Viking Valiant blows fuse now has low plate current?

[radionut]

I had fired up the valiant and was talking to some people for less than 5 minutes. Next I heard a hissing sound I assume the fuse in the power cord. After replacing the fuse I only have about 150 mA of plate current. Anyone have an idea of what might be wrong?

I should mention that if the ocsilator switch is in the C1 position I have the problem as described above. How ever if it is in the VFO position i have plenty of Plate current. I was using an xtal when this problem happend.

Thanks

[ke7trp]

Hissing sounds like you might have lost an output tube.  Could really be anything.  Open it up and do a good inspection.  The nose will help find what burned.   My guess, The bandswitch or course loading wafer is fried. Very common.  I lost that twice on my valiant.  I also lost the Drive control, Is it smooth and working?

C

[radionut]

when you say output tube you mean a 6146? all three are illuminated that their bases. The drive pot is smooth and and does change the meter readings.

 I don't smell anytrhing burnt here..thanks

[Pete, WA2CWA]

I had fired up the valiant and was talking to some people for less than 5 minutes. Next I heard a hissing sound I assume the fuse in the power cord. After replacing the fuse I only have about 150 mA of plate current. Anyone have an idea of what might be wrong?

I should mention that if the ocsilator switch is in the C1 position I have the problem as described above. How ever if it is in the VFO position i have plenty of Plate current. I was using an xtal when this problem happend.

Thanks

Fuses generally don't hiss. If the rig works fine (you only said "I have plenty of plate current") in the VFO position and doesn't in the crystal position, then the problem lies somewhere in the crystal circuitry section. i.e. intermittent connection, cold soldered connection, intermittent bridged connection, carbon track somewhere, etc.

[ke7trp]

Try another coarse loading position and see if the current comes back  When my switch wafer failed, I heard it sizzling right before she shorted and blew the fuse
 C

[Knightt150]

Hissing noise's in high plate voltage transmitters 700 to 800volt varity is generly caused from a electrolytic cap or maybe a two or five watt resistor. I have never in my 50 years of electronics heard a glass fuse make a noise. Unplug the radio and use your nose that will tell the story sometime.

John W9BFO

[N8ETQ]

Yo'

   Could be the sound of carbon tracks being etched into the
866 sockets. Replace with ceramic.

73 es GL

/Dan

Hissing noise's in high plate voltage transmitters 700 to 800volt varity is generly caused from a electrolytic cap or maybe a two or five watt resistor. I have never in my 50 years of electronics heard a glass fuse make a noise. Unplug the radio and use your nose that will tell the story sometime.

John W9BFO

[WQ9E]

If you have a very early production Valiant you may also have breakdown in the wiring between the 866A cathodes and the LV transformer.  These leads has HV DC on it and the early production Valiants used regular hookup wire which isn't up to the voltage stress.  Breakdown will result in destruction of the LV transformer if not fixed immediately.

Are both 866A tubes still glowing with the HV on?  Is the modulator idling current also down?  If so this is a good indication that the HV has dropped significantly.

When you start working on the Valiant, before you turn it upside down you need to loosen the set screws on the VFO coupler or the bakelite coupler insulation will break.

Once the 866A tubes have been turned on their side (or upside down) they need to be run with the plate switch off for at least 5 minutes to vaporize any liquid mercury that has gotten where it shouldn't, otherwise you run the risk of flash over and plate transformer damage.

[ke7trp]

Good points.  It very likely could be the 866 sockets and wiring. 

C

[radionut]

Thanks for all of your thoughts here a few more details

with it set to VFO and a grid current of 8 when I flip the PTT switch I get 300 mA of plate but it drops to about 225 qucikly and I am unable to adjust it much

With it set to an xtal socket and 8 mA of grid when you flip the PTT I get 125 mA grid to remains steady and I can not adjust it.

In the past I replaced the 866s with 3B28s. One of teh 3B28s is loser in the socket than the other but it has always been that way.

I hope this sheds for light.
Thanks!

Thank you!