|[AMRadio] AMRadio Digest, Vol 73, Issue 11|
k2lrc at k2lrc.com
Fri Feb 12 14:05:32 EST 2010
Rob, Fair Radio in Ohio...
-73- Peter K2LRC
In God We Trust !
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Rob Atkinson
Sent: Friday, February 12, 2010 1:55 PM
To: Discussion of AM Radio in the Amateur Service
Subject: Re: [AMRadio] AMRadio Digest, Vol 73, Issue 11
Jim, where do you get a 4D32 these days?
> First off, I have an HT-20 on the air and it does well on AM, so the
problem is not generic to the transmitter design. I have not used a light
bulb for a dummy antenna, at least not recently, but my average-reading watt
meter does not bobble during modulation. I would expect a light bulb to get
brighter during modulation, not dimmer, which is something you also know.
> From the list of things that Larry suggested, above, I would not think
that #1 would not be a cause of this particular problem. Human voice audio
is not symmetric, so you can achieve more full modulation by selecting the
better phasing connection, but neither phasing connection should cause
"downward modulation." #5 is also not likely to be the problem if the rig
has the original modulation transformer. The other suggestions are all
likely causes. Another one might be a very flat (low gain, low emission)
4D32 final amplifier tube.
> Let me know how much final grid drive you are running and what the loaded
plate current is for the final amp. The manual recommends 260 ma plate
current for CW and 320 ma for phone, but I don't run any more than 200 ma
for either phone or CW. 4D32's are too expensive! It also recommends 10 ma
for grid current. The ARRL Handbook ratings for a 4D32 are a maximum of 240
ma for CW and 220 ma for phone, with 12 ma of grid current for the CW
condition and 10 ma for phone. I can compare your operating parameters to
the ones I'm running currently on my rig. Mine is tuned up on 14286 right
now in anticipation of the Classic Exchange AM event on Sunday.
> Good luck,
> Jim Hanlon, W8KGI
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