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Old 6th Dec 2018, 4:36 am   #1
sven_swe
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Default Taylor 45C Valve Tester Resistor question

Hello all,

It seems like a resistor has been changed in my Taylor 45C valve tester, and I am uncertain why and what the original value was?
When looking at the schematics it seems like this is the 2.2K resistor (R12) on the main switch which is in series with R16 (270k) that is mounted on the gas test button.

What is there now are two 270ohm resistors in parallell?? This is changed since the resistors looks new and the red paint from solder joints are gone.

Am I right that this is the R12 2.2K resistor from the schematics originally? And why would the reson be to change it to 135ohm(the two in parallell)?

I have attached the latest schematics I could find and also a picture. It is a later model with the meter behind the front panel.

Many thanks in advance,
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Old 6th Dec 2018, 8:54 am   #2
David G4EBT
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Default Re: Taylor 45C Valve Tester Resistor question

Unless I'm mistaken, those two resistors appear to be clearly marked 2,700 - not 270 and if that so, the resistance would be 1,350 - not 135 Ohms. In series with R16 (270k), the total resistance would be 1,350 + 270k = 271,350. The circuit calls for 270,000 + 2,200 = 272,200. Thus, the actual resistance will be just 0.3% lower than the circuit calls for.

As to why they were fitted, I'm just guessing, but whoever did it may have just chosen the closest values that he had to replace a dud 2k2 resistor. If so, he did it for practical reasons - not technical.

You tester looks in nice condition!
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Old 6th Dec 2018, 9:13 am   #3
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Default Re: Taylor 45C Valve Tester Resistor question

That is fine in that position, see them changed a fair bit with all types of resistor, but it only had an Erie 1 watt 20% fitted in the first place.
A word of caution, be wary of using switch cleaner liberally on the selectors, the wafers become conductive, which spells the end of the tester as the switches are not available.
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Old 6th Dec 2018, 10:02 am   #4
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Default Re: Taylor 45C Valve Tester Resistor question

I read 270 Ω in each resistance. Perphaps the person who change them read 2700 and thought he was doing a correct job.
 
Old 6th Dec 2018, 10:10 am   #5
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Default Re: Taylor 45C Valve Tester Resistor question

It'd be easy enough for the OP to check the value with a meter.
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Old 6th Dec 2018, 12:49 pm   #6
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Default Re: Taylor 45C Valve Tester Resistor question

Quote:
Originally Posted by David G4EBT View Post
Unless I'm mistaken, those two resistors appear to be clearly marked 2,700 - not 270 and if that so, the resistance would be 1,350 - not 135 Ohms. In series with R16 (270k), the total resistance would be 1,350 + 270k = 271,350. The circuit calls for 270,000 + 2,200 = 272,200. Thus, the actual resistance will be just 0.3% lower than the circuit calls for.

As to why they were fitted, I'm just guessing, but whoever did it may have just chosen the closest values that he had to replace a dud 2k2 resistor. If so, he did it for practical reasons - not technical.

You tester looks in nice condition!
Hi David and thanks for your reply. I just measured the resistors and they read 135 Ohm, so it's two 270 Ohm in parallell. I also thought it was 2700, but a closer look and measure showed 270 Ohm.

Still a bit uncertain, hope I read the schematics correctly, is it supposed to be 2.2k? Should I change it then to 2.2k?

Stephen, thanks for the tip about the wafers. What value did you have in yours on that resistor?

Many thanks,

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Old 6th Dec 2018, 1:03 pm   #7
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Default Re: Taylor 45C Valve Tester Resistor question

All the 45C testers I have seen have had 2k2 in that position
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Old 6th Dec 2018, 1:09 pm   #8
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Default Re: Taylor 45C Valve Tester Resistor question

Thank you, wonder why it's been changed to 135ohm??
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Old 6th Dec 2018, 1:14 pm   #9
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Default Re: Taylor 45C Valve Tester Resistor question

Does the tester work as expected?
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Old 6th Dec 2018, 1:18 pm   #10
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Default Re: Taylor 45C Valve Tester Resistor question

I don't have so much to compare it with yet. I meaured the voltages and they seem to be ok. Not sure in which part this resistor plays part. The schematic is very difficult to read. If someone has some hints about a suitable test it would be much appreciated.
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Old 6th Dec 2018, 2:07 pm   #11
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Default Re: Taylor 45C Valve Tester Resistor question

If you don't have a valve with known figures to compare with then a NOS one is the next best thing, the resistor only comes into play during tests on mutal conductance and rectifiers. I would suggest a double triode for the GM test using the data as a guideline for the expected output.

The diagram you posted is very bad and has been modified to allow testing of even more types of valves...if you can follow it.
A very worthwhile change to the tester is to fit a multiturn 2k potentiometer in place of the A control. make sure its rated to 2 watts, the ones from China are fine using 6mm shaft.
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Old 6th Dec 2018, 3:33 pm   #12
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Default Re: Taylor 45C Valve Tester Resistor question

Thanks Stephen for info. I will check the pot, it's jumping a bit.

Unfortunatley I do not have a proper reference double triode valve but I will try, need to get one.

I also noticed that the dogbone resistor on top that is supposed to be 2k is actually 2.2k.
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Old 7th Dec 2018, 1:19 pm   #13
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Default Re: Taylor 45C Valve Tester Resistor question

So far as I can make out the function of the 2.2k resistor that was first referred to won't affect the results of a mutual conductance test or a gas test, the gas test resistor is 270k so the effect of a 2.2k in series with it will be negligible , looks like it's in series with the control grid when testing certain rectifier valves, the Taylor 45D appears to employ the same.

Lawrence.

Last edited by ms660; 7th Dec 2018 at 1:28 pm. Reason: Addition
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Old 7th Dec 2018, 7:16 pm   #14
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Default Re: Taylor 45C Valve Tester Resistor question

Thanks,

Until now I have seen 4k, 135R and 1.2k in this position from looking at forum posts and pictures. All seems to have been modified to these values from the original 2.2k. Wonder why?
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Old 7th Dec 2018, 7:29 pm   #15
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Default Re: Taylor 45C Valve Tester Resistor question

Yours was the last revision of 45C before it changed to the 45D
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Old 11th Dec 2018, 3:32 am   #16
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Default Re: Taylor 45C Valve Tester Resistor question

Quote:
Originally Posted by ms660 View Post
So far as I can make out the function of the 2.2k resistor that was first referred to won't affect the results of a mutual conductance test or a gas test, the gas test resistor is 270k so the effect of a 2.2k in series with it will be negligible , looks like it's in series with the control grid when testing certain rectifier valves, the Taylor 45D appears to employ the same.

Lawrence.
Thanks for info Lawrence, been decrypting the schematics so now it makes more sense. There are better scans available.

I have two manuals though, and they are slightly different. One is blue and one is beige colored. No dates of printing available but data is different which makes it a bit confusing.
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