Welcome, Guest. Please Login or Register
Decware Audio Forums
11/24/14 at 05:19:14


Pages: 1
Send Topic Print
EF86 > EL84, Comments on this circuit ? (Read 3112 times)
fabian
Verified Member
**




Posts: 6
EF86 > EL84, Comments on this circuit ?
07/29/11 at 00:47:02
 
Hi there, I plan to implement this circuit, the only differences will be these ones :

EF86 : 250V B+, 82K or 87K plate resistor , 1.5K cathode resistor to get 1.65mA at about 112V plate-to-cathode. CCE Mod using 0,1 uf cap.

EL84 : 290V p-k, and 45mA (200 Ohm cathode resistor)

Coupling cap : 0,01 uf (mundorf).



Any comments, suggestions,  advices?
Back to top
 
 
  IP Logged
dank
Seasoned Member
****


pair of dual 18
Imperials

Posts: 275
Re: EF86 > EL84, Comments on this circuit ?
Reply #1 - 07/30/11 at 13:44:45
 
Some things for consideration:

1)  Typically a 1k 2w resistor is used in the g2 screen connection.  I'm not sure why its there, but it usually is.  It may have something to do with frequency response, isolating the screen capacitance from the signal.  It may be very subtle as to what this resistor does.  Your design might benefit from two of these resistors, one for each stage.

2)  I think you will have a lot of noise issues with that large of a input pot.  Noise from touching the volume control (or even getting close to it) may be a problem.  I use 47k, 10 times less.

3)  Your bypass caps on the cathode resistors seem a little small.   100-1000uf would be more typical.  Also be aware that the cathode resistor on the output stage is sometimes made excessively large, power wise, so if an output tube shorts it doesn't take the cathode resistor with it.  I've seen anywhere from 5w-25w on amps like this.

4)  I would question the size of the coupling cap.  0.01 uf seems small, 0.1 uf would be a more typical value.

Good luck and let us know how it turns out

Dan
Back to top
 
 
  IP Logged
azazello
Verified Member
**




Posts: 18
Re: EF86 > EL84, Comments on this circuit ?
Reply #2 - 08/03/11 at 19:46:22
 
Cathode resistor EF86 must be between 100 - 500 ohm /not 100 kohm/, interstage cap must be 270 nF. Pot must be between 10 - 50 kohm. Cap 10 uF/400v must be more 100 uF. Both cathode caps must be 500-1000 uF.....
Back to top
 
 

Hi-End is back proportional to the number of composite parts!
  IP Logged
Pages: 1
Send Topic Print