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 Post subject: TV-7/U Flea Market Find
PostPosted: Sep Mon 19, 2022 3:37 am 
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Joined: Jul Fri 12, 2019 9:05 pm
Posts: 77
Location: Houston, TX
I picked up a TV-7/U today at a flea market for $25. Just the tester and tube data book in the case, no other attachments or accessories. I pulled and tested the Type 83 and 5Y3 GT tubes on a simple emissions tester. No shorts, and both tubes tested very strong and appear to be the originals tubes (both are JAN with some nice markings on the base). I'll test them both again later on a better tester for leakage and transconductance. The bases are loose on both tubes, but the retainers have held them steady and in place for many years. The case and face of the unit have seen better days, but the face cleaned up ok. All knobs turn smoothly or as they should. The line cord is cracked in a few places and was in and out when I tested for Ohms, so I will need to replace that before firing it up. The inside looks all original. There is a full schematic attached to the inside of the case that is in perfect shape.

I've worked on a few very simple emissions testers, but this one looks a bit more complicated. I know this is one of the earlier models and that the TV-7D/U is much more desirable, but I think this one could be a nice little tester.

Is this a good candidate for repair/restoration?
Any suggestions for first steps that I should do or not do with this tester?

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03 TV7U_Chassis.JPG
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04 TV7U_PrecisionResistors.JPG [ 1.94 MiB | Viewed 932 times ]


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Mon 19, 2022 6:59 am 
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Joined: Dec Sat 28, 2019 3:18 pm
Posts: 1386
Location: Corinth, TX, USA
Great find. Is the meter good? The power transformer? Otherwise, it looks like it mostly looks like it just needs cleaning.

I notice the pin straighteners are missing (second picture, to the right of the tube manual).

The pictures don't show all the switches. The first TV-7_ uses phenolic switches. The "B" and onward models use ceramic wafers. That is why they are somewhat more desirable.

If you don't know, BAMA has the manuals.
http://bama.edebris.com/manuals/military/tv7u/

John


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Mon 19, 2022 1:24 pm 
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Joined: Jan Thu 01, 1970 12:00 am
Posts: 11864
Location: Beaver Falls, PA. USA
Location: Beaver Falls, PA
An emission test will be fine for the 83 and 5Y3; they are both diodes. Nice find!

The TV-7 was my first tube tester, 50 years ago. I still have it.

_________________
Tim KA3JRT


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Mon 19, 2022 6:28 pm 
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Joined: Feb Fri 13, 2009 4:09 am
Posts: 813
Location: Santa Clara, CA
Location: Santa Clara, California
Be gentle when winding the line cord onto the cleat in the lid. Mine is missing completely, looks like the spot welds failed at some time in its past. It's rather a pain to coil the line cord properly and locate the plug between the knobs so the lid will close.

-- Bob


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Mon 19, 2022 7:24 pm 
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Joined: Jan Thu 01, 1970 12:00 am
Posts: 7612
Location: Montvale NJ, 07645
Nice. You stole it for that price.
The 83 and 5Y3 never go bad in these from normal usage.
Clean it up and try it out.


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Tue 20, 2022 1:58 pm 
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Joined: Jul Fri 12, 2019 9:05 pm
Posts: 77
Location: Houston, TX
KX5JSC wrote:
Great find. Is the meter good? The power transformer? Otherwise, it looks like it mostly looks like it just needs cleaning.


These are things I need to test. I'll have a detailed look at the components and swap out the power cord, then bring it up slowly. Thanks for the BAMA link.


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Tue 20, 2022 2:08 pm 
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Joined: Jul Fri 12, 2019 9:05 pm
Posts: 77
Location: Houston, TX
Bob E. wrote:
Be gentle when winding the line cord onto the cleat in the lid.

Thanks for that information, will do!


Scott wrote:
The 83 and 5Y3 never go bad in these from normal usage. Clean it up and try it out.

The 83 has some junk on the inside. Looks like some type of carbon build up, but it tested very strong. I really want to de-solder the tube pins on both tubes and re-glue the bases. I'll give it a brief run after I have a good look at it.


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Tue 20, 2022 3:44 pm 
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Joined: Jan Thu 01, 1970 12:00 am
Posts: 18284
Location: S. Dartmouth MA USA
Quote:
The 83 has some junk on the inside. Looks like some type of carbon build up, but it tested very strong. I really want to de-solder the tube pins on both tubes and re-glue the bases. I'll give it a brief run after I have a good look at it.
The flaked carbon coating will lay on the side of the tube structure and do no harm.

Do not take apart the tubes to fasten the bases!

