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 Post subject: Re: TV-2/U repair
PostPosted: Oct Sun 07, 2018 7:45 pm 
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Joined: Mar Thu 29, 2018 3:41 am
Posts: 171
Location: Portland Oregon
Howdy Steve,

Thanks for the reply.

As you know, the AN/URM-105 has a 1000 Ohm per volt AC meter and a 20000 Ohm per volt DC meter.

I shunted my FLuke 83 DMM (10M impedance) with the resistors for the following AN/URM-105 voltage ranges:

DC - 20000 Ohm/Volt:
Full Range.........Shunt Resistor
1......................20000
10....................204000
100..................2500000
1000................I just used the 10M of my DMM

AC - 1000 Ohm/Volt
Full Range Shunt Resistor
10.....................10000
100...................101000
1000.................1111000

I mathematically played with the numbers for R36. Currently, the resistor is 257K Ohms. The spec is 250K Ohms. I can fix that. You are right about the linearity of my meter being a little wonky. I can't quite get all of the readings to fall within 2.5%. I'll double measure these values. R63 is also a little high. It is measured to be 28020 it should be 27800. This resistor should be within .5%. I'll change R36 first and check how it affects the voltages in Plate selection R and S.

I'll load the 0.625V filament setting with a 1KOhm resister and see what it draws down to. Currently, I have been using a 10KOhm resistor in parallel with my meter.

We'll see how the screen voltages measure once I change R36. According to the manual, I was supposed to set the plate voltages to those listed and then set the screen voltages. For selector K, I was supposed to set the plate for 125V and the screen for 180V. This does not make any sense to me at all (I cannot see why one would want to run a tube this way). Same goes for the selector L (plate 125V, Screen at 135V). So, I think that the manual is wrong. I need to figure out why selectors K, M and P screen voltage did not achieve the plate voltage.

My Gas, Short and Filament continuity test checks good. My cathode bias resistance is off:

Cathode Bias Resistance

Range.......Spec......Measurement
A..............47.........54
B..............94.........105
C..............141.......158
D..............188.......218
E..............288.......218

The Shunt control test is not good. I made a pseudo TS-682A/GSM-1 by using a DC power supply, adding a current limiting resistor in series with the ammeter on my DMM.

I measured full scale Quality meter measurements at:

Shunt......Current for FS
10...........3.34 mA
86...........0 - meter floated up to FS

I have to figure out why this is happening! I'll spend some time trying to figure out what could be happening here.

Do you have any suggestions for how to fix the Signal, and Shunt test results?

Dave


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 Post subject: Re: TV-2/U repair
PostPosted: Oct Sun 07, 2018 7:55 pm 
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Location: Sunbury, Ohio 43074
Why not take a few minutes and check your meters for linearity? All you need is a 1.5V battery, a resistor, a multi turn potentiometer, and a DVM. Hook those all in series. If the meter movement tracks your DVM current readings from zero to full scale, it's linear. If not, it's not. You'll have to know approximately at least what the meter movement's sensitivity is of course.

Select the fixed resistor to limit the current so if you turn the trimpot to minimum you don't blow the meter movement by putting the full 1.5V battery across it directly. This would be bad. The fixed resistor value will depend on the sensitivity of the meter you are testing.

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 Post subject: Re: TV-2/U repair
PostPosted: Oct Sun 07, 2018 8:49 pm 
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Location: Littleton, MA
TechyMechy wrote:
According to the manual, I was supposed to set the plate voltages to those listed and then set the screen voltages. For selector K, I was supposed to set the plate for 125V and the screen for 180V. This does not make any sense to me at all (I cannot see why one would want to run a tube this way). Same goes for the selector L (plate 125V, Screen at 135V). So, I think that the manual is wrong. I need to figure out why selectors K, M and P screen voltage did not achieve the plate voltage.

I don't think the manual is wrong. Looking at the circuit, the test makes sense. Why it's set up that way, I've no idea, but that's the way the TV-2 is designed.

