Seeking help about my 2A3 to 45 conversion - Page 2

arnoldc · 12th June 2003, 07:58 AM

Quote:

Originally posted by mig-ru
By the way, you might want to get rid of the grid resistor on the 45, just cuts out power being made by the preamp stage.

Hi Dmitry,

I'd like to know more about that! Why is required for a 45 and not on the 2A3 on the same circuit?

Please enlighten me

bournville · 12th June 2003, 09:49 AM

The use of a 'grid stopper' resistor before the input grid of the output valve is to help reduce the dangers of parasitic oscillation - ideally the resistor should be connected as close to the grid connection on the valveholder as possible. The effect on such a resistor on overall gain is negligible.

Is it necessary on your new circuit? If your 45 amp has a greater gain then it might be more susceptible to parasitic oscillations I suppose... You may find that it is not strictly necessary although many designers like to include these resistors to help ensure stability, as the cost is so small, both in physical cost and in loss of gain.

arnoldc · 13th June 2003, 12:32 AM

many thanks for the excellent explanation.

cheers.

mig-ru · 13th June 2003, 01:28 AM

i stick to the "more is less" concept. less components in sound path, the better. so why not leave it out and see if oscillation develops, if so just stick the resistors in.

arnoldc · 14th June 2003, 02:05 AM

Quote:

Originally posted by mig-ru
i stick to the "more is less" concept. less components in sound path, the better. so why not leave it out and see if oscillation develops, if so just stick the resistors in.

Agree with you. I prefer KISS too...

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12th June 2003, 09:49 AM	#12
bournville diyAudio Member Join Date: Feb 2003 Location: Birmingham, UK	The use of a 'grid stopper' resistor before the input grid of the output valve is to help reduce the dangers of parasitic oscillation - ideally the resistor should be connected as close to the grid connection on the valveholder as possible. The effect on such a resistor on overall gain is negligible. Is it necessary on your new circuit? If your 45 amp has a greater gain then it might be more susceptible to parasitic oscillations I suppose... You may find that it is not strictly necessary although many designers like to include these resistors to help ensure stability, as the cost is so small, both in physical cost and in loss of gain.

13th June 2003, 12:32 AM	#13
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	many thanks for the excellent explanation. cheers.

13th June 2003, 01:28 AM	#14
mig-ru diyAudio Member Join Date: Jul 2002 Location: Boulder, CO	i stick to the "more is less" concept. less components in sound path, the better. so why not leave it out and see if oscillation develops, if so just stick the resistors in.