Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Sat 16, 2021 1:04 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 79 posts ]  Go to page 1, 2, 3, 4  Next
Author Message
 Post subject: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 6:12 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
I have been going through the military calibration process for my TV-7D/U. I took heed of the fact that it calls for a 1000Ω per volt meter and used appropriate resistors to load my meter for the measurements. Everything went swimmingly and is in spec, except for the very last step. That’s the part after you set r113 and r114 using a 50v supply with 10K resistor in series to “simulate” a tube under test for ranges B and C. The part that isn’t working out is where you test a 6L6 on range B, and then lower the bias unit you get 120 on the scale. I get 117 or so, not 120. The instructions say to adjust r114 after switching to scale C, and center the meter on 60. Since the first reading is off, the second reading gets wacky. I tried 2 different tubes, but it’s possible they’re both too old to perform this test properly. I’ll try some 6L6 tubes I’ve got in the morning, but am wondering if there is something else that I’m missing that is causing this problem? I reset the line adjust after inserting the tube and letting it warm up.

I did do this whole process slightly differently than the military manual suggests, since I wanted to start with setting the filament voltages, rather than starting with the plate/screen voltages. I set the line adjust and the adjusted r134 so that all of the filament voltages were as close to the middle of their ranges as possible, and then adjusted bias, screen, etc. hopefully This isn’t the cause of my problem.

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 8:17 am 
Member
User avatar

Joined: Nov Mon 02, 2009 7:01 am
Posts: 5376
Location: Lincoln City, OR 97367
Greetings to anchorman and the Forum:

You wrote:
Quote:
I did do this whole process slightly differently than the military manual suggests, since I wanted to start with setting the filament voltages, rather than starting with the plate/screen voltages. I set the line adjust and the adjusted r134 so that all of the filament voltages were as close to the middle of their ranges as possible, and then adjusted bias, screen, etc.


I have not reviewed the calibration procedure for the D/U variant, but this does not sound like a good idea to me. Tube filament voltages are usually specified to allow for a 10% variation while still having the tube function properly. However, the Gm readings are referenced to exactly 150 volts B+, 130 volts screen and 2.5 or 5 volts grid signal voltage (at least for other versions of Hickok testers and I think the D/U variant as well). If you depart from these values to make the filament voltage exact, you will definitely have poor calibration.

Best to stick to the procedure in the manual.

Regards,

_________________
Jim T.
KB6GM


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 10:38 am 
Member
User avatar

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11078
Location: Sunbury, Ohio 43074
I tend to agree with JT. The calibration procedures for this tester, and really for anything else, were put together by the factory engineers that designed the instrument, or in this case, in consort with the military engineers, and should be followed to the letter. The only exceptions would be if there was an error in the manual, or if there has been something modified over the years which should have its own instructions.

The calibration procedure usually also has to be done in order, since later steps almost always depend on the previous steps having been done properly. This is why sometimes you can use the cal procedure to troubleshoot... start with step 1, and if you get to a part of the procedure that does not give the proper results, you may have isolated the problem to those circuits .... the last one that was good, and the first that was bad. Most of the time lol. :mrgreen:

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 4:12 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
Looks like I got this in the wrong forum. If this can be moved to test equipment, I would appreciate it!

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 4:17 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
Jthorusen wrote:
Greetings to anchorman and the Forum:

You wrote:
Quote:
I did do this whole process slightly differently than the military manual suggests, since I wanted to start with setting the filament voltages, rather than starting with the plate/screen voltages. I set the line adjust and the adjusted r134 so that all of the filament voltages were as close to the middle of their ranges as possible, and then adjusted bias, screen, etc.


I have not reviewed the calibration procedure for the D/U variant, but this does not sound like a good idea to me. Tube filament voltages are usually specified to allow for a 10% variation while still having the tube function properly. However, the Gm readings are referenced to exactly 150 volts B+, 130 volts screen and 2.5 or 5 volts grid signal voltage (at least for other versions of Hickok testers and I think the D/U variant as well). If you depart from these values to make the filament voltage exact, you will definitely have poor calibration.

Best to stick to the procedure in the manual.

