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Featured VT: The 6BQ7

Posted 19th January 2013 at 07:01 PM by Miles Prower

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This is a small signal dual triode in the nine pin mini format. From the spec sheet:
Quote:
The 6BQ7A is a miniature, medium-u, twin triode primarily designed for use as a cascode radio frequency amplifier in very high frequency TV tuners. In this application, its performance is characterized by low noise figures and high gain.
From the piccie, it's obvious that this is indeed a high frequency triode. It has the additional advantage of a high gm, made possible by the comparatively enormous cathodes. These are much larger than those of other small signal types like the 12AU7, 6FQ7, 6SN7, 6C4. The 6BQ7 also has a u-Factor that falls nicely between types like the 12AU7 or 6FQ7, and the 12AT7.

The spec sheet even includes a composite plate characteristic for cascode operation. What you don't find is any mention of any sort of audio applications. The RCA Receiving Tube Manual does make a concession...
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Boozehound Labs MM Phonostage

Posted 19th January 2013 at 05:06 PM by MagnumOpus

I needed a decent RIAA, and have found that I really like the sound of J-Fets. Maybe its purely metaphysical, maybe not. Still I am thrilled with the sound of of this thing. It it buildt with the kit from Boozehound Labs ebay listing.

At first I thought it sounded somewhat "too fast", too dynamic, too..."bouncy"..but when settled in..I am just flabbergasted by how sweet sound so little money can buy.

The only thing is the power supply. I have tried to different wallwarts, both incredibly noisy, and both switchmode, allthough my latest is regulated it still produce a lot of noise. So, I am building a Sigma 11 to power this thing, I'll have to live with the noice for now, it will only be for a couple of months anyway.

Pictures to come when I remove it from my setup to take som gut-pictures .
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Featured VT: The 6J5

Posted 19th January 2013 at 02:37 AM by Miles Prower

This type is a singleton triode with an octal base. As nine pin mini types proliferated during the early 1950s, few singleton triodes were made, and the few that you do find are almost always VHF amp types intended for 400MHz+, running as grounded grid amps. Most triodes were made in pairs, such as the 12A*7 series, or the 6FQ7, 6DJ8, etc. If you need a singleton triode in the seven or nine pin mini format, you will either have to go with a type like the 6C4 (a type that is not recommended as an audio triode, but rather a low power, Class C RF driver/final) or make a pseudotriode from a small signal pentode. (The 6AU6 works nicely for this, and it has a u-factor that fits nicely between the medium-u triodes like the 12AU7 and the high-u types like the 12AT7 or 12AX7).

The 6J5 appeared with the Octal base, and metal envelope. There is also a glass Octal as well, but is much harder to find, and more costly to acquire. Regardless of packaging, the type is a small signal, medium-u,...
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