John -
There are a few ways to do this. I'm not familiar with the Acom unit,
but apparently it doesn't require much drive.
1. Construct a "power pad" to put between the TR-7A and the amp input.
This is probably the "best" way from a distortion standpoint, but
inconvenient unless you use the amp all the time. Running any SSB
transmitter with very low Mic Gain is not a good idea, since the S/N
ratio of the AF stages is at its' worst.
2. Construct a small power supply to feed a "fake" ALC signal to the
ALC input on the TR-7A and crank the voltage up to where you can run the
TR-7A Mic Gain at 10-11 O'clock and not overdrive the amp. When you
want full output from the TR-7A, just turn off the ALC voltage.
3. Construct your own ALC circuit in the amp using the method in the
L-7 or some other amp with similar circuit topology.
4. You "may" be able to turn the internal ALC pot on the TR-7A to limit
it's maximum output to a level that won't overdrive the amp. Again, no
convenient way to enable full power for stand-alone operation.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
John Stringer wrote:
Way back in the 80's I used a TR7 with an L7 which ,of course, had ALC.
Everything worked well together.
Now, about 27 years later I have bought a nice TR7A and am trying to use it
with my modern Acom 1000 linear which has no ALC provision.
There is one problem as a result. I have to turn the drive-meaning
microphone gain- down VERY low so the TR7 is operating long before it's own
ALC kicks in. As a result there are considerable output swings to the linear
which often causes it to kick out. Turning down microphone gain even further
helps but then the average output is very low.
I need to be able to operate the TR7 so it's ALC is working whilst giving a
LOT lower drive.
Any suggestions? John. GI3KDR.
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