Dx-100b no audio then no RF output

[n2ry]

Greetings,

Looking for some starting advice before I rip into it. At first I lost modulation, but had a good carrier, in the process of checking voltages and such, suddenly I lost Rf out, HV is around 600 in voice and about 640 in CW.
Oddly in grid meter position, its showing negative deflection. I heard no pops or smoke, just suddenly no RF

I haven't really done much since it happened, except check V6(12by7) & V7(5763)

Any ideas are much appreciated to get started.

Rich
n2ry

[N8ETQ]

Hey Rich,

  See if that OA2 is lit, that will indicate the LV supply is there.
The bias supply is via the 6al6 , or they used a dropping R off
the plate supply for the screens of both the RF PA and Modulators.

  GL

/Dan

[steve_qix]

The negative deflection of the grid meter suggests a final amplifier tube grid short (or some component in the grid circuit has failed).  That's where I would look first.  You should be able to remove the HV rectifiers and debug just the driver and grid circuitry. 

If it's a grid short in a tube, chances are both of the RF finals didn't fail at the same time... see if the problem clears up with either one of the finals plugged in by itself.

Let us know 

Regards,

Steve

[n2ry]

thanks Steve,
no RF and neg grid reading turned out to be a bad 6146,
it didn't show right away in the toob checker, only after about 2-3 minutes did it apparently break down,
so RF is back and now back to the original prob of almost no audio out.
with a d104 plugged in and the audio gain all the way up, i can just barely hear a sound in a receiver.
Checked all the usual audio toobs. have to make room to setup the scope now......

Rich

[n2ry]

ok - here we go .... scoped the audio stages, ea tracing the signal ( or lack of signal back), all of sudden - there it was on the scope, and then i was able to hear it on the receiver fine !!!!!!
I had unscrewed the pale from the chassis in the audio corner. Strange, put everything back together --- no audio,  undid the plate again and moved it around, audio came back --- hmmmmm cold solder joint maybe
not alot of room to work in that corner.
Well, now its back together, I have audio deflection on the meter - but the output meter DROPs on modulation and the scope is not show audio signals...

Tomorrows another day ....

Rich
n2ry

[n2ry]

thinking about the downward modulation again - could this be caused by the changing of the 6146 i did before hand ?
Would the finals need to be neutralized again ?

Rich

[W3SLK]

Rich said:

Would the finals need to be neutralized again ?

If memory serves me, the DX-100B uses a piece of 'straight wire' to neutralize by sitting on the envelope of the tube. I don't thing it uses a 'mechanical type' of capacitor.