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Re: PARALLEL WIRING A TWIN TRIODE 12AV7

Postby PIANOLYDIA » Mon Jun 10, 2013 1:50 pm
I have concluded That I will use LED'S OR Battery Biasing.
I may try both options to see which is going to sound better! Ed, What do you think of this implementation also I changed the 12AV7 Volatage Resistor to 47k As per Geeks Recommendations. That will divide the 47/2 = 23.5K to each Plate So; this is good! Any comments? May need to place 3 LED's in series on both Cathodes yielding 4.8V+ Each SIDE. So my Calculations are as follows: I am going to set the PV each side at 131V i AM GOING TO ASSUME A mU OF ABOUT 30 and that yields me around g(V) set at -3.25V our Bias will be 7.5mA setting up the V/mU = 131/30 = Bias Voltage of 4.36V next I took 4.36V/7.5mA = 1.34K Cathode bias Resistors. each side. But' I am only going to be concerned here with the Bias Voltage and getting that set up as a fixed Bias. So LED's are a fixed Bias I presume? So I will need (3) Red LED's to make sure I will be able to maintain the 7.5mA current to yield that 30mU out to the output tubes Hopefully...... Any comments?
Ed, I need your Calculations here. Thanks so much you guys, Geek, DeathRex, etc....Pianolydia

How big will the input signal be at max volume going into your 12AV7? Why do you need to parallel the triodes?

See the links below which show how to convert a single 12ax7 section VA in the Quicksilver 8417 to parallel 12ax7 sections.

http://www.bonavolta.ch/hobby/en/audio/ ... 0Push-Pull

http://www.triodeel.com/8417.htm

"A. Find 330K ohm resistor [Plate resistor] attached to 12AX7 socket. Change to 150K.

B. Find the 820 ohm resistor [Cathode bias resistor] attached to 12AX7 socket. Change to 390 ohms."

The plate resistor should be halved. The cathode bias resistor should be halved.

In your original schematic, the plate resistor is 22k. You more than doubled it to 47k. It should be 11k. (10k is fine.) You'll change the gain with a 47k resistor.

What (if any) was the value of the original cathode bias resistor?