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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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Old

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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Featured VT: The 6BQ6

Posted 18th January 2013 at 01:45 AM by Miles Prower

The 6BQ6 as an audio final came to my attention as a chance result of finding
an old article from a Portuguese (Brazilian? -- it was written in Portuguese)
ham magazine. This described a simple AM plate modulator that claimed an output
of 30W (fixed bias) or 25W (cathode bias) that used a push-pull pair of these
VTs. You would expect to see 6L6s or 807s used in this particular application.
Why 6BQ6s, and what were they?

The 6BQ6 is a large signal beam former. It has no audio pedigree
whatsoever, and the spec sheet makes no mention of its use as an audio final.
During the 1950s, screen sizes and deflection angles increased, giving a larger
viewing area, and a shorter CRT for more compact TV sets. This development meant
that the usual audio finals and RF types became increasingly unsatisfactory for
horizontal deflection duty. New types more suited to the task were developed,
and one such type was...
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Rating: 2 votes, 5.00 average.

Featured Vacuum Tube: The 807

Posted 15th January 2013 at 10:05 PM by Miles Prower

Featured VTs: The 807

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807

The first of the beam formers is also one of the most enduring types: the 6L6. Developed by RCA in the mid-1930s, this type was originally intended for use as an audio final. It included other, then new, features besides the elimination of an actual, physical suppressor grid required to smooth out the screen grid "kinks". This included the now standard Octal base (up to eight pins possible, and with a keyed base for proper socket alignment) and a metal envelope. The latter was made in one of two ways: a glass envelope VT slipped into a metal shield can, or using the shield can as the envelope, with a glass base to bring out the connections. Other improvements was to give the control grid and screen grid the same pitch and wire diameter. By overlaying these two grids, the negative control grid serves to "shadow" the screen, thereby reducing the useless...
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Modification of the S.M.S.L. sAp VI headphone amplifier

Posted 14th January 2013 at 11:29 AM by rjm
Updated 28th January 2013 at 12:33 AM by rjm

I couldn't even build it myself for the price they are selling it at, $50 on ebay. It caught my eye for the linear, split power supply. I love the chrome 3-pin power connector, too.

As is usual when you buy cheap ultra-Chinese audio gear via eBay some adjustments are needed, however.

The basic problem seems to be a little mix up with the input coupling capacitors. It came with polar electrolytic capacitors, following the markings on the circuit board. If you lstudy the schematic I sketched up below you will notice the input signal and DC offset can swing in both positive and negative directions relative to the op amp inputs - polar capacitors in this position are a bad idea.

I recommend anyone buying this to replace the input caps with Nichicon Muse ES or similar 4.7 uF or 10 uF bipolar electrolytic caps. (I have some extra I can mail out. pm me if interested.)

Other than that it's a pretty solid circuit as far as I can see....
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Maze Back Horn

Posted 10th January 2013 at 11:01 PM by DougL

http://www.diyaudio.com/forums/full-...w-you-can.html

I want to make this for Adam.
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Old

Headphone amps are hard.

Posted 9th January 2013 at 10:41 AM by rjm
Updated 21st January 2013 at 07:12 AM by rjm

The $50-from-China-via-ebay NJM4556-based headphone amp, pictured below, fails the "Is thing thing on?" test. With 16 ohm, 104 dB/mW headphones there is a faint-yet-audible background hiss when the unit is powered up and the volume is turned all the way down. The hiss increases only slightly as the volume is turned up (input disconnected).

The output noise of an op amp is normally estimated from the input-referred voltage noise density multiplied by the gain, and the current noise density multiplied by the gain and the sum of the input impedances on the inverting and noninverting inputs. The NJM4556 datasheet does not give a figure for current noise, but a reasonable guess is 1 pA/sqrtHz. The voltage noise density is estimated at 8 nV/sqrtHz.

Total noise is

Vn (output) = sqrt [(i_n R_s)^2 + e_n^2 + 4kT R_s] * Gain

Working from a source impedance of ~10k, I get about 18 nV/sqrtHz or -138 dB.

[Revised according...
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Old

6C33C OTL Amp Comes to Life

Posted 8th January 2013 at 12:45 AM by wlowes

This is the continuation of my personal journey to build my first tube amp.
It was a very happy day yesterday when the first mono bloc powered up and produced music. I was pretty comfortable that I had not made mistakes that would result in smoke, but really did expect some issues with hum, grounding or tube substitution. But nothing! Hum was barely audible with my ear on the speaker or from the chassis. And music played! My first test flight was one channel only driven by a Sony Walkman on a small Totem speaker. Even under these conditions the sound was pretty good, and really started to open up after the first 60 minutes. I was like a proud father
The first picture shows the pair with a Rotel CDP in the middle for scale.
I will not be able to fully know the sound until both are wired, broken in and hooked to the good speakers and source. I think they will be amazing. Already better than the very respectable chip amp they replace. There is a switch...
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Old

my tube_you

Posted 6th January 2013 at 02:32 PM by suwaned (tube audio friends suwaned)
Updated 1st July 2013 at 11:25 PM by suwaned

Preamp cleo4 Triodedick's

The First falling in Love with TUBE, when i had heard the preamp B406 my friend.

I have build the first Project tube , preamp B406 single stage.

final:
Preamp with Phillips B406 and Phillips D3a with output line transformer Hasimoto HL10K_600.
rectifire Valvo AZ1.
Thank you for your Help and advised my Friend "The_Manta" and my friends_audiotube.



Test Preampcleo4 with OLT
https://www.youtube.com/watch?v=EW1HYcXLm2g




My system:

https://www.youtube.com/watch?v=mQFL8X9hIeM
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