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Author Topic: T-368 Exciter  (Read 26643 times)
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k4kyv
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Don
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« Reply #25 on: February 04, 2010, 11:23:28 AM »

Brian, Do you have a schematic for the power supply you used for the T-368 exciter? I have one here and need to build a supply. Thanks. I don't think anybody mentioned it here but most of the PTO's of that type have a fundamental frequency of 1-2 MHz so you can cover 160 by bypassing the doubler.

The T-368 PTO has a fundamental frequency of 1.5-3.0 mHz.  The lowest frequency range feeds the PTO signal directly to the output stage.  The other ranges insert one or more multiplier stages in between.

Another mod I made to mine was to add a vernier drive mechanism to the main tuning knob to slow down the tuning range.  I used a Jackson Bros. mechanism.  They come in two forms, to English measurements and to metric.  The English size fits the shaft snugly with zero slop.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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This message was typed using the DVORAK keyboard layout.
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k4kyv
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Don
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« Reply #26 on: February 04, 2010, 03:33:29 PM »

If the shaft is too snug, you may need to turn it down slightly.  You have to  remove it to cut it to length anyway. At the time I didn't even own a drill press, so after cutting and de-burring the shaft I chucked it in a hand drill and used automotive emery cloth. I tried to insert the shaft into the drive, but it wouldn't fit, so I  revved up the drill while gripping it by hand with the emery cloth, and "polishing" the shaft. I did this over and over until I wore away enough metal to allow it to snugly fit, requiring some, but not too much, force to shove it in. That way, the drive and shaft were perfectly aligned.

If the shaft fits loosely on the drive, I would suggest finding a 1/4" diameter piece of brass rod and fabricating a new one, using the above procedure.  My previous attempt involved using a National Velvet Vernier mechanism, which ended up slightly eccentric due to lack of quality in the drive and a loose fit on the shaft.  The result was that the knob would noticeably bind once per turn while rotating it.

The Jackson Bros drive requires enlarging the shaft hole in the panel and drilling two mounting holes in the panel, but these are hidden by the knob. The previous National drive required making a mess out of the panel, but luckily I had a spare panel from the junker I used to salvage the bandswitch section from.

Yes, that modified exciter unit required a lot of work, which took me a whole summer to complete and get it working to my satisfaction.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

- - -
This message was typed using the DVORAK keyboard layout.
http://www.mwbrooks.com/dvorak
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