Use PVA (Elmer's) glue applied with a toothpick, gently massage the joint so the glue follows the baseline but don't "drown". Wipe the excess from the joint, use masking or other easy to remove tape to center and secure the tube while the glue sets, then remove tape.

The tubes get warm but not scorching hot so PVA is fine and safe.

Avoid any unwarranted concern for the 83, it is a unique tube and not only rectifies but also regulates... Pick up a spare if the price is right but probably you will never need it...

Tubes from the early 20's will have connection problems at the tube pins, de-soldering, cleaning and re-soldering will often restore those tubes.

Use of other glues risks excessive adhesion and shrinkage which can break the glass at the bond line. Meaning, No urethane (gorrilla type) or cyano-arcylic (super-glue) adhesives.
Beware dousing switches and potentiometers, some tube types and leakage tests are at high gain. Any leakage from a contact cleaner residue will cause erratic readings that can be difficult to correct.

Best advise for dirty contact is to depress one of the buttons then massage other buttons by repeated depressions. As for other potentiometers, massage by cyclic turning a dozen times.

There is a chart online to correlate the meter readings to transconductance, this tube tester does test amplifier tubes for that characteristic.

If there are ferrite beads on some of the wires from tube sockets that is the latest edition of the TV-7...

The power cord is rubber insulated, some turn gooey, some get hard and flake and others stay in perfect condition for many years. Replace the cord with a similar type. FWIR it is 3-wire if it is not and it appears original, keep it the same.

The two missing tube adapters are for tube one would never encounter on a daily basis, so hunting and paying a premium for those adapters is not needed.

Do not mess with any internal adjustments or shotgun components unless the readings become unrealistic.

I paid a premium for my version of this tester, ($675) but I wanted it in an unmolested condition.

Lucky, lucky :)

Chas

_________________
List' & I will Enchant Thine Ear


Last edited by Chas on Sep Wed 21, 2022 3:06 am, edited 1 time in total.

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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Wed 21, 2022 2:30 am 
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Joined: Jul Fri 12, 2019 9:05 pm
Posts: 77
Location: Houston, TX
Chas wrote:
Quote:
Luck You :)Chas

LOL!! Back at you! I've overpaid for my share of vintage equipment that I just had to have. I had never seen one of these in person and didn't know what it was until I opened the metal box. I was pleasantly surprised. I also had to carry it about a mile back to where I was parked. This little tester has some big weight to it.

Thanks for the advice and for the information on the 83. The inside of that tube looks like it is toast (seriously, burnt toast), but it tested strong. I will follow your lead and work through the switches and knobs using that method. All the knobs turn nicely and the buttons spring back with good resistance. I will give them a good run through as you suggested. It is a two wire and I likely have a couple of good quality candidates in my collection of power cords.

One more thing I did want to ask about is the meter (I have not tested it or the transformer yet, which I hope to be able to get to this weekend). Is the meter sealed and should not be opened? I have worked on a few tube testers where it is ok to take the front cover off the meter and clean the glass on the inside. I have not gotten to that point yet but I would like to clean the inside of the glass at some point, if possible.


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Wed 21, 2022 3:05 am 
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Joined: Jan Thu 01, 1970 12:00 am
Posts: 18284
Location: S. Dartmouth MA USA
Quote:
Is the meter sealed and should not be opened? I have worked on a few tube testers where it is ok to take the front cover off the meter and clean the glass on the inside. I have not gotten to that point yet but I would like to clean the inside of the glass at some point, if possible.
FWIR it is a Phasotron, a totally sealed meter. In consideration the tester is military and would have been used in rather hostile environments. The cover/bezel is "sweat soldered" to the case. The terminals passing through rubbers seals.

Yes, some restorers have opened them to replace a broken glass. But opening for "routine cleaning" should not be done.

_________________
List' & I will Enchant Thine Ear


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Wed 21, 2022 6:59 am 
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Joined: Dec Sat 28, 2019 3:18 pm
Posts: 1386
Location: Corinth, TX, USA
Chas wrote:
Quote:
The 83 has some junk on the inside. Looks like some type of carbon build up, but it tested very strong. I really want to de-solder the tube pins on both tubes and re-glue the bases. I'll give it a brief run after I have a good look at it.
The flaked carbon coating will lay on the side of the tube structure and do no harm.

Avoid any unwarranted concern for the 83, it is a unique tube and not only rectifies but also regulates... Pick up a spare if the price is right but probably you will never need it...


If you buy a spare, make sure that you buy an 83 as opposed to an 83V tube. Thread discussing the difference here:
viewtopic.php?t=256512

John


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Thu 22, 2022 2:51 am 
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Joined: Jul Fri 12, 2019 9:05 pm
Posts: 77
Location: Houston, TX
Thanks. Good read about the differences of those 83 and 83V tubes. Might have missed that otherwise.


