[AMRadio] Driver Xfmr

[Donald Chester]

>From: Gary Schafer <garyschafer at attbi.com>

>Just put a resistor in the plate of the audio driver tube, in place of the 
>transformer primary. I think around 10k 2 watt will work ok...It will work 
>as an auto transformer >to couple audio into both tubes. ...  gain will be 
>somewhat less than with the transformer.

I did a similar trick with a Ranger to get the DC off the primary of the 
driver xfmr, but used the cap to couple audio to the primary of the dinky 
little xfmr in that rig.

To avoid loss of gain, the trick is to return the resistor to the HIGH 
VOLTAGE that supplies the plates of the modulators and finals, not the low 
voltage DC that the transformer was originally connected to.  That way, the 
resistor will drop the DC voltage back down to about the normal operating 
voltage of the tube.  You might want to use two 10k 2 watt resistors in 
series, since the DX-100 runs more HV than the Ranger.

BTW after I got it working, the bass response was substantially improved.  
Then I disassembled the little driver xfmr and restacked the laminations 
like a power xfmr, without the core gap.  That drastically improved the LF 
response.  It's been over 20 years, but as I recall, the audio to the grids 
of the modulator tubes was flat to below 50 cps.  I didn't try to do 
anything to the dinky mod xfmr in the ranger, but everyone commented on how 
much better it sounded.

Don K4KYV

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