[AMRadio] Modulator troubles


Donald R. R Moore wa5ffk at juno.com
Fri Feb 23 09:09:04 EST 2007


I had a similar experience working on a Gates Broadcast transmitter, a
BC-1J.  This transmitter used two audio driver transformers driving two
pairs of 6B4G's.  I had one of the driver transformers go bad.  I had two
Identical modulation transformers that I replaced them with.  After
connecting and running the transmitter , all meter indications indicated
that it was working as normal, however it was modulating a very low
percentage.  After many hours of work, I reversed the leads connected to
the output of the two driver transformers, and my modulation came back to
normal.

Don W5FFK/Kansas

On Mon, 19 Feb 2007 21:54:06 -0600 "Joe Walden" <w5jdy at intergate.com>
writes:
> >From Joe w5jdy in Okla.   My experience with a modulator.    I 
> replaced the
> audio drive transformer in a Viking II (the one feeding the grids of 
> the
> final modulator tubes) with a brand new in the box Hammond 
> Transformer from
> Antique Radio in Tempe Arizona...  I had mod current but distorted 
> audio and
> a real low modulation per-centage. Even the dummy load light bulb 
> dimmed on
> mod peaks.
> After many,many moons,the trouble
> was located.   The NIB Driver transformer was wired wrong inside.  
> It had
> two individual windings for the grids
>  and they were phased wrong inside the transformer.  It was a 
> nightmare...
> All
> voltages and currents were as the manual stated and I had good audio 
> from
> each grid to ground but hardly any audio from grid to grid.   As I 
> say the
> mod tubes
> were bucking each other... It was running Push-Push instead of 
> Push-Pull?
>  I emailed Hammond and they sent me another NIB
> same part number transformer NO Chg.and the trouble was totally 
> corrected...
> 90% Plus Modulation NO distortion.... If you replaced any new 
> parts,look
> there first???   w5jdy  Joe in Okla.....
> 
> 
> 
> 
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