I say again, position H and K on the screen selector are wired together. If you're not getting the same voltage on both H and K, then something is mis-wired or the switch is bad.

Your 83V is average responding on AC, so you should be good there.

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Last edited by stevebyan on Nov Mon 26, 2018 11:30 pm, edited 1 time in total.

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 Post subject: Re: TV-2/U repair
PostPosted: Oct Mon 08, 2018 2:24 am 
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Joined: Mar Thu 29, 2018 3:41 am
Posts: 171
Location: Portland Oregon
Barry, I did check the linearity of the Grid, Plate, and Screen meters. They are very linear 1000 Ohms/volt. I put a 20K Ohm resistor in line with my power supply and put my Fluke 83 in series. The biggest deviation I had on the full scale was 0.1 mA on all three meters. I will read up on the filament and quality meters. I'm not too sure what they are. I want to know before I start to mess with them.

So, now I have to figure out why my plate and screen voltage isn't linear across the different resistor ranges. I know my ability to measure is better than this.

I looked carefully at S3 but couldn't see any issues on the disks 3 and 4 rear. The contacts are definitely good on disk 4 rear. It is nearly impossible to see disk 3 rear. I understand what you are saying about the H and K sharing the same tap off of T2 and they should have the same voltage (as does G and J), but it isn't happening.

G, H, and J have the same plate voltage G>H>J for screen voltage
K, L, and M have the same plate voltage K>L>M for screen voltage
N, P, and Q have the same plate voltage N>P=Q for screen voltage

I will be looking into the Signal circuit a little closer

The screen voltage meter is a bit of a puzzler for me. The meter is off of the cathode 6X4 and has resistors R54, 55, and 56 to set teh voltages and current through the meter. I cannot figure out why this is coupled to the plate voltage as is the signal test meter.

Also, I need to determine why my shunt test was wonky.

I appreciate any input on this. I"m going to be ordering some capacitors, etc. tonight.

Dave


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 Post subject: Re: TV-2/U repair
PostPosted: Oct Mon 08, 2018 4:30 am 
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Joined: Mar Thu 29, 2018 3:41 am
Posts: 171
Location: Portland Oregon
I was also wondering what your thoughts were regarding:

1. Capacitors. I will be replacing C1 and C2. The C1 I have in my tester is a 14000uF, 50Vdc cap. I was thinking of getting a 105C working temperature capacitor replacement. In the manual and from other pictures, people have 20000uF, 50Vdc cpapcitors in their tester. Should I get a 20000 uF capacitor? Also, C2 is 330uF, 6WV. Is it OK if I get a bigger cap than 330uf?

2. Resistors vs. trim pots. I'm not really worried about spending an extra $25-$30 for the right resister. Would you get trim pots so you can "dial in" the correct resistance or would you use standard, metal film resisters? I had one buddy tell me that trim pots can change from vibration.



Thanks for you input.

Dave


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 Post subject: Re: TV-2/U repair
PostPosted: Oct Mon 08, 2018 6:26 am 
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Location: Sunbury, Ohio 43074
There's really no need for 105 degree caps, but is no harm other than cost in using them.

I already mentioned that using a pot instead of a fixed resistor adds a possible point of "mechanical" drift, and is unnecessary. Best to use precision resistors where they are called for. Sometimes you can use a "standard" value that has been hand selected for the proper resistance, i.e. a 10% resistor that is picked because it's actual value is precisely what you need..... like that. Or you can use parallel/series combos in the same way to achieve absolute precision. Or, you can just buy the right precision resistor. If the existing ones are wirewound, it's hard to see why they would need replacement........

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 Post subject: Re: TV-2/U repair
PostPosted: Oct Mon 08, 2018 7:08 pm 
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Joined: Mar Thu 29, 2018 3:41 am
Posts: 171
Location: Portland Oregon
Hi Barry,

I missed your comment about trim pots drifting due to vibration, etc.

