Ah! Just spotted the later posts here. Re the three resistors in the HT line of the Model 59 (Megacycle Meter); I cannot offer any comment on the rationale of the two 6k8's. The separate 5k6 allows a tapping which relates to the fact that the 59 will also act as a wavemeter, detecting RF signals and indicating them both on the meter and via headphones.
The manual for the 59 describes how it can best be used in various roles as a GDO (including antenna work) and also as a means of measuring L, C, Q and mutual conductance. Sadly, it's over 3MB so I cannot upload it.
As stated above, I built a FET GDO back around 1970 but there have been times when it has given spooky readings which were hard to explain, most recently, when playing with a 5MHz dipole. If you spend time Googling "GDO's" (which I have
) you find questions here and there about FET GDO's (and Wrangler has expressed similar concerns). I think some people believe that a valve may be better, or even a bipolar transistor, but I'm not stringent on this; whatever rocks your boat! I am interested in building another GDO, I'm now cooling off the tunnel diode option and heading towards an Acorn, perhaps a direct copy of the Model 59.
B