Homebrew VFO for DX60? Need advice on Freq

[VE3LYX]

I built a Vfo for my DX . Have it done wired for the factory plug and was bench testing it. Seems very stable . Was unable to get it to wobble with anything mechanical so I am happy there. Then I had a terrible thought. I dont know what freq the DX60 wants. Same as a crystal would be on the same freq? (IE 3725 out means 3725 VFO freq?) I am currently able to tune 3.62 to 4,2 mcs. I can pad it to keep it below 4mcs but is that how it works with these DX 60s? Will it multiply for 40M etc like a crystal or do I need band switching in the vfo? If so I will just stay on 80M with my friends. Dumb questions I am sure but when you dont know you gotta ask.
Don VE3LYX

[W4AMV]

The Heathkit HG10 is the matching VFO for the 60. I do not have the manual in front of me, however, I believe it doubled from 80 to get to 40 and so on. In any case, check the HG 10 manual for the frequency plan. Ideal case, your HB VFO should match that plan.

[W4AMV]

Here is the plan:

[VE3LYX]

Thanks. Very helpful.
I have the VFO padded so it now tunes from just under 3600 to 3995. Solid as a rock on the test bench and quiet too. (no PS noises etc) Hopefully that will transfer to when it is injecting the rig. I guess I am only good on 80M with this deal. That is fine as that is where I use it. Hartley circuit with a 12AX7. Built in a stainless steel kleenex decorator box with a double front wall. The XYL picked it out from a brief discription I gave her when she went shopping.  Who'd a thunk it. Decorator VFOs .
I see I have to change the front label to 80M. That is fine.
Don
Thanks again for the straight forward help.

[K9PNP]

Interesting construction.  Looks like you have to remember where not to rest a finger when tuning with the tube there.  Hey, it works and is stable and that design works for you.  I have built some different looking items in my time also.

[VE3LYX]

You cant really tell in the pic but the tube is totally recessed in the hole. In about 3/4 inch from the surface. I am surprised how stable it is. I keep wondering"what did I forget." I built a homebrew AM rig with the same style VFO it is also very stable so I have become partial to this circuit. Also I dont need a schematic. It is engraved in my memory. 12ax7 is running with the filament in the 6 volt mode which it as provision for.  Anyway it sure does look different.
Don

[VE3LYX]

Ok, I plugged it in. When I switch to VFO mode on the switch I can hear it in the rx when I tune it  It is nicely centered on the desired band and sounds good.  That means the VFO is working but I am thinking it should be not on when I am not transmitting. I tried the standby switch VFO goes off. (there goes my neat PTT deal)  But the signal is not getting into the DX60. No grid current and so no anything. Checked the HG 10 schematic. It must be wired right.It has filiment and B+ turns off and on when I choose VFO. Could it be something wrong in the rig? A missing relay or something? Note from VFO does not change when I hit TX mode so I know it isnt dying out from lack of drive power. A second section of a 12ax7 should do the job anyway. I mean have enuf push to make it work.
Don

[VE3LYX]

OK, I fixed it myself. My mistakes. I messed up. When I was moving wires around switching the ground side of the filiments to centre I must have pushed the output cap out of the way right over and touching the tube socket chassis lug which is very close. Since I dont see well up close I guess I didnt notice so while I was making a nice signal in my osc side the buffer was feeding ground. I also found an iffy solder connection on the buffer side of the vfo plate. I repaired both and it works nicely. Tunes well and tx loads as it should. Now to insert a relay for the VFO B+ so it doesn't run when I am in my HB standby mode (when the front switch is not on stby but key circuit is open. ) VF0 tunes from 3650 to  3950kcs which is about perfect for my ops. 12ax7 hartley osc feeding the other side of the 12ax7 though a 100pf cap which goes out the door on a similar cap to the vfo injection jack. All power is from the octal plug on the rear of the DX60 as per factory. Cost ? I believe the XYL said the designer box cost $9.95. Everything else came from the junk box and the design out of my head. All I need now is some AM contacts through the week to test it out. Unit plugs in and sits nicely on the left hand corner of the DX 60.
Don
I am tempted to get another designer box and do a driver/ PA deal so it can also be a standalone station. Maybe a cathode modulation unit
"Easy son ur gettin carried away!"