OK. I have a ton of precision resistors. I know I have resistors out of spec so I should change those - especially the ones that are used to calibrate the meters.

I need to figure out why my Shunt testing is providing such weird results. I'll follow the schematic and determine what is going on. I'll also try to test my quality meter and see how it behaves. It is a 10,000 Ohm/volt meter with a 150uA FS. I'll try to figure out how to get a reasonable current measurement and hook up a 100K resistor between my DC power supply and my DMM-ammeter.

I was about ready to purchase capacitors last night but then my buddy told me that he may have these. One item I noticed is that the picture on:

https://digilander.libero.it/pasqua49/C ... tester.htm

Clearly shows that the 20000uF capacitor is a 15WV. The capacitor I have in my tester is 50WV. There is a significant price differential on these capacitors. Does someone know what is the correct speck for C1?

Lots of work left to do to get this right.

Dave


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 Post subject: Re: TV-2/U repair
PostPosted: Oct Mon 08, 2018 7:34 pm 
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Location: Sunbury, Ohio 43074
It looks like 2000uF, not 20,000. A bit tough to tell from the picture. The voltage should at least match that of the original part, although more is not a problem. Never less. Are you certain those need to be replaced? Mine are originals. The TV2 lives in a sealed case, so it's subject to a whole lot less environmental stress than some other equipment.

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 Post subject: Re: TV-2/U repair
PostPosted: Oct Mon 08, 2018 8:25 pm 
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Joined: Mar Thu 29, 2018 3:41 am
Posts: 171
Location: Portland Oregon
Hi Barry,

As far as the capacitors, C1 and C2 have much higher dissipation than the other capacitors. I did recheck the picture and it is a 2000uF capacitor which also aligns with the schematic. C1 was shown on the schematic to be .002 - and I'm assuming that this is .002 f, which is 2000 uf. C2 has a spec of 100 on the schematic, which I'm assuming to be 100uf. The can for the C2 says it should be 330uf, but I measured 680 uf with a dissipation of .72. The can for the C1 says it is 14000uf but it read to be 18000uf with a dissipation of 0.417. I don't have the ability to test them for leakage.

Something is wrong with my quality meter testing using the 5th echelon. With the shunt at 10, my current to get full scale is 3.34 mA. It should be 4.95 mA. When I turn the shunt to 82, something is floating the meter to full scale. I didn't have tp provide any current. I know that the quality meter is a 10,000 Ohm/volt and requires 150uA for full scale readings. Hence, something is amiss with the circuitry. I need to look at the schematic and see if I can figure out what is happening.

I'm not too sure if the capacitors are bad, but I don't have any way to really test them. I have to take them out of the tester to test them for leakage, and I wonder if it would be best to replace them with new caps.


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 Post subject: Re: TV-2/U repair
PostPosted: Oct Mon 08, 2018 9:03 pm 
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Location: Sunbury, Ohio 43074
Quote:
C1 was shown on the schematic to be .002 - and I'm assuming that this is .002 f, which is 2000 uf.

I have never seen a schematic refer to a capacitor in farads unless it is over 1 Farad, which yours will not be. Your .002 should be .002uF, not 2000 uF. If I remember I'll bring home my TV2 manual tonight and I can talk about all of this a bit more intelligently.

Stand by. Don't buy any parts yet :)

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 Post subject: Re: TV-2/U repair
PostPosted: Oct Tue 09, 2018 12:14 am 
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Location: Sunbury, Ohio 43074
Dave, at this point, since you seem to have a "mostly working" TV2, I would suggest you go back to square 1. Either start with the calibration again and proceed through the rest of the steps, or as an alternate jump to the 5th echelon and do a performance test. If you come to ANY item that is off, STOP right there and find out why.

I get the impression that you may be chasing either too many things, or worse, chasing ghosts.