Regards,


All values for plate, screen, grid signal, etc, are in spec. Measured with an accurate DMM loaded properly to match the conditions spec'd in the military manual. I tried a couple of other 6L6 tubes, and one of them made it all the way to 120 in the test. tubes that don't test as strong do seem to correlate with not working in this test. I need to dig through the ones I have and see if I can find the one that tests the best, and see if it works.

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 4:48 pm 
Member
User avatar

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11078
Location: Sunbury, Ohio 43074
You might just want to order a brand new 6L6. I got one from JJ if I recall, and I use it for a "rough" calibration tube and a tester of the tube tester. It never gets used for anything else, so for me, it's plenty close to a test fixture.

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 8:30 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
I found what appear to be a couple of NOS 6L6GAY and a 6L6GB in my piles. What is "normal" for new 6L6 on a properly calibrated TV-7?

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 8:40 pm 
Member
User avatar

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11078
Location: Sunbury, Ohio 43074
anchorman wrote:
I found what appear to be a couple of NOS 6L6GAY and a 6L6GB in my piles. What is "normal" for new 6L6 on a properly calibrated TV-7?

That is the 64 billion dollar question :) The concept of the "bogey tube" vanished long ago when the manufacturers took their secrets with them. All we can do today is estimate .

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 8:49 pm 
Member

Joined: Dec Sat 23, 2006 5:49 pm
Posts: 1450
Location: San Tan Valley, AZ
Or you could send it to Dan Nelson and be done with it. That's what I plan to do with mine. I've had it 35 years and it needed calibration when I got it. What's my hurry, right?

_________________
Always be yourself. Everybody else is already taken.


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 9:26 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
electra225 wrote:
Or you could send it to Dan Nelson and be done with it. That's what I plan to do with mine. I've had it 35 years and it needed calibration when I got it. What's my hurry, right?


Zero fun in that. By all accounts, Dan is a smart and capable guy, but he's not a magician. There's nothing he's doing that most of us can't do if we take the time to learn.

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 10:04 pm 
Member
User avatar

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11078
Location: Sunbury, Ohio 43074
Quote:
I found what appear to be a couple of NOS 6L6GAY and a 6L6GB in my piles.

"appearances" are meaningless :) I have that confirmed every time I look in the mirror :mrgreen:

Buy one bright shiny new one, and at least you'll have a place to begin ....

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Thu 01, 2021 11:28 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1620
Location: Canyon Lake, TX
anchorman wrote:
I found what appear to be a couple of NOS 6L6GAY and a 6L6GB in my piles. What is "normal" for new 6L6 on a properly calibrated TV-7?

A NIB 6L6WGB measures 40 on my TV-7D/U. I keep that tube with the TV-7 and check it every year or two. I have been doing that for the last 20 years . . . no change during that time. My TV-7 never leaves my shop so it never gets knocked around.

_________________
What happens under the chassis stays under the chassis.


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Fri 02, 2021 12:00 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
Thanks for the data point, Ed! I’m going to got through the calibration process at least one more time, and see where that gets me.

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Fri 02, 2021 5:02 am 
Member
User avatar

Joined: Mar Sun 20, 2016 11:04 pm
Posts: 1114
Location: Mesa, AZ 85206
Another possibility is to build a Hickok ACS (alternating current sink)...I have one that someone made, but I just use the military way of doing it..

Steve


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Fri 02, 2021 5:54 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
I found some out of spec resistors. I've read that the 47 ohm resistors on the selector switches can be a problem. one of them is double what it ought to be.

Alan Douglas mentioned here they ought to be carbon comp resistors:
https://antiqueradios.com/forums/viewtopic.php?f=8&t=125771

"By the way the 47 ohm resistor ought to be a small carbon comp, not a metallized film or anything good. It's there as a fuse, and I've seen metallized resistors go dead short when they fail, and glow white. Carbon comps just smoke and open up. Lots cheaper to replace a resistor, than a bias pot."

