|[AMRadio] Ranger Audio... the numbers|
garyschafer at comcast.net
Thu Nov 16 23:35:57 EST 2006
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of Jack Schmidling
> Sent: Thursday, November 16, 2006 10:02 PM
> To: Discussion of AM Radio in the Amateur Service
> Subject: [AMRadio] Ranger Audio... the numbers
> I can not do a freq response test because I do not have a proper sig
> gen. Mine is a cheap step job and the amplitude is all over the place.
> I put a 1khz sine wave into an earphone sitting on the mic and measured
> p-p values with a scope....
> Pin 2 V7A (grid)........ 5mv
> Pin 7 V7b (plate)........50 mv
> Pin 2 V8 grid............. 3 v
> Pin 1 V8 plate.......... 40 v
> Pin 5 V9/10 grid........ 20 v
> Pin 3 V9/10 plate....... 10 v (standby)
> Pin 3 """"""""""....... 50 v
> I assume that where the voltages dropped it had something to do with the
> transformer being across the output and the standby more for the mods.
> I all cases, the amplitude dropped a bit and the sine wave got a little
> "bent" when going from stdby to phone. It flattened out slightly.
> In the case of the grids of the mods.. a great deal of distortion was
> seen when in the phone mode. Only an approximation of a sine wave with
> jagged festoons all over. None of this was seen when looking at the
> plates in the phone mode.
> So, what can we make of this?
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.
You could be driving the modulators into too much grid current and causing
the bias to shift around.
Check the jumpers on the plug in the back to be sure that the proper taps on
the mod transformer are selected.
Check the clamp tube circuit. Could be holding the screen slightly low on
the 6146 and clipping the modulation peaks to the screen.
Check modulator screen voltage.
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