[AMRadio] Ranger Audio... the numbers

Gary Schafer garyschafer at comcast.net
Fri Nov 17 11:57:11 EST 2006

It's beginning to sound like a partially shorted mod transformer. With 20
volts signal on the grids of the mod tubes I would think that you should see
at least 200 volts on the plates??

Could be bad 6L6's.

The reason that you see a slightly distorted audio pattern on the audio
amplifiers when in tx and not in standby could be the result of the negative
feedback loop trying to correct distortion from the mod transformer.

Can you easily get high modulator plate current with audio applied? Will the
mod plate meter peg or nearly so if you hit it hard? If it will that is an
indication that the tubes are good and the transformer may be shorted.

Gary  K4FMX

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of Jack Schmidling
> Sent: Friday, November 17, 2006 9:45 AM
> To: Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] Ranger Audio... the numbers
> Gary Schafer wrote:
> > Check at the center tap of the mod driver transformer with your scope
> and
> > see if you see anything there. Could be a bad or missing bypass cap
> there.
> It's brand new but I didn't have a 15mf so I used a 47mf.. ditto for C59A.
> > Check the jumpers on the plug in the back to be sure that the proper
> taps on
> > the mod transformer are selected.
> All ok.
> >
> > Check the clamp tube circuit. Could be holding the screen slightly low
> on
> > the 6146 and clipping the modulation peaks to the screen.
> Screen voltage is 150 and the nom is 190.
> However, R35, the Modulator Screen Voltage Adjustment resistor seems to
> go to the clamp circuit and it is not at all clear what is going on
> here.  It seems to me that diddling with it changes the screen voltage
> on the 6146.
> So does diddling with the modulator current effect the 6146 screen
> voltage or do I have a screen voltage problem?
> > Check modulator screen voltage.
> It is the nominal 250V... but again, why is it nominal if that resistor
> is there to diddle with the current?
> js
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