6DJ8 Variants, Have you tried any of these?

[CpuZapper]

6AQ8 (9AQ8, PCC85), 6BK7B, 6BQ7A (6BZ7).

I have read they all sound better than the normal 6DJ8’S.
I will be trying them in an Aikido and think they might all be good as output tubes but what do you think?
Anyone try them as input tubes?

If you liked them did you have a favourite operating point?

[Geek]

6BQ7 beats and ECC88 for sonics, IMO.... just not in noise/microphonics unless you get one like a tank.

I can't remember the op point.

Cheers!

[Shannon Parks]

Working from memory here, but I think I did some bench tests of the 6BZ7s - after being a little excited about them - and found their linearity was lacking compared to 6922s.

[EWBrown]

the 6BZ7s, 6BQ7s, 6BK7s and 6AQ8s are mainly RF tubes, generally used in the front ends of FM tuners, and they may be too noisy or microphonic for most audio usage, especially in higher gain (phono and tape head) stages.

Similarly, 12BZ7s are not a good 12AX7 replacement, they have the same mu as 12AX7 (100) but the gm is twice and the rp half that of 12AX7. Basically each section equates to two paralleled 12AX7 triodes. These can also be noisy and microphonic in audio applications, some are good and some are really bad... YMMV, etc...

the Russian 6N1P-EVs are a better choice, the gain / mu is about the same, but the gm and rP are different, so some circuit tweeking would be needed.

The 5670 / 2C51 / WE396A is also a good alternative, also the gm and rp are different than 6DJ8 / 6922 / ECC88, but they are a better choice than the RF tubes. These tubes have a totally different pinout than the 9A or 8AJ tube basing, so they are not simple drop-in replacements.



/ed B

[Geek]

To drift us slightly OT... trioding a 6EJ7 makes for a very linear and low noise ECC88-like half section.
(6EJ7 triode is as close to EF86 triode in performance of a non-SQ tube as you may find and a heckuva lot cheaper!)

Cheers!

[EWBrown]

Thanks for the 6EJ7 tip!

I'll have to try some of those out in the future.

/ed B

[EWBrown]

Another IF pentode which may have some interesting audio applications is the EF184, It has a similar gm and rp as the 6EJ7. so it should be similarly applicable.

http://frank.pocnet.net/sheets/010/e/EF184.pdf

(I just checked through TDSL, EF184 and 6EJ7 are interchangeable)...

I obtained over a dozen of these, NOS/NIB Amperex Bugle Boy EF184s last October at thge NEAR-fest hamfest in Derfield NH. Seller had numerous "flats" (beer cases) filed with tubes, for $15 each, and the se held up to 120+ tubes each. hey were a mix of used, pulls and NOS / NIB,
and he did allow cherry picking so I exchanged the numerous 1B3s, etc ffor more "useful" and intresting tubes. The EF184s werre just a "blind shot" as they 1: looked nice, and 2: had more possible applications than 1B3s and other TV rectifiers...

These have the external "screen" around the anode, and being Amperex BBs made them doubly interesting... Especially when they averaged at under 15 cents each Yellow_Light_Colorz_PDT_06

The "flats" didn't have a lot in the way of truly "desirable" tubes, but then I got these on the second day of the 'fest and I'm sure that all of the good ones were already well picked over... I was there both days, but not over Friday night, and that is when some of the best deals seem to surface...

It was too darn cold and I didn't want to freeze my butt off while "car camping".

/ed B

[CpuZapper]

Tubes for 15 cents would be great.

I paid about $1.00 each for the tubes in my list.

Living on the Canadian tundra a buck a tube is a steal.
I will try them and let you know.

(6BK7B, 6BQ7A) Rk=200 Ohms aprox.
I was thinking the high transconductance of the 6BK7B would be worth a try as a output tube.

[EWBrown]

Sometimes these hafests are awash with cheap tubes, other times tubes are nearly absent.