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Fri 23, 2022 5:00 am 
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Joined: Jul Fri 12, 2019 9:05 pm
Posts: 77
Location: Houston, TX
Ok, so I tacked in a new 2 wire power cord and slowly brought the tester up to full power (115V) on a variable transformer and dim bulb setup. The pilot light (power) came on and there was no excessive or unexpected amp draw. The fuse didn't light up at all. I pressed the Line Test button and the meter responded, but stopped abruptly at 39 on the meter, 40 if I gave it a little tap. Increasing and decreasing the Line Adjust did nothing to the meter either way. It looks like the meter is simply sticking at 40. Everything else looks good. The tube tester is quiet, no hums, pops, odd smells, or anything else. I left it on for a few minutes and didn't notice any heat around the transformer area or any other area on the face plate.

I installed a display on my variable transformer (VT) which shows Voltage, Current, Power, and Energy. When the tube tester is in the OFF position the display on the VT reads 115V, 0.03A, 0.2W, 274Wh respectively. This is normal for my VT with no load. When the tester is powered ON and the Line adjust is in about the center position the VT display reads 113V, 0.06A, 5.2W, 274Wh. Again, nothing alarming or unusual in my mind. If the meter was working properly I might be inclined to do more testing, but I thought it might be best to not push anything and possibly blow out the meter or something else.

Anyone need parts for their TV-7/U? JK, I am not going that route. Any suggestions are welcome.


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Fri 23, 2022 9:30 am 
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Joined: Jan Wed 15, 2020 11:29 pm
Posts: 2237
Location: AUSTRALIA
Location: Queensland.
You really don't need to bother bringing up the line voltage on a Hickok tube tester slowly.

Why ?

The reason is that the entire tester operates on the principle of full wave rectified pulsed DC. Non of it (the rectifier outputs) are filtered by electrolytic capacitors, quite unlike a typical radio or TV where the output of the rectifiers feed electrolytic caps, often aged.

However, if you stop to consider it, even in the case of the typical radio and TV, with aged electrolytic caps, where the notion of slowly raising the line voltage on a Variac, might have some pseudo plausible merit, I'm afraid the logic is defective there too. It won't stop people advising you to do it though, recommending to every man and their dog, or on a score of you-tube video's that it is the smart thing to do. But the logic is defective.

I'm afraid that if the aged electrolytic caps in the apparatus under consideration cannot handle an abrupt power up, they are too old to be considered worthy of reliable ongoing service.

This is why for all of my restorations I replace them, in advance, before powering the apparatus up, so as to avoid any trouble. Some people are too apathetic, looking for shortcuts, or penny pinching to do this, and they "hope for the best" that the original aged caps will reform and sometimes they "get away with it" and save a few dollars, even though it is a poor proposition to power a >40 to 50 year old tube based appliance without fitting new electrolytic caps first. But these remarks are bound to buy an argument from the converted so we will leave it as my opinion to avoid that discourse.

One beauty of the Hickok tube tester design, was the genius of having the entire tester powered by one precision power transformer. Also, to use the current difference on alternate half cycles to unbalance the meter bridge. The designers of the AVO testers in the UK didn't think of this (they were not as smart) and they required the operator to balance out the static current and only one half of the line cycle was used. Also their units contained two transformers, not one.

So when it comes to dynamic tube Transconductance tester design, Hickok outsmarted everybody else. They patented their design and definitely a case where a patent was warranted.


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Fri 23, 2022 12:14 pm 
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Joined: Jul Fri 12, 2019 9:05 pm
Posts: 77
Location: Houston, TX
Good information, and interesting advice; however, I don't think everyone that brings up an old device slowly using that method is either penny pinching or looking for shortcuts. If you enjoy this hobby (all this is for me anyway) you know that any piece you start working on will take dedicated time and resources. No doubt. Otherwise, we could all take the biggest shortcut of all and simply part out anything in question then go buy a nice working model with those funds. I have a working TO-6 and I guess I could reform caps if that was something I was interested in doing, but that's not not my method. I prefer to install new components when necessary, but I also see the wisdom in doing a little testing first.

My goal was to avoid applying full throttle to a piece of gear that's been at rest for a while and easing it back online for a basic system check. Everything looked good during the initial visual inspection, but I wasn't sure if I would even have basic power or if the meter was working (which it is, but has issues). I am comfortable with that method and would probably do the same even if I had installed all new caps from the very start. These days, if I just pop up from a sitting position I tend to need a few seconds to make sure nothing else pops :o . Necessary or not, I think bringing up an old device slowly feels the same to me in that way and is not harmful.

