DX-100 update... I dont thing the mod tranny or the HV is the problem...

[kf6pqt]

This should be easy to check with an ohmmeter.  Put ohmmeter from pin 7 of the VFO tube (from the top of the tube socket, you need not get into the box) to ground with the rig turned off and the AC cord pulled.  The put the Plate Switch in the on position and you should see very low resistance.  The only thing in the circuit is the RF choke in the cathode lead of the 6AU6.  If you don't see the meter read very low, then you have an open, which is causing the trouble for you.

This is only good when the switch is in the vfo position. OPen when in the xtal position, but that is correct, correct?

[kf6pqt]

Lets review here:

It ain't:

The plate switch
mode switch
xtal switch.

What else could be "pulling up" the osc cathodes?

[Jim, W5JO]

Jason, if the cathodes of the osc and buffer tube go to ground with the mode switch in phone and the VFO/Xtal switch in VFO and the plate switch on, then there are only few thing that could cause no output.

1. The oscillator is not working, no plate voltage or screen voltage or the filaments are not on.  Or one/both of the510 pf. caps in the divider circuit are bad.
Do you have regulated voltage on the VFO when the VFO is selected?

2.  The clamp tube circuit is not right.

3.  Are you sure the bandswitch is right for the band you are selecting. 

4.  The 5763 stage is giving trouble.

There just isn't a lot to go wrong.  I would suggest you use a scope and follow the signal from the grid of the 12BY7 to the grids of the 6146s.  If you don't have signal on the grid of the 12BY7 and the clamp adjustment is correct, it may be time to go into the VFO box.

[kf6pqt]

Ok, the osc IS working in the fone position... IF I ground its cathode. works fine and normal in CW.

Could something be "pulling up" this line?

[Jim, W5JO]

Ok, now trace that wire and be sure it attaches to the same point the cathode wire on the 12BY7 is.  You say when you put a clip lead on the 12BY7, everything works.  That lead us to say there is a wiring mistake on the CW-Phone switch terminal that goes to the plate switch.

[kf6pqt]

Ok..... (deep breath)

A previous owner, NOT the guy I bought it from, had replaced the 1625 modulators with 6146's, and did a bunch of other hokey mods to it. I bought it. It worked. It sounded kind of crappy, and was getting worse, so I decided to rip out the modulator section and rebuild it as stock. Which I think I did.

Now, I get no RF (no oscillator, nuthin)  with the mode selector in Fone position with the plate switch on.

Its normal to get no oscillator at all in fone position with plate switch off.

It IS normal to get the oscillator running, and final grid drive, in CW position with plate switch off.

IT DOES THIS.

And of course, it seems to work just fine in CW mode, plate switch on.


I'm using the xtal, not the vfo, as the vfo dial has come loose and is waaaaaay of frequency.  I'm pretty certain back in early July when I was put this thing back together, I had the same problem using the vfo. I'll check this.


When I put a cliplead from the 12by7 cathode to ground, I get the oscillator, regardless of the mode switch.

The mode switch, the xtal switch, and the plate switch all seem to be doing what they are supposed to.

Now... where to go from here?  I want this stupid thing off of my work bench, its keeping me from starting some more interesting projects!

That lead us to say there is a wiring mistake on the CW-Phone switch terminal that goes to the plate switch.

This wiring has not been touched. I only worked on the modulator and speech amp sections. The thing USED TO work, GFH (among others) heard it.

[kf6pqt]

clarification... the hokey mods were in the modulator section only... rest of the tx seems bone stock.

[kf6pqt]

FIXED.

All roads returned to the mode switch. But it seems to be working!!! Aaaargh!

So, I went and bought the smallest tube of Deoxit I could find, and just now swabbed some on the mode switch (wafer rotary) contacts, and cleaned 'em up best I could.

WORKING!!!!! 

Thanks everyone for your help!

Now, on to fix the audio...

-Jason kf6pqt

[Jim, W5JO]

Well good.  My only issue with Deoxit is that it will eventually wear off.  If you can, turn the contacts so you can get to the wiper and use a pencil eraser to clean that part of the switch.  Usually that is where the problem is.   

Use a magnifier and be sure the contacts are in line where they should be.  Sometimes the little rivet will loosen over time.  If that should be the case, you will have to remove the contacts with a Dremmel then put the contacts back with a 2-56 screw and nut.  Then solder the nut to the screw once everything is aligned.

Another thing is those contacts can be reformed by heating them with a soldering gun or iron.  They will return the almost normal shape with heat application.

Hope everything keeps working