[TenTec] delta 580 transmit trouble

[Andy Gluis]

hi
I wonder if you could post a query I have re the Delta 580 please.
i have the above model which is exhibiting a problem where the transmit 
power is down to 25 watts on 160 mtrs and about 50 watts on all other 
bands except 40 where the power output is around 100 watts.Rx 
performance is fine on all bands.
I have changed the swr protection diodes and realigned the band pass 
filters to no avail.
I have checked the dc operating conditions on all the transistors from 
the mixer to the pa and they are all ok.
I found that the drive level to the pa is down to around 180 milliwatts 
so the pa etc is ok.
I also found that by bypassing the emmitter network on the 2n3866 
pre-driver transistor I could get full power output but had instability 
and gain compression trouble.
Incidentally alc has been disabled during testing so that part of the 
circuit is not causing any trouble.
Has anyone else come accross this before?
73
Andy
VK5AAQ