I am still looking for advice on the meter and if there is anything I can do about the sticking issue. If this meter is sealed and there is not much I can do, I may start sourcing a replacement. If anyone has replacement advice (such as would a replica be fine or should I try to find something that is NOS or one that is used but in good condition), I would appreciate that information as well. Thanks!


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Fri 23, 2022 2:20 pm 
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Joined: Sep Sun 22, 2013 2:11 pm
Posts: 33
Location: Corpus Christi, Tx
Great find! Daniel Nelson, the TV7 Guru, sells replacement meters for it. His email: djn@ieee.org


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Fri 23, 2022 2:25 pm 
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Joined: Sep Sun 22, 2013 2:11 pm
Posts: 33
Location: Corpus Christi, Tx
I have this more recent email address for Daniel Nelson: djn16@cox.net


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Fri 23, 2022 2:28 pm 
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Joined: Jul Fri 12, 2019 9:05 pm
Posts: 77
Location: Houston, TX
tdbassman wrote:
I have this more recent email address for Daniel Nelson: djn16@cox.net

Awesome, thanks!!


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Sat 24, 2022 9:40 am 
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Joined: Jan Wed 15, 2020 11:29 pm
Posts: 2237
Location: AUSTRALIA
Location: Queensland.
Good information, and interesting advice; however, I don't think everyone that brings up an old device slowly using that method is either penny pinching or looking for shortcuts. If you enjoy this hobby (all this is for me anyway) you know that any piece you start working on will take dedicated time and resources

Unfortunately, few people have figured out exactly how the Hickok tube testers work, or indeed what is important servicing them. Those who do charge for their services and repair jobs and look to inspire confidence in customers put themselves forward as "expert repairers" and calibrators.

I have no other motive aside from technical interest, to comment on these matters, other than technical knowledge and offer advice to help people for free. I'm not selling a service or trying to make money from it. I wonder who is the better proposition to "believe". Maybe the old joke about the "expert" has some oblique merit here; the "ex" is a has been and the "Spurt" is a small drip.

This is why you will find all sorts of incorrect advice (on the internet) about adding diodes to the meter circuit and people claiming to be experts on servicing tube testers and all manner of other vintage apparatus. Or how about we do a "tear down". This sort of thing reminds me of a 5 year old pulling a clock apart and not being able to put it back together.

The best thing you can do to help yourself, is to study the design of tube testers, as many use different operating principles than the Hickok, read up on the Physics of Vacuum tubes and try to conclude for yourself, what makes sense and what is nonsense. Depending on how impressionable you are, with star spangled You-tube videos or testimonials from other people regarding "services", fact from fiction might be hard to distinguish.

There are a number of assumptions and misunderstandings about tube testers. Even urban myths.

I wrote an article once to clear some of this up, but whether it will help you, like all things technical,the Devil is in the detail:

https://www.worldphaco.com/uploads/Hick ... e_ACS..pdf


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 Post subject: Re: TV-7/U Flea Market Find
PostPosted: Sep Sat 24, 2022 5:59 pm 
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Joined: Jul Fri 12, 2019 9:05 pm
Posts: 77
Location: Houston, TX
ACORNVALVE wrote:
Maybe the old joke about the "expert" has some oblique merit here; the "ex" is a has been and the "Spurt" is a small drip.
This is great! :lol:
ACORNVALVE wrote:
I wrote an article once to clear some of this up, but whether it will help you, like all things technical, the Devil is in the detail
Thanks for the link to your article! I have read many of your contributing posts on this forum. Good stuff, and very consistent. I am a novice (but not young) in this field, impressionable (takes practice at my age), enjoy a good star spangled YouTube video (another phrase I am tucking away for use later) on repair every now and then, and digging into details such as the information offered in your article. I weigh it all against my needs and then decide what works best for me.

I have received, and have read, a ton of advice on this forum and find the time I spend considering it all to be worth while. However, there are some folks out there with a new and/or interesting take on well established methods. Call me naive, but I seek out this type of thing. It's also largely why I ask for input in the first place (that, plus I am still learning). I am sure Picasso must have run into a lot of criticism when he first presented Cubism to the art world. Some may have never accepted or warmed up to it at all, but that didn't make his novel departure from the highly embraced standards any less genius. Great contributions, in part or as a whole, can come from unexpected sources and might even appear useless at first. I enjoy reading as much as I can and using or adopting what makes sense to me.

You do a great service, sir. Thanks again for your input here, it is truly appreciated!


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