Taylor 47A Meter

[David Simpson]

Any 47A meter experts out there? Meter characteristics seem fine - - 249.5uA fsd, with a res of 325 ohms & 89.3mV from my TE 2003N.
However, meter sticky, & I found a heap of wee flakes of the white paint which covers the inside of the casing . Having flaked off just beneath the front pivot. Is this a common problem with Taylor VT meters ? Do these meters take kindly to remove the whole movement & examine the armature gap for crud ?

Regards, David

[David Simpson]

Well, no answers to my meter debris question. Not to worry, at least its working, more or less.
However, I've returned to the 47A, after being diverted to other stuff(See "Sad Times"). Need to test & calibrate the additional multimeter panel. The resistance ranges zero pot was knackered, so changed it. Made a sleeve to fit a 1.5V AA cell into the wee battery holder, works fine. Meter goes haywire on AC though, so the wee rectifier is obviously phooked. Any suggestions for a couple of diodes to replace it ? I've a few OA81's, and heaps of more modern silicon ones - 1N4007's & such.
Great diagram of the Measuring Circuit on page 9 of the handbook, but a pity it doesn't give values of the resistors used for multiplying & shunting.
Talking of main circuit diagrams,(see picture), especially small handbook ones, I always get them magnified up to A3 & printed off at the village pharmacy.

Regards, David

[David Simpson]

Well, the AC Volts FW rectifier circuitry is pretty rudimentary. Tried several pairs of NOS diodes, but no joy. This meter just loves to vibrate, even with temporary filter circuitry added. Reminds me of a 2 Panel AVO whose damping springs have gone weak. Thankfully, the meter works reasonably well on all valve testing functions, plus ohms & DC volts and mA. Sticks occasionally a bit, but considering the amount of flakey paint debris removed, I'm not surprised. Surprisingly, the mA/V tests compared favourably to my AVO Mk3, using standardised valves.
It came with an original 1943 Valve Chart Booklet, but I needed a later pdf edition I had on file, as the ABC Selector codes have changed for the 47A, and the old booklet doesn't have a Vg column, just Va & Vs.
Just a couple of valve holder adaptors to make, then my chum can have it back.
Guess this thread can be closed, Moderators.

Regards, David

[Freya]

Hi David,

Only just seen you post, I have seen several meters with tiny bits of loose rust around the magnet area. removing was best done with a cocktail stick and some blu tac. The diodes that I use for the rectifier replacement are GEX34.

This model is extremely prone to transformer failure when left on for even short periods.

[David Simpson]

Thanks for the reply, Stephen. No evidence of any rust particles near the stator, just the wee pile of paint flakes found beneath it. I hadn't heard that the 47's were prone to transformer problems. I guess its worth noting by folk who own & use them. This one certainly had a bit of a hum whilst turned on. but then it is well over 65 years old & looks like its had a lot of use in the past. Thankfully it still gives correct Va, Vs, Vg & Vh. However, don't think I'd be keen to run a VT136, or an EL37 or KT88 at full whack through it for any length of time. Mind you, Taylors, like Hickoks , & other AC operating VT's of that era, test valves at the lower end of the Ia/Vg curve & don't monitor Ia. Anyway, the pro's & con's of AC operating VT's & VCM's have been banged -on enough in recent months & years.

Regards, David

[David Simpson]

When using "Search" prior to raising this thread, I came across Norman Raeburn's excellent thread of 13th Oct 2017 & subsequent replies & links. Duncan Leece's reply of 15th Oct mentions a SPEARETTE Valve Holder Adaptor (a No9). Its actually Duncan's 47A which I've been working on, and my final job is to sort out adaptors. The Spearette No9 (B9A to I.O.) has the following connections :- Pin 3 - - Pin 1, Pin 1 - - Pin 4, Pin 5 - - Pin 7, and the red Top Cap lead goes to I.O. Pin 8. The rest of the pins are unconnected. What on earth is it used for, I wonder ? Did Spearette make a number of valve tester adaptors ?
It does seem that Taylor's old range VT's don't follow AVO's practice of connecting all valve holders numerically. I.e. The 9 position switches A, B & C don't always follow AVO's Thumbwheel Switch assembly's selection. Their 1940's design thoughts obviously relied on a number of 1920's, 30's & 40's valve manufacturers always sticking to a pretty standard pin/electrode layout.
I've made up a couple of additional adaptors, but they are just pin number to same pin number. So wont always work with every valve tested on the 47A. Perhaps the Spearette Company made a range of adaptors just for Taylors.

Regards, David