You must verify that your test equipment is reading properly (which I think you may have accomplished with your shunt resistors). Personally, i'd stop right now and get the proper meter. Old VTVM's are dirt cheap even if you buy a restored one. But if you are SURE your meter is reading correctly, you're ok to proceed along those lines.

A lot of times, in something as complex as this tube tester, you can miss a single step or mis-do a single step, and odd things happen from then on. It's all too easy. .. we've all done it multiple times. Reading back through all your posts, I think you may be on information overload... in the case of a voltage that is off, stop and look for why. While it can be helpful at times to see what else may be off, in this case each system is somewhat isolated from the others, so it should not be too hard to pin down what is causing the bad reading without getting a dozen other bad readings to chase. The troubleshooting guide can be helpful, but running through an alignment and stopping when something will NOT align properly, then finding out why before proceeding, is probably the more prudent approach.

The key is not to be impatient, and if you come to ONE step that is wrong, find out why before you proceed too much further. Also, along the lines of replacing components, I'd be very hesitant to replace any resistors unless there is a compelling need to do so. If you do, make absolutely sure you replace with the value ON THE RESISTOR, not on the schematic, unless you are 100% certain that someone mis-replaced one in the past. Gear of this vintage had manufacturers constantly tweaking their equipment without always updating schematics and manuals. As I noted before, wirewound resistors unless showing signs of overheating or actually being open, seldom if ever fail. They simply do not change. Carbons, yes they can, but in THIS instrument, I'd suspect them last unless, again, they show signs of overheating.

Just a few advanced troubleshooting (tube stuff) tips :)

The

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 Post subject: Re: TV-2/U repair
PostPosted: Oct Tue 09, 2018 2:49 am 
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Joined: Mar Thu 29, 2018 3:41 am
Posts: 171
Location: Portland Oregon
Thanks for the tips Barry. I plan on starting resistor replacement this week. Make a change, test, make a change, test, etc. I'll fix what I definitely know what is bad and see how that affects the 5th echelon testing. I plan on using this as my primary tester, so I want to make it robust.

I have a favor for you. Can you check you TV2 for the capacitor values?

Dave


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 Post subject: Re: TV-2/U repair
PostPosted: Oct Wed 24, 2018 4:55 pm 
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Joined: Dec Mon 05, 2011 1:10 am
Posts: 347
Some thoughts:

>If the SCREEN VOLTAGE won't adjust high enough when the PLATE VOLTAGE is set relatively low, that's probably because the PLATE adjustment is like a Variac to the power transformer primary ... cutting back the primary voltage to lower the plate voltage will also lower the voltage to the plates of the 6X4 screen supply rectifier, thus limiting the maximum voltage available to the SCREEN adjusting pot. Be sure the screen supply filter capacitors are good and the 6X4 tube is good and strong. I've never done it, but maybe a solid state replacement for the 6X4 might boost up that voltage.

>You can't rely on the fuses to prevent burning out the main power transformer. I once lost a TV-2 that way ... a slightly leaky filter capacitor in the bias or screen supply must have gotten gradually worse and gradually heated up the transformer till it developed an internal short. Moral of the story: REPLACE at least the bias and screen filter caps with high quality modern ones ... no need to worry about appearances, re-stuff cans, etc., just be conservative on capacitance, voltage and temperature ratings.

>I don't really understand exactly what those "20 VAC" and "35 VAC" marks on the PLATE VOLTS meter mean, but they DO NOT correspond to the voltage you will read with any common meter. As you noted, the actual (RMS?) voltage is way less than the meter reading ... maybe they have marked the meter scale for "peak" or "average absolute" or something else??? But, any which way, I have seen the exact same "problem" any time I have tried to do that check.

