4 x EL34 in A class

[Geezer]

  Hoffman Amplifiers
    > Tube Amp Building - Tweaks - Repairs
        > 4 x EL34 in A class      
 
<< Prev Topic | Next Topic >>  
Author  Comment  
Leevi
Junior tube assistant
Posts: 128
(3/31/04 8:33 am)
 4 x EL34 in A class
--------------------------------------------------------------------------------
 I'm planning an A class power amp with 4 EL34s. I think the plate voltage will be on the level 250-300V and idle current less than 100mA. My question is: Should I use a common cathode resistor together with a cap for all four power tubes or should each power tube have a separate cathode resistor with cap. What is a good value for the cathode resistor(s).
/Leevi
 
jc
I only work on Fender's
Posts: 694
(3/31/04 5:42 pm)
 Re: 4 x EL34 in A class
--------------------------------------------------------------------------------
 I would at least use 2 cathode resistors so that you can remove a pair of tubes to run the amp with less power. Plus you will be able to use 10 watt resistors. If you use 1 resistor for each pair of EL34 I would start with a 150ohm 10 watt.
 
Jackson Ampworks
Junior tube assistant
Posts: 2
(3/31/04 11:44 pm)
 Re: 4 x EL34 in A class
--------------------------------------------------------------------------------
 The spec sheets say that at 250V on the plates that you should bias the tubes at 100mA. Anything higher than 250V I would think it would be best to bias them at 90% of max plate dissipation.
Brad Jackson
Jackson Ampworks
 
Leevi
Junior tube assistant
Posts: 129
(4/1/04 12:42 am)
 Re: 4 x EL34 in A class
--------------------------------------------------------------------------------
 The data sheet below says that on 250V plate voltage and on -14,4V grid 1 voltage the grid 2 serial resistor is 2000 Ohm. Respectively on -13,5V grid voltage the grid 2 resistor is 0.
Does the latter case really mean that I should connect the B+ directly to the grid 2 (without any resistors).
The power provided by the tubes is with that setup 11W which mean that the max power of the amp will be ~45W.
The total load impedance what the tubes see is according to my calculation ~2 Kohm. Do you agree to my assumptions?

www.triodeel.com/6ca7ap2.gif

/Leevi
 
 
 << Prev Topic | Next Topic >>

 

 Topic Commands
 Click to receive email notification of replies
  
jump to:  Tube Amp Building - Tweaks - Repairs (New)New Product Suggestions (New)Praises - Complaints - Suggestions (New)Buy - Sell- Trade (New)Archives (New)    
 

- Hoffman Amplifiers - Tube Amp Building - Tweaks - Repairs - Hoffman Amplifiers -



Powered By ezboard® Ver. 7.32
Copyright ©1999-2005 ezboard, Inc.