[3083joe]

Don't mention it.  I think I might have those tubes your looking for.  Check the classified here.

You got some nice tubes there!

 

[Neogeo333]

Thanks Joe, trying to unload some before I move.  More to come in these few days.  

 

[dminches]

Yeah. I have 32s and 35. Prefer the 35s a bit more.
Ordered a pair or 31s will be here next week.
Probably try some 34s just because. The 33s are hard to find and really expensive.

 
The ECC35 is not a direct replacement for an ECC32 the same way a 6SL7 can't often be used instead of a 6SN7 and vice versa.

 

[3083joe]

The ECC35 is not a direct replacement for an ECC32 the same way a 6SL7 can't often be used instead of a 6SN7 and vice versa.

Yeah. Probably true. But it can in my wa22.
But Won't need once I get Glenn's 300B

 

[gibosi]

Glenn...
 
Sometimes I see an amp that has an "automatic bias circuit" which is said to eliminate the need to rebias the amp after changing tubes.
 
I wonder what this means? Is it actually possible to design a circuit that can reliably detect the proper bias of any given tube and make the proper adjustments? If so, how would something like this work?

 

[Neogeo333]

For me sometimes the advantage of manual bias is to be able to dial in the right amount to your liking.  Some tube sound better when pushed a bit further than their designed spec.  Like my KT120 tubes if I set it to there spec it sounds good but when push just a bit more it sounds better to my ears of course.  Sometimes is for the own safety of the amp to not push it too much and auto bias help in that way.   I vote for a manual bias in all my amp.

 

[gibosi]

I should have been more specific. I was looking at the owner's manual for an Elise, which is a 6SN7/6AS7 OTL manufactured by Feliks Audio. I wouldn't have thought that an amp like this would even need such a circuit?
 
http://feliksaudio.pl/en/products.html
 
And the manual can be seen here:
 
http://feliksau.unixstorm.org/pliki/elise_en.pdf

 

[Sfox7076]

It is probably a cathode bias. You can read about that on numerous sites. I don't love power amps with cathode bias, even if all preamps are done that way.

 

[2359glenn]

  Glenn...
 
Sometimes I see an amp that has an "automatic bias circuit" which is said to eliminate the need to rebias the amp after changing tubes.
 
I wonder what this means? Is it actually possible to design a circuit that can reliably detect the proper bias of any given tube and make the proper adjustments? If so, how would something like this work?

Fixed bias has a negative power supply that is adjustable that is applied to the grid of the tube through
a resistor.
 
Auto bias / cathode bias
A tube needs a negative voltage on the grid to control the current through the tube.
In auto bias the grid is tied to ground through a resistor. And the cathode has a resistor to ground
when tube starts drawing current it makes a voltage drop across that cathode resistor. So now
the cathode is positive in respect to ground and the grid is grounded or at 0 volts. So this looks
like a negative voltage on the grid. Different tubes will draw a different amount through the cathode
resistor changing the voltage drop or the potential between the cathode and grid.
 
Personally I like the sound of fixed bias. That cathode resistor has to be bypassed with a nasty
electrolytic capacitor.
A amp just sounds better without this stuff in the signal path.

 

[gibosi]

Glenn,
 
Thanks for the explanation.  I am surprised at how simple the circuitry is as I envisioned something much more complicated. But still, it is adding more stuff into the signal path. What I take away from this is that when designing an amp, one should weigh the advantages of auto biasing versus the drawbacks... Interesting stuff indeed. Thanks again.

 

[whirlwind]

It is going to be one great Saturday night.
 

 
 
 
                                                                 +
 

 
 
 
                                                                 +
 

 
 
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                                                             =
One great Saturday night !
 
 
Glenn, thank you very much again, for making this amp for me....you will never know how much I am enjoying it.
 
George, thank you for the tubes, I have listened to this combo for pretty much the whole day...and really look forward to more listening tonight.
 
Glenn, your 42EC4/PY500 tubes are coming your way...I will ship them out this tuesday along with a few other goodies for you to enjoy, while you are building amps.

 

[3083joe]

It is going to be one great Saturday night.






                                                                 +






                                                                 +





                                                             +





                                                             =
One great Saturday night !


Glenn, thank you very much again, for making this amp for me....you will never know how much I am enjoying it.

George, thank you for the tubes, I have listened to this combo for pretty much the whole day...and really look forward to more listening tonight.

Glenn, your 42EC4/PY500 tubes are coming your way...I will ship them out this tuesday along with a few other goodies for you to enjoy, while you are building amps.

Very nice. Enjoy the night.
Oh and I love the GEC 6as7, best driver out there

 

[rosgr63]

SO The Isley Brothers are on the decks.
 
Fixed versus Auto Bias?
The KISS principle applies here too for me been the last S off the word - Glenn who knows me well would agree. 

 

[parbaked]

Originally Posted by rosgr63 /img/forum/go_quote.gif
 
The KISS principle applies here too for me been the last S off the word - Glenn who knows me well would agree. 

KISS = Keep It Simple Sexy?
 
Hi Stavros...nice to see you!!

 

[rosgr63]

Hi Steven yes simple & sexy
 
EDIT:I am the S-stupid part.........