No,
that doesn't work. You forgot the resistance of the heaters themselfs which is in parallel to Rb.
A simple series resistor will do:
(7,4 V-6,3V)/2,1 A = 0,52 Ohms with a power rating greater than (2,1 A)²·0,52 Ohms = 2,3W.
Try 1R|| 1R or 1R 
1R2 each minimum 2 watts or 0R47 or 0R56 minimum 5 watts.
"||" means "in parallel"
Bernd
No,
that doesn't work. You forgot the resistance of the heaters themselfs which is in parallel to Rb.
A simple series resistor will do:
(7,4 V-6,3V)/2,1 A = 0,52 Ohms with a power rating greater than (2,1 A)²·0,52 Ohms = 2,3W.
Try 1R|| 1R or 1R
"||" means "in parallel"
Bernd
Hi Bernd - thanks for that, I used 2 1R 3W in parallel - they get very hot though - too hot to touch - is that OK?
Hi,
most of the heavy duty resistors are specified at rated power for a surface temperature of 120...180 °C. So you have them to mount safely.
BTW What voltage du you now measure?
Bernd
Hi,
most of the heavy duty resistors are specified at rated power for a surface temperature of 120...180 °C. So you have them to mount safely.
BTW What voltage du you now measure?
Bernd
Hi Bernd - got 6.1, mains varies here 
Other slight thing is at bias pot I have -24V but cannot get any lower than -37mV accross R51 or R52 - is that OK?
Thanks
Steve
Hm,
that's not so much difference but it should be possible to adjust it even below 35 mV.
What neg. voltage do you measure at the junction of R45/46 and to what negative maximum is it adjustable by VR9 (10k bias pot)?
Bernd
Sorry, you wrote already that you have -24V - but it is across VR9 and R63, isn't it?
Hm,
that's not so much difference but it should be possible to adjust it even below 35 mV.
What neg. voltage do you measure at the junction of R45/46 and to what negative maximum is it adjustable by VR9 (10k bias pot)?Bernd
Sorry, you wrote already that you have -24V - but it is across VR9 and R63, isn't it?
No - at VR9 to R63 I have -8.7V, at VR9 to R46 -25.3V and at R51 or R52 I have -34mV tonight - With Mains voltage of 241.5 - It varies between 235 -250 Here so readings change depending on time of day/night 
So a power conditioner would help.
Is 240 V the nominal mains voltage in your country?
Bernd
So a power conditioner would help.
Is 240 V the nominal mains voltage in your country?Bernd
In UK it's now supposed to be 230 V +10% −6% since EU "harmonisation". In practice the average is 240V. I've done my testing when the voltage has been high so am happy now 
Thanks very much for your help - on to woodwork now to build Cabs !
Steve
Sie haben noch kein Benutzerkonto auf unserer Seite? Registrieren Sie sich kostenlos und nehmen Sie an unserer Community teil!
