Optimum driver valve for an interstage-transformer-driven SE 300B

[needsp]

Hi

I didn't mean your mu value was wrong. But I asked for drivers with a mu of about 20, for the reasons I explained

Paul N

[bappe]

Hi,
I've used both triode connected el84 and the Russian 6n6p with very good results. I run the 6n6p through a LL1660 driving a gm70 today with very good results, and it is cheep and plentiful :-). In this application it sounds slot more refined AND powerful than the ecc99.

BR,
Anders

[Shoog]

You beat me to it, I was going to suggest the EL84 or EL86. Both drivers with real gain, lots of muscle and a universally liked tone.

Do not discount the option of using a higher mu valve and then stepping down in the interstage - that allows you to beat the residual losses in the IT into submission with a very large stick.

Shoog

[JohanB]

Originally Posted by needsp

Hi

I didn't mean your mu value was wrong. But I asked for drivers with a mu of about 20, for the reasons I explained

Paul N

Look for the "supertube" E282F Used by many in this application.
mu 27 and output impedance of less than 1 KOhm in triode mode
Triode connection data aviable here: http://frank.pocnet.net/sheets/009/e/E282F.pdf


Johan

[Rod Coleman]

Hi Paul,

6П15П is very hard to beat in this position! Many higher-gm triodes and triode-connected pentodes are excellent performers when the anode voltage is fixed (and therefore great in cascode) - but at high voltage the curves slump to the right (to use a crude approximation).

Purpose-designed Output valves, including line & frame video outputs are the best field.

Have you checked out the 6Ф6С?

Nominal point is at 250/250v -16,5v for 35mA. Only 3mA/V though, and the base is not what you want.

6П15П has different builds though - and some Reflektor (Saratov) made types are characterised like 6П14П. Other Reflektors may be different, and there are also Orel-factory parts. Also, the 6П15П-EB tough version. These are the examples I have here, but there may be others.

[needsp]

Hi Babbe

What are your operating conditions for the 6N6P and EL84M? I'm trying 6N6P at 210 V anode, - 8 V bias, 20mA at the moment, to maximise the available voltage swing. But might sound better with -6 or -7 V of bias and a lower anode V?

I used a triode connected 6P14P- aka a "EL84M"- for a long time at 230V/26 mA/26 mA. Compromise to optimise output swing available, while running within ITX's current limits- far away from its spec sheet optimum conditions (48 mA)!

Hi Shoog

Step down ITX sounds interesting. Do have any links to relevant documentation? Though it would require considerable investment in new ITX's

Hi JohanB

Had a quick look at the triode connected specs of the E282F. Ia (not including Ig2!) 40 mA at 110V on the anode and - 2 V bias! Nowhere near enough output swing V to drive a 300B- or am I missing something?

Many thanks

Paul N

[needsp]

Hi Rod

Glad you weighed in!

I used the 6П15П-EB (6P15P-EV) version in triode connection, after your earlier (emailed) suggestion. My operating conditions- 215 V plate, -6.0 V bias, cathode current 19 mA, are a compromise- the plate V is a bit higher, and the current a little lower than I'd ideally like, to get the bias up to -6 V. Even then I'm getting only a possible +/- 125 V swing. The TJ Mesh plates I'm using are fixed bias at -95 V for 68 mA with 420 V on the plate (28 W dissipation), so I'm not avoiding, at full output, cut off of the driver by as much asI'd like, yet the plate will instantaneously go over 300V- not sure if curves still good here. Whatever, I think I prefer the 6P15P to all comers so far. Though the 6P14P- despite its low current operating condition- had its charms

6Ф6С/6F6S looks a bit of a brute :-)

Paul

[JohanB]

Originally Posted by needsp

Hi JohanB

Had a quick look at the triode connected specs of the E282F. Ia (not including Ig2!) 40 mA at 110V on the anode and - 2 V bias! Nowhere near enough output swing V to drive a 300B- or am I missing something?

Many thanks

Paul N

If you look at the triode connected caracteristics on page 7 in the data sheets,
http://frank.pocnet.net/sheets/009/e/E282F.pdf
you can see that a E282F:
@Ua=125V, Ug1=-3V, Ia (+Ig2)=25mA, the E282F can swing +-80V at no load & +-70V at 8KOhms shunted load
This will give 140 to 160Volts Peak to Peak in the inductive transformer load and will be more than enough to drive the 300B, even into the grid current area.
I also think the distorsion caracteristics of the triode connected E282F vill cancel much of the distorsion in the 300B.
Can be fine tuned by resistive loading of the transformers primary/secondary to perform better transient response.

Johan

[needsp]

Hi Vinylsavor

Originally Posted by Vinylsavor

Hi!



Have you ever seen the plate curves of a triode connected E810F? Not datasheet curves, real ones. I have examined it with a curve tracer. While good for small signals it gets quite non-linear at the outer regions. I would not use it as a driver in a power amp.

I have used it in LCR phonostages and there it works nicely.

Best regards

Thomas

Thanks for that. Information about real world behaviour in this application is just what we need!

Paul N

[barossi]

Hi,

what about E180F in triode mode:

http://frank.pocnet.net/sheets/009/e/E180F.pdf

mu=50 a bit high, probably with choke load?

Kind Regards

Hauke