Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Ed_Chambley on March 14, 2012, 03:01:31 pm
-
Attached here is the power section of a Matchless Chieftain. It looks different from others I have seen and I do not understand the choke and why it is used the way it is. I am building a power section for 2 EL34's and ran across this. It looks as the choke is filtering the plates as well as the screens. There are very large resistors as well. What is the reason/benefit of such.
-
Matchless is fond of using parallel B+ nodes after the choke. Look close. The choke is not filtering the PA plates.
By using parallel nodes, one and only one resistor is used to determine the B+ for any node. And the node B+ voltage is totally independant of any other node. That's not the case with the more familiar series B+ nodes.
-
I noticed that about the chieftain too long ago when i built my first amp and used the chieftain as a model for the cathode bias output. But i never figured out why they use parallel nodes like that. All i could figure is maybe the wanted more voltage than a series rail would allow. Maybe one stage needed to be too low to allow the later stages enough voltage? Any idea as to why?
-
Yes, it is not filtering the plates. I see. What is the need for such a large choke? 20H and 160ma and is it necessary. I like the separate resistors and caps for each tube cathode. I actually have the parts and plan to use this for power section. Looking at Mullards Datasheet on EL34's running at 375 v cathode Rk is 260 ohm per tube. Why the large wattage resistors?