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 Taylor 45C valve tester Mutual Conductane problem.
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 Return to top of page · Post #: 1 · Written at 9:59:57 AM on 17 March 2019.
Jimb's Gravatar
 Location: Kanahooka, NSW
 Member since 18 November 2016
 Member #: 2012
 Postcount: 712

Hi all .
Some time ago I acquired a Taylor 45C at the time I replaced one of the bridge rectifiers .
Testing Mutual conductance I know it works for some valves .
I should be able to work this out but my head goes into overload . I am trying to test the mutual conductance of some 12AU7'S
According to the manual the A B C switch settings are 283 for one triode and 590 for the second triode. The switch settings for A Band C for the 590 section give a sensible reading however not so for the 283 side you can't get a positive meter reading and it won't null out.
The meter needle swings negative . I have tried to work out the switch positions using their examples and confuse myself further.
I have tried several valves I am sure at least some of them are ok.
Again I DO HAVE a complete manual for this .The problem to a degree lies with me. What elements do switches A B and C control .Or can each switch control any element ? I get lost in trying to follow the switch positions or the explanation given.
Can anyone confirm settings for A B and C 283 are correct for a 12AU7 I have looked at the others which are more or less the same 12AX7 ECC82 etc and they all have the same switch positions. Is this a miss print or have I another unresolved problem with this tester?
I know these testers are very versatile however if you are unsure if all circuits are ok in the tester because it is old and second hand and you run into a problem like this I get confused.Not sure how many of these are out there .
I can well understand not getting a reply to this however thought I would give it a try.
Regards Jimb


 
 Return to top of page · Post #: 2 · Written at 11:46:15 AM on 17 March 2019.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 1253

I also have a Taylor 45C and can confirm the 283/590 settings for a 12AU7.

Be aware that as the boss told Sol in the Castrol ad, oils ain't oils with the 45C - there are a number of versions with minor variations. Did your manual come with the tester?

Mine didn't and I acquired the manual later. My serial number is 330119 and I haven't been able to convince myself that the manual is applicable. For example my tester has a resistor R9 (220 ohm) which is not on the circuit in the manual.

There is a European chap somewhere who has been trying to sort out the serial number spans of the variations. I haven't touched on this for several years so I don't know where that is at.

I also replaced the selenium rectifier bridges with silicon diodes. Beware that mutual conductance measurement depends on the phasing of the various waveforms and if you get the diode directions wrong it won't work. I will have to revisit all this, together with how the ABC settings work to get it back into the mind again. I'm not surprised that you are confused. I was never absolutely convinced that I had got my head around this tester's workings.

Beware also that the ABC switch innards are made of plastic which can crack either through the shaft hole and/or at the detent ball holes, with age. These selector switches get a hard doing. Have managed to repair both problems. Not fun. Good idea to replace the 0.1 μF 300V cap - mine developed a short.

All that said it has been very useful. Make notes of readings for any working valves tested. These readings may be preferable to the values in the valve charts given your modifications. My Valve Chart is marked 8/60 at the bottom of the front cover which may or may not mean August 1960.

Good luck.


 
 Return to top of page · Post #: 3 · Written at 12:21:16 PM on 17 March 2019.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 1253

PS Have searched Taylor 45C here and found my previous cogitations on the setting of the 45C posted here:

https://vintage-radio.com.au/home.asp?f=2&th=831#8250

After two years I won't "second guess" what I have said there.


 
 Return to top of page · Post #: 4 · Written at 1:44:29 PM on 17 March 2019.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6678

From Googling around, it does seem that confusion about the ABC switch settings for that tester is not uncommon. There is this comment regarding 'multiples':

QUOTE: Valves with multiple electrode assemblies, such as a Dual Triode (eg 12AU7) or Triode Pentode (ECL80), you will need two sets of Selector settings, corresponding to the two assemblies. The one not being tested is kept dormant, by earthing the Anode and Screen to 0 = C position.


See: https://www.vintage-radio.net/forum/showthread.php?t=131934

And in this thread, mention is made of various errors/addenda and someone has even created a Windows app to assist with the ABC settings:

QUOTE: for any given valve socket it will, from a pin-by-pin list of electrodes, determine the required positions of the ABC switches.
Conversely, given the ABC switch positions, it will provide a list of electrodes and corresponding pin numbers. This can be helpful when attempting to determine the settings for valves not included in the Valve Charts, and for checking the Valve Charts for errors; of which there are quite a few.


See: https://www.vintage-radio.net/forum/showthread.php?t=23877

Compared to the Taylor, my B&K 747B is a delight to use.


 
 Return to top of page · Post #: 5 · Written at 2:23:54 PM on 17 March 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5239

I note comment on a failed cap: It is pertinent to remember that test equipment of the valve era, often used the same components, e.g. caps. I have been obliged to repair several meters & bits of test equipment, of that era.

An AVO 7X, failed caps; Heathkit OS-1 Oscilloscope, clear the board & replace every component on it; BC-221-N Frequency Meter, resistors & caps & so it goes....

I actually scored a 110V "Knight" Valve tester recently.

