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 Post subject: Gonset Communicator III front end mod
PostPosted: Jun Wed 15, 2022 11:06 pm 
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Location: Milwaukee WI 53219
I saw a tube and resistor replacement mod for a quieter front end for the receiver. The article was aimed at the 2 meter version and the author said the results were quite noticable. I'm wondering if the mod is worth doing for my 6 meter version of that transceiver. All tubes mentioned here are pin compatible.

The author replaced a 6BS8 with a 6DJ8 which is supposedly much quieter due to its higher transconductance, shorter internal grid structure due to the use of a special grid frame, lower internal capacitance and can operate at a lower plate voltage. A resisitor was added to knock plate voltage down from 125 to 90 volts and its mentioned other needed voltage parameters fall into place along with that reduction.

My 6 meter version uses a 6BQ7 and I'm wondering if there would be anything to gain by doing the mod on mine. Has anyone here tried this mod on either version of the Communicator III or other radio using these tubes?


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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 12:51 am 
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You might be better off adding a nuvistor preamp ahead of the 6BQ7. The 6CW4 or 6DS4 are fairly low noise tubes and have a nice gain factor. You might consider dropping the gain of the 6BQ7 to reduce internal tube generated noise. Or get rid of the 6BQ7 completely and use 2 nuvisors. Or, put a low noise MOSFET preamp ahead of the 6BQ7 and also dropping the gain of the 6BQ7.
Of course, this is not a highly sophisticated transceiver, so is it really worth the time and effort to diddle with the front end. This is not a band that's overrun with AM signals.

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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 2:57 am 
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Location: Milwaukee WI 53219
6 meter AM gets used twice a week. Tuesdays for a local net and Thursdays talking with a local friend. I worked almost all states back in the good old days and I'm hoping for the chance to do so again.

I have a mosfet 6 to 10 meter converter that also can run just the 6 meter preamp. But I would prefer the easier tube and resistor swap and keep the converter on a different receiver. I'm happy with the receive as-is but if there is a chance this easy mod actually works I'll do it.

I would just plow ahead and do it without asking for opinions but Audiophile I'm guessing are the ones who drove up the price on the 6DJ8 when they discovered it for audio preamps. IIRC some of the popular tube sales sites have no stock and their prices were in the 30-40 dollar range. I got the radio cheap so it won't kill me to buy an expensive tube but I don't want to do it without knowing more about if it will be worth it in my situation.


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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 4:58 am 
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Greetings to forumuser and the Forum:

"Quite noticeable" isn't much of a yardstick. If you could get noise figure or sinad measurements before and after, that would be a lot better. In the absence of such numbers, I would hesitate to change to a tube like the 6DJ8. They are hideously expensive if you can find them and I seriously question whether or not they would be worth the money.

Back in the 1960's, the front end tube of choice was the 6BZ7, which was supposed to be better. I think later tubes are double-marked 6BQ7 / 6BZ7, but in the old days, the plain vanilla 6BZ7 was supposed to be the better tube. A lot of subjective opinion there too without a lot of objective fact.

As long as the receiver performs well enough to hear your friends, then I'd leave well enough alone. If the band ever opens up, you will probably discover quickly whether or not your receiver is adequate.

Also bear in mind.... unless you are running the high power amplifier after the Communicator, you are probably only getting 7 or 8 watts out. Anyone you work (unless its another Communicator) is likely to be running at least twice that much power, or 3 dB.... and I very seriously doubt that the 6DJ8 will give you 3 dB of improvement.

Just my $.02 worth; your mileage may vary.

Regards,

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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 1:49 pm 
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I hear ya. The article was just a one page pdf file lacking key before/after measurements and was about the 2 meter Gonset which may be noisier than my 6 meter version. His observation was the internal noise was so low now that he had to turn the volume up higher than before to hear it. He didn't come right out and say it so I have to assume that sensitivity stayed high.

There is a guy about a mile from my place advertising a NOS 6DJ8 on ebay for 20 bucks. It certainly doesn't look NOS in his pics but for half the price of new maybe I'll get it and try the mod. I'm not really looking to grab extra signals out of the noise level that I couldn't hear before. I would like to hear a bit less internally generated hiss on the signals of some of the weaker guys on the net or when I have the radio running for a long period of time listening for a band opening. Maybe I should add a tone control instead. :lol:


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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 2:53 pm 
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I would go with Pete's third suggestion and add a single stage low noise solid state amp ahead of the existing cascode stage, and maybe drop the gain of it a bit.

Modification of the three is almost nil in this case since you don't have to fool with tube heater voltage string/add resistors like you would when changing tubes. The preamp can just be inserted in the signal path at the antenna jack for the III's receiver input and powered by one or two 9 volt batteries depending upon circuit configuration (some of the SS cascode designs will want higher voltage). Any of the 70s through early 80s ARRL handbooks should have a suitable design. The end result will be less expensive, work better, and without modification to the Communicator.

Jim, My Communicator III has the 6BZ8 indicated on its schematic, probably a production change over time. Voodoo audio types have discovered this tube along with most of the nuvistors for their magic mouse milk preamp designs so all have an idiot tax added to their market price.

Rodger WQ9E


Last edited by rsingl on Jun Thu 16, 2022 3:51 pm, edited 1 time in total.

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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 3:49 pm 
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Location: Milwaukee WI 53219
In it's defense, the 6DJ8 is a drop-in replacement and needs only a plate resistor added.I'll test with the preamp half of my homebrew 6 to 10M converter. I have a couple ARRL books from the 70s. I'll see what they have to offer and what I have in my parts stash.

thanks.

edit: Would I reduce gain on the tube front end by tweaking its input transformer or would I have to change components to reduce it's gain properly?


