6DJ8 Variants, Have you tried any of these?

[Geek]

Hi Ed,

IIRC, EL36 is pretty durn close to 6BQ6GTB.....

Yeah, on papaer. She sounds completely different.

Some mates have discovered though that the 6BQ6GTB is an sweet little PP tube with a 4400 ohm A-A load Yellow_Light_Colorz_PDT_11

And don't forget there are 7DJ8, 6GU7/ 8GU7, 6CG7/ 8CG7 tubes that will drop in a 6DJ8 socket.

6CG7/ 8CG7/ 6FQ7/ 8FQ7 bias up identical to a 6SN7GT. So any schematics for 6SN7GT can be applied to the minatures within their Vamax.

Cheers!

[EWBrown]

6GU7 / 8GU7 are close to 12BH7A, slightly different rp and gm, but gnerally "close enough", within a few % points. 6DJ8 socket compatible.

I'll have to look for some EL36s, as they aren't nearly as commonly available around here as are 6BQ6GTBs.

The 1965 ARRL Radio Amateur Handbook has a 6BQ6GTB based modulator, which could easily be modified / upgraded for audio use, with a 4KCT:8 OPT and changing the valueof the interstag coupling caps.

The same publication also had another modulator based on 6GK6s.

/ed B

[Geek]

I'll have to look for some EL36s, as they aren't nearly as commonly available around here as are 6BQ6GTBs.

Practically unobtanium. There's some NOS Tesla brand floating around, but seem to personify inconsistency Yellow_Light_Colorz_PDT_20

Cheers!

[EWBrown]

Maybe I'll stick with 6EM7s and their numerous derivatives. They are great performers, readily available, and about as cheap as dirt. True, AES and other vendors seem to be watching the boards, and when a lowly "plinker" suddenly gains desirability, their prices do trend upwards, or else the supply suddenly "dries up". OPEC aren't the only ones savvy to these tricks Yellow_Light_Colorz_PDT_11

THe "audiophool council and conspiracy" is unfortunately alive and well and all too active :o Yellow_Light_Colorz_PDT_08 Yellow_Light_Colorz_PDT_04

If I do get the "EL36 itch" I can always start out with 6BQ6GTBs, then change to the unobtainium tubes if I ever manage to find any of them... Yellow_Light_Colorz_PDT_11

[Geek]

If I do get the "EL36 itch" I can always start out with 6BQ6GTBs, then change to the unobtainium tubes if I ever manage to find any of them... Yellow_Light_Colorz_PDT_11

I have a pair.. Sylvanias I believe



Yellow_Light_Colorz_PDT_05

[EWBrown]

Right now, all of my tubes 'n' stuff are about a thousand miles away from me... I probably won't be able to get back into serious building and testing until late summer / early fall... Gotta get the NH place sold and the move completed, starting in early June. I already have one "nibble" on the house, but that's only a "maybe" at present.

May 2009 update: I now have a much more serious "nibble", so hopefully the wheels wil start turning faster, now

/ed B

[EWBrown]

As discussed here:

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

The operating characteristics for a trode strapped 6EJ7 / EF184 have been recalculated:.

The mu is still the same, at 55, but the gm and rp have changed.

The "old" values were gm = 5 mA/V, and rp = 11000 ohms.

It has been changed to gm = 15 mA/V and rp = 3700 ohms.

Basically they havve changed by a factor of three, gm increased 3X, rp decreased to a third..

The mu is the product of gm and rp, so the amplification factor remains the same at 55X.

Max plate voltage is 250V, max plate current 25mA and max pd is 2.5W, as before.

I have yet to put these tubes to work in an SRPP, mu-follower or simple grounded cathode VA stage, that happens after I finish my move to NC this summer.

And that process starts next week! I aim to git 'r' done by late July at the latest. Stay tuned... May 29th (this coming Friday) is my last day at the old salt mine, and then "free at least.... "

/ed B

[Impmon]

6BQ7s: Used these to make a cascoded LTP voltage amp/phase splitter. This type definitely likes to operate with an unusually high Vpk in order to operate linearly, so it's not suitable unless you have a high enough Vpp. As an audio cascode LTP (cascoded BJT CCS in the tail) it sounds just great.

Since this is an RF type with no pretenses to audio use, beware of microphonics. The worst offenders seem to be the ones with the heaters in series. The ones with the heaters in parallel aren't usually microphonic.

6BQ7 Loadlines

There is something squirrelly about the plate characteristic. Is that an undocumented variable-u characteristic?

[Gingertube]

EL36 are the same as 6CM5 which is a tube which was in darn near every tube television set in Australia and New Zealand. Any OZ supplier will have stacks of 6CM5 at reasonable prices. NOS are A$27 (less than US$20) from EVATCO in Brisbane, Australia. Note: EVATCO are'nt the cheapest place to deal with, but have a huge stock and will generally have what you want. I have about 12 left plus a matched hextet set aside for the refurbishment of a Philips Guitar Amp which used 6 in parallel push pull for around 150 Watts.
They were also the "standard" tube in all of the PA Amps for hire companies back in the 70's.
Cheers,
Ian

[Geek]

NOS are A$27 (less than US$20) from EVATCO in Brisbane, Australia.

I'd never pay more than $8 or $9 for them, That's what they go for in the US: http://www.thetubecenter.com/vacuumtube ... -6CZ5.html
(near the bottom)

Cheers!