Suggestions for TR7 transmit problem?
 

My faithful Drake TR7 (SN 3119/ purchased new in April of 1979) has
developed a power output problem. The TR7 generates normal power output at
turn on, but after a few minutes of transmission the ALC becomes active and
starts cutting back the power, with the output shutting down to a fraction
(1/10th) of normal power. It appears to continue to work (CW, SSB, and psk),
but the reflected power jumps up (suggesting out-of-band energy). The
antenna is not the problem. I have checked the transmit relay, cable and
board connections, and switch contacts. All appear to be OK and not
contributing to the output problem. Running reduced power (25 watts) slows
down the ALC coming on a little, but not for long. The TR7 receiving is
stable and normal for all modes and all bands. The problem is not band
related either.

Has anyone seen this problem or have an idea what is going on?

Any suggestions on the best place to get it repaired?

Andy, K4YKZ

Suggestions for TR7 transmit problem?
 

In article itvrg.823019$084.209575@attbi_s22, "AK"
wrote:

My faithful Drake TR7 (SN 3119/ purchased new in April of 1979) has
developed a power output problem. The TR7 generates normal power output at
turn on, but after a few minutes of transmission the ALC becomes active and
starts cutting back the power, with the output shutting down to a fraction
(1/10th) of normal power. It appears to continue to work (CW, SSB, and psk),
but the reflected power jumps up (suggesting out-of-band energy). The
antenna is not the problem. I have checked the transmit relay, cable and
board connections, and switch contacts. All appear to be OK and not
contributing to the output problem. Running reduced power (25 watts) slows
down the ALC coming on a little, but not for long. The TR7 receiving is
stable and normal for all modes and all bands. The problem is not band
related either.

Has anyone seen this problem or have an idea what is going on?

Any suggestions on the best place to get it repaired?

Andy, K4YKZ

My guess is that some transistor in the xmit circuit is going into
oscillation, could be the transistor has gone bad, could be a resistor
is breaking down, could be one of the cap's (feed back) is breaking down

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