Quote:
Originally Posted by BassoonBloke
If you do decide to increase the caps to 32+32uf, you will probably need to change the rectifiers to GZ34's as GZ32's do not like the extra capacity.
|
I guess the problem is that there isn't enough resistance in the anode circuit to allow the capacitor upgrade. I've just made some measurements on a Quad II mains transformer and the half-secondary resistance is about 60 ohms. The primary adds slightly less than 11 ohms multiplied by the turns ratio squared (310V/240V=1.3, which squares up to 1.69) i.e. about 18 ohms. That makes 78 ohms in total, which will increase a little as the transformer heats up.
The Mullard data sheet for the GZ32 says it needs a minimum of 100 ohms if it's going to be loaded with 32uF. It only needs 50 ohms if the first cap is 16uF (the one after the choke is much less of a problem). One solution would be to insert a couple of 22 ohm resistors, one in each anode. However this would drop the HT voltage a little. Changing to a GZ34 is a much better solution. Not only can it handle more capacitance (even 60uF only needs a series resistance of about 55 ohms) but it also draws less heater current than the GZ32 so will be slightly more gentle on the mains transformer.
Cheers,
GJ