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Old 24th May 2006, 02:41 AM   #1
rdf is offline rdf  Canada
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Default 955 Acorn tubes

A friend gave me a couple sleeves of these still common and popular-with-hams triodes. The plate curves looked promising. Attached below is a spectral analysis, conditons as noted in png name, of an RCA 955 driving a 200 kohm load 23 volts p-p, max requirement for my EL84 SE. 2nd harmonic is about 0.12 %, third 100 dB below fundamental. Not quite as low as the 6C45 currently in place but the 955 seems to scale nicer. 45 volt p-p raises THD to 0.25% second, third 100 dB down. 6 volts p-p results in 0.03% 2nd, 3rd below the noise floor of my kit. A Raytheon has 70% the 2nd but shows a little fourth.

Rp is a bit high at ~11.5 kohm under these operating conditions but no deal breaker for an EL84. Has anyone tried them in a circuit and have an opinion on sound?
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Old 24th May 2006, 06:50 AM   #2
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Hmmm, looks like they might be fun to play with

Do I hear phono input stage?
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Old 24th May 2006, 04:20 PM   #3
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I toyed with the idea of two acorn tubes driving a BUF634 chip for a headphone amp but never got around to it. Not many people carry acorn tube sockets, only one online store had them listed.
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Old 24th May 2006, 07:27 PM   #4
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Gain seems a little low for a phono stage, about 25 best case. Hmmm, maybe with a little transformer coupling at the front end? Wait, don't get me started in too many directions.

I'm not worried much about the sockets save for price. A couple of E-bay dealers carry them. For testing purposes female Sub-mini D insert-style pins work fine when sleeved with heat shrink to maintain tension. Phono pins might be the close to the right size too. Certainly good enough for a trial run install.
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Old 24th May 2006, 10:08 PM   #5
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Quote:
Originally posted by rdf
Gain seems a little low for a phono stage, about 25 best case. Hmmm, maybe with a little transformer coupling at the front end? Wait, don't get me started in too many directions.
Cascode bottom tube
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Old 6th April 2009, 12:14 AM   #6
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Default Re: 955 Acorn tubes

Quote:
Originally posted by rdf
A friend gave me a couple sleeves of these still common and popular-with-hams triodes. The plate curves looked promising. Attached below is a spectral analysis, conditons as noted in png name, of an RCA 955 driving a 200 kohm load 23 volts p-p, max requirement for my EL84 SE. 2nd harmonic is about 0.12 %, third 100 dB below fundamental. Not quite as low as the 6C45 currently in place but the 955 seems to scale nicer. 45 volt p-p raises THD to 0.25% second, third 100 dB down. 6 volts p-p results in 0.03% 2nd, 3rd below the noise floor of my kit. A Raytheon has 70% the 2nd but shows a little fourth.

Rp is a bit high at ~11.5 kohm under these operating conditions but no deal breaker for an EL84. Has anyone tried them in a circuit and have an opinion on sound?
rdf,

Dusting off this thread and bringing it back from the dead. Did you ever do anything with this tube?

Thx,
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Old 6th April 2009, 12:32 AM   #7
rdf is offline rdf  Canada
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Hi korneluk. A 7-pin equivalent, the 9002, did service as the front end of an EL84SE and later a 6CW5 SE for years. Loved it. I've since collected a stack, including some of the pentodes, for future use.
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Old 6th April 2009, 12:33 AM   #8
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I have a few of these destine for a line stage one day.



Nick
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Old 6th April 2009, 12:43 AM   #9
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Quote:
Originally posted by rdf
Hi korneluk. A 7-pin equivalent, the 9002, did service as the front end of an EL84SE and later a 6CW5 SE for years. Loved it. I've since collected a stack, including some of the pentodes, for future use.
Thx. Any hints as to the operating points?
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Old 6th April 2009, 02:36 AM   #10
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One of the audio magazines from a long time ago (either Glass Audio or VTV) had an article listing distortion measurements on a sizeable list of triodes. The 9002 had the best numbers in the list. I have been collecting them ever since, but I haven't had the time to test them myself yet. If remember the same article (or at least the same issue) called the 01A "magical" driving the price up over night, and even casuing some antique radios to be raped for their tubes.

Not that I would condone this practice but an old and very rusty Atwater Kent that I found in a pawn shop for $25 provided me with the tubes for a "magical" line stage. And an old Sparton's tubes live on as the output tubes in a Tubelab SE. Both radios are stashed away in case someone wants to restore them, but I believe that they are too far gone.
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