UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Taylor 45c Valve Tester - a caution -and an appeal for information sharing

Ross_ZL1RDM · 11th Apr 2007, 1:34 pm

Hi;- I have a Taylor 45C also with undated original book (also shows 1-0-16 for ECF80) but with hand typed (copied) Alterations, & Additions, date April 1961. A more pressing problem for me is that the lower gm 3mA/V range seems to work OK, and give accurate bogey values for NIB mil valves, but that valves (i.e. KT88) requiring the gm 15 mA/V range caused the tester to hum (traced to loose HT mounting bolts, but still ...) and give erroneous and unrealistically low readings (checked later on a friends calibrated AVO VCM163) - I am wondering if the selenium rectifier is a problem, and whether I need to incorporate (& how much?) series resistance if I replace it with silicon diodes ... I would like to be able to be sure that I am getting decent gm value readings on both ranges! I'd be grateful for any tips or suggestions; also, my scanner has a fault at present, but when I can, I'd be happy to upload the 1961 data if it is of any interest or use, or previously unreferenced? ... ;=})

Thanks & regards;- pleased to discover this forum! Ross~

PS: I also identified and replaced a few resistors that were showing drifted values, and took some pics to aid me, but have not yet drawn them up to the given circuit diagram, which lacks any values. Given the nature of the 45C operation (unsmoothed half-wave DC etc) I am not sure of the importance of the voltage drop across the selenium rectifier for calibration, or whether partial failure on its part could cause erroneous readings as above ... ?

[E&OE;- it's late, here in the antipodes;- some of this is from tired memory!]

11th Apr 2007, 1:34 pm	#10
Ross_ZL1RDM Diode Join Date: Apr 2007 Location: Auckland, New Zealand Posts: 4	Re: Taylor 45c Valve Tester - a caution -and an appeal for information sharing Hi;- I have a Taylor 45C also with undated original book (also shows 1-0-16 for ECF80) but with hand typed (copied) Alterations, & Additions, date April 1961. A more pressing problem for me is that the lower gm 3mA/V range seems to work OK, and give accurate bogey values for NIB mil valves, but that valves (i.e. KT88) requiring the gm 15 mA/V range caused the tester to hum (traced to loose HT mounting bolts, but still ...) and give erroneous and unrealistically low readings (checked later on a friends calibrated AVO VCM163) - I am wondering if the selenium rectifier is a problem, and whether I need to incorporate (& how much?) series resistance if I replace it with silicon diodes ... I would like to be able to be sure that I am getting decent gm value readings on both ranges! I'd be grateful for any tips or suggestions; also, my scanner has a fault at present, but when I can, I'd be happy to upload the 1961 data if it is of any interest or use, or previously unreferenced? ... ;=}) Thanks & regards;- pleased to discover this forum! Ross~ PS: I also identified and replaced a few resistors that were showing drifted values, and took some pics to aid me, but have not yet drawn them up to the given circuit diagram, which lacks any values. Given the nature of the 45C operation (unsmoothed half-wave DC etc) I am not sure of the importance of the voltage drop across the selenium rectifier for calibration, or whether partial failure on its part could cause erroneous readings as above ... ? [E&OE;- it's late, here in the antipodes;- some of this is from tired memory!]