I won't go into the time, around 20 years ago, that someone had a "crap load" of NOS NIB Western Electric 300Bs for sale for $15 each, at Deerfield, back when it was called "Hosstraders"... :o Yellow_Light_Colorz_PDT_21 :o Yellow_Light_Colorz_PDT_21 :o

And I was too doggone dumb to realize what they really were...

Oh, well, live and learn. Some lucky "SOB" is probably putting his kids thru college on the proceeds from those...

/ed B

[Ty_Bower]

And I was too doggone dumb to realize what they really were...

Don't feel too bad. At least you're not the guy who sold them. Yellow_Light_Colorz_PDT_16

[EWBrown]

Does anyone have the 6EJ7 / EF184 operating characteristics for triode-connected operation?

I have some basic info, but the one thing I'm lacking is the triode-connected rP (internal resistance). It is about 350K ohms in pentode, I'd SWAG that the rP is a LOT lower in triode mode. (yep, it is...)

I am trying to work this one up on tube-cad.

update:

I almost answered my own question:

Courtesy of those wonderful folks over at The Geek Zone:

http://geek.scorpiorising.ca/GeeK_ZonE/ ... pic=1006.0

and that leads to:

http://www.tubes.mynetcologne.de/roehre ... triode.pdf


/ed B

[EWBrown]

I ran the 6EJ7 mu-follower, re-configured for 6.6 mA with 270 ohm cathode resistors, on Tube CAD, as SRPP "B" and it comes out VERY closely.

Good one!

Once I found that triode strapped gm = 5.0 mA/V and RP = 11K, mu = 55, then everything fell very nice into place.

Update: that has since been re-calculated to: gm - 15 mA/V, RP = 3700 ohms, and mu still = 55.

Now I can put those 15 cent EF184s to some good use Yellow_Light_Colorz_PDT_06

Some other info that I found elsewhare, showed triode-connected EF184 with a CCS plate load, running at 18 mA :o would yield a gain of 61X, and a voltage output of 76V @ 5% THD, and 0.09% @ 10V output. B+ is 300V, plate voltage is 148VDC, and a plate dissipation of 1.9W, and G2 of 0.8W

Those values do seem somewhat "extreme". :o

For now, I am using these values for Tube CAD:

mu = 55; gm = 15.0 mA/V; rp = 3,700 ohms; Imax = 25mA; Vmax = 250V; Cgp = 0.01 pf; and triodes = 1.

Cgp for pentode is 0.005 pF, I don't know if this holds true in triode mode, so I SWAG'ed 0.01 pf for this value.

FWIW, they look pretty good in "basic" SRPP as well, with a max output of +76/-76V with 330 ohm RKs and 350V B+. .(SRPP D in Tube CAD).

I'm getting "itchy" to get down south so I can get working on some new priojects (and get away from the frozen wasteland, forever).

/ed B

[Geek]

Thems is little gems Yellow_Light_Colorz_PDT_01

I gave 'em a whirl at driving an EL36 in AB2 straight from a mu-follower of trioded 6EJ7's and they can drive!

Cheers!

[EWBrown]

IIRC, EL36 is pretty durn close to 6BQ6GTB, and if one goes for the "weird" filament voltages, 25V for example) the choices are: PL36, 25BQ6GTB, and the quirky little 25E5 which was used in the Sansui 1000 (predecessor to the 1000A which used 7951s). The 1000 was an amplifier in the true "plinkertron" spirit. Yellow_Light_Colorz_PDT_03

FWIW, 6BQ6GTB has nearly identical operating characteristics to 6AV5GA, and we know well what they can do in triode mode Yellow_Light_Colorz_PDT_06

/ed B

[TerrySmith]

And don't forget there are 7DJ8, 6GU7/ 8GU7, 6CG7/ 8CG7 tubes that will drop in a 6DJ8 socket. If pin 9 ain't grounded there is the 6AU7/7AU7, same as the 12AU7 except the filaments.

I ordered a few 7AU7's from AES last year @ $1.80 ea, all were RCA clear tops!