[Boatanchors] Re:Valiant Question/Help

Sun, 18 Apr 2004 06:36:14 -0500

Tom,

It's not a modification, it's a production change.  Somewhere around Oct 
1958 of Valiant production the tapped resistor arrangement for deriving 
modulator and final bias was changed to the dual pots that you see in 
your Valiant.  This eliminated interactions between final grid current 
and static modulator plate current.  Description of this appeared in 
"Viking Valiant Information Bulletin #1" which came out at that time.

There's a copy of the bulletin on BAMA.

regards,

Mahlon - K4OQ

> --__--__--
> 
> Message: 4
> Date: Sat, 17 Apr 2004 15:03:08 -0500
> To: [email protected]
> From: Tom Norris <[email protected]>
> Subject: [Boatanchors] Valiant Question/Help
> 
> I am going over a Johnson Valiant that I came across
> a while back and recapping and replacing what needs
> to be replaced, sent the bezel to Dee Almquist for
> refinishing, etc. But have a question about the bias
> circuit.
> 
> The schematic shows a tapped resistor for bias adjustment.
> This TX has a pair of 5k pots, one each for mod and RF
> bias. Is this a "normal" mod? Looks like a 5 watt pot for
> audio and a 10 watt for RF. For some odd reason both pots
> have seized and need to be replaced - just wondered if I
> *really* need to look for an nice, fun to adjust tapped
> resistor as stock, or just replace the pots, which are much
> safer to adjust. Just looking for an opinion.
> 
> Power seems low right now, all tubes that did not check
> good were replaced, as were any out of spec resistors.
> Other than the currently broken bias pot which might
> be contributing to this, are there any other "gotchas"
> I need to look for? Everything else *looks* normal
> other than bias.
> 
> Thanks for the help - just not familiar with Johnson gear,
> can repair most Collins gear with my eyes closed.
> 
> Tom
> KA4RKT