PTO

[WBear2GCR]

To take up the slack in a sliding assembly, even an acme threaded rod intended for this use, the usual method is to use two nuts "loaded" against each other, often one is held solid, the other is spring loaded. Although in some cases the second nut is just judiciously adjusted and set. The nuts on a steel acme rod are usually bronze so that they set in and are a very low slop fit... I suggested using delrin or nylon for this use.

Before that I suggested a spring and cam (as in some early table radios).

And before that I suggested the body of a micrometer, already nil slop and re-settable and very fine thread.

                            _-_-

[W9LCE]

what is Delrin?  Nylon I'm familiar with - and had not previously considered  using it - it might have less proximity effect on the oscillator coil.

based on the referenced approach by ZL2PD - where a block is screwed in and out - controlling a mounted bronze slug that is inserted into the oscillator coil - it extends out of the middle of the block between the threaded shaft or bolt and his "bamboo rod".

I have been considering getting a bronze bar - maybe 1/2"x3/8" some 2-3" long - cutting treads in (2) 1/4" holes (one toward one end for the threaded control bolt the other centered for the bronze slug) and sliding the bar on something on the other end (to prohibit it from twisting - per his "bamboo rod").  This could as easy be nylon or ?delrin (probably would need to get a larger piece).  Either would have less loading effect on the oscillator coil.

He does mention using springs on the bamboo rod, to "improve the feel of the tuning arrangement".

I have obtained a Gates Turns Counter Dial (per your suggestion) - and a 90 degree gear mechanism [in order to place the oscillator box against the front panel of the transmitter (or separate oscillator - I have a damaged Heath HG-10 VFO) -to allow a marginal frequency reading by dial pointer - from the movement of the tuning mechanism].

Jim [WD5JKO] sent me his 1964 Rambler automobile radio - which has a very interesting approach on PTO tuning.  I am studying it, to see how I might be able to use it - possibly in an extensive rebuild on a scrapped National NC57 receiver, but doubt if I can duplicate it elsewhere.  The radio presents a dial reading by using a pointer that pivots on one end - and multiplies the actual movement.  I had thot of that, but they are doing it.  (Maybe even make the NC57 be "Amateur Band" with 1st and 2nd IFs.)

(Have you heard of those 12 volt "space charge tubes" used in auto radios in the 50's? - I saw a paper of a Ham receiver using those - I am looking at "Emergency/Disaster" equipment and operations - a totally 12v receiver would be different!)

That is somewhat future - right now, I am just an old man, trying to get "back on the air" - moving to this tiny city lot - and its middle of WINTER.

[N2DTS]

For getting on the air, a vfo using a variable capacitor and some B+W coil stock is easy and works very well.
Calibration with anything other then a freq counter is very hard to do with any quality.

[W9LCE]

OK - I got a Collins PTO - where can I get a schematic on this?  I've hunted -

It has two tubes - both 6AU6 - the one is a 6AU6W, the other is a 5749/6AU6 - probably a replacement.   These may tell where the unit came from.

I've also gotten a couple LMOs - from SB401s - so I am getting some decent Oscillator sources (although my SB400 didn't hold stable enough to do PSK31).  I did find a schematic for these.

But I still am going to go PTO - just for stability.
- maybe build my variant of the one by ZL2PD.

Maybe I will be stable enough to even do PSK31 - which is where THIS whole thing started.

[KC2ZFA]

which collins pto do you have ? the drum (that contains the coil) should be marked.

The 5749 is the 6BA6W...if you have the 70H3, see below.

[W9LCE]

I don't know

there is no metal drum - this was mentioned in the purchase (I do think there are things I don't know) - - no wonder I got it so "cheap".   Well, it still may be better than what I have -

I have downloaded a couple papers about it - one showing several pictures of internals - and its operation - the other listing some statistics on 17 types of the PTO.

The covering seems to be a hard clothlike material - from what I have found out, this is likely an inside insulating layer, with the mechanism inside.  I had already determined that I needed to mount it inside a cage or can - just to give it necessary isolation from nearby radiations. 

The shaft is a 1/8th inch stub - from pictures, there was a gear head mounted on it, which I do not have.   

According to the schematic I am missing the "plug" connections for the wires.  I do have the "coax" shielded output wire (to P801), and a woven shield with three wires inside (to P802 - wires A, B, C -  shield being D, E - yes the ad mentioned that an "oven wire' had been "cooked" - E, F)  The one paper that I downloaded, mentioned that PTO 70E-15 used in the 51J did not have the thermostatic oven, so I guess I am without!

I do intend to mount this in a separated case and plug its output in the "crystal"/VFO plugs of one or other transmitters - as use or repairing requires.  I will be building a small outside power supply for it - such as I have on the LM Meter.

[WBear2GCR]

Delrin is a nylon like plastic.

There is also molybdenum filled nylon which is quite machinable.

Online there are a number of resources that dissect the Collins PTO.
You might get some good ideas from them?

The Collins PTO has a metal can over the "guts" with shaft and tubes on the end.

                    _-_-

[N2DTS]

I started building an exciter using the pto out of a T368.
It runs from 1.4 to 3.2 MHz or something like that.
I want it to do 80 and 40 meters, and the pto will cover both if I double and triple it.
I would have done a vfo, but would have to switch something to get the range, which would have added another switch.
Since the pto has been sitting around for 25 years or more, it was time to use it.
output to a 6AG7 into a 6146, I will also make provisions to be able to plug xtals in.

Not sure if the pto will run all the time and the 6AG7 and 6146 get keyed or it all gets keyed.
Frequency display is an issue, a direct pto tune is about 20 turns so any pre made dial scale is out.
A frequency counter on the output would work but would not be on all the time.
I use the srd-iq as a frequency reference and can just spot, but some sort of display on the vfo would be nice.
80 and 40 meters only, for now, may play around with modulating it at some point.
Front panel is drilled and power transformer holes on chassis drilled so far.

[VE3LYX]

Sounds like a simple set up is getting over complicated. I have several here. Shouldn't take more then an hour or so to build. I have two solid states. A 20m TX on AM and a 80M receiver known as slugabsorb. It is a regen and it perm tuned. the absorb comes from the use of a pot and an absorption loop to keep the regen just below osc point. Both tune very nicely and smoothly. Take you coil form (mine are both same size BTW). Double freq in megs will give you the number of turns for the same approx freq on 40M (40M only)So 14 turns will get you in the park. Put a fixed cap across it to bring it where you want. IE 100 pf or 200pf or whatever you need then all tuning is by your slug. I always build a hartley and centre tap (and I do mean centre or middle) for solid state I like a FET For tubes a triode (Kiss principle) The rx I built on 80 does a great job and even SSB can be handled with ease. I have a slugged coil in my Hb VFO for my DX60B and have asked myself a thousand times why I am using a variable cap to tune it when I could be using the slug if i had mounted it in a spot where I could access it. Someday I hope I will correct that oversite on my part. I also have in the works a slug tuned 40m rig cathode modulated  using a 12ax7 osc buffer and a 829B final in parallel.  It is a rainy day project so it will get done when it gets done. You can discuss this for a year or build it in a hour. I vote for the build even if just the perm tuned osc by itself. Famous American race engine builder Smokey Yunick once said "One good experiment beats 1000 expert opinions." I have found it to be sound advice and I am confident so will you. Go fer it!
don