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Sideband · 2nd Oct 2004, 9:15 pm

Hi Dave.

Well done!!

Your calculations seem correct if I work it in reverse (the way I'm used to doing it with a known anode impedance) so 7094/4=1773.5 and then take the square root of that and it comes out to 42.11 which is the ratio :1. So you need to find a valve with an anode impedance of around 7000 ohms. In practice you could probably use anything from 6000 - 8000... it really isn't going to do any harm. Just make sure the current through the valve is not excessive.

Back to your original posting..you can't really take too much notice of DC resistances on transformers...it's the impedance thats important and it seems you've learnt a good way of finding it out.

With regard to the hum cancelling coil (hum bucking coil) I think this should be in SERIES with the speech coil but in reverse phase.

Good luck.

Rich.

2nd Oct 2004, 9:15 pm	#5
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Bush PB53 Output stage problems Hi Dave. Well done!! Your calculations seem correct if I work it in reverse (the way I'm used to doing it with a known anode impedance) so 7094/4=1773.5 and then take the square root of that and it comes out to 42.11 which is the ratio :1. So you need to find a valve with an anode impedance of around 7000 ohms. In practice you could probably use anything from 6000 - 8000... it really isn't going to do any harm. Just make sure the current through the valve is not excessive. Back to your original posting..you can't really take too much notice of DC resistances on transformers...it's the impedance thats important and it seems you've learnt a good way of finding it out. With regard to the hum cancelling coil (hum bucking coil) I think this should be in SERIES with the speech coil but in reverse phase. Good luck. Rich. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....