Gonset G77

[sndtubes]

Just picked up a pretty nice set of Gonset mobile twins (G77A / G66B) at Dayton.  I haven't tested them yet, but probably need some work.  I was wondering if anyone knew of any mods out there for the G77 transmitter?  Google didn't really return much.......  Any other thoughts/comments also welcome.

[Pete, WA2CWA]

Why not get the transmitter up and running to specifications and then decide if any modifications are needed for it. Considering the lack of diddle documentation for the G-77 on the web, most users probably were/are satisfied with its performance as designed.

[WD5JKO]

While I don't always agree with Pete, in this case his advice is sound. 

Bring up that rig stock, or as stock as possible. If the vibrator is shot, and If you are using the Tx as a base station, then maybe try feeding the vibrator transformer directly with 12VAC.

The modulator is unique in many ways. There is an effort made to shape the frequency response with both a low cut, high cut, and a mid-range boost. It will be interesting to evaluate the design. The .PDF schematic on the Bama mirror seems to miss some of the circuitry, in particular between the 12AU7 audio driver and the interstage transformer.

The use of 6BQ6's with zero bias, G2 driven is a Gonset proven method. On the G76, it is similar, but uses a 6CM6 audio driver (6AQ5 variant with 9 pin base) to drive a pair of 6DQ6's. With some simple mods, I've made the G76 modulator very good where stock was just fair.

Good luck,
Jim
WD5JKO

[WQ9E]

I have a G77A/G66B pair and the audio sounds "OK" with a decent dynamic mic, I have found a Shure 444 sounds pretty good.  The audio is definitely range restricted but it is a lower power mobile transmitter so it was a good choice for the intended application.  It is not broadcast quality but it sounds better than the majority of the Japanese all mode rigs running AM.  I wouldn't place any bets on how well the stock modulation transformer will hold up running old buzzard style transmissions if you really extend the LF range.

I just picked up some Morrow gear, an MBR-6 receiver and a couple of transmitters (MB-560A and MB-565).  The Morrow units have switch selectable restricted range with clipping or extended range (100 hz-10 Khz. rated) so it will be interesting to see how different they sound.

[sndtubes]

Thanks, guys.  Oh, I had intended to get it going "stock" but was just curious if there were any "upgrades".  Yeah, unfortunately the manuals on Bama are not great, so I'll need to keep a lookout for better ones.  These units appear mostly stock, although someone has replaced the vibrator with a transistorized oscillator circuit.  This will be a longer term project as I have others waiting before this one.  You all know how that goes!

[WD5JKO]

although someone has replaced the vibrator with a transistorized oscillator circuit.  This will be a longer term project

  I wonder if you can take a picture, or can post a schematic (if available) of that oscillator circuit. With 12V, to get decent efficiency, the old method was to use germanium power transistors, and hope the zitters don't get too hot and go into thermal run-away. Today with modern power FET's with just a few milli-ohm on resistances (RDS ON), there are options a-plenty to improve upon these old circuits. I re-did an old Adcom DC-DC converter using power FETs where I drove the FETS with a PWM chip such that the LV B+ was regulated. I can pass that circuit along if anybody is interested.

Jim
WD5JKO