DX100B Restoration

Brian Carling bcarling at CFL.RR.COM
Thu Mar 3 21:23:45 EST 2005

Excellent thanks Gary.
I will try a new 6AU6 and VR tube first and see if that stops the 
chirp. The drift is probably not excessive. Just typical tube rig 
warm-up problems.

I may eventually use an external VFO anyway.

I REALLY appreciate your comments and observations. All very 


On 3 Mar 2005 at 11:26, Garey Barrell wrote:

> Bry -
> The DX-100 VFO is essentially the VF-1.   This VFO as designed is
> quite capable of chirp-free, drift-free (for it's era), operation.  
> Changing the VR tube voltage or regulating the plate voltage have
> little or no effect.  It is an Electron Coupled Oscillator, and the
> plate voltage has no effect on the oscillator, and very little on the
> loading.
> Part of the drift problem is a result of the temperature variations in
> the DX-100, both warm-up (at least an hour because of the huge mass of
> metal), and from transmit to receive.  The latter is especially
> noticeable with AM "old buzzard" transmissions.
> Solder, mounting hardware, and especially the bus wiring are all
> contributors (or detractors) of stability.  Make sure the bus wiring
> especially is well soldered and not "under tension" from
> point-to-point.  It also is a good idea to "exercise" the trimmer caps
> a little and verify the ground connection.  DON'T over tighten the
> mounting hardware, they will break!  A little liquid Deoxit on the
> switch contacts and tube pins ONLY.  DON'T spray anything all over
> everywhere.
> Replacing the 2.2k 1/2W resistor in the grid circuit with a 1W helped,
> both with drift and minor instability, and probably a carbon film
> would be even better today.
> The silver mica caps are reliable, but some have replaced them with
> Dur-Mica's.
> A GOOD VR tube is essential, just because they glow doesn't mean they
> are stable.  Many "dither" a few volts.
> Selection of a GOOD 6AU6A is also necessary.  There is a BIG
> difference from tube to tube, even "new" ones, especially with regard
> to chirp.
> 73, Garey - K4OAH
> Atlanta
> Drake C-Line Service Manual
> <http://hr99.home.mindspring.com/R-4C_Servicez/>
> Brian Carling wrote:
> >Say guys,
> >
> >I just got this DX100 and it is clean when using crystal control but
> >the VFO drifts and chirps really badly.
> >
> >I was thinking of dropping the voltage regulator from 150V to 105V.
> >Any thoughts on this?
> >
> >73 de AF4K, Bry
> >  
> >

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