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valve input stage and driver/phase inverter coupling
valve input stage and driver/phase inverter coupling
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Old 16th October 2019, 11:03 PM   #1
Matt Rowland is offline Matt Rowland  United Kingdom
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Default valve input stage and driver/phase inverter coupling

I attach 2 schematics showing different ways of coupling a gain stage to a driver/splitter stage. Which is the best configuration?
Thanks. Matt
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Old 16th October 2019, 11:16 PM   #2
rayma is online now rayma  United States
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I use the second one, because the signal is directly connected to the next grid,
instead of going through a coupling capacitor.
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Old 16th October 2019, 11:39 PM   #3
Matt Rowland is offline Matt Rowland  United Kingdom
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Thanks rayma. I was thinking along those lines, but wonder if the capacitor grounding the grid for ac, has any negative effects?
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Old 17th October 2019, 12:07 AM   #4
rayma is online now rayma  United States
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Quote:
Originally Posted by Matt Rowland View Post
Thanks rayma. I was thinking along those lines, but wonder if the capacitor grounding
the grid for ac, has any negative effects?
The second stage cathode being at an elevated potential could cause some extra hum,
but the filament could also be elevated. The RC filter to the lower grid needs to be effective
at removing the signal. The first plate DC voltage does affect the operating point of the
second stage.
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Old 17th October 2019, 08:32 AM   #5
Chris Hornbeck is online now Chris Hornbeck  United States
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Both are poor choices unless there's a very compelling reason to *not* have normal drive to both output valves.


All good fortune,
Chris
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Old 17th October 2019, 10:50 AM   #6
Ketje is offline Ketje  Belgium
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Even better
Mona
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Old 17th October 2019, 11:00 AM   #7
Matt Rowland is offline Matt Rowland  United Kingdom
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Mona. Thank you for that. I hadn't seen that version of the schematic. My concern is that the constant current tail will have 130volts across it and the transistors aren't rated for that voltage. Also will the ECC99 heaters need elevating? Cheers. Matt
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Old 17th October 2019, 11:16 AM   #8
DF96 is offline DF96  England
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Quote:
Originally Posted by Matt Rowland
I was thinking along those lines, but wonder if the capacitor grounding the grid for ac, has any negative effects?
The capacitor grounding the grid has almost the same effect as a coupling capacitor, but most people do not realise this. A good LTP phase splitter will have high differential-mode gain and low common-mode gain. The LTP input signal appears between the anode of the previous stage and ground. To pick up this signal one LTP grid has to be coupled to the anode, and one has to be coupled to ground. At least one of these connections has to include a capacitor to block DC. It doesn't matter too much which grid you choose to have the capacitor.
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Old 17th October 2019, 01:14 PM   #9
Ketje is offline Ketje  Belgium
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Quote:
Originally Posted by Matt Rowland View Post
Mona. Thank you for that. I hadn't seen that version of the schematic. My concern is that the constant current tail will have 130volts across it and the transistors aren't rated for that voltage. Also will the ECC99 heaters need elevating? Cheers. Matt
It's a ~11mA CCS with 10k in series, you loose 110volts there, no problem.
The +15V supply can have an other value, 6...24V is ok.
And yes elevate the heater to 50V, enough for the 6N6/ECC99 and not to much for other tubes.
Mona
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Old 17th October 2019, 01:47 PM   #10
Matt Rowland is offline Matt Rowland  United Kingdom
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Many thanks DF96 and Mona. Very helpful. Best. Matt
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