I will be digging around for some of these. There are others that are more off than they should be. really odd is r140 that is supposed to be 2.7K, but the markings look like brown, gray, red, gold which says 1.8K...

edited for clarity

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Fri 02, 2021 6:25 am 
Member
User avatar

Joined: Nov Mon 02, 2009 7:01 am
Posts: 5376
Location: Lincoln City, OR 97367
anchorman wrote:
I found what appear to be a couple of NOS 6L6GAY and a 6L6GB in my piles. What is "normal" for new 6L6 on a properly calibrated TV-7?


I don't have a TV-7 D/U; I have a TV-7 B/U. I understand the scales are different. The B/U uses a "quality" scale which can be translated into GM with an appropriate table. I don't know if the D/U reads GM directly or uses a scale similar to the B/U.

However, if you can translate the D/U readings into Gm, take a look at the tube chart for a Hickok 533. The Gm values given in this chart (and related ones) are the average values of a large number of brand new tubes that Hickok purchased for the purpose of determining that average. The Gm numbers given in the chart are therefore average for a brand new tube. The "English" scale on the 533 is calibrated to have the meter pointer at the left edge of the green "Good" zone when the Gm is 25% below average for small signal tubes and 35% below average for power tubes.

So, if your 6L6 reads close to the Gm value given in the Hickok 533 chart, it is new and performing at an average level for a new tube. If it is not more than 35% below the Gm value given in the 533 chart, Hickok still considers it "good", but it is certainly not new and is approaching the end of its useful life.

Note that the Gm values in the 533 chart are derived using the standard Hickok circuit using the voltage values specified in the calibration procedure.** Therefore, it is possible to determine a reasonably accurate value of Gm for a given tube as tested in a Hickok circuit and that tube should serve as a "bogey" tube thereafter for similar testers.

** There will be differences for tube testers using 2.5 volts of grid signal as opposed to the 5 volts of the 533; I think the D/U actually has three different signal voltages depending on the "range" selected, but consultation with a tube chart for a 2.5 volt grid signal tube tester should allow you to see the same average. I doubt the D/U will test a 6L6 at less than 2.5 volts of grid signal. What it actually uses for a 6L6 will have to be determined by the operator.

Regards,

_________________
Jim T.
KB6GM


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Fri 02, 2021 6:57 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
Hi Jim,

That’s a good tip to check the 533 data. The main difference between the D/U and the B/U is the additional test range F for very high transconductance tubes. Strangely the very low signal voltage range on the D/U is not used except for a handful of tubes that nobody has. And tubes like 12Ax7 can’t take advantage of the low signal voltage in the 1v range on range D, because the transconductance of that tube is low enough that the pass/fail point would be around 6 or 7 on the scale of 120 (same as all other tv-7 testers), and maybe not so accurate or useful of a test.turns out that if a person trusts results for a 12ax7 on the tv-7, they can trust the results on an I-177b too. The 6L6 is tested on scale D using 1v Test signal, but perhaps a meaningful comparison can be drawn to one of the newer testers that use similar test voltage?

I’m going to upgrade a few resistors tomorrow, and see if that changes anything. There are a couple involved in the mutual conductance test that might be causing the problem, specifically one that is on the #3 push button. R116? I’m going to go for the easy to reach ones and see if they fix the problem before I have to take more of this apart. That and R140 that is the wrong value entirely.

I tried calibrating with the 83 that is relatively unbalanced and a basic solid state one that has two 10ohm resistors connected to two 1n4007 diodes with a fuse in the middle, but the results were the same with not being able to calibrate range C properly. The 5y3 is pretty close to balanced, definitely more so than the spare I have. The symptom being identical is what led me to start diving into the resistors. Hopefully one or more of them being replaced solved the problem.

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Fri 02, 2021 8:55 am 
Member
User avatar

Joined: Nov Mon 02, 2009 7:01 am
Posts: 5376
Location: Lincoln City, OR 97367
Greetings to anchorman and the Forum:

To determine if the 83 (or your diode substitute) is doing the job properly, perform the test below.

WARNING! Be sure that the tube tester is isolated from ground, preferably with an isolation transformer when performing this test. Be sure to isolate the ground pin on the TV-7 power cord from actual ground; otherwise you may see fireworks with a grounded scope.

Note: Set up the TV-7 to test a 6L6 for this measurement.