[WBear2GCR]

consider either a ball bearing vernier drive unit to go between the freq adjust and the knob, for improved control over fine frequency... or a circuit variation that will permit fine +/- adjustment of frequency once ur close... just an idea.

                    _-_-bear

[VE3LYX]

Yes & I have a box of old ball bearing verniers. Also a large knob gives better control although to be honest it was easy to put on freq since it is only 1.66 kc per degee rotation. A normal old AC/ DC broadcast set was 6.1 kc per degree rotation.
Don

[VE3LYX]

I had a hunch it would work so I tried the VFO with the rig on 40 Meters . Tunes up and gives same power approx as on 80M  so it doubles easily from the oscillator freq. Also on 40 you cant hear the VFO in the rx when on stndby mode (my way.) Next I need to try it on air with a QSO to make sure it is good.
Don

[n1uvi]

I found I needed an 80 Meter VFO as well as a 40 Meter VFO to cover
all bands on a DX-60

[VE3LYX]

Ok, Well it does transmit on 40 with an 80 VFo but actually I never use it on 40 anyway. While the VFO works good and is stable I am getting a RF leak in the shack when using it that is getting in my mic circuit. Since I can hear the VFO all the time on the companion rx at about an S6 I assume that I need to do some serious shielding of the power cable and perhaps back of the VFO cabinet. I may test it on another Hb rig and see how it behaves there. Meanwhile I am back working on my HB Screen modulated rig. It works well but lacks power so needs another tube to drive the twin 6l6 linear in to a reasonable power zone. Also needs some improvements in the PA tank circuit.
Don

[wb1ead]

Hey Don..neato job on construction!..seems ur using the HG10B vfo as ur guideline..dat's FB..however if memory serves me going back 3 decades on mine then..it had I'm pretty sure tube shields..my VF-1 sure does on both tubes in there..just wondering if that might help with the signal level being heard on ur rcvr and maybe being picked up on ur mic circuit?..for sure enclosing the backside will help in that regard too..agn nice job!!         73 de DAVE

[n1uvi]

you might want to look into using the DX 60's grid block keying scheme
the grid keying voltage is available on the accessory plug and could
provide a keying method for the oscillator. Basicly a negative bias voltage is
applied to the grid of the oscillator tube, cutting it off. When the DX 60
is keyed, the bias is removed causing the VFO to operate. Normally you
would key the VFO along with the rig.

I use a key switch plugged into the KEY jack for keying. ( IE foot switch or finger switch
or the switch inside a desk mic). It saves the mode switch from arcing
and burning up on standby. A common problem with some old rigs caused
by switching from standby to AM to transmit, and back to standby to receive, without using a key.

There is a negative voltage on the key jack, and a little current does flow when the
switch is keyed, so a rugged, insulated switch would be in order.

An 80 meter VFO should drive the DX 60 on 80,40,and 20 meters,
you might find you need a 40 meter VFO for 15 and 10, but if it's  
fifth and seventh order harmonics are strong, the 80 may be all you need,
although you might comment on the stability then, if you try that.

[VE3LYX]

Thanks guys. Ok , I actually have a tube shield for the 12ax7. I enclosed the back and  shielded the power cabling yesterday. Still have to solder the shield to its proper pin. If it still leaks Rf I will try the tube shield. Yes you are right about the circuit. I combined my favorite osc circuit with the HG10B circuit. 
FB on using it on 80M & 40M. I get a nose bleed above 40M so not to worry.
Yes I also use the key jack. I have a foot switch, probably from an old sewing machine plugged into the  key jack. I have been using it that way since about the second week after I bought it. I used to use the same foot switch on my Viewstar linear back when I was young and foolish and owned such silly things.  So the old circuit shut down the osc or the buffer when keyed? I see the Key circuit in the diagram. I hate to go digging around in there now. I am a bit clumsy and this turned out better then I planned!
Don

[n1uvi]

yes the VFO should be off when not transmitting and on only
when the rig is keyed. With the VFO on all the time you will hear
it in the receiver, no matter how well you shield it.

