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 Post subject: Heathkit VF-1 with three tubes
PostPosted: Apr Fri 10, 2020 5:02 pm 
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Location: Bath, Maine 04530
I am getting ready to restore a Heathkit DX-60. I remembered that I had a box with some VFOs in it. I found this VF-1 and started to open it when I discovered it had been modified with the addition of another tube and a pot in the front. I went all over the interweb to try and find what this mod is with out any luck. Does anyone know if this mod was ever published or is it just a one off. I might have to stripe it down and rebuild it stock. I have not put any power to it yet. There are a couple resistors disconnected. The tubes are: OA2, 6AU6WA, 6AL5, With a 5787 under it. Also had a neon added. Any help would be great, Thanks, Carl.

EDIT the standby switch is wrong but I have the correct one.


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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Fri 10, 2020 5:06 pm 
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Those ceramic tube capacitors will be bad. Personally, I'd put it back stock. The workmanship is horrendous. I've seen most of the modes for the VF-1 and that is one I've never seen.

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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Fri 10, 2020 5:09 pm 
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I have not seen the mods posted on the internet. Likely amplifies the 10 volts output. You can try it as is, or simply remove the mods.


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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Fri 10, 2020 5:46 pm 
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Location: Falls Church VA 22180
Looks like 4 tubes to me.

Pete, one mod I remember was an added tube as a cathode follower buffer to eliminate loading and chirp as well as feeding into a low impedance circuit. Maybe a Johnson?

Brad


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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Fri 10, 2020 7:10 pm 
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Brad, the 6AU6 is the Colpitts oscillator, that only leaves the pencil tube as a possible buffer? The layout and wiring suggest it is not in the RF path.

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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Fri 10, 2020 7:34 pm 
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Pete, there are 3 tubes on top and only a 6AU6 and 0A2 were original, The one back by the BNC connector has a lot of RF appearing wiring underneath. I dont know what the subminiature tube was used for.


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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Fri 10, 2020 7:52 pm 
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I think it’s been converted for FSK. The additional pot on the front panel adjusts the shift. This modification was published in the 1960’s.


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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Fri 10, 2020 9:06 pm 
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hbr nut wrote:
I think it’s been converted for FSK. The additional pot on the front panel adjusts the shift. This modification was published in the 1960’s.



Good eye!!!

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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Fri 10, 2020 9:17 pm 
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I will strip it down to the chassis and rebuild it all new. Carl

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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Fri 10, 2020 10:10 pm 
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Maybe a pilot light in the hole drilled for the extra pot.


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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Sat 11, 2020 12:05 am 
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J. Hill wrote:
Maybe a pilot light in the hole drilled for the extra pot.

I got ahead of you on that one. LOL Thanks, Carl

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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Mon 13, 2020 4:10 pm 
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Joined: Jun Mon 22, 2015 6:21 pm
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Location: Bath, Maine 04530
hbr nut wrote:
I think it’s been converted for FSK. The additional pot on the front panel adjusts the shift. This modification was published in the 1960’s.

Sure looks like you guys are correct. FSK. I have found similar mods on the Heathkit DX-100. Thanks for your time, Carl

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 Post subject: Re: Heathkit VF-1 with three tubes
PostPosted: Apr Sun 19, 2020 9:44 pm 
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Joined: Jun Mon 22, 2015 6:21 pm
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Location: Bath, Maine 04530
Peter Bertini wrote:
Brad, the 6AU6 is the Colpitts oscillator, that only leaves the pencil tube as a possible buffer? The layout and wiring suggest it is not in the RF path.

Peter, The pencil tube is a voltage regulator about 100 volts. Carl

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