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PixelPlay 23rd June 2008 04:15 AM

Interesting linestage optimizing ideas
2 Attachment(s)
I am not sure of the origin of this interesting circuit however I have had it in my system for some time now and do love the sound however as always we would like to see if it can be improved upon. Perhaps add a ccs etc. Your ideas and input would be greatly appreciated in modifying this schematic and perhaps identifying its origin?


kenpeter 23rd June 2008 05:13 AM

This input signal is completely bypassed to ground through both
the 470uF and/or the battery. If this is the same circuit you claim
currently to have a working example, then I suspect you might
not have drawn it out accurately.

Were those two components perhaps in the cathode leg of the
circuit instead? And why a battery instead of an LED??

PixelPlay 23rd June 2008 05:49 AM

Hi kenpeter
Thanks for looking at the schematic. I have double checked the board and it is on pins 2 & 7 which are the grid. They definitely go to the two components and then to ground. The only reference that I have found of a similar circuit without the 470uf cap is in "Valve Amplifiers: Morgan Jones" he states that the valve is biased by superimposing the bias voltage onto the grid via resistor 221K, which prevents the battery from short circuiting the signal. The coupling cap prevents the signal from shorting the battery. Resistor 70k is the output resistance of the signal.


analog_sa 23rd June 2008 06:41 AM


Originally posted by PixelPlay
I have double checked the board

Then you should do well to triple check. The only way this circuit makes any sense is with the 70k in series with the battery, not with the signal source. Otherwise, the circuit is a big yawn - fixed battery bias common cathode feeding a "Miss Piggy" done with a most unsuitable tube.

ray_moth 23rd June 2008 01:07 PM

Your schematic is obviously incorrect. It can't possibly pass a signal the way it's drawn, with an AC dead short on the input tube grid, as stated by kenpeter and analog_sa.

Another thing, what is a 0.47uF resistor? (plate load of the 5814A)

PixelPlay 23rd June 2008 10:18 PM

2 Attachment(s)
Thank you all for your observations. I have found that you were correct there was a 221K missing in the schematic. The corrected drawing is attached.

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