Monday, October 12, 2009

My New "Boonton" Model 59 GDO

Here is my big acquisition from the Nutmeg Hamfest this weekend. It is the classic Measurements Corp. Model 59 Megacycle Meter. Some of us would know it as the "Boonton Grid Dip Oscillator." From what I've been reading, a variant of this unit was first produced in World War II. The manual, available here and here on the Internet, bears a 1947 date. The company was sold to Edison in 1953, so this unit was probably produced in the early 1950's. (The meter/power supply unit is serial #750, the oscillator head is #695, the coil set is #734.)

The developer was the well-known engineer Jerry Minter. (See his interview that prominently shows the Model 59.) His was one of a number of instrumentation companies active in Boonton, N.J. after the War. There was no connection to Hewlett Packard. (An impression I had at one time.)

I used a Model 59 extensively in the 1960's and 70's, but I did not know that it was a classic even then. Now, it's very satisfying to have my own! It is far superior to the Heath GDO and tunnel diode dipper that I have also used. I see one advertised at $75 on E-Bay, but I got mine for about half that.

The grid dip oscillator is a very handy item for generating signals, checking for resonance, and making rough frequency measurements. This one covers the range 2.2 to 420 MHz in 6 bands.

[Click photos for more detailed versions.]

It is necessary to inspect all new equipment here at AA6E. (The unit was in remarkably good condition. It worked the first time and only needed a little cleaning.) This device had wonderful "build quality" -- as we say these days. The important part is the tunable oscillator assembly, which is meant to be hand held. The inner works are all gold plated (!) and very sturdy. A single 955 "Acorn" triode tube is the active element. Lead inductances are kept very low to allow UHF operation.

Dial calibration is meant to be quite good. Each unit's coil set is supposed to be calibrated to work with a specific oscillator head, although my coil set's serial number doesn't match my oscillator. The tuning "feel" is very smooth.

The power supply uses a 5Y3 GT rectifier and an OD3/VR150 voltage regulator tube. The red filaments and the purple regulator discharge, along with the incandescent (!) pilot light, are a treat by themselves. Not shown is the neat wiring harness beneath the power supply chassis.

Now I need to build another RF gadget!
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