JE 45/2A3 SE 2001 edition

Mc_Goertz · 2nd March 2010, 12:52 AM

Hi all,

My question is in this schematic for the power tube cathode resistor this 2001 edition is using 1.5K, while for SRPP schematic its using 880ohm, and the older model is 2X1.5k.
Is the 1.5K for the 2001 edition is meant for 45 tube or can I use it for 2A3 tubes?
45/2A3 means this circuit can be used for either 45 or 2A3 tube without any modification on the circuit?
Need some clarification I almost done the amp then notice the other value of cathode resistor on the other JE circuit
I intend to use 2A3 tube only so the 1.5K for cathode resistor is okay.

Thank you very much
Mac_G

alexg · 2nd March 2010, 01:05 AM

Can you please post the schematics?

Mc_Goertz · 02:09 AM

Hi Here is the schematics, its also tap on 5K impedance, while other 2A3 is using 2.5k for the output transformer. and here's the link http://members.myactv.net/~je2a3/simple45.htm
thank you

azazello · 2nd March 2010, 07:18 AM

Hi!
If You use 2A3 with recom. plate current 60 ma, the bias will be -90 v with res. 1,5 kohm.
This bias is very big /recom. is 45-55 v for best mode/. Cathode res. must be
800-1000 ohm.
If You use 2A3 with plate current 35-40 ma, 1,5 kohm is suitable, but sound
will be bad.
I think /I use in my 2A3 820 ohm Mills/ res. must be less 1 kohm.
1,5 kohm is for tube 45 with plate current 35-40 ma.

Mc_Goertz · 2nd March 2010, 07:46 AM

Thank you very I'm a newbie based on the circuit cathode voltage is 55V where it come from and how to compute it (cathode voltage).

based on 2A3 data sheet plate dissipation = 15W max

Some circuit use 880ohm but difficult to find I have a 820ohms but the Plate dissipation will be 55V/820 = 67ma
275V x 0.067A = 18.425W which is over the 2A3
max is t okay, if okay then I will
use it or is there need to do some modification on the circuit I intend to use 2A3 tub only. thank you

Mc_Goertz · 2nd March 2010, 09:29 AM

Hi all, tried to search then now know how to compute the cathode voltage based on the 60ma current recommend for 2A3 and the bias voltage recommendation of 45V - 55V using the ohms law to calculate the cathode resistor. thank you

2nd March 2010, 12:52 AM	#1
Mc_Goertz diyAudio Member Join Date: Jan 2010	JE 45/2A3 SE 2001 edition Hi all, My question is in this schematic for the power tube cathode resistor this 2001 edition is using 1.5K, while for SRPP schematic its using 880ohm, and the older model is 2X1.5k. Is the 1.5K for the 2001 edition is meant for 45 tube or can I use it for 2A3 tubes? 45/2A3 means this circuit can be used for either 45 or 2A3 tube without any modification on the circuit? Need some clarification I almost done the amp then notice the other value of cathode resistor on the other JE circuit I intend to use 2A3 tube only so the 1.5K for cathode resistor is okay. Thank you very much Mac_G

2nd March 2010, 01:49 AM	#3
Mc_Goertz diyAudio Member Join Date: Jan 2010	Hi Here is the schematics, its also tap on 5K impedance, while other 2A3 is using 2.5k for the output transformer. and here's the link http://members.myactv.net/~je2a3/simple45.htm thank you Last edited by Mc_Goertz; 2nd March 2010 at 02:09 AM. Reason: picture to small

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2nd March 2010, 01:05 AM	#2
alexg diyAudio Member Join Date: Jan 2005 Location: Philippines	Can you please post the schematics?

2nd March 2010, 07:18 AM	#4
azazello diyAudio Member Join Date: Aug 2008 Location: Bulgaria	Hi! If You use 2A3 with recom. plate current 60 ma, the bias will be -90 v with res. 1,5 kohm. This bias is very big /recom. is 45-55 v for best mode/. Cathode res. must be 800-1000 ohm. If You use 2A3 with plate current 35-40 ma, 1,5 kohm is suitable, but sound will be bad. I think /I use in my 2A3 820 ohm Mills/ res. must be less 1 kohm. 1,5 kohm is for tube 45 with plate current 35-40 ma.

2nd March 2010, 07:46 AM	#5
Mc_Goertz diyAudio Member Join Date: Jan 2010	Thank you very I'm a newbie based on the circuit cathode voltage is 55V where it come from and how to compute it (cathode voltage). based on 2A3 data sheet plate dissipation = 15W max Some circuit use 880ohm but difficult to find I have a 820ohms but the Plate dissipation will be 55V/820 = 67ma 275V x 0.067A = 18.425W which is over the 2A3 max is t okay, if okay then I will use it or is there need to do some modification on the circuit I intend to use 2A3 tub only. thank you

2nd March 2010, 09:29 AM	#6
Mc_Goertz diyAudio Member Join Date: Jan 2010	Hi all, tried to search then now know how to compute the cathode voltage based on the 60ma current recommend for 2A3 and the bias voltage recommendation of 45V - 55V using the ohms law to calculate the cathode resistor. thank you

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