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 Post subject: Gonset G-33 Sensitivity Control
PostPosted: Dec Tue 04, 2018 10:48 pm 
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Joined: Jan Wed 25, 2012 8:24 pm
Posts: 12
I acquired a Gonset G-33 a few years ago and am finally getting around to restoration. One shortcoming was the "Sensitivity" control which switched between AM and CW. The former owner gutted the control. I have to replace it and a few other parts. Problem is the 20K pot had a switch which was SPDT. I had one of these radios years ago and don't remember if the switch worked when the control was fully counter-clockwise to put it in the AM mode. I assume it was. Is anyone familiar with this model? I probably will have to drill a hole in the front panel (ack!) and install a switch since finding a pot with a SPDT seems unlikely. Then too, I don't know if the pot is audio taper. It seems to me that it was. Thanks!

Mike Kuehl W9ZSL


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 Post subject: Re: Gonset G-33 Sensitivity Control
PostPosted: Dec Wed 05, 2018 12:10 am 
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Joined: Dec Sun 14, 2008 3:33 pm
Posts: 862
Location: Tokyo
An internet photo suggests AM ('phone') was clockwise, CW counter clockwise.

Move this question to the Communications Receivers forum. Someone there will know. And don't drill a hole!

Rob


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 Post subject: Re: Gonset G-33 Sensitivity Control
PostPosted: Dec Wed 05, 2018 3:07 am 
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Mike,

I don't have a G33 schematic but the switch probably simultaneously killed the AGC and engaged the BFO when taken out of the full gain AM position; in this case the switch would switch states as you enter/leave full clockwise rotation. Depending upon how the receiver is set up, a dual pole switch might have been used but I would get a schematic before replacing anything. I suspect the G33 is a fairly basic receiver so the BFO function may be obtained by causing an IF stage to go into oscillation.

Different tapers will be used for a RF gain/sensitivity pot depending upon how it is implemented so again the schematic is important here.

And I would stay away from drilling any new holes. Pots with switches attached are pretty common and many pots (and switches) were designed so that the correct combination could be put together in a service shop so you may be able to transfer a switch from one pot to another. If a complex (i.e. dual pole) or other oddball switch is needed, then use the switch on the pot to control a relay that will provide the necessary poles.

Rodger WQ9E


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 Post subject: Re: Gonset G-33 Sensitivity Control
PostPosted: Dec Wed 05, 2018 9:59 am 
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Joined: Dec Sun 14, 2008 3:33 pm
Posts: 862
Location: Tokyo
Tube line-up: 6BE6, 6BA6 (2), 6AV6, 6CM6, 6X4.

I couldn't find an online schematic but it's fairly obvious: 6BE6 converter, two 6BA6 IF stages, 6AV6 det/AVC and first audio, 6CM6 audio output, 6X4 rectifier. The IF is 1650KHz. No separate BFO tube, no BFO pitch control. Regeneration in one of the IF stages would be the easiest, cheapest way, and would explain the 'sensitivity' control pot with an AVC on/off switch.

Is a schematic available? Do you have the manual? If so, what does it say about operating the 'sensitivity' control? Perhaps, as Rodger suggested, it's an IF gain control, that in one extreme position, shorts the AVC to ground and sets one IF stage into oscillation. There's bound to be a way to get this to work. No need to drill a hole.

I remember this receiver from the early 1960s. IIRC, Radio Shack or Lafayette offered a rebadged version, at a higher price.

Rob


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 Post subject: Re: Gonset G-33 Sensitivity Control
PostPosted: Dec Wed 05, 2018 6:33 pm 
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Joined: Jan Wed 25, 2012 8:24 pm
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I do have a schematic / manual reprint. The switch on the sensitivity control is SPDT and active in the fully-clockwise position. Past the click is AM. Go counter-clockwise past the switch click and you're in CW / SSB mode. I didn't have any problems with my original G-33 and worked 38 states with the radio. The "BFO" was sensitive to vibrations because if you bumped the cabinet, it would warble. Finding a replacement for that control is going to be tough considering the switch is SPDT and works when in the full-clockwise position. I certainly don't want to drill a hole! The cabinet is in exceptional condition. I also acquired another DX-20 XMTR that I can pair with the Gonset to recreate my early 60's Novice station.

The switch connected to the control is at the top right-of-center in the diagram with the control itself in the cathode circuit of V2.


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 Post subject: Re: Gonset G-33 Sensitivity Control
PostPosted: Dec Wed 05, 2018 7:32 pm 
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Mike,

Thanks for posting the partial schematic. For CW that switch grounds the AVC and removes the ground from the feedback loop created by C14 and C15 which places V3 into oscillation.

You may have difficulty finding a pot with a SPDT switch but those with SPST switches are easy to find and that can be used to control a small relay to provide the needed SPDT function, you may have to settle for a push/pull activated switch because typically these switched pots are used for power switches with the switch changing state at near full CCW instead of full CW. But this modern switch plus relay will allow you to avoid drilling any new holes and with the push/pull type switching you would have variable IF gain for both CW and AM.

Rodger WQ9E


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 Post subject: Re: Gonset G-33 Sensitivity Control
PostPosted: Dec Wed 05, 2018 8:08 pm 
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Joined: Jan Wed 25, 2012 8:24 pm
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The push-pull switch with relay is a good idea. There is enough room on the chassis for one. I tested the tubes yesterday and ordered three NOS ones. There is a leaky 10 mfd electrolytic. I have a replacement for that. I just hope the main filter cap is good. It's a funky Mallory PC-mount type with pins instead of terminals. I'm working on a few projects. Had a bout of heart problems and they put a pacemaker in me this summer. Had a lot of stuff to do that has been put off for the past three years. One of them was a total rebuild of a Heathkit AT-1. I scored a chassis, the switches, coils and other odds and ends then acquired everything I needed...new components, front panel and cabinet. I have to re-paint the cabinet but that project is finished AND IT WORKS!


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 Post subject: Re: Gonset G-33 Sensitivity Control
PostPosted: Dec Thu 06, 2018 2:30 am 
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Joined: Dec Sun 14, 2008 3:33 pm
Posts: 862
Location: Tokyo
A minor footnote: Lafayette Radio sold the G-33 as the HE Forty One. The only internet reference I could find is this short ARF thread:

viewtopic.php?f=5&t=297404

My novice station was not unlike yours: National NC-105 (also a 6BE6 converter followed by two 6BA6 IF stages) and a homebrew 6L6 transmitter, about 25W. (I moved up to an HT-40 when I got my general). Anyway, that combination worked well enough for lots of 40 meters contacts. Nice thing about the 6L6G was watching the shifting violet gas patterns as I keyed it. Quite mystical for a 14 year old, sitting in the dark at 2 a.m.

I hope your heart problems are behind you. I envy you the fun you're going to have with that G-33 and DX-20, AT-1.

Rob


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 Post subject: Re: Gonset G-33 Sensitivity Control
PostPosted: Dec Thu 06, 2018 5:24 pm 
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Joined: Jan Wed 25, 2012 8:24 pm
Posts: 12
One of my other projects was building an exciter based around a 6AG7 and 6L6. Got the schematic out of the '49 West Coast Handbook. I'm going to use it with a parallel 807 amp from the '57 ARRL Handbook and AM modulate through ART-13 iron with another build from the '49, I have a couple 600 VDC power supplies and should get a 120 watt input rig when finished. Heart is doing better. The pacemaker helps a lot. I just hope one of my RF projects doesn't fry the thing, HI,HI!


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