[Johnson] Viking Valiant Modulation

[dsmaples at comcast.net]

Paul: The biggest problem I have found in the Valiant audio chain is (a) the driver transformer and (b) the sizing of some of the bypass and coupling caps.  Significantly oversizing the bypass and coupling caps and replacing the driver transformer with one from AES got me pretty good frequency response down to 100 Hz (I swept it with an audio generator and scope on the modulator grids).  Below that things still are not very good.  I have seen some mods to turn the driver tube into a push-pull device, but not sure if I'm ready to commit that level of surgery...

Dave WB4FUR



-------------- Original message -------------- 

> I'm renovating a Valiant. I've made the usual audio chain mods to improve 
> the frequency response. 
> 
> However, when I monitor the modulated wave form on a scope I notice that as 
> you take the audio lower in frequency that the modulation gets distorted. 
> Its OK down to about 500Hz, but below that gets progressively worse. The 
> drive to the 6146 modulators is reasonably distortion free. 
> 
> Is this a feature of the original modulation transformer? Is a better 
> transformer available? 
> 
> Thanks 
> 
> Paul - KW7Y 
> 
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