[Hammarlund] HX-50 VFO Wobble

[Bill Stewart]

Tnx Ken and Glen for more votes on trying other tubes.
I will put that first on the list to try.

You mention the VFO tube plate voltage...
The HX-50 plate voltage spec is 23vdc.
When I first checked it, it was abt 12vdc. Changed
some O/T resistors, but didn't improve much. Finally
I lowered the plate dropping resistor (R134) until
I got the voltage to around 18vdc...but no change in
tone.
73 de Bill K4JYS

----- Original Message -----
From: "Kenneth G. Gordon" 
To: "Bill Stewart" <cwopr at embarqmail.com>
Cc: Hammarlund at mailman.qth.net
Sent: Thursday, November 20, 2014 7:14:51 PM
Subject: Re: [Hammarlund] HX-50 VFO Wobble

On 20 Nov 2014 at 18:57, Bill Stewart wrote:

> I have changed the VFO tube...6AU6 (V105) and replaced a few O/T resistors
> around the VFO tube. I re-heated solder joints around the VFO. Tried to polish
> the VFO capacitor wiper and de-ox'ed it. Also de-ox'ed the 6AU6 tube socket. 

6AU6s are somewhat problematic: their quality varies a lot.

My advice is to replace that 6AU6 with a 6AH6WA or the military numbered 
equivalent, the 6485.

I routinely use 6AH6s in every oscillator circuit that would normally use a 
6AU6 since I discovered a long time ago that the 6AH6WA when used in a 
VFO works much better.

Also, if you use a 6AH6WA, you can reduce the plate voltage from the 
normal 150 VDC to 108 VDC, thereby reducing heat, drift, and chirp.

Ken W7EKB