PLATE SUPPLY BALANCE TEST

11. Connect a DC coupled oscilloscope to pin 3 of the octal socket. Use pin 8 as a common for the scope. Press P3.
Observe the plate voltage and obtain a display on the scope that shows the rounded peaks of the 120Hz pulsating DC with as high a gain as possible. Set the vertical position on the scope to move the trace downward as you adjust the gain upward to maintain the top of the trace on the screen. Verify that the alternating peaks of 120Hz DC are of equal amplitude. Release P3.

Because of the way the Hickok test circuit works, this measurement is very important. Any imbalance between the alternate peaks of the plate voltage will cause micromhos to be either added to or subtracted from the actual tube Gm, depending on which peak is greater.

Edit: Add TV-7 setup note.

Regards,

_________________
Jim T.
KB6GM


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Sat 03, 2021 2:01 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
Hi Jim,

Thanks for the tip. I’ll give that a look when I get these out of spec resistors replaces. No luck finding carbon comp 47ohm 1/2W resistors in my stash, but I did find some NOS 62R 1/4 watt, and in a coffee can of random resistors that I sort of thought was junk stuff, I found some new 16R 1/2W. So I paralleled the 62, and put in series with the 16, and I get pretty close to 47R. I’ve been lugging around that coffee Can for years, and feel mildly vindicated for hoarding it and it’s contents now ;) The great uncle, who had filled the coffee can with “junk” and also gave me this tester would be proud to know I had saved and then used it all.

Still have some more of these 47R carbon comp resistors to replace, and a few others that will get done with metal film, then try to calibrate again. Already with r102 replaced, my screen voltage supply is up to 131.7V so I’ve actually got some room for adjustment on R130 now (was previously maxed out). Onward to check and see if this make it possible to calibrate range C with the 6L6, and then finish replacing more resistors.

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: Tv-7d/u calibration problem. Need guidance!
PostPosted: Apr Sat 03, 2021 9:19 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
I replaced one other 47R resistor, the one on the grid circuit. The one in the plate circuit measured 62 ohms, which is too high, but putting jumpers in there and adding 180 ohms in parallel to bring it into spec didn’t make any meaningful difference in the readings on the meter, so I decided to leave it alone for now. I’d have to take the switch bank out to get to that one, and I wasn’t in the mood to fuss with them when it wouldn’t make a big difference in the readings.

I repeated the “tube simulation” with 50v ac supply and 10k resistor in series with it. This time I followed some directions from the blue glow site, and first set r113 and r115 both at 41 ohms. I’m not sure where they got it notion from, but I figured, it’s supposed to be a balanced circuit, might as well start sort of balanced. Then I went back to the army instructions, and adjusted r115 because I was a little short of 40 on the B range. Switching to C range, I set R114 so that the meter read 20. In principle, this is all you need to do, and you’re calibrated enough... kind of.

The next test/task in the army instructions is to insert 6L6 go to range B, turn bias down from 100 until the meter reads 120... mine still won’t read 120, even on. Tubes that test and look new, compared to some pulls that came from a hard life as a regulator in a HV supply. One reason I’m a fan of holding onto some “bad” tubes in addition to good ones, to confirm that the tester is actually working. Mine still won’t get to 120. But if I set at 100, and switch to range C, it does show 50 on C. Much above that and they stop tracking properly. I.e. for max value I get of 118 on range B, I get 80 on range C. So I decided to be happy for now that new 6L6 tubes read about 60% more than the reject point indicated in the test data. Newish looking 12AT7 was likewise about 60% of above the reject point. I found a NOS one in original box, but had already put everything away at that point, so will test it another day.

Unless someone has an explanation for why I can’t get the 6L6 test where the ranges get set to go all the way to 120, and there’s some more fiddling to do, I’m going to call it good, and get on to the next step, which is overhaul and calibration of two I-177b testers, and building some little transmitters.

_________________
filling in the gaps in my education...


Top
 Profile  
 
Post New Topic Post Reply  [ 79 posts ]  Go to page 1, 2, 3, 4  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: Barry H Bennett and 30 guests



Search for:
Jump to:  


































Privacy Policy :: Powered by phpBB