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Re: d'ya think RM drives EL84's too hard!?

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Tre'

(P)

In Reply to: d'ya think RM drives EL84's too hard!? posted by Timbo in Oz on February 2, 2007 at 17:53:07:

Well, if you need power, you need power. But CCS plate loads for the input and driver stages and a Real Class A operating point and load for the output tubes gives less distortion. I like the idea of less distortion from electronics.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

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I LIKE power!, and I was asking a technical question of Ray. - Timbo in Oz 19:03:19 02/02/07 (2)
AFAIK PP CCS'd EL84M's/7189 IE A1, are gonna struggle to dissipate 20 watts in pure A - continuously - as at idle, even in pentode mode*.
And, so long as I have a watt or three of A in AB1 I'll be happy.
Especially if fixed bias, were used, so I could adjust over the power tubes life.
And I might go with a CCS on each input/gain stage, even TWO single triode input tubes (6C45?), with an extra socket!
With fixed (adjustable) bias for each PP tube I think we'd be getting pdclose to SE sound, anyway!
MY spkrs are 91db/w, and an EASY 8 ohm load, I'd just like more reliability, AND a little more headroom!
I would need to upgrade the power trannie anyway - for the 'CCS'd pure diff'l opt stage' route, to be worth doing - as I don't want to LOSE power, either!
*I don't even KNOW what continuous output the OPTxers could cope with.

Warmest
Timbo in Oz
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
- I'm not sure of the question but I have some comments - Russ57 06:14:27 02/03/07 (1)
  [AFAIK PP CCS'd EL84M's/7189 IE A1, are gonna struggle to dissipate 20 watts in pure A - continuously - as at idle, even in pentode mode*.]
  The 7189 is rated at 12 watts anode and another 2 watts for the G2. So a total of 28 watts for a pair of tubes. A CCS in the common cathode circuit set for 20ma would therefore not be a problem if the B+ isn't too high.
  
  [And, so long as I have a watt or three of A in AB1 I'll be happy.]
  I doubt you will feel that way once you go to real class A amplification. Especially when in pentode a tube is very critical as to the best load. When in class A the tube sees half the plate to plate load but when it moves to class B it suddenly sees only a 1/4 of the plate to plate load. Not good for a pentode. THD will be many times higher and you can dang sure hear the difference.
  [Especially if fixed bias, were used, so I could adjust over the power tubes life.]
  If anything fixed bias allows wider current variations through the tubes
  
  [With fixed (adjustable) bias for each PP tube I think we'd be getting pdclose to SE sound, anyway!]
  I don't understand why you thing a pentode class AB1 stage is going to sound like a class A1 SE stage stage simply because of fixed bias.
  [MY spkrs are 91db/w, and an EASY 8 ohm load, I'd just like more reliability, AND a little more headroom!]
  Yes, you do have to take the speakers into account.
  [I would need to upgrade the power trannie anyway - for the 'CCS'd pure diff'l opt stage' route, to be worth doing - as I don't want to LOSE power, either!]
  No, there is simply no way to have the same power in class A as you can in class AB. There is no need to change the PT and nothing would be gained. If anything class A would usually be run at lower voltage and higher current. A small first cap followed by a choke can make this happen and then the PT could deliver more current.
  
  [*I don't even KNOW what continuous output the OPTxers could cope with.]
  In class A the output power will be lower and the OPT's will have less to cope with. The CCS on the output tubes (if done right) will force perfect AC balance something no other method can do. You could still use a little fixed bias to adjust for equal standing bias.
  
  Russ
  - See above under Ray Moths' post, too - Timbo in Oz 17:50:26 02/05/07 (0)
    And tah!
    Warmest
    Timbo in Oz
    The Skyptical Mensurer and Audio Scrounger
    And gladly would he learn and gladly teach - Chaucer. ;-)!
    'Still not saluting.'

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