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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 4:22 pm 
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About 1970, there was an article in QST about modernizing a Cimmunicator. I saw it recently, but don't remember a date. And yes, a solid state preamp.

That article is now further in the past than the time between Communicators and that article. It was about the time whe there were articles about moving AM VHF rigs to FM. Transmit easy, more work needed for receive.


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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 6:11 pm 
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Just checked the QST/Ham Radio magazine archives for Gonset Communicator. There was an article in QST in 2014 and then jumps to July 1962 There was also some articles back in 1958 but none on a modernization.
Maybe it was in 73 or CQ magazines.

Jul 2014 - QST (Pg. 95)
The Gonset Communicator
(Vintage Radio)

Author: Allison, Bob, WB1GCM
This item is not available for download by Members | Why not?
(For QST articles from 2012 forward, use the archive search function from within any digital issue.)
Report a problem with this entry

Jul 1962 - QST (Pg. 49)
Gonset GC-105 2-Meter Communicator
(Recent Equipment)

Author: Tilton, Edward, W1HDQ
Article: QST Archive [PDF]
Report a problem with this entry

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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 8:54 pm 
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"The '70 Communicator" by Doug Blakeslee, QST for July 1970, page 15. He actually repackages it, and the preamp is a common source jfet.

I had it out toreread Sabin's article on Solid State Receivers.


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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 10:03 pm 
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I found it just using "communicator" as the search word. Search Gonset communicator and it doesn't come up.
Typical JFET preamp.

Years ago I built RF preamps for my Kenwood TS-600 (6 meter) and Kenwood TS-700S (2 meter) multimode transceivers using a MOSJET 3SK48. This transistor is low noise/high gain and was also used in the Sony IC-2010 portable receiver. They worked very well and are still in both transceivers.

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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 11:18 pm 
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I typed in all forms and combinations of words for google searches. I'm thinking their personalized suggestion models for me are not the same as what you guys have.

The main place I saw with qst archives stops at 1969 and I couldn't find the 1970 magazines anywhere else. Typing in just "communicator" got me zero hits for anything radio related let alone something specific for the Gonset Communicator 3. Even searching "3sk48 preamp circuit" brought up a bunch of preamp circuits but none I could find for that fet. I won't bother listing all the other word searches I tried. Hard to believe its so difficult.


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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Thu 16, 2022 11:29 pm 
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I don't find websearches find things at that American Radio History site. Sometimes things show up, but it may be at other sites.

Even the search engine there seemstogive too many results even when I know a specific article (but not title).

The QST article is nothing special, but since it's about a Communicator, proof of solid state preamps. A change to the output coupler, solid state diodes in the power supply, and a transistor audio chain for transmit.

Any of the Handbooks or ARRL VHF Manual from around thenhas suitable preamps. And in the FM and Repeater Manual that came out fifty years ago. The preamp is generic, so either it came from a previous article, or was used as an example later.


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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Fri 17, 2022 12:16 am 
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forumuser wrote:
I typed in all forms and combinations of words for google searches. I'm thinking their personalized suggestion models for me are not the same as what you guys have.

The main place I saw with qst archives stops at 1969 and I couldn't find the 1970 magazines anywhere else. Typing in just "communicator" got me zero hits for anything radio related let alone something specific for the Gonset Communicator 3. Even searching "3sk48 preamp circuit" brought up a bunch of preamp circuits but none I could find for that fet. I won't bother listing all the other word searches I tried. Hard to believe its so difficult.


My search for the Communicator was done in the periodical archive section of the ARRL web site. If you're not an ARRL member, you can't access their magazine archives.

The 3SK48 preamps were designed by me so they don't appear on the web. However, generic MOSFET RF receive VHF preamp schematics are abundant on Google: https://www.google.com/search?q=mosfet+ ... efox-b-1-d

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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Fri 17, 2022 5:28 am 
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Greetings to forumuser and the Forum:

Quote:
I would like to hear a bit less internally generated hiss on the signals of some of the weaker guys on the net or when I have the radio running for a long period of time listening for a band opening.


The radio does have a squelch control, you know.

Regards,

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KB6GM
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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Fri 17, 2022 3:17 pm 
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Good common sense suggestion. I tried using the squelch but on some days it was opening and closing so much from atmospheric conditions or neighborhood noise that it became as annoying as the constant hiss.


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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Fri 17, 2022 3:44 pm 
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In the late fifties, there was a long article in CQ about mods to the Communicator. It was a compendium. And no, I don't recall the date, and CQ isn't generous about back issues.

But I'm sure one of the tips was about using the squelch to copy CW. Not perfect, but the squelch gave a bigger contrast between on and off.


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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Fri 17, 2022 10:50 pm 
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mblack wrote:
In the late fifties, there was a long article in CQ about mods to the Communicator. It was a compendium. And no, I don't recall the date, and CQ isn't generous about back issues.

But I'm sure one of the tips was about using the squelch to copy CW. Not perfect, but the squelch gave a bigger contrast between on and off.


There was an article called "Communicator Notes", January 1957, author Don Stoner.

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 Post subject: Re: Gonset Communicator III front end mod
PostPosted: Jun Mon 20, 2022 3:32 am 
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I get to do some experimenting with tube replacement. At a swapfest today there was a large tube seller that had a bunch of NOS and used 6DJ8 tubes so I bought one of each at very good prices. I'll post in the near future with my results.


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