Marc


 
 Return to top of page · Post #: 6 · Written at 5:20:31 PM on 17 March 2019.
Jimb's Gravatar
 Location: Kanahooka, NSW
 Member since 18 November 2016
 Member #: 2012
 Postcount: 712

Thank you all for your contributions.
I spent considerable time replying to your contributions however it disappeared. So this is attempt 2.
The manual did not come with the unit. The serial number is 2881383.I feel a bit happier knowing others find this unit confusing .I may well be a sandwich or two short of the full picnic however this is a dog to use maybe it still has unresolved faults. I too had replaced the selenium rectifiers when I first got it. I was trying to repair an B & K model 960 Transistor Radio Analyst and wanted to test the pair of 12AU7'S this is how all this started.
My favourite tester is the Hickok 510 unfortunately this was made before 9 pin valves came out. I have had this for 50 plus years, when I was younger and still had some grey cells left I made an adapter that plugged into an 8 pin socket plus the top cap connection making the ninth pin however I have lost it and no longer have the patience to reinvigorate the grey cells to redo this. When time permits and my level of patience improves I will revisit this. It would appear the tester has yet another fault.
Regards Jimb


 
 Return to top of page · Post #: 7 · Written at 6:08:40 PM on 17 March 2019.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6678

I spent considerable time replying to your contributions however it disappeared.

You posted a similar response in the older thread referred to by STC830. Perhaps that explains the apparent disappearance?


 
 Return to top of page · Post #: 8 · Written at 7:05:24 PM on 17 March 2019.
Jimb's Gravatar
 Location: Kanahooka, NSW
 Member since 18 November 2016
 Member #: 2012
 Postcount: 712

Thanks GTC


 
 Return to top of page · Post #: 9 · Written at 8:42:09 PM on 17 March 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5239

That sounds a bit like a cheap Tech thing I have here which will likely be terminated. I don't need three valve tester's especially when that one has to be run with an isolation transformer. Its instructions also defy interpretation.

If it is to be saved I need to dismantle it & find out why it has earth leakage? Earth leakage & a metal cabinet on a device built with no earth, is one of those things you put a defect tag on & quarantine, until its fixed.


 
 Return to top of page · Post #: 10 · Written at 8:46:03 PM on 17 March 2019.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6678

Earth leakage & a metal cabinet on a device built with no earth is one of those things you put a defect tag on & quarantine, until its fixed.

Unless it was an extremely rare and valuable item, I'd bin it. Otherwise, cord comes off and it becomes shelf-ware.


 
 Return to top of page · Post #: 11 · Written at 11:27:24 AM on 18 March 2019.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 1253

Something to look out for is that the grid control knob may have shifted on its shaft. If so it may not be possible to correctly set the grid voltage and measure mutual conductance. Found online was a procedure to reset this and might be worth doing especially if you have had the knobs off the tester.

https://www.vintage-radio.net/forum/showthread.php?t=46161

"To reset the 'grid volts' control, connect a sensitive voltmeter between cathode and grid sockets and set perspex pointer so that zero volts on the meter coincide exactly with '0' volts marking on the escutcheon (it will be found that the pointer will then turn below the '0' mark on the escutcheon). If the grid volts pointer has not been reset correctly, mutual conductance readings on the tester will be inaccurate."

This was found by its poster stapled to a circuit diagram for the tester so is from the horse's mouth.


 
 Return to top of page · Post #: 12 · Written at 1:39:25 PM on 18 March 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5239

I know another in the Radio Club also has 1.5 of them. So for curiosity alone I will investigate. Always interesting for future reference, to ascertain why it went awry. I love Leader SG-11 & another Tech Signal generator (among several things spotted) that have a cap from line to a metal case & chassis.

Normally its a crapacitor & not a line capacitor: Where there is a transformer: That cap goes & the frame is grounded.

Sets with shielded transformers also get grounded.


 
 Return to top of page · Post #: 13 · Written at 1:43:47 PM on 18 March 2019.
Jimb's Gravatar
 Location: Kanahooka, NSW
 Member since 18 November 2016
 Member #: 2012
 Postcount: 712

Hello STC830.
Thank you I have tried various settings of the grid control pot from fully anticlockwise to fully clockwise.
It makes no difference. Pot A does not increase the meter reading above zero. Pot B works bucking the meter bakwards below zero. I was wondering if you actually tried a 12AU7 in your tester or a 12AX7 or ECC82?
It would definitely prove this tester is faulty. The rectifiers I previously changed and Marcc was correct about the capacitor there is only one and it was leaky I have since replaced it with no positive results. I have not checked or replaced any of the ceramic caps. I have only in my life ever found one faulty. It pretty well only leaves the switches.
They look ok and I just do not want to go there.
Regards Jimb


 
 Return to top of page · Post #: 14 · Written at 5:50:13 PM on 18 March 2019.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 1253

I'll dig through my valves and see if I have a 12AU7, 12AX7 or ECC82 and run the tests. Might take a few days as I have a house repair job on the go at the moment.

Found my crib notes for the tester. Mutual conductance was as follows in case it is any help:

-filament V as per manual
-anode & screen volts as per manual
-circuit selectors ABC as per manual
-set test selector 3mA/V or 15 mA/V*
-A & B fully anticlockwise
-advance knob A until meter pointer at X (or X2*)
-advance knob B until meter pointer at zero
-press meter button and read off mutual conductance
* 3mA/V or 15mA/V depending on expected result.
X or X2 depending on whether meter indication is off scale.


 
 Return to top of page · Post #: 15 · Written at 6:30:44 PM on 18 March 2019.
Jimb's Gravatar
 Location: Kanahooka, NSW
 Member since 18 November 2016
 Member #: 2012
 Postcount: 712

Hello STC830.
That would be a great help when you have the time.
I could send you a couple of new old stock 12AX7's and you could just keep them if you can't find any.
My test procedure is the same as yours.
Regards Jimb.


 
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