>Once you have the Gm bridge, and its associated SHUNT pot, within spec, you really don't need to worry much about the accuracy of all those other meters. Just use them as a rough guide and patch in a cluster of cheap (<$19@) DVM's for much better accuracy than you will ever be able to get using the originals. An octal or 9-pin mini Pomona or Vector test socket adapter makes it real easy (albeit a tad tedious to set up if you're testing a bunch of different tube types). If you want to save a few $, just remove the submini adapter from the second octal socket and poke in some "stakes" you can make from (10 gauge?) wire snippets or even suitable size nails. I have found the widely-available AN8008 DVM's to track spot on with a fancy $$$ Fluke "NIST traceable" DVM for both DC and "True RMS" AC voltages.

>There are at least two different versions of the roll charts of tube test data. I'm not sure which is "better", or if maybe they are meant for use with different models or even different serial numbers of the tester.

>There are lots of errors and inconsistencies in the Army manuals. Maybe somebody has catalogued them all someplace, but I haven't seen it if they have?

>I like to run a tube tester through a "Kill-A-Watt" meter to keep an eye on the current draw or power consumption. Many problems that can eventually kill your transformers will show up as a gradual increase in mains power draw.

>Pay special attention to residual ripple in the bias power supply. A little bit there can really mess up the Gm reading. Won't hurt to parallel patch in an extra 50 to 100 uF of filter capacitance.

>While the roll chart test settings are OK for most "good / bad" tube checking, you can always "roll your own" tests using whatever combination of element voltages you like (up to the power supply limits, of course). The SIGNAL and SHUNT settings published by Nolan "Redneck" Lee, Alan Douglas and others allow you to make "near lab quality" mutual conductance measurements. That's the one really great advantage that the TV-2 family has over the rest of the pack of "Hickok-oid" tube testers.


^^;;^^


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 Post subject: Re: TV-2/U repair
PostPosted: Nov Mon 26, 2018 8:54 pm 
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Location: Portland Oregon
It's been a while since I've been able to work on my TV-2/U. I was able to work on it this Thanksgiving weekend.

Here's the status thus far:

1. I replaced all of the capacitors. I just don't trust the older electrolytics and I don't have a way to test them at voltage. I replaced the following:

C1 - 2200 uF, 65V capacitor (the cap in the tester were 1400 uF, 50V)
C2 - 330 uF, 50V capacitor (the cap in the tester were 330 uF, 6V)
C3 - 100 uF, 250V capacitor (the cap in the tester were 50uF, 200V)
C4 - 2 ea. 10 uF, 400V capacitors (the caps in the tester were 10 uF, 250V)

I'm using the TM 11-6625-316-35 manual for qualifying the tester (Echelon 5 testing).

I also had to change a number of the blue, 1% resistors in the tester. When I unsoldered them, the caps fell off of the resistor element. I also changed out other out of spec resistors, especially those used to limit the currents in the meters.

I think my plate meter has lost it's linearity. My plate meter over predicts the voltage on the high end by roughly 2% (so I'm only getting 245V at the socket when my meter reads 250V - G, H, J ranges) and under predicts the voltage on the lower voltages (N, P, and Q; N range I am reading 92.5V at the socket when the meter is reading 90V, P range - 66.5V at socket when meter is reading 65V, and Q range - 64.5V at socket when meter is reading 62.5V).

I'll try to test the plate meter for linearity with a better DVM. I initially used my 3.5 digit Fluke 83 for linearity measurements, but I will use my 5 digit fluke when I retest.

My Screen meter is OK, but not great. It measures (DVM/meter on the TV2) about 1.4%(3V) low on Ranges GHJ to +2% (0.9V) on Range Q. I'm OK with this variability. The spec in the manual is +/-5V!

I have passed all of the echelon 5 tests except for the plate voltage (results above) and the Shunt Control test. The filament voltages, signal voltages, and grid meters are really quite good. I don't have that special tester described in the manual for the Shunt Control test so I have tried to simulate it with a DC power supply, a current limiting resistor, and run the current through my DVM - but it wasn't working right.

Has anyone ever passed the Shunt Control Test on page 40, Ch 4 of the TM 11-6625-316-35 manual without using the TS-682A/GSM-1? If so, how did you check this?

