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Old 13th December 2011, 10:51 AM   #1
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Default cascode tubes

Hey Everyone,

Which tubes make good cascode tubes? MJ writes that the only tubes designed to work with the cascode are the 6922/6DJ8. I have a 12AU7/12AU7 long tail phase splitter in the amp now and at high volume there is too much distortion. Its a Dynaco Mark VI with four KT88 outputs. I could use a 6922 in the preamp position and keep the 12AU7 in the phase splitter position. Or use 6922's in both ala Joe Curcio's Mark III design. But would the 6922 as phase splitter have enough drive for four KT88's? And if I use the 6922/12AU7 combination could both tubes be run with the same plate voltage? I often see the 6922 run at low voltages, around 90 or so.

Kevin

Last edited by mr2racer; 13th December 2011 at 11:10 AM.
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Old 13th December 2011, 10:52 AM   #2
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ECC2000
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Old 13th December 2011, 10:54 AM   #3
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http://www.tubezone.net/pdf/ecc2000.pdf
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Old 13th December 2011, 12:41 PM   #4
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Hi Joachim,
Nice to hear from you. Have you heard this tube? How does it compare to the 6922/6DJ8?
Kevin
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Old 13th December 2011, 12:48 PM   #5
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That is a good for cascodes tube too, also ECC88, PCC88 and all the variants. Yes, the ECC2000 is slightly better and less noisy then the 6DJ8. It was the last tube that Valvo developed in the late 60th so it is fairly recent. It is a bit rare though and may have gotten expensive.
How it sounds against the 6DJ8 is hard to tell. The circuit is important and also the particular manufacturing, older ones are usually better. I posted my reply because the ECC2000 is optimized for cascodes from the beginning. When you study the specs you will notice that the two systems inside are slightly different. One system belongs in the bottom and one system belongs in the top.
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Old 13th December 2011, 01:39 PM   #6
DF96 is offline DF96  England
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Other cascode valves are ECC84/6CW7 and 6BQ7. Most cascode valves, having been designed for VHF receiver RF stages, are likely to have some degree of remote cutoff characteristics so not suitable for audio except for very small signals such as phono preamps. ECC88 is an exception, as there is a separate remote cutoff version - the ECC189.

Cascode valves are designed to work well at low anode voltages, and in some cases this may mean that they don't like high anode voltages.

The 12AU7 has low mu, so should only be used as a LTP phase splitter if the tail is a CCS.
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Old 13th December 2011, 02:00 PM   #7
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Quote:
I have a 12AU7/12AU7 long tail phase splitter in the amp now and at high volume there is too much distortion.
I think your distortion problem can not be solved with cascode preamp.
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Old 13th December 2011, 03:14 PM   #8
TheGimp is offline TheGimp  United States
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Has anyone tried the 6N14P in Cascode.

The data sheet always shows it with section 1 on the bottom and section 2 on top which may indicate it was designed for Cascode operation.

It is an HF tube so no audio related data present.

Likewise, 6N23P-EB shows Cascode operation but it is supposed to be an equivalent of the 6DJ8/ECC88 so that would be consistent with that tube.
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Old 13th December 2011, 03:20 PM   #9
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Quote:
Has anyone tried the 6N14P in Cascode.
Yes. I have built a FM-band preamplifier with 6N14P.

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