker box trips.
Any thoughts before I tear into this old beasty?
73 de
K5OG
Fred

[W7TFO]

Sounds like a filter cap went to sleep, or maybe is just groggy.

Hit 'em with a meter before you beat the rest of it about the head and shoulders by running it that way.

Maybe you have lost the bias supply, or the HV filter section can't stand the gaff anymore.

73DG

[WQ9E]

Fred,

Try it first on high power CW and see what happens.  If it is OK on CW then suspect maybe some RF getting into your audio causing LF audio oscillation. 

My first internal check would be RY-303 to see if you have  contact problems.

While you have the mainframe out of the pedestal, check for dust/debris buildup on the grid compartment fan.  (not related to your current problem but cleaning it will keep your 4-250/4-400 tubes happier.

[WQ9E]

If you are still using 872A rectifiers instead of SS replacements I recall that Bill Orr described a situation where MV rectifiers would develop some sort of oscillation mode causing tremendous current pulses to be drawn.  I don't have his handbook handy but I believe he clearly described the issue and how to avoid/cure it.

[K5OG]

Thanks for all the input.  I am using 872As and did think they might be an issue.  Perhaps arcing over under full load.
Trips in all Hi tap modes.
Amp is extremely clean.
I've replaced one relay but can't recall if its 303.  Will pull it out a little and check all relay contacts as well.
Going to run it in Lo tap for a bit and then try Hi tap again.  Let the MV rectifiers and caps wake up a bit.
73
Fred

[w4bfs]

sounds like hv breakdown .... time to use a ballast box and start isolating loads .... please use extreme care

[flintstone mop]

Can you safely look inside when you key the TX to see/listen for any straining of the P.S.?
Be careful....something didn't like the move. A tube may have bitten the dust.
An 872 might be arcing from laying in the wrong position.

[ke7trp]

Freds got it. Its probably easier to turn out the lights and key it up.  I went 12 rounds with a transmitter arcing on high power and after the lights went down, I saw the arc and then fixed the damn thing.