I still haven't figured out the Plate meter R and S ranges and how the AC voltages relate to the red lettering on the meter.

Does anyone have an extra TV-2/U plate meter? I don't have any of the bogey tubes listed in the manual. Does someone know how to make a precision test tube so I can get some idea if this is giving good results? I tested a 6V6 tube last night and it barely passed GM testing (but I don't know how good the tube actually is).


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 Post subject: Re: TV-2/U repair
PostPosted: Nov Tue 27, 2018 5:50 pm 
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Posts: 347
[quote="TechyMechy"]

>...

I still haven't figured out the Plate meter R and S ranges and how the AC voltages relate to the red lettering on the meter.

Does anyone have an extra TV-2/U plate meter?

=============================================================================

I have posted an "analysis" of how the emission test for diodes on Ranges R and S appears (to me, at least) to work.

In a nutshell:

The 20 VAC and 35 VAC voltages applied to the tubes being tested are taken off two separate taps on the main power transformer.

When you adjust the PLATE rheostat, it's like putting a Variac on the primary winding of the transformer ... adjusts ALL the secondary winding voltages at once.

The PLATE meter does not measure any of these AC voltages directly. Instead, it measures the "averaged" DC voltage at the filament of the 83 rectifier tube. On Ranges R and S, the #83 tube is operated in half-wave mode, producing a train of approximately half-sine arches at 60 Hz. The "geniuses" who designed this circuitry apparently somehow figured out the appropriate resistances to be put in series with the PLATE meter such that it would deflect to the red "20 AC" or "35 AC" when the 20 VAC or 35 VAC taps are right on. Bloody damn kludge, IMHO! I have measured the actual (RMS) voltages at the transformer taps and found them to be generally in "pretty good" agreement with the red marks on the PLATE meter(when corrected from RMS to AVG), so I suppose they got it right, or at least as good as could be expected. I have been thinking of maybe installing a couple of new test points in the panel of my personal "keeper" TV-2 so I can hook up a DVM directly to the appropriate points (with safety seeries resistors,of course).

I wouldn't spend the $ to replace a working TV-2 PLATE meter unless it was REALLY bad, like sticky or open or broken glass or something gross like that. I don't rely on those meters for much more than "ballpark" measurements anyway. For serious measurements (well, as "serious" as these testers are capable of, anyhow), I use a 9-pin or octal test adapter to hook up some cheap (<$19), accurate Chinese DVM's. (AN8008's) ... OK, some PITA setup work involved, but nobody uses a TV-2 for quick-n-dirty anyways.


^^;;^^


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 Post subject: Re: TV-2/U repair
PostPosted: Nov Tue 27, 2018 6:45 pm 
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Location: Portland Oregon
Thanks for the reply!

Shoot, I'm not too sure I fully understand what you are saying....sorry! Could you please correct me if I'm wrong?

My DVM reads 11.4 Vac on the socket when I should be reading 20Vac (via the red lines on the plate meter) on Range R
My DVM reads 19.6 Vac on the socket when I should be reading 35Vac (via the red lines on the plate meter) on Range S

For the R range:

Since my DVM is measuring RMS voltage and the meter is measuring an average voltage and the 83 is only using 1/2 of the AC signal:

11.4Vac from meter/1.11 = 10.27V RMS (single sided)
2 * 10.27 VRMS = 20.54 Vrms-ac - multiply it by 2 due to 1/2 of the AC signal due to the 83 Tube. = this is the true voltage applied to the plate in AC mode.

Or, my meter error is 2.7%

Likewise - from the S range:

19.4Vac from the meter/1.11 = 17.65 V Rms (single sided)
2 * 17.65 VRMS = 35.3 Vrms-ac

Or, my meter error is 0.9%

Is this what you meant?

Also, have you ever completed the Shunt Control Test on page 40, Ch 4 of the TM 11-6625-316-35 manual without using the TS-682A/GSM-1? I can't find any information on this tool.

