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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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11th Aug 2009, 11:14 am | #1 |
Tetrode
Join Date: Jan 2006
Location: Preston, Lancashire, UK.
Posts: 62
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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 |
11th Aug 2009, 11:25 am | #2 |
Dekatron
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Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
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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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11th Aug 2009, 1:20 pm | #3 | |
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Re: VFO/Buffer Unit?
Quote:
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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11th Aug 2009, 8:25 pm | #4 |
Tetrode
Join Date: Jan 2006
Location: Preston, Lancashire, UK.
Posts: 62
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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 |
11th Aug 2009, 10:21 pm | #5 |
Retired Dormant Member
Join Date: Jul 2009
Location: Buckinghamshire, UK.
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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 |
11th Aug 2009, 10:38 pm | #6 |
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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. |
11th Aug 2009, 10:45 pm | #7 | |
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Re: VFO/Buffer Unit?
Quote:
Al. / Skywave. |
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11th Aug 2009, 10:55 pm | #8 | |
Tetrode
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Re: VFO/Buffer Unit?
Quote:
Steve |
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11th Aug 2009, 11:02 pm | #9 |
Tetrode
Join Date: Jan 2006
Location: Preston, Lancashire, UK.
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Re: VFO/Buffer Unit?
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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11th Aug 2009, 11:45 pm | #10 |
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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. |
11th Aug 2009, 11:47 pm | #11 | ||
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Re: VFO/Buffer Unit?
Quote:
Al. |
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12th Aug 2009, 9:49 am | #12 | |
Tetrode
Join Date: Jan 2006
Location: Preston, Lancashire, UK.
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Re: VFO/Buffer Unit?
Quote:
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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12th Aug 2009, 11:23 am | #13 |
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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. |
12th Aug 2009, 4:53 pm | #14 |
Tetrode
Join Date: Jan 2006
Location: Preston, Lancashire, UK.
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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 Last edited by Dave Moll; 12th Aug 2009 at 8:53 pm. Reason: unnecessary quote removed |
12th Aug 2009, 11:30 pm | #15 |
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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 |
12th Aug 2009, 11:54 pm | #16 | |
Tetrode
Join Date: Jan 2006
Location: Preston, Lancashire, UK.
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Re: VFO/Buffer Unit?
Quote:
An interseting curio if nothing else. Steve |
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13th Aug 2009, 10:21 am | #17 |
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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! |
13th Aug 2009, 1:18 pm | #18 | |
Tetrode
Join Date: Jan 2006
Location: Preston, Lancashire, UK.
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Re: VFO/Buffer Unit?
Quote:
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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13th Aug 2009, 10:13 pm | #19 | |
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Re: VFO/Buffer Unit?
Quote:
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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13th Aug 2009, 10:48 pm | #20 |
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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 |