[Johnson] Viking Desk Modulation

[Dennis Petrich]

Also, make sure you are using the right tap on the mod iron??  Sounds like you might have the wrong impediance ratio....

k0eoo

-----Original Message-----
From: johnson-bounces at mailman.qth.net
[mailto:johnson-bounces at mailman.qth.net]On Behalf Of Rodger
Sent: Monday, January 14, 2008 4:39 PM
To: Tom Elmore
Cc: Johnson at mailman.qth.net
Subject: Re: [Johnson] Viking Desk Modulation


Hi Tom,

This is a curious condition with the modulation being low in both high 
and low power positions, if it were just in the high position I would 
suspect the HV rectifiers.  Check the 810 bias and also make sure that 
you have plenty of audio and RF drive.  I am using a Ranger 1 with my 
Desk and there is plenty of audio to cause clipping if one isn't careful.

As another thought, with the meter set to the grid position measure the 
resistance from the 810 grid to ground to make sure there isn't a high 
resistance connection where the RF Deck plugs into the mainframe as this 
would create additional operating bias.

73, Rodger WQ9E

The Tom Elmore wrote:
> Hello All, I recently inherited a Viking Desk Kilowatt from a SK friend of mine. I returned it to service after almost a year. It seems to make output power 275 low power and +700 watts high power. When looking at the modulation on a scope though it appears to be only modulating about 80% in either low or high power. 
> I have changed out the 810's and 4-400 and see little improvement. I do notice that when I approach 80% modulation on the scope that both positive and negative peaks appear to curl slightly instead of going flat like I thought I would see with clipping.  Anyone have any thoughts or experience on where to look next ?
>
>
>
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> -Tom / KA1NVZ 
> Anchorage, Alaska 
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