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Old 11th Aug 2009, 11:14 am   #1
Nostaticatall
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Default VFO/Buffer Unit?

Another piece of vintage gear that I need help in identifying - it must be that time of year when you look through stuff that you've collected over the years and not done anything with!

Anyway this was mounted on the front panel of an uncompleted homebrew transmitter. This however is definitely not homebrew although it has been modified. The two PL259 sockets and the two valves on the rear don't appear to be part of the original setup and internally there's a lot of stuff that ought not to be there! I'll let the photographs do the talking.

If anyone knows what it is from I would be very grateful.

Steve
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Old 11th Aug 2009, 11:25 am   #2
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Default Re: VFO/Buffer Unit?

Well, it is almost certainly a VFO

There is a mixture of Hallicrafters and TU5 tuning unit parts, the case is nothing I am familiar with, but is almost certainly of American origin, and probably Radar, or radio nav type stuff.

HTH
Sean
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Old 11th Aug 2009, 1:20 pm   #3
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Arrow Re: VFO/Buffer Unit?

Quote:
Originally Posted by Nostaticatall View Post
The two PL259 sockets and the two valves on the rear don't appear to be part of the original setup and internally there's a lot of stuff that ought not to be there!
Steve
Yes - the two UHF sockets (aka SO239) certainly don't look original - far to new & clean for a start! I'm not sure about the valves at the back, though - although the capacitor clamp (if that is what it is) plus earth strap on one of them has me scratching my head a bit. I can only assume that this is a belt-and-braces method of maintaining the valve screening to chassis. Perhaps the metal can connection to pin 1 has come adrift; not uncommon.

However, since the front panel states "Buffer tuning", I would expect these two valves to comprise the oscillator and buffer. I can well believe that the unit's insides have been modified. Any chance of a photo of the innards - and possibly a cct. diagram?

Al. / Skywave.
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Old 11th Aug 2009, 8:25 pm   #4
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Default Re: VFO/Buffer Unit?

OK, I've dismantled it and taken photos of the inside. From what I can see there is a mix of original American components and British ones that have been used when it was modified. The right angled reduction unit is nicely engineered and is by General Electric - the date stamped on it is "Sep 11 1942" Both valves are 6AG7s.

Steve
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Old 11th Aug 2009, 10:21 pm   #5
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Default Re: VFO/Buffer Unit?

The SO 239 sockets were used by the US on WW2 equipment, so they may be original, I centainly have equipment of this period where they are original.
I am fairly sure the PL259/SO259 was an American UHF plug circa WW2
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Old 11th Aug 2009, 10:38 pm   #6
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Question Re: VFO/Buffer Unit?

Thanks Steve.

Certainly an interesting item, and well built too. No, I don't recognise it, but I'll hazard a guess that is was originally intended for use on some non-Amateur Radio freq. & has later been modified to do these freqs. One Q. though - if it is a VFO (and I'm sure that it was - and is) to excite a TX, why two UHF sockets? Are they wired in parallel?

Al. / Skywave.
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Old 11th Aug 2009, 10:45 pm   #7
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Arrow Re: VFO/Buffer Unit?

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Originally Posted by anthonys radios View Post
I am fairly sure the PL259/SO259 was an American UHF plug circa WW2
My understanding is that the SO239 / PL259 names started life as Amphenol catalogue entries, but the generic name is 'UHF'. All a bit academic now, since these days 99% of all radio enthusiasts know what is meant by the terms SO239 / PL259 - and probably 'UHF' (as in connectors).

Al. / Skywave.
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Old 11th Aug 2009, 10:55 pm   #8
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Default Re: VFO/Buffer Unit?

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Originally Posted by Skywave View Post
Thanks Steve.

Certainly an interesting item, and well built too. No, I don't recognise it, but I'll hazard a guess that is was originally intended for use on some non-Amateur Radio freq. & has later been modified to do these freqs. One Q. though - if it is a VFO (and I'm sure that it was - and is) to excite a TX, why two UHF sockets? Are they wired in parallel?

Al. / Skywave.
Al - there's an 800pf cap between them.
Steve
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Old 11th Aug 2009, 11:02 pm   #9
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Default Re: VFO/Buffer Unit?

Quote:
Originally Posted by anthonys radios View Post
The SO 239 sockets were used by the US on WW2 equipment, so they may be original, I centainly have equipment of this period where they are original.
I am fairly sure the PL259/SO259 was an American UHF plug circa WW2
I really don't think that these sockets are original - that's not to say that they weren't SO239s originally - these really are pristine all over and I would have expected some silver plate tarnish after 60 odd years! I think I'll remove one and look for any giveaway markings on them like 'RS'
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Old 11th Aug 2009, 11:45 pm   #10
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Arrow Re: VFO/Buffer Unit?

