My name is Graham, I'm from the UK and I have an A12 which I have modified using Steph's @Skunkie mods and I'm over the moon with the difference it has made.
I've tried a bunch of different tubes with the A12 and have settled for while now on a Gold Lion GZ34, Gold Lion 12AX7 and the EL34 alternates between the UK-EL34 from PSVANE and the Winged C svetlana.
Recently I wondered what a different rectifier might be like and came across a CV5745 British Military tube which is a GZ33. I think they were made by Mullard and it seems like decent quality. It mainly got my interest because it looks very cool, being a tall coke bottle shape. I bought it and popped it into the A12 and it worked beautifully. Now, I'm not a tech and I dont really understand the intricacies of B+ voltage etc... but can follow a schematic and solder well.
My question is, will using the GZ33 in the Skunkie modded A12 cause any problems? Do I need to change the values of any of the components to correct the bias for the GZ33 as I understand it draws more current? I just want to make sure I'm getting the most out of the tube and I'm not going to cause the amp to melt down in ball of fiery death!
Any input from this great community would be gratefully accepted.
Best Wishes, Graham
The problem with using a GZ33 is the heater current. A GZ34/5AR4 used 1.9A and a GZ33 uses 3A. We have no way of knowing what the power transformer is rated for but given a 5AR4 can easily handle the current this amp needs, I wouldn't risk roasting the power transformer using a GZ33.
@Skunkie I was wondering if you had any ideas about this? Thank you in advance