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koØm
05-28-2013, 10:46 AM
Greeing to all,

I have an interest in building an amplifier around a GS35-b Triode tube, I am going to make this a multi-band amplifier. I have the complete Tank circuit from a Drake L4-b and, I am trying to use this as my output network.

As with any project, there are some issues, the band switch has been repaired because the contacts that are in use for the 10 meter band have been fried. I serviced the switch and, indexed the useless contacts out of the line of fire; this left me with the ability to only support 4 bands. 80 meters thru 15 was a complete no-go.

I dumped the vertical 80 meter coil and re-worked the rest of the tank coil and switch; I added a tap for fewer turnes at 10 meters, used the old 10 meter tap at the 15 meter switch etc. Coming to the end of the coil, where the 40 meter tap was, that tap is now connected to the load gang. In position "10 m" all the taps are shorted out except 2 turns; in the "40 m" position, none of the taps are shorted by the switch and the whole coil is active in the network.

I am working with a MFJ-259 Analyzer (the first model) and, with a Plate load of about 2500 ohms, (planning on running about 4000 volts at 500 mills) all ham bands fall into tuning range.

Now that you have the setup, here's the question: "For a given frequency, if your circuit tunes with more capacitance (Tune) in one position but also tunes in another position with more turns on the tank coil but less Cap on the Tune side, what could be said about the coil, the, Q and which position for that "Given Frequency" would be best to tune at"?

Mel

koØm
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K7SGJ
05-28-2013, 10:51 AM
Tell me what the specifics of the band switch are. I may be able to help you out with another one. How many sections, positions, composition, and I would assume it's not a make before break style.

koØm
05-28-2013, 05:45 PM
Tell me what the specifics of the band switch are. I may be able to help you out with another one. How many sections, positions, composition, and I would assume it's not a make before break style.
It's the stock band swiitch from the Drake L4-b amplifier

http://i111.photobucket.com/albums/n150/Paws264/2011/DCP01047.jpg (http://s111.photobucket.com/user/Paws264/media/2011/DCP01047.jpg.html)

It was a 5 position switch with a shorting wiper with 2 contact points per band.

http://i111.photobucket.com/albums/n150/Paws264/2011/DCP01048.jpg (http://s111.photobucket.com/user/Paws264/media/2011/DCP01048.jpg.html)

The two sections fit together and the coil is soldered in the aft side.

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koØm
05-28-2013, 05:50 PM
This was how it started out but, with the 80 meter coil installed but, the circuit would not tune so, I dumped the coil and the box it was mounted on.

http://i111.photobucket.com/albums/n150/Paws264/2011/IMG_20110701_113416.jpg (http://s111.photobucket.com/user/Paws264/media/2011/IMG_20110701_113416.jpg.html)

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K7SGJ
05-28-2013, 07:23 PM
Okay, I haven't been inside of the L4 series before, and didn't know how they did the band switching. Unfortunately, I wouldn't have anything close. Sorry, but good luck on the project.

koØm
05-29-2013, 05:08 PM
I have this burning desire coupled with a bunch of parts lying around but, that Tune Capacitor will not take the 4000 VDC that it really takes to make that tube work. I have choices, buy a Vacuum Variable and a heavy-duty band switch or, take out the GS35b tube and stick a 3-500z in it's place.

The stuff has been taking up space too long.

.

NY4Q
05-30-2013, 01:44 PM
buy a Vacuum Variable and a heavy-duty band switch

Do this...