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Old 5th Sep 2019, 2:39 pm   #1
DoubleWound
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Default Taylor 45C Grid Volt Calibration

Yet another post on the Taylor 45C but I have scoured everywhere for information

My Taylor 45C seems to work well but I cannot be sure of the grid volt calibration which is of fundamental importance to obtaining accurate mutual conductance readings.

So I kindly ask other owners of this instrument to connect their 'scope to the G1 and K sockets of a valve holder and post a reply. It will be very useful to see if my 45C is similar to others.

This is what I get with grid volts set to 10V (and I've also got results for 1V, 5V and 15V).

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All the relevant resistors and power supply in my 45C are to Taylor specification.
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Old 5th Sep 2019, 6:31 pm   #2
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Default Re: Taylor 45C Grid Volt Calibration

What are the peak to peak results for the 1V, 5V and 15V settings?

Lawrence.
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Old 5th Sep 2019, 8:23 pm   #3
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Default Re: Taylor 45C Grid Volt Calibration

Very nice Initiative, I have two Taylor 45C's. Unfortunately I don't have a fancy scope like you, only my old Tektronix from the 70's. Let's see if I can come up with something.
Would be interesting if you posted all values, like mentioned in previous post
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Old 5th Sep 2019, 8:26 pm   #4
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Default Re: Taylor 45C Grid Volt Calibration

I sort of shelved mine, couldnt get sensible readings and ran out of things to check.
scope readings on the sockets would be really useful.
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Old 6th Sep 2019, 1:41 am   #5
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Default Re: Taylor 45C Grid Volt Calibration

Here's my result. Long time since I used the scope..

I have a little bit lower values than you it seems. Stock values on components. Taylor #2 has silicone diodes instead of the selenium rectifier. But they are very much alike in the results.
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Old 6th Sep 2019, 6:58 am   #6
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Default Re: Taylor 45C Grid Volt Calibration

I am grateful for the feedback folks.

In answer to the question from ms660 the "peak to peak" figures on other settings are below and I have deducted the small +ve value:-

Dial Setting / Scope Peak Reading
1V / 1.5V
5V / 6.0V
10V / 12.0V
15V / 17.0V

I have checked that the knob position at 0V is correct and that the meter is accurate (not that the meter is involved in this analysis).

My conclusion is that this is how the instrument left the factory but I would still appreciate as much feedback as possible from users of good unmolested 45Cs using a 'scope to determine voltages.

Last edited by DoubleWound; 6th Sep 2019 at 7:12 am.
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Old 6th Sep 2019, 11:46 am   #7
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Default Re: Taylor 45C Grid Volt Calibration

I did a quick calc based on the transformers output voltage shown in the schematic using a "perfect diode" I calculated 1.178 volts per grid volts setting, ie: 17.67v p to p for the 15 volts setting, 11.78v p to p for the 10 volts setting etc.

So throw the diodes forward voltage drop (whatever that may be) into the mix and the waveform you displayed isn't that far out taking normal component tolerances and mains voltage variations into consideration.

Lawrence.
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Old 6th Sep 2019, 12:21 pm   #8
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Default Re: Taylor 45C Grid Volt Calibration

Lawrence, that is really helpful information and is starting to put my mind at rest.

I will take some accurate measurements of the actual transformer VAC output and the half wave rectified voltage disconnected from the rest of the instrument circuit. I'll continue to use a 'scope since my Avo 8 or DMM may not give the true picture for a half wave rectified voltage.

I'm actually surprised that Taylor seems to have failed in publishing the data I seek. Maybe some member here has Taylor 45C Service Sheets if they ever existed.
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Old 6th Sep 2019, 2:52 pm   #9
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Default Re: Taylor 45C Grid Volt Calibration

Just an update to say that:

The "disconnected" output of the transformer is 20.9Vrms.

The "disconnected" half wave output is 28.4Vpp.

Temporarily substituting the original Taylor diode with a UF4007 the "disconnected" half wave output rose to 30.4Vpp.

I still hope to receive some more 'scope readings connected to G1 & K from other owners but for the time being I'll assume my 45C is OK.
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Old 6th Sep 2019, 9:52 pm   #10
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Default Re: Taylor 45C Grid Volt Calibration

I just tested again with another scope, now more in line with yours. Good to see, seems like it's more in order. A little high though.

Grid Voltage Setting Gid voltage OSC Vpp
2 2.5V
5 6V
10 12.4V
15 18V
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Old 6th Sep 2019, 10:14 pm   #11
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Default Re: Taylor 45C Grid Volt Calibration

Sven, this is really good feedback - thanks.

If more 45C owners came back with their results we may be able to ascertain what Taylor should have published in the first place.
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Old 6th Sep 2019, 10:26 pm   #12
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Default Re: Taylor 45C Grid Volt Calibration

We could also create some "standardized tubes" to pass around, like they did here for the AVO testers if that would be of interest. I surely would like to compare mine with others, its a great little tester the Taylor 45C.
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Old 10th Sep 2019, 11:13 am   #13
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Default Re: Taylor 45C Grid Volt Calibration

Quote:
Originally Posted by sven_swe View Post
We could also create some "standardized tubes" to pass around, like they did here for the AVO testers if that would be of interest. I surely would like to compare mine with others, its a great little tester the Taylor 45C.
That would be very interesting to carry out.

Although my resistors are within Taylor tolerances I'm going to replace them with spot on values when I get back from holiday later this month. If there's any change in grid voltages I'll post again.