I have a 9 pin test socket. I guess I will buy a bunch of AN-8009's and use these for the very accurate measurements. I was also thinking of making a calibration chart which I would put in the lid for the plate meter. The plate meter is the only meter that seems to be out of calibration (according to the Echelon 5 testing). The filament is quite good (within +/-1% on all values except for the 0.625V tap), the grid is quite good (within 0.5% for all three ranges - full range, but within 1.5% on any value), the signal red line is quite good (within 0.5% on all ranges) and the screen is well within the specs of the manual (max error is 2.7V when the spec is +/-5V). The plate meter is the only grumpy one!


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 Post subject: Re: TV-2/U repair
PostPosted: Nov Tue 27, 2018 6:54 pm 
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Quote:
The "geniuses" who designed this circuitry apparently somehow figured out the appropriate resistances to be put in series with the PLATE meter such that it would deflect to the red "20 AC" or "35 AC" when the 20 VAC or 35 VAC taps are right on. Bloody damn kludge, IMHO!


If I may .... think back to the time when these testers were being designed. Engineers did not have access to all the tools, or knowledge, or experience that exists today. They WERE in fact geniuses at AC design, transformers, and yes even Kludges!!

These days, as seen in endless posts here and elsewhere on the net, people seem to want the precision of a $25,000 lab grade instrument out of a 75 year old tube tester, which btw is testing things that had nowhere near "precision" anyway. Tubes. Yup, analog devices, manufactured within a fairly loose range of tolerance for most parameters.

That's not to say you should not try and get the most out of your tube tester. But there IS kind of a point of diminishing returns. :)

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 Post subject: Re: TV-2/U repair
PostPosted: Nov Wed 28, 2018 5:27 pm 
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TechyMechy wrote:
Shoot, I'm not too sure I fully understand what you are saying....sorry! Could you please correct me if I'm wrong?

My DVM reads 11.4 Vac on the socket when I should be reading 20Vac (via the red lines on the plate meter) on Range R
My DVM reads 19.6 Vac on the socket when I should be reading 35Vac (via the red lines on the plate meter) on Range S

For the R range:

Since my DVM is measuring RMS voltage and the meter is measuring an average voltage and the 83 is only using 1/2 of the AC signal:

11.4Vac from meter/1.11 = 10.27V RMS (single sided)
2 * 10.27 VRMS = 20.54 Vrms-ac - multiply it by 2 due to 1/2 of the AC signal due to the 83 Tube. = this is the true voltage applied to the plate in AC mode.

Or, my meter error is 2.7%

Likewise - from the S range:

19.4Vac from the meter/1.11 = 17.65 V Rms (single sided)
2 * 17.65 VRMS = 35.3 Vrms-ac

Or, my meter error is 0.9%

Is this what you meant?

Also, have you ever completed the Shunt Control Test on page 40, Ch 4 of the TM 11-6625-316-35 manual without using the TS-682A/GSM-1? I can't find any information on this tool.

> ...


As best I recall at this time, I WAS NOT strictly following the "echelon" test instructions. Since I had the TV-2 out of its shell, it was pretty easy to measure the AC voltages straight from the transformer taps ("upstream" side of the limiting resistors on the resistor board). I THINK that the socket voltages you would get using the "echelon" method SHOULD be the same, but I haven't actually confirmed that or traced through the circuitry.

I was using a Fluke ScopeMeter, so I was able to look at the waveforms as well as have the meter calculate "AVG", "RMS", "P-P", etc. for me, so I didn't hae to do any of the calculations. If I Recall Correctly, the "AVG" AC voltage measured this way matched up "pretty well" with the values of the red lines on the PLATE meter.

The important point here is that the PLATE meter is NOT seeing this AC voltage at all, but rather a train of half wave rectified pulses from the #83 tube. Somehow, the designers were apparently able to get the PLATE meter, an averaged DC reading device, to show when the average AC voltage is 20 or 35 V. IMHO, a tricky relationship at best, given that it depends on the response curve of the #83 tube, which can vary a lot from tube to tube (I wonder what effect a solid-state #83 would produce!). Hell, why not just read the AC voltage directly and be done with it? I think I'll add a couple of pin jacks to my TV-2 so I can do just that.

