You might have as much as 500 or 1000 pf in that long RCA cable.
Measure it.
In case it is a large capacitance, you might need a Cathode Follower.
1000 pF has 8k Ohms of capacitive reactance at 20,000 Hz.
The 6C45pi plate resistance, rp, is about 2500 Ohms.
rp drives the plate load resistor (or plate current source), in parallel with the
cable capacitance, and in parallel with the amplifier input resistor.
If the plate load is a current source (very high impedance), and the amplifier input is a very high resistance and low capacitance, then:
you have the rp of 2500 Ohms driving 8000 Ohms at 20,000 Hz.
The voltage divider at 20,000 Hz is 8000 Ohms/(2500 + 8000 Ohms).
The voltage divider is 0.76.
The u of the 6C45pi is about 40.
At 100 Hz the gain will be about 40.
At 20,000 Hz, the gain will be about 40 x 0.76 = 30.5
That is -2.4dB below the low and mid frequencies (too much high frequency
roll off).
The 6C45pi has about 10,000 to 20,000 micro mhos of transconductance.
If it is used as a cathode follower, it could have about 100 to 50 Ohms of output impedance, that is much more suited to drive 1000 pF of cable capacitance.
Measure it.
In case it is a large capacitance, you might need a Cathode Follower.
1000 pF has 8k Ohms of capacitive reactance at 20,000 Hz.
The 6C45pi plate resistance, rp, is about 2500 Ohms.
rp drives the plate load resistor (or plate current source), in parallel with the
cable capacitance, and in parallel with the amplifier input resistor.
If the plate load is a current source (very high impedance), and the amplifier input is a very high resistance and low capacitance, then:
you have the rp of 2500 Ohms driving 8000 Ohms at 20,000 Hz.
The voltage divider at 20,000 Hz is 8000 Ohms/(2500 + 8000 Ohms).
The voltage divider is 0.76.
The u of the 6C45pi is about 40.
At 100 Hz the gain will be about 40.
At 20,000 Hz, the gain will be about 40 x 0.76 = 30.5
That is -2.4dB below the low and mid frequencies (too much high frequency
roll off).
The 6C45pi has about 10,000 to 20,000 micro mhos of transconductance.
If it is used as a cathode follower, it could have about 100 to 50 Ohms of output impedance, that is much more suited to drive 1000 pF of cable capacitance.
Great idea, I have a Sowter TVC I was going to use on the input, i need to look up those specs, sse it could work on outpout or i could use trans in and out i guess.Are you willing to use a pair of transformers after the 6C45? The common 5K:600 output transformer (fine to go parallel feed to keep costs down) will work well to reduce the gain of the 6C45 and help you drive those cables.
I have a comparable tube in use, type 6S4 is a small 9 pin, with about half the gm of a 6S45. The beast is rigged as LTP for each channel and a 20k:600 line driver output TX is the load. SE input to one side, and balanced output from the 600R secondary. 6S45's work just as well, and though subtle, are an improvement over the 6S4's.
cheers,
Douglas
cheers,
Douglas
type 6S4 is a small 9 pin, with about half the gm of a 6S45.
Half?! Try 1/10th.
Half?! Try 1/10th.
The Russian...if you don't believe, I'll offer you the opportunity to think you are going to take all my money in a wager I will offer you...
There is a comparable 6S3 too...
cheers,
Douglas
Yes, the datasheet says no less than 40mA/V. The 6S4/6S4A is about 4.5mA/V.
(BTW - I have 6S4As in my system currently, but no 6C45Ps)
I did not say '6S4A'...rest assured there is another, as well as a similar 6S3.
cheers,
Douglas
Oh, you mean the 6C4P? You shouldn't leave off the "P", as there's also the 6C4C which is completely different than the 6C4P, 6S4A, and 6S4.
The full type is 6C4P-EV in the samples I have in hand, there is also the 6C3E...
You should get some...
cheers,
Douglas
Are you liking them more than a 5842? They look to be similar, but not quite the same operationally.
Have not tried a 5842 in that app yet. I need them in solidly matched pairs.
cheers,
Douglas
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