The AM Forum

Hi Folks,

I'm working on a DX100B that tunes up okay on 160 and 80 but not on 40 and above. It looks like L7 10mH rf inductor is open? It fails a continuity check and reads about 110 ohms of resistance. What would be a suitable replacement for L7? I assume I can't just throw any old 10mH choke in there but I'm not sure how to select the correct one.

Thanks 73
kevin - KD1NW

A continuity check implies you expect a very low resistance, seems to me 100 ohms is reasonable.  I don't have a diagram that shows the various part nomenclature (i.e. L1, L2, etc), The only 10mH I spotted is in the plate path to the 12BY7.  If it was open the TX wouldn't work on any band.   Check the plate voltage on the 12BY7, if is is OK so is the choke.

If that choke is not L7... let us know where it is in the circuit!

GL,  N2BC

Hi,

Thanks you're right, I see my mistake now and how it wouldn't work on any band. It is the 10mH in the plate path to the 12BY7 that I was questioning. I was expecting a lower resistance like the other the inductors in the same plate path which are around 1 ohm. I'll do what you suggested and check the plate voltage of the 12BY7. If it's okay then its back to the drawing board. Thanks again and sorry for the confusion.

73
Kevin - KD1Nw   

387 V, looks about right. Thanks

VFO issues?

Possibly, but the vfo appears to be working. I'll go through the "In Case of Difficulty" section of the manual again, so I can have an accurate description of my problem.  That way I can spare torturing everyone with a guessing game. After making such a basic error with L7, I want to make sure I at least have a proper description of the issue before I ask for more help.  :-\

Thanks 73

Did you try a crystal on 40m ?

I've had problems with a dx-100, cracked wafer inside, wound up replacing the whole VFO box.
Also had a open cap under the chassis cause a similar issue, off hand can't remember which one.

GL,

Rich
n2ry

Thanks for the reply Rich. Actually, I can't use crystal operation on it. The person who built it didn't include the crystal socket and instead ran the connection to an SO-239, I guess for an external VFO. The other SO-239 looks like it is for a mod monitor connection possibly. These two would have been used for the SSB adapter but have been re-purposed.

Anyway, I'm embarrassed to say, it appears what ever I was doing previously to tune up on 40 meters was obviously operator error. I just went downstairs and went through the tune up procedure on 40 meters. There is no issue. Plenty of drive 5 to 6ma easy, 250 ma plate at 700 volts. Around 110 -120 watts CW output.

I'm really sorry to have bugged everyone on this one.. thanks for trying to help

Thanks 73
Kevin - KD1NW

Perfect ending Kevin .......  GL hope to hear you on the air sometime

Rich
n2ry

No other way to learn about ur rig! :D

I think it is safe to say everyone has done pretty much the same thing at one time or
another! I have.

Thanks Bear  :)

WA2EHV generously gave me the radio,  giving me another radio to work on! It was a little bit of a challenge because there are a number of undocumented mods. Even the spot button is not wired up anything like the standard mod.  Anyway, its working and sounds pretty good. Now I need to put into an operating position and get it on the air. I'll let him klow and maybe he'll be able to hear it on the air! Here's a pic.. she's not a beauty queen but that fine by me!