The AM Forum

Some ideas: Ditch the battery and run it off some solid state, variable bias current source.

Put diode and cap in a home of their own, and run a length of cable to a large (3 inch or better) 1 mA meter.

Should be easy to make a VLF head and a UHF head.  A TD should sing up to at least 700 MHz, if not higher.

http://www.americanradiohistory.com/Archive-Radio-Electronics/60s/1961/Radio-Electronics-1961-04.pdf


Matt

I remember seeing those tunnel diode projects when I was a kid, not yet knowledgeable in 'tronics.  There was even a little receiver article I remember from then based on the t.d. also, FM BCB or VHF aircraft AM? I think.

This is not the one I was picturing, but on page 62:

http://www.americanradiohistory.com/Archive-Poptronics/60s/63/Pop-1963-06.pdf

Sources through distributors, I saw the diodes for $36 to $100!, but are available on ebay from Russia, Latvia, Ukraine and Romania for good prices.

The published gate dip meter projects might be better in the long run, but the simplicity is attractive for playing around at least.

Apparently the published circuit worked, BUT a circuit suggestion - I would try adding an appropriate r.f. bypass capacitor(s) from the meter side of the diode right to the ground end of the LC circuit however.

Chapter 14, page 352 Figure 14.8 of this GE transistor manual is a similar circuit as Rufus' article and has the r.f. bypass capacitor:

http://w140.com/ge_transistor_manual_1964-ch14_td.pdf

Get a load of Figure 14.6 on the same page - 4 milliwatts cavity oscillator at 6 GHz!  1964.

Good luck OM.

I like that idea.

:-)

I was also thinking about a UHF choke in the path from anode to meter.  As I said, it would be nice to have a remote head and a large mA meter.