I have a sick DX70 (not TH). The output power on the hf bands has
gradually fallen from 100w to less than 50w over the last few months.
Same effect on all bands, except for 80m, where the power has only
dropped to about 80w.

I've independently verified the external power meter I use against a
Bird wattmeter, and the power input is still 12v DC, so it has to be the
radio.

Ideas anyone?

--
73
Ian, G3NRW

I've got a couple:

1.Get a schematic and replace the components in bias circuit(s) of the
PA.
then
2. Get a service manual and retune the PA setting bias as indicated.

3. (you might get away with just 2.)

4. Then again it could be the ALC ;-)

(....5. or the drivers)

Aternatively send it off to Castle Electronics as they seem to know
what they are doing - they rarely quote input power in terms of Volts
DC for example.

Is that the output into a dummy load?? I use one in the car and the power
drops off rapidly above 1.5 to 1 SWR. You haven't moved the internal power
switch, this reduces the output to 50W max.



Steve H
"news" wrote in message
...
I have a sick DX70 (not TH). The output power on the hf bands has
gradually fallen from 100w to less than 50w over the last few months.
Same effect on all bands, except for 80m, where the power has only
dropped to about 80w.

I've independently verified the external power meter I use against a
Bird wattmeter, and the power input is still 12v DC, so it has to be the
radio.

Ideas anyone?

--
73
Ian, G3NRW

In message , Steve H
writes
Is that the output into a dummy load??

Yup.


You haven't moved the internal power
switch, this reduces the output to 50W max.

Nope.

--
Ian

In message .com,
G1LVN writes
I've got a couple:

1.Get a schematic and replace the components in bias circuit(s) of the
PA.
then
2. Get a service manual and retune the PA setting bias as indicated.

3. (you might get away with just 2.)

4. Then again it could be the ALC ;-)

(....5. or the drivers)

I have the service manual, but unfortunately don't have an audio signal
generator or scope any more, so cannot do much in the way of testing.

My current thinking is that either the PA (or driver) is dying, or that
the thermal conductivity between the PA and heatsink has degraded
(however, the PA does not seem to run any hotter than originally, and
the fan very rarely kicks in -- again, no more so than when it was new).



Aternatively send it off to Castle Electronics as they seem to know
what they are doing -

Good tip. I'll call them today.


they rarely quote input power in terms of Volts
DC for example.


I only quoted that to eliminate the PSU from the equation. A drop from
12v to 11.5 volts can make quite a difference to the output power.


--
Ian