good driver tube with 150mA heater?

[SemperFi]

I need a decent driver (for PP triode output stage) and I only have 150mA for the heater so 12AY7 can work, but are there any 12V versions of tubes like 6EJ7? 12AU7 looks like a good driver tube, but from what others report it's not a very good tube. ?
I'd love to use a cheapo pentode triode strapped and prefer 6EJ7, but in this case I must have a 150mA heater.
Any suggestions?

 

[DF96]

12AT6?

 

[Shoog]

12AU6

Shoog

 

[Parafeed813]

The ECC81/12AT7 is often seen as a driver in PP amps.
You could even use an ECC83/12AX7 if you put mosfet source followers after them...

 

[SemperFi]

Thnx Shoog, that looks like what I want!
the other options are too high-ohmic. I want lower mu and low rp for driver duties.

 

[SemperFi]

Btw I will use two of these since it's a PP driver ckt. The heaters are placed in the tail of the PP output triodes and are in series. The idle current is coincidentally 150mA.

 

[Merlinb]

There's nothing wrong with the 12AU7. It's better than a 12AT7 at any rate.

 

[SemperFi]

yeh I think so too. Especially as a driver. They are pricier than Shoogs suggestion tho.

 

[Merlinb]

They are pricier than 12AU6 tho.

Won't you need two of them, = 300mA?

 

[SemperFi]

heaters placed in series.
It's driving 6AS7 and the tail has planty of voltage.

 

[SemperFi]

How bout
17EW8 or 6211? Anyone tried those?

 

[Sodacose]

TDSL parametric search turns up these:

12AH7
12AT7
12AU7
12AX7
12AY7
12DF7
12DT7
12DT8
12SL7

 

[SemperFi]

Thnx for tips Sodacose. 12AH7 looks interesting. Need to check if I can fit octals where these tube are going.

 

[Sodacose]

My pleasure! The 12DT8 also intrigued me as I was looking at specs for these. Might just be a 12AT7 variant though.

 

[soulmerchant]

I need a decent driver (for PP triode output stage) and I only have 150mA for the heater so 12AY7 can work, but are there any 12V versions of tubes like 6EJ7? 12AU7 looks like a good driver tube, but from what others report it's not a very good tube. ?
I'd love to use a cheapo pentode triode strapped and prefer 6EJ7, but in this case I must have a 150mA heater.
Any suggestions?

6EJ7 triode strapped has an a gain of around 45 right? Why do you need so much gain for a driver stage?

ok.. maybe I don't want to know, but from my experience, all great drivers need some current, and that needs some heat. 150mA just won't get you much heat. No other way to design around getting some more filament current for your driver?

Too bad you don't have a bit more filament current. If you did, you could use the 12B4.... but the heater needs 300mA.

 

[soulmerchant]

It would help to know what you are trying to drive. If miller capacitance is not an issue then I guess there is a lot of choice out there and wimpier tubes will do it well enough.

edit: if you are driving 6AS7 then 12AU7 is a fine choice - but you won't get a gain of 45 out of it. I think it has a gain of 15-17. I still prefer 12B4 though...

 

[SemperFi]

Youre right Soulmerch! I hope I would have caught that if I had 300mA and about to wire them in. They are an example of cheap pentodes that triode well. I use a pair to transformer drive a pair 6V6 in a guitar amp.
The 6AS7 amp is also for guitar and they overdrive nicer with some gate drive. I think Shoog's suggestion are worth trying.

 

[Ketje]

There exist also tubes with 100mA heater, the U series.You put a resistor in parallel for the missing 50mA. The UF80 and UCC85 are nice tubes.
Mona

 

[Shoog]

My personal experience is that the xAU6 series has a tendency to generate a reasonable amount of 2nd harmonic distortion where other pentodes do not. No harsh edge to this little valve. It makes an excellent, capable and cheap all purpose small signal pentode with no real downsides ( I have yet to hear a microphonic one despite their reputation for been microphonic.

Shoog

 

[davorin]

7695 or 50FE5 !
Very good driver for big output transmitting triode!