[AMRadio] DX-100B Low Output on 15 and 10 Meters

George Pritchard gpritchard at comtechpst.com
Mon Oct 18 09:09:01 EDT 2004

Easy fix: Just spread out the turns on the "double-coil"... the one made
with the continuous length of heavy wire at the grid-tank for the finals.
The reason is that this drastically improves the Q and you will probably see
a 2-3 ma grid drive improvement. The turns of the coil pair are usually
close spaced (touching) when people build the kit. I also pulled off the 47K
1/2W Q loading resistor off the driver's plate coil. Tuning is sharper, and
provides more drive. Also, There is a cap you can add to the crystal
oscillator that increases the VFO output, but I forget exactly... I think it
is at the screen of the crystal oscillator. That was a good mod. I can get 8
ma grid drive on TEN and 110 watts out with 120% modulation peaks (audio
George AB2KC

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Mark Bell
Sent: Sunday, October 17, 2004 10:12 PM
To: AM List
Subject: [AMRadio] DX-100B Low Output on 15 and 10 Meters

Folks --

I'm getting low output on 10 and 15 Meters.  Typical output on the other
lower bands is well over 100 Watts.

All tubes test good, and I re-did the Buffer Coil adjustments as per the

After tune up on 15 Meters, here's my readings:

Driver current is at 6 ma
Ig is at 2 ma
Ip is 250 ma
Output power 50 W

After tune up on 10 Meters, my readings are:

Driver current is at 6 ma
Ig is at 2 ma
Ip is 250 ma
Output power 65 W

As a reference, after tune up on 20 meters, my readings are

Driver current is at 6 ma
Ig is at 6.5 ma
Ip is 250 ma
Output power 130 W

Just for "fun",  on both 15 and 10,  I upped the driver current to max,
which was 10 and 7 mA respectively.  The respecitve Ig's were 10+ and 5 mA,
and the output power (both bands) jumped to 80W.

So, seems I have a problem with the grid current on 10 and 15 M.  I figure
I'd start looking at the circuit around the Driver section of the
bandswitch.   I was wondering, though, is this a known problem with the
DX-100B that might be attributed to (perhaps) neutralization?

Any and all comments welcome.

Thanks & 73

Mark K3MSB

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