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Old 11th April 2009, 12:18 AM   #1
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Default 6ak5-45

Hi Diyers,

My next project is to change my 6F8G RC 45 Set based on the circuit 6SN7 cascade similar to the Sun Audio.
The idea is 6AK5-45. 6AK5 very close 717A (Yamamoto use in the 45, pentode 717A
I designed the following circuit, corrections and suggestions welcome, again Thanks, Martin.
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Old 11th April 2009, 09:08 PM   #2
kevinkr is offline kevinkr  United States
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If you are connecting it as a pentode you should show that clearly, right now the schematic is incomplete.

I'm not a big fan of pentode drivers with DHT, that said if you find one with really high transconductance and high anode current like the 7788, D3A, C3G, etc, results can be pretty good.

In general you need to be aware of the miller capacitance and I feel that although the near 62K source impedance of your driver should yield a -3dB point of around 91kHz with a Cmiller of around 28pF, additional strays will quickly eat into the available bandwidth. I generally prefer source impedances that are a great deal lower than this. (A couple of K ohm)
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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Old 29th July 2009, 07:04 PM   #3
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Hi Martin V56,
I think that your schematic have an error. You have a 1uF capacitor between the anode and ground at the pentode. This makes that almost all the signal will be directly to ground, so no signal at the grid of the next valve (45).
If you want to use the pentode wired like a triode, you must take out that capacitor, or if you want to use the pentodo like pentode, you must polarize the G2 from +B with a proper resistor and your condenser to gnd, and taking the output signal from the plate.
Anyway, the 45's filament seen to be shorted...
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