I don't expect much change but the old resistors are bound to creep up in value as time goes on.
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Old 10th Sep 2019, 4:34 pm   #14
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Default Re: Taylor 45C Grid Volt Calibration

45C #1

Grid Voltage Setting Grid voltage OSC Vpp
2 2.2V
5 6V
10 11.1V
15 14V

45C #2

Grid Voltage Setting Grid voltage OSC Vpp
2 2V
5 5.5V
10 10.3V
15 15.8V

Taylor 47

Grid Voltage Setting Grid voltage OSC Vpp
2 3.5V
5 7V
10 12.4V
15 16.7V

Taylor 45

Grid Voltage Setting Grid voltage OSC Vpp
2 2.8V
5 6.6V
10 11.6V
15 15.5V

My other 45c is out on loan, and the other two 47`s have bad transformers
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Old 20th Sep 2019, 4:28 pm   #15
DoubleWound
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Default Re: Taylor 45C Grid Volt Calibration

Quote:
Originally Posted by Freya View Post
45C #1

Grid Voltage Setting Grid voltage OSC Vpp
2 2.2V
5 6V
10 11.1V
15 14V

45C #2

Grid Voltage Setting Grid voltage OSC Vpp
2 2V
5 5.5V
10 10.3V
15 15.8V

Taylor 47

Grid Voltage Setting Grid voltage OSC Vpp
2 3.5V
5 7V
10 12.4V
15 16.7V

Taylor 45

Grid Voltage Setting Grid voltage OSC Vpp
2 2.8V
5 6.6V
10 11.6V
15 15.5V

My other 45c is out on loan, and the other two 47`s have bad transformers
Very helpful information - thanks very much.

I'm just back from holiday today and I'll post my figures again after I've changed some more resistors to exact Taylor values.
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Old 23rd Nov 2019, 2:54 pm   #16
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Default Re: Taylor 45C Grid Volt Calibration

It's taken some time but I've replaced most resistors and pots. I did not replace the special graded Pot A. At the same time some cosmetic improvements were executed as shown:-

Click image for larger version

Name:	Taylor 45C Complete.jpg
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ID:	194212

So, using a scope again, here are some grid volt results, peak to peak.

1V 1.5V
2V 2.8V
5V 6.6V
10V 12.8V
13V 16.5V
15V 19.9V

I cannot see what more I can do to ensure this tester meets the original Taylor 45C grid volt calibration.

If any other owner wishes to have one of my valves for comparative testing of gm then just give me a PM.
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Old 24th Nov 2019, 12:11 am   #17
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Default Re: Taylor 45C Grid Volt Calibration

Quote:
Originally Posted by DoubleWound View Post
It's taken some time but I've replaced most resistors and pots. I did not replace the special graded Pot A. At the same time some cosmetic improvements were executed as shown:-

Attachment 194212

So, using a scope again, here are some grid volt results, peak to peak.

1V 1.5V
2V 2.8V
5V 6.6V
10V 12.8V
13V 16.5V
15V 19.9V

I cannot see what more I can do to ensure this tester meets the original Taylor 45C grid volt calibration.

If any other owner wishes to have one of my valves for comparative testing of gm then just give me a PM.
Hi!
Sure, I think that would be an interesting project. Maybe some more will join. Passing around a tube has been done here before. I have one from David Simpson that we also might be able to use, let me check.
I'm in and I have two Taylor 45C to check against. I'll send you a PM.
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Old 8th Dec 2019, 10:03 am   #18
DoubleWound
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Default Re: Taylor 45C Grid Volt Calibration

Following the restoration of my Taylor 45C and calibrating the grid volt pointer at 0V with a scope I sent three valves to sven swe.

He did a very professional Gm comparison on his two Taylor 45Cs and an AVO.

I'm delighted to say the results were very close and I now know that my Taylor is good to use.

I hope that sven swe will post his results with commentary.

I will be pleased to send the same valves to any other user of the Taylor 45C or for that matter a user of any type of valve tester.

Thanks Sven.
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Old 13th Dec 2019, 11:36 pm   #19
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Default Re: Taylor 45C Grid Volt Calibration

Hi all,

As DoubleWound mentioned I tested three valves from him on my two Taylor 45C and me newly restored AVO MK3 with settings to simulate the 45C. Gladly the results are very similar and my MK3 can confirm this as well. This is interesting and as mentioned, if other owners would like to chime in it would be great. I also checked with my scope that the grid volts are aligned for my both machines.

Attached is a small summary with the results. I think they are within spec., only one up to 7% but readings of meter, slightly different mains voltage etc are not included as calculated deviations in this test, so I think it is ok.
These are great little testers!

Sorry for late reply, but I have been a bit ill this week.

Typo has been corrected

Many thanks again DoubleWound!
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Old 14th Dec 2019, 9:33 am   #20
DoubleWound
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Default Re: Taylor 45C Grid Volt Calibration

sven_swe's analysis has been of tremendous help to me.

Since then I have now tested a brand new ECC83 and got the correct Gm. Up until then I had only tested old valves so it was not possible to know if the 45C was accurate until his report.

I suppose minor variations between instruments are inevitable and, at the end of the day, will have no effect for valve matching or the ability to weed out a valve that is on its last legs.

Yes, I think they are great little testers although I would advise users to add more earthing bonds to various parts of the cabinet.
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Last edited by DoubleWound; 14th Dec 2019 at 9:39 am. Reason: Wrong picture posted
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