I'm sure that you're right. ISTR that the UHF connector was in use in the USA prior to 1939 / 1940, which is probably the period this item dates from. Besides, if it has been modified for AmRad use, I would have expected the modifier to have replaced the original badly-tarnished ones as a matter of routine. (I would )

Al. / Skywave.
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Old 11th Aug 2009, 11:47 pm   #11
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Default Re: VFO/Buffer Unit?

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Originally Posted by Nostaticatall View Post
Quote:
Originally Posted by Skywave View Post
Thanks Steve.

Certainly an interesting item, and well built too. No, I don't recognise it, but I'll hazard a guess that is was originally intended for use on some non-Amateur Radio freq. & has later been modified to do these freqs. One Q. though - if it is a VFO (and I'm sure that it was - and is) to excite a TX, why two UHF sockets? Are they wired in parallel?

Al. / Skywave.
Al - there's an 800pf cap between them.
Steve
Hmmm. Someone's 'idea' of an attenuator? Hi and Lo O/P?

Al.
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Old 12th Aug 2009, 9:49 am   #12
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Default Re: VFO/Buffer Unit?

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Quote:
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Al - there's an 800pf cap between them.
Steve
Hmmm. Someone's 'idea' of an attenuator? Hi and Lo O/P?

Al.

Ha! You're probably right on that. I took both of the sockets off (there's no ID on them) but I can now see that the holes have either been enlarged or made from scratch so definitely not original.
Steve
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Old 12th Aug 2009, 11:23 am   #13
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Arrow Re: VFO/Buffer Unit?

Fascinating. Presumably then, originally there was one socket there - and possibly a UHF-type. They look quite new - probably fitted in the past 5 years? Upon reflection, if the 800pF is a Hi / Lo O/P fitment, we would have expected a resistor, not a cap. So I'm still a bit puzzled. Unless one O/P has RF + HT/dc, and the other is RF only, by virtue of the cap.

Do you not have any idea of this item's history, former ownership? Did you get it from an Amateur Radio Rally? Find it in a skip?

Again, I'm just curious - but also trying to help.

Al.
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Old 12th Aug 2009, 4:53 pm   #14
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Default Re: VFO/Buffer Unit?

I appreciate your help Al and everyone elses too. I'm sure we'll eventually get to the bottom of it.

I thought too that the capacitor was just for DC isolation - as far as I can see, the main output is straight from the buffer tuning cap which looks like it does have HT potential there. I think I may have to draw the circuit out if I get time.

As far as its history is concerned, It was installed in the front panel of an incomplete homebrew 813 based CW transmitter. It was incomplete because the chap died before he could finish it. That was about ten years or so ago. I bought a lot of gear from this silent key's son which included several AR88s, RA17s & accessories and a Hallicrafters S28.

So, no more than that do I know. I have searched the web high and low before I posted here to see if I could identify it but to no avail. As Sean has already pointed out it, the tuning arrangement looks like it's straight from a TU-5. Also, I've seen the large headed screws used on Collins equipment before. From an internal marking I can date it from 1942, although it could obviously be slightly later. It is an interesting piece and I was certain that someone would have been able to identify it immediately as most WWII gear was made in such large quantities; it was difficult not to be aware of most of the gear.

Steve

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Old 12th Aug 2009, 11:30 pm   #15
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Default Re: VFO/Buffer Unit?

It does seem to have quite a mixture of commonly identifiable components. One is tempted to say it was home made but then why the modification record label?
I suggest it may have been an experimental piece of kit made in WW II but not taken into production, at least not in that physical form.
Pat G3IKR
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Old 12th Aug 2009, 11:54 pm   #16
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It does seem to have quite a mixture of commonly identifiable components. One is tempted to say it was home made but then why the modification record label?
I suggest it may have been an experimental piece of kit made in WW II but not taken into production, at least not in that physical form.
Pat G3IKR
That makes sense Pat. The more I look at this, the more I am convinced that it's a one off. The front panel legends are definitely original and yet the hole for the key jack is drilled through the mod label. the same goes for one of the valve holes in the rear panel It's easy to identify the undisturbed original parts and wiring and yet their placement leaves a lot to be desired.

An interseting curio if nothing else.

Steve
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Old 13th Aug 2009, 10:21 am   #17
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Question Re: VFO/Buffer Unit?

Re: Post 1, pic. 1: Front panel controls. Any idea what the "CORRECT" control does?

Re: Post 4, pic. 4: what are the shafts labelled A1, A2, H, H for - & what do they do?

