The AM Forum

HI AGN FROM TIM...QUESTION:..'PICKED UP A HEATHKIT PTO AT A 'FEST FER 50 CENTS..I UNDERSTAND THIS THING OPERATES FROM 5-5.5MHZ. IT'S ALL THERE,6AU6,ETC. WIRING ON THE BACK IS FER B+,FILAMENT,GND AND BIAS. OUTPUT IS FROM A RCA JACK...OK...HOW DO I GET THIS THING TO OPERATE AS A VFO ON 40,OR 75?..I'M THINKING ABT BUILDING A TRANSMITTER,AND DUG THIS THING OUT,THINKING I MIGHT BE ABLE TO USE IT...SOOOOO OPINIONS?....SK..

You could build up a xtal controlled osc circuit operating at 12.5 mhz for 40 meters and 9 mhz for 80 meters and feed the PTO output into a mixer circuit along with the xtal osc output.

This IMHO seems like a lot of work to end up with a 2 band vfo with no freq readout dial (unless you had the Heathkit circular dial and drive mechanism. At any rate, you would need some sort of vernier drive to slow down the tuning rate.

Just pickup a Heathkit VF-1 or Johnson 122 and build it in to your rig....they would drift more and as such be more authentic and old buzzardly!!!  ;D

There are other ways but this just came to mind.

You will kill the tracking if you modify the pto. BTW mixing it with 9 MHz will cover 80 and 20 meters. The best PTO for you would be the one used in the T195 I think they cover 1.5 to 3 MHz. It has 2 tubes one is a buffer. gfz

Not to mention the Heath PTO/VFO operates backwards.

IT's probably a VFO not a PTO.
You could modify (remove) some of the fixed caps and the
variable inductor will tune up to 7 mhz. (7.0 to 7.5)

I've done this a couple times in the past for 40M qrp HB projects.
There should be a schizo online somewhere (BAMA). If not, let me
know and I'll find my notes in my archives.

The heath thing was assembled at the factory. It was called an LMO and has a variable cap inside. I have a solid state one and yes it will require a gear since it tunes backwards.

Not all were factory built Frank.
Early on they were assembled with the rest of the kit.
I built 3 HW101s and all the VFOs were in pieces parts w/ the kits.

Either way Tim, you'll hafta make a new dial plate.
A pair of Jackson ball drives back to back works great for tuning rate reduction.

Interesting my SB401 and SB303 were factory assembled one a tube the other solid state.

Yup. Bad part of the HW101 is...
Once assembled, you'll play hell ifn ya need to get into the VFO for repair.
Dis-assembly takes at least an hour !!!!!

You're both right, the SB series had pre-assembled LMOs (some tube, later ones solid state), the HW series had VFOs that you had to build.

73 John

Yup now I remember. The HW series came out after I bought my 401/303

And...the SB-101 LMO was tube and the SB-102 was solid state.

Were the LMO's built by Collins or some other manufacturer and sold to Heath?

 ;D

Collins made PTOs, not LMOs.  The PTO would be way too pricey for Heathkit to even consider.

73 John

I believe that the Heathkit LMO's (at least the later ones) were built by TRW

AND....for there price and vintage, they were quite stable. There was not a lot of warmup drift and after they stabilized they stayed just about dead on. I have heard of claims of <200 hz per week.

PS: I have an old SB-102 thats in real nice shape....maybe I will drag it out and make some measurments.

Yup, I think it was TRW my first one for the SB303 had problems so Heath replaced it and yes it was very stable. I later bought one at the TRW flea in Ca. I peaked inside and saw a number of temp. comp caps. I could see why it was sold as a completed module.

A few months ago, (before I moved) I took a tube heath LMO (6AU6) pulled out the tube, shoved an FET in the tube socket, applied +12v to the B+ pin and wah-lah! Worked like a champ and no filament voltage required!!... I have a few of these LMO's.. they're very stable... One is being used in my homebrew AM exciter project, just as someone mentioned, the output mixed with a fixed xtal oscillator is the way to go. That's exactly how Heath did it..... who cares about backwards/forwards... ;D ;D

Homer Simpson......"dial goes left... dial goes right... dial goes left.. dial goes right..."





 

I've done the same thing to Collins PTOs, Glenn.

<ducking and waiting for the Attack of the Collins Collectors>

John,
Which fet did you use. I would like to do a T195 pto. Did you plug into the tube socket or did you go under the hood?

I had an HW101 with a solid state LMO and it went bad on me.   As BIL said, it took hours to get it apart in an unsuccessful attempt not to mangle it.  Replaced the transister in five seconds then did battle for hours again to get it back together.

No fun.

John;

You probably didn't know at the time that it is highly illegal to mod Collins gear.  ::) ::)

I can't tell you how many times I've been lambasted for even suggesting such a thing!
Same goes for military gear..(God forbid!)

...the modification police are everywhere!   ;D ;D

I used an MPF-102... plugged into the tube socket topside for testing, then soldered it directly to the tube socket tabs inside the box.

Frank, dunno, I think it was a MPF102 or equivalent.  It was one of those miniature PTOs with two soldered in submini toobs, I have no idea what radio they were out of.

And Glenn, yes, the Modification Police are everywhere.  I've seen more than my share of harebrained ham modifications and some times you gotta shake your head, but at the end of the day the owner has every right to do whatever he wants to his radio - including throwing it out a window if he wants.  I was sorely tempted with the 75A4 I briefly owned  ;D

73 John

I completely aggree John.

On the 75A4, I've owned a couple over the years, wasn't impressed, sold them. On the other hand, my favorite tube, hamband receiver is the Collins 75S-3B which I still own.... a great receiver.

I want to convert a T195 pto to solid state then drive multipliers to a 100 watt broadband amplifier strip from a Raytheon marine rig. that would be a perfect driver for the class e final.

I had a beautiful 75A3 that I unloaded after a few years. It had the weirdest J.S bias circuit. It was too nice to modify and stock it was junk.