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Old 10th Mar 2021, 4:43 pm   #1
davidh1041
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Default Ten Tech Corsair VFO problem.

My Corsair is suffering from back-lash with the permeability tuning of the VFO. This is a common problem with this model and i bought a refresh kit to recon the VFO. This kit comes with new bearings, shims etc and a packet of grease. This grease is red in colour and a consistency like Vasoline. I have rebuilt the VFO with the kit, taking care to clean all the old grease off and it's worse than it was before. I think that the new grease had dried up as the kit is at least twenty years old and i thought at the time it was a bit thick.
My question is can anyone suggest a better grease to use? I was thinking of gas tap grease, but i can't find my tubes of this. Any suggestions gratefully received. Regards David
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Old 10th Mar 2021, 8:24 pm   #2
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Default Re: Ten Tech Corsair VFO problem.

There is a Ten Tec group on Groups.io where Im sure you will get good advice

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Old 10th Mar 2021, 8:42 pm   #3
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Default Re: Ten Tech Corsair VFO problem.

I used a general purpose grease on my Argonaut which has the same mechanism (Castrol LM, because I happen to have a tub of it to hand) and have had no problems.
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Old 11th Mar 2021, 7:50 pm   #4
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Default Re: Ten Tech Corsair VFO problem.

Thanks fred. i have applied to join a Ten Tec group on Groups io. And thanks Dave i will try a multi purpose grease.
Regards Dave
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Old 12th Mar 2021, 4:39 pm   #5
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Default Re: Ten Tech Corsair VFO problem.

I am just contemplating the fifth (!) rebuild of my TenTecs.

I have two TenTec radios,and I've had to accept this VFO clean/regrease as a routine task. I have tried various greases, with varying degrees of success. The most successful so far has been a molybdenum disulphide grease (Castrol MS3), but it is still one grease for two very different requirements.

These are :

1 A very low-friction, low pressure grease for the metal to plastic interfaces. This must be plastic-safe (not cause stress cracking of the plastic)
2 A high pressure thixotropic grease for the metal/metal surfaces in the epicyclic ball drive.

The next regrease will be done with Molybdenum grease in the ball drive, and white lithium grease in the metal/plastic sliding bits. (White lithium grease seems to be what is used in CD players , VCRs etc. Molybdenum is typically used for wheel bearings in heavy vehicles, as far as I can see).

Make sure the rear bearing washers and spring are also greased as they can cause a jerky rotation and consequent tuning jumps. (Also - it's best to arrange some sort of earthing wiper for the input tuning knob shaft. That's a design weakness which causes the frequency to vary when your hand approaches the tuning knob).

Some people on the TenTec discussion group have used teflon grease, but I have my doubts about that - I feel it's TOO low-friction, and will cause the ball drive to slip. It's fair to say that there's lots of differing views, but all agreeing that the factory-provided green or red stuff isn't up to much in the longer term.
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Old 12th Mar 2021, 9:17 pm   #6
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Default Re: Ten Tech Corsair VFO problem.

Quote:
Originally Posted by Granitehill View Post
Also - it's best to arrange some sort of earthing wiper for the input tuning knob shaft. That's a design weakness which causes the frequency to vary
Here's how I cured that problem (hand-capacitance on 10 metres) with my Argonaut:
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Old 12th Mar 2021, 10:55 pm   #7
Granitehill
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Default Re: Ten Tech Corsair VFO problem.

Quote:
Originally Posted by m0cemdave View Post
Quote:
Originally Posted by Granitehill View Post
Also - it's best to arrange some sort of earthing wiper for the input tuning knob shaft. That's a design weakness which causes the frequency to vary
Here's how I cured that problem (hand-capacitance on 10 metres) with my Argonaut:
That is brilliant !
Simple and elegant - I'll use that in my next rebuild.

Thinking about it - the TenTec VFO is an ingenious idea, but flawed in implementation. Your suggestion looks like a part of an upgrade kit ?
Also - turned brass replacements for the moulded plastic bearing components, with a proper ball race thrust bearing.
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Old 13th Mar 2021, 12:13 am   #8
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Default Re: Ten Tech Corsair VFO problem.

America really followed Collins in terms of permeability-tuned VFOs.

Part of the trick is how to spread windings to get a linear law.

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Old 14th Mar 2021, 1:05 am   #9
m0cemdave
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Default Re: Ten Tech Corsair VFO problem.

Quote:
Originally Posted by Granitehill View Post
Your suggestion looks like a part of an upgrade kit ?
I didn't use an upgrade kit. I happened to have some bronze contact strip (although not the posh silver plated type) and I made a small supporting bracket from a piece of Aluminium angle. The job was done while I had the PTO assembly apart for re-greasing.

The PTO coil in an Argonaut is not attached to the VFO circuit board and just needs two wires disconnecting and a few screws removing to detach it from the radio, so it was easy to work on. I fitted the bracket to the frame after drilling two holes for fixing screws. The contact strip was fitted to the bracket using a pair of small screws (M2) and some care was needed in determining the correct placement.

I re-used the existing parts when reassembling the PTO. The only piece that was broken was a shaped plastic "ramp" washer that mates with the end of the spiral gear. I made a new one by carefully cutting a thick nylon washer to the correct profile. I think I also changed a couple of washers to reset the tension on the thrust bearing.

I suspect these things will always need to be dismantled and re-greased every 15 years or so.
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Old 14th Mar 2021, 1:13 pm   #10
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Default Re: Ten Tech Corsair VFO problem.

Well done...!!!

R-390A PTOs also use a similar pressure contact to keep the shaft grounded like that...!!
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Old 20th Mar 2021, 9:29 pm   #11
davidh1041
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Default Re: Ten Tech Corsair VFO problem.

Very interesting idea's on the PTO problems. I used LM grease before i saw the reply from Granitehill and have to say so far it has transformed the performance. No more backlash and no more jerky tuning and jumping in frequancy. Time will tell, but with an ambient temperature from 6 to 18 degrees it is stable.
Thanks for all the interesting replys. David.
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Old 28th Mar 2021, 1:36 pm   #12
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Default Re: Ten Tech Corsair VFO problem.

Here's an update on the choice of appropriate lubes for the TenTec VFO. I came across a summary of the various grease choices for mixed steel/polystyrene/brass interfaces on a vintage machines site - so quite appropriate here, I think.

http://wiki.vintagemachinery.org/Gre...brication.ashx

Paragraph three in the intro points to calcium grease for electrical stuff, closely followed by lithium. Probably not modern automotive greases as it seems they aren't good for "Red metals". Molybdenum grease not OK - not kind to brass or bronze, so I won't use that next time.
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