[VE3LYX]

Got it working. Tested on air.
I shielded the back by enclosing the rear of the unit with a sheet of aluminum. I took the powr /rf cable and found the ground at the vfo. I unwound an old AC DC loop areil and hand wound the thin wire around the cable all the way to the octal plug to make a shield then grounded it at the VFO (Which is grounded through the cabling as well.) I had one of those old push on tube shields and shoved it on the tube through the hole in the front. I was nervous so I waited a couple of days to try it but had it up and going this afternoon. Rf in the mic section is gone. Receiver interference while noticiable is way way down. You could actualy operate unless other station was not too strong. For now I just switch the Cyrstal swith off VFO back to crystal while on standby. That kills the VFO  but leaves the heaters on. It will do for now. I need a bit more drive on the grid setting to use the VFO. I would like to be able to switch to VFO and not change the setting from Crystal. Perhaps VFO output should be stronger. There is a large value resistor in the plate circuit. I could cut the value in half and see if it likes it but at least I now have a working VFO and the radio behaves when I use it.
Don VE3LYX

[n1uvi]

FB Sounds like you got a handle on it.
I recall reading about some simple changes to make to an HG-10 to increase the output
not sure where that was now. I acquired an HG-10 used, and when I opened it up I found the
circuits highly modified for higher output. Very different from the Heathkit schematics altogether. Someone beefed it up for use with a different rig other than a 60 I think,
that’s the only thing I could figure. Anyway, would love to see the circuit you end up
with when your finished.

[VE3LYX]

There is not much to the circuit.  A 12ax7 (using 6 volt heater set up)with an old hartley style osc. (grd -gridleak , cathode tap and ground fed coil with an approx 75 pf variable in parallel. . Plate has the usual RFC and feeds the section section grid of the same tube through a 100pf or so cap which is wired as a normal amp and pumps to the Dx60 through another cap of RF quality (as opposed to audio). I choose this particular osc because I have found it with minor shielding to be oblivious to hand capacity. Even in my wooden AM HB set this type of osc does not bounce around which always impressed me. Range wound up bang on with minor padding. Just inside 80m band at both ends. B+ supply has I think if my memory serves me (it is early and I havent had enuf coffee) a 100k in series I may parallel that to see if it likes it or not without messing with the main circuit. That part I stole from the Hg10 schematic I believe. (Always build similar first then get cute if necessary)
Don

[VE3LYX]

Our normal 3725 Am spot was occupied today so I had to jump off the rock and use my hb VFO. Laugh if you like but I was nervous. It worked well. except for my stupidity. I kept switching it off and forgetting to turn it back on when I replied. I know why I was doing that before but dont need to now. Chalk it up to a brain fart. Anyway technically it worked well. I may just stay on it forever and let the rocks gather some dust. This was the first QSO with it. Thanks to Al VE3AJM . If I hadnt been stupid we would have had an ever longer QSO. There I was babbling away for several minutes and noticed my meter was not bouncing. I had switched the crystal switch off VFO which cuts the VFO B + . Since I shielded it I dont need to but got in the habit of doing it when testing. My apologies to AL if he sees this. I was nervous using this on air for the first time.
Don Ve3LYX

[VE3LYX]

For some reason I dont yet understand the rig seems to work better with this VFO then it did with crystal operation. Perhaps it is because of the different drive setting required. I dont know but whatever  am happy with it and have started using it all the time instead of the rocks. It seems stable, is easy to spot in on frequency. Who knows what tomorrow will bring but for now I am happy I built it and finally screwed up enuf nerve to use it.
Don Ve3LYX-
BTW shielding works well enuf you cant here the VFO unless you crank up the RF gain and have a carrier of someone tuning up to work off of. This works great as you can just zero beat to that and ur there. Return setting to normal RF gain setting  and operate.