If your PLATE meter is not agreeing as well as you would like with the actual AC voltages from the transformer taps, it MAY not be the fault of the meter. Maybe your #83 tube has a conduction curve that is different enough from the "standard" assumed by the designers to mess up your readings?


No, I have never tried to do the SHUNT calibration check. Both the SHUNT pot and the measuring circuit "bridge" resistors are wire-wounds that are unlikely to have drifted over time. I HAVE run 3 "bogey" tubes which were "certified" for the TV-7 series testers (by Blueglow Electronics, IIRC) ... got results within around 10% ... not GREAT, but apparently well within expected tester-to-tester variations, according to the gurus like Paul Hart.


^^;;^^


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 Post subject: Re: TV-2/U repair
PostPosted: Nov Wed 28, 2018 7:48 pm 
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Joined: Mar Thu 29, 2018 3:41 am
Posts: 171
Location: Portland Oregon
Liberated Manuals has a copy of the TM-11-6625-316-35 manual that has an addendum that directly addresses testing of the R and S settings on the plate switch:

http://www.liberatedmanuals.com/TM-11-6625-316-35.pdf

If I followed their procedure, I measured values within the expected range. Also note that the procedure for Shunt Control Test changed greatly. I will write more tonight, but when I followed the Shunt Control Test, the current values for the 10 reading on the shunt resistor is out of spec (something like 4.10 mA vs. 4.92 mA (spec), but the Shunt 90 setting is within spec (but not great). I need to figure out *WHY*. I hope my quality meter is OK.

I also was playing with the linearity of my plate meter last night. I think that the meter is fine, but the settings for the N, P, and Q ranges are reading high voltages. I have to figure out why. I don't know if this is a fundamental transformer issue or? I am going through and carefully measuring all of the voltages/resistances to ground and also the resistor values throughout the tester. Trying to trace out the schematic is almost beyond my capability....but I will give it a real try tonight. I think I will try to use the marker function in Foxit on the schematic...That might be better than piecing together paper schematics and using ink markers.


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 Post subject: Re: TV-2/U repair
PostPosted: Nov Thu 29, 2018 2:30 pm 
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Joined: Dec Mon 05, 2011 1:10 am
Posts: 347
TechyMechy wrote:
Liberated Manuals has a copy of the TM-11-6625-316-35 manual that has an addendum that directly addresses testing of the R and S settings on the plate switch:

http://www.liberatedmanuals.com/TM-11-6625-316-35.pdf

If I followed their procedure, I measured values within the expected range.


Yes, I have seen that "Change No. 1" addendum; it seems to be right after the cover page in most all of the manual copies available online. But I never paid much attention to the details or tried to do the "echelon" testing for the R and S emisssion test settings. If it worrks for you, CONGRATULATIONS!

Personally, I long ago concluded that the goal of setting the PLATE meter needle to the red marks was to get the transformer tap voltages to 20 and 35 VAC (AVG). That SEEMS to work out about right on the one TV-2 that I have actually taken the trouble to check out to that level. HOWEVER, it looks like the addition of that 3000 Ohms resistance would cause a substantial drop from the transformer tap voltage. So, maybe my conclusion about setting the transformer tap voltages is wrong. At this point, I´m more confused than when I started.

With all the errors, revisions and inconsistencies in that Field and Depot Maintenance Manual, I begin to suspect that it must have been written to confuse The Enemy! Maybe, somewhere on The Dark Web, there may be a copy of the top secret REAL manual. Or, maybe some really dedicated fellow (NOT me!) will spend a few weeks and write one; Nolan "Redneck" Lee comes to mind, but I believe that he has moved on to other areas of interest.



^^;;^^


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