A while ago I set about refurbishing a Bird 43 'Thruline' power meter which was a bit knocked-about from years of service, and also had a dodgey meter movement. I did a paint job on the case with some nice colour hammerite smooth which looks quite nice and a lot tidier than the scruff state it was in. Having found the price of the genuine meter movement I thought I'd look about for alternatives and found a 'replacement' available from the an amateur supplier of valves and stuff in the USA. As the exchange rate was quite healthy even considering the postage costs I ordered one which arrived within about a week. On fitting and testing it was giving low readings so I did some tests and found that although it was correct at 30uA FSD it was the wrong internal resistance. Checking an original it had 1340 ohms, and this one had 4.6kohms. I contacted the supplier who proceeded to tell me I was talking bull-s**t, but on further explaining my readings he said he had sold hundreds of them and had never had a problem with them but nevertheless refunded all my costs.
I took him at his word (mistake !) and after Christmas ordered another, and have now tested that and the internal resistance is 3.96kohms, not much better than the fist one and nowhere near correct to give accurate readings, it reads about 38w instead of 60w.!
Now to decide whether to bite the bullet and order a genuine unit to get this unit into use and put these two in the junk box for use in some future project, or whether to go through a recalibration of the scales.
Note to self, avoid anything with SVC on the dial :-(
I took him at his word (mistake !) and after Christmas ordered another, and have now tested that and the internal resistance is 3.96kohms, not much better than the fist one and nowhere near correct to give accurate readings, it reads about 38w instead of 60w.!
Now to decide whether to bite the bullet and order a genuine unit to get this unit into use and put these two in the junk box for use in some future project, or whether to go through a recalibration of the scales.
Note to self, avoid anything with SVC on the dial :-(