The AM Forum

A friend of mine last evening gave me a Siltronix 90-6 VFO he had left over from his Crazy Band days. (He's a ham now, so I guess we can forgive him his youthful transgressions  ;D)

As far as I can tell, it's intended to work only with certain synthesized CB radios and won't do me any good on my DX-60A. Is that correct, or am I missing something?

73,
ldb
K5WLF

It's been years but; ifn I remember the 90-6 ran at 7.8Mhz, or there abouts. The radios used the 3rd (23Mhz) overtone to operate on. So you should be able to suck the VFO master osc. stage down to 7 Mhz without too much trouble. That'll get you 40 - 10 at least.

A quick Google:
http://www.cbgazette.com/siltronix_chart.html
http://www.cbtricks.com/miscellaneous/vco/siltronix/model_90/index.htm

I did that very thing, back in the day. My dad was into CB and picked up a model 90 somewhere. It wouldn't work on his old Tram, so he gave it to me to hack up. I cranked it down to 7mhz and used it on my homebrew 25w CW transmitter. I remember that large vernier knob for the VFO worked great...can't remember how I killed the output during receive, but I did it somehow. :-)

Dave WB4IUY
www.WB4IUY.net

Thanks for the info, y'all. I WAS missing something as I read the manual. The part about the fact that the oscillator was running at 7+ MHz. I just paid attention to the part about the final output freq to the CB.

Thanks again,
ldb
K5WLF

I had played with one a couple of months back and re-wound the tank inductor. It's now parked on 75m. The only thing is I don't think it has enough output in stock form. If I get the Harvey Wells running this weekend, I'll revisit it and see.

Phil

Siltronix was courtesy of Swan so if cheap they are worth picking up for the drive assembly itself.  You can shift the VFO as needed or use it as a basis for a homebrew VFO. 

The early/mid 70's ARRL handbooks contained construction details for a homebrew VFO with an additional SS output amp stage for providing greater excitation for transmitters that needed more drive.  This would provide a good design for an add on amp if the VFO doesn't provide enough output for your rig.

It is definitely a nice drive setup. I've got the '75, '76 and '77 ARRL Handbooks, so I oughta be able to find the VFO project. If I can get the Siltronix slid down there, it'd be a nice touch to create a new dial scale for it. That'd let me know if I still remember how to run the CAD software.

ldb

Phil,

UPS just dropped off my new frequency counter, so I you have any notes or tips left over from your conversion project you'd like to share, they'd be appreciated. I'm going to try and get the Siltronix so it'll feed the DX-60A on, at least, 80, 40 and 20.

Thanks,
ldb
K5WLF

Yes, and you could use a frequency divide by 2 to get it down to 75 m and a divide by 4 to get it down to 160.  Idea courtesy STeve QIX.  Might also take some filtering to get rid of the harmonics from the digital stuff

Al

Larry,
           How's it going with the Model 90? I had to take a break on mine so I could get the Bandmaster going, but I'll be back with it in a few days.

Changing the freq. output was experimental by winding a new tank coil and playing with the number of turns and it's now generating RF in the 75m range. Just by playing with the fixed capacitance and original coil, it will cover 40m. Next, I plan on adding a better voltage regulator circuit and and additional stage of amplification to boost the output. I'm real close to being back on the air!

Phil

Phil,

I've been away from it for a couple of days. Gotta put the pickup in the shop for a new engine, and haven't had much chance to play at the bench. Got a four-day weekend coming up this weekend (Spring Break - advantage of working at a university) and since I'll be afoot, I'll have some time at the house to spend on it.  Thanks for the update.

Larry