[Icom] IC706 power out- 2

[icom@mailman.qth.net]

Thanks for the comments re my posting on this subject.  Here's a follow-up.

Checked DC voltage at the power connector.  In receive, 13.10 volts, pretty much
what the supply is putting out.  In FM transmit, 11.97 volts (but supply output,
which is regulated, remains at 13.1, where it was set.)  On 80, 40, 30, 20 and
17, this gives 95 to 102 watts output into a dummy load.  Increasing voltage so
that the power at the Molex connector is 13.00 VDC did NOT make any noticeable
difference in power output.  This test, though, did tell me there is a 1.5v
(approx) drop in the power cable. 

I then switched to 10 meters.  Output was, with 11.98 VDC at the Molex
connecotr, 77 watts on 28.500.  I increased voltage until it was 12.99v at the
power connector.  This increased RF output only two watts, to 79 watts.  

So the problem is not the DC voltage being delivered to the radio.  I also
noticed, as one would expect, the current draw from the power supply was lower
on ten meters (after all, less RF power out) by about three amps, than it was on
20 meters.  

I find myself wondering if this radio has always had lower power output on the
upper bands, as I never went to the trouble of measuring it before.  I noticed
it purely by accident this time.  Curious, I tried two other transceivers, plus
a transmitter, on the dummy load and got output that I expected from each of
them. Only the 706 has reduced output below expectations.  

There are four modifications to this radio.  The famous 'yellow wire' mod which
allegedly increases VHF sensitivity.  The open transmit mod, to allow transmit
anywhere in the HF range.  (Incidentally I tried this, too, into the dummy load
and found, for example, 16 mhz had somewhat reduced power, while 17 mhz it went
back up to 100 watts, but the difference was not substantial.)  A mod that
produces 12 VDC on transmit for keying an external reed relay, and a mod that
has since been removed, that was the addition of a transistor to do the same
thing - key an external relay.  The 'yellow wire' mod could conceivably affect
transmit power on VHF, but has not apparently done so, as I actually get about
11 watts or better out on 146 mhz.   None of the other mods could affect output
by band. 

At this point I'm just curious as to whether anyone else has an original 706 and
has found reduced power output on higher HF frequencies.  After all, this radio
is seven years old, and has been a good and reliable performer. It still seems
to be.  It may be there IS no problem?  



--
Ed Brooks, W5HTW
http://w5htw.home.att.net/index.html
Active since June 1956 Extra since
Jan 1970