It's intriguing to note that although the jack socket has been clearly fitted at a later date than the attachment of the Mod. label, the wiring to this jack socket looks appropriate to the period of original manufacture. So presumably there was not, originally, a provision for connecting a Morse Key. So perhaps in the original TX, it was not the osc. or buffer that was keyed, but a later stage? Perhaps the original TX was AM only (unlikely ) ?

This is starting to sound like a part from a one-off pre-production / development unit.

Overall, this is a fascinating mystery item
.

Al. / Skywave.

Last edited by Skywave; 13th Aug 2009 at 10:39 am. Reason: Add more questions!
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Old 13th Aug 2009, 1:18 pm   #18
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Default Re: VFO/Buffer Unit?

Quote:
Originally Posted by Skywave View Post
Re: Post 1, pic. 1: Front panel controls. Any idea what the "CORRECT" control does?

Re: Post 4, pic. 4: what are the shafts labelled A1, A2, H, H for - & what do they do?

It's intriguing to note that although the jack socket has been clearly fitted at a later date than the attachment of the Mod. label, the wiring to this jack socket looks appropriate to the period of original manufacture. So presumably there was not, originally, a provision for connecting a Morse Key. So perhaps in the original TX, it was not the osc. or buffer that was keyed, but a later stage? Perhaps the original TX was AM only (unlikely ) ?

This is starting to sound like a part from a one-off pre-production / development unit.

Overall, this is a fascinating mystery item
.

Al. / Skywave.

The 'Correct' control is just a 'fine tune' - a small variable capacitor in parallel with the main tuning Capacitor.

The 'shafts' are pins that mate up with sockets in the back panel which carries the captive lead to the host for heater and HT supplies.

The aluminium upper chassis parts have been hand crafted and a good job has been made. Bolts nicely counter sunk and the fact that the pins mate up with the socket shows that the alignment of those is good. The original upper deck could have been used as a template for this to make the job easier I suppose. All the nuts and bolts for the upper deck are British BA types and a mix of brass and steel which definitely is not original.

I'm beginning to get the feeling that originally it might have used acorn valves and wouldn't have had the holes drilled in the back as the valves would have been inside. I've no more evidence for this but you know how you get an instinct?

The key jack doesn't look like it belongs there but the front panel markings are original and typical of the era - definitely not a DIY job.

Thanks for the input Al - it's appreciated.
Steve
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Old 13th Aug 2009, 10:13 pm   #19
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Arrow Re: VFO/Buffer Unit?

Quote:
"Thanks for the input Al - it's appreciated".
No, No - the pleasure's all mine! I really enjoy tackling mystery items like this - so much to speculate on - that is until someone comes along and declares "Ah-Ha! I know exactly what that is! It's a . . . ." and then promptly spoils the fun

And thanks for the replies.

The more I look at the photos, the more things I see that puzzle me.

In Post 4, pic. 1, the small variable cap. definitely looks Jackson Bros. / Eddystone to me.
The main tuning condenser reminds me of a RF-27 unit I once owned.
Yes - I think I understand your comment about Acorn valves: the fact that there is a hole cut through the Mod. label (pic. 3) and then Octal valves fitted does seem a bit strange.

In pic. 3 there is a bright shiny can with - is that "M & B" ? - embossed on it. > > > There may be a clue here. < < <
And do I see a couple of Phillips 'bee-hive trimmers' just beneath it?

The key jack looks UK-origin to me, but as you say, the legending on the front panel does say "key". The wiring to it looks original. Perhaps just the key-jack only was replaced. You did say that this entire unit was once associated with an 813-based c.w. only TX. Hmmm.

Finally, I notice the silk-covered flexible cabling. I do recall this from early UK equipment - including floor-standing lamp-standards!

All very mysterious - but fascinating.

Al. / Skywave

Last edited by Brian R Pateman; 13th Aug 2009 at 10:19 pm. Reason: Quote fixed.
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Old 13th Aug 2009, 10:48 pm   #20
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Default Re: VFO/Buffer Unit?

Just had another closer look. There does not appear to be a coil associated with the variable caps (I agree one is from RF26/27 but were not uncommon in other equipment, the other I would say is also common WW II Jackson). The only "coil" I can see is on the other side air spaced and not stable!!. What is the large round silver object that looks like a screening can?
The slow motion drive I have only ever seen on the TU units associated with a large US airborne TX. BC675?
The more I look at it the more I wonder whether it is an amateur made piece of kit put into a convenient surplus box. That was quite a common thing years ago when new boxes were hard to come by and were never as rigid as the surplus ones. Not many had the know-how or facilities to make their own to that sort of standard. That could explain a number of things including why the modification record has been drilled through. That sort of box might well have been a filter of some sort not requiring controls and hence largely undrilled.
Dunno!!
Pat G3IKR
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