These are some comments I have sent to the BA list. I'm definitely not an expert on the TV-7, but a beginner, so it is only a reference for those starting with these nice testers.
I've just received a nice TV-7C/U tube tester. It was made in Canada by Stark Electronics Instruments Ltd. (S/N 340) and has two inspection tags from Canadian Marconi Co. in the case, saying that it was overhaul-repaired by them and calibrated in 2 January 1973. The meter has also the Stark brand on it. The cosmetics are very good and the case has been repainted (probably in 1973!) very well.
One good thing is that the tester arrived with some extra adapters:
-One of them is attached to the cover, in the lower left corner (when opened), and has four different sockets, from left to right: large 9 pin (magnoval?), large 8 pin (similar to octal but with different pin size), British 4-5 and British 7 pin.
-Another adapter is the 832A adapter, which appears to be completely new.
-There is also an 8 pin adapter, similar to a socket saver, which plugs in the octal socket.
-Another curious adapter is the Hickok 1050-50.
I think all the usual accessories are here: two grid caps, power cord, 7 and 9 pin straighteners. It also has two spare lamps.
Main question about the tester is the manuals; it has TWO complete sets of the setup data (TB 11-6625-274-12/1), dated 17 January 1962. There is also a loose sheet (TO 33AA21-5-31C), dated 15 January 1965, which is a supplement for the January 1962 book, but it is missing one corner (upper right), so in the rear part there are some tube numbers missing (can you tell me them?).
I have also a supplement titled 'TB 11-6625-274-12/1 Changes No.1', dated 31 May 1962, which is 6 pages long. There is also an incomplete document (only pages 5-6, 35-42, which is the last page) which appears to be an older tube data set, as it is made of hard paper and has less pages (42) than the other complete book (85?).
I wonder if somebody would like to swap one of my January 1967 data sheetsset for another more recent (mine are originals, but a good copy of an updated manual would be welcomed also). It would be a plus if you could include a collection of the supplements published. Of course, any difference in sheets number would be gladly paid.
Another manual I would like to find is the Depot Service and Maintenance Manual, as I want to check the calibration and, anyway, have it as a reference.
Please, any help will be greatly appreciated!
I've been looking at one known problem in my TV7-C/U, the filament voltage. The seller told me that he 'needed to put it manually, with the help of a voltmeter, in order to get accurate results'. Well, I've checked the voltage and, as a sample, in the 6.3V position, I get about 5.3V. The same happens in all filament positions. So I've opened the tester (nice work, BTW!) and gladly found it has a plastified schematics copy inside. I've measured the voltage at the transformer primary and, between points 1 and 2, I have only 74VAC when the LINE ADJUST is in the meter center (and this winding is rated at 130WV, 94V). So I suspected about the LINE measuring circuit... Looking into it, it has, among other components, two 1K/5% resistors, which go to a dual diode component and then to the meter. Well, one of them measures, IN CIRCUIT, about 1.3K and the other one about 3.5K (not too near its 5% tolerance, hi!). So I have thought about cheating the tester by adjusting the LINE ADJUST so the filament outputs are right, to be sure the meter circuit is wrong. But, when I approximate that point, the LINE FUSE lights clearly. I have mesaured the current drawn by the tester at about 330mA when it says is right and about 600mA when I say it is right (correct filament voltages). So the questions are: when the tester is operating right, does the LINE FUSE bulb light?. And which current does the tester draw when it is without any tube connected?.
Any help will be welcomed!.
Thanks and best regards.
Some months ago I posted a message regarding the arrival to my shack of a nice Stark TV-7C/U, made in Canada... Well, I assumed the 'C' model should be an special model, manufactured in Canada. Right!. But I also assumed that the 'C', as in the abecedary, was a model between 'B' and 'D' and, most probably, a canadian 'B', as it was missing the extra high gm range of the 'D' model. WRONG!!!. Looking at the wonderful 'Operator's and Organizational Maintenance Manual' (TM-11-6625-274-12) pictures, I have found that my unit is EXACTLY as the 'original' TV-7/U model. So here is my guessing: the 'C' version was designated just after the TV-7/U was 'ported' to Canada. Then, when 'A' and 'B' were obsoleted, as 'C' was already used, they skipped it and went to 'D' model.
So I think I should change my WEB page comments about my unit :-)!
GOOD news is that differences between the model I thought I had ('B'), and the plain TV-7/U are few. And I have a 'rare bird', as 'C' models are someway scarce ;-)
BAD news is that my power transformer is bad: it drawns about 390mA WITHOUT rectifier tubes plugged; in fact, in the workbench, with ALL secondaries removed and 93V (nominal voltage) applied to the primary. When aligned to match the LINE SET (which is also aligned properly), with rectifier tubes, I get a reading of 550mA. The manual claims 45W (390mA), but WITH tubes. It is not too much, but enought to light the LINE FUSE (and, what is worse, to upset me!).
WORSE news is that I bought a replacement transformer in USA, shipped it to an intermediate USA location and then to Spain (imagine the total shipping costs :-( ) and this one appears to be also BAD, as it performs like the 'original'... One easy measure I took was the DC resistance of the primary winding: 2.7 Ohm in both cases. The manual claims for 10.5 Ohm... Could anybody check this in his TV-7?. All the models are exactly the same in this part.
Well, at least now we have 'The Real TV-7C/U Story' ;-)
Hello BA list readers!
I just told you (some messages ago) that a TV-7C/U is THE SAME as a TV-7/U... Well, looking with greater detail at the TV-7 'Field and Depot Maintenance Technical Manual' (TM 11-6625-274-35, dated 15 March 1962) I have found some slight ;-) differences between them. Of course, the ELECTRONICS are exactly the same in both models, BUT the panels differ as follows:
|BIAS and SHUNT Controls||markings engraved on a dial||markings etched in the panel|
|SHORT Lamp||no panel marking||panel marking|
|Storage clip for AC plug||NO||YES|
|Storage clip for test leads||NO||YES|
|Gasket around cover edge||NO||YES|
So, what does this mean?. As there is a table explaining all of these parameters for all the TV-7 models (except, of course, the 'C' model), my model is EXTERNALLY just as the TV-7B/U. This is what confused me at first glance!. One hint to know that the electronics are the same as the plain TV-7, is that in the internal bottom part of the box, you have a plastic schematic for the TV-7/U, and it appears to be original.
Well, hope not to bore too much with these small details, but I thought it was best to put all straight!.
I would like to find other TV-7C users, to comment a bit about our units... Any takers?.