EF86 too weak. is it true what they say?

[pietro_moog]

hi guys. i'd like to add an EF86 to a Spitfire project, it will be a small combo.
do you think vibrations are gonna destroy the tube so fast as people say?
are modern tubes like EH ones more rugged?
i'd like the easy way, just mount the tube on a plastic socket and forget it.
do you guys have good experiences with that?

[greekie]

It's a hard tube to have in a combo. I'd try a 12AT7 or 12AX7 in a cascode setup first. That sounds 90%+ of the way, and is much more rugged!

YMMV

[imaradiostar]

Or...trust me on this one...use a 6au6. Run it with much lower plate and screen resistors so it has a little less gain and sounds more "pentodey." It'll use a bunch more plate current than an EF86 but that really shouldn't be an issue. It'll also drive a lower load which is good. They're cheap and plentiful enough that it shouldn't be an issue if one gets microphonic.

jamie

[clyde1]

I've tried an EF86 in a combo amp, wouldn't cut it.

[imaradiostar]

II've had decent results with a cascode in a combo. Much less microphonic. With a 12ax7 it needs a cathode follower or mosfet buffer or it isn't as sparkly as a pentode. With a 6dj8 you can use lower plate resistance and get pentode like gain without a cathode follower.

I have a chassis and turret board mostly completed for a 6u8 based amp. It puts the triode in front of the pentode so microphonics shouldn't be as much of an issue and I can get a little bass rolloff while hitting the pentode harder for more compression. I've never seen a guitar amp do it quite the way I'm trying. It should be a fun experiment.

JT

[clyde1]

Hi Jamie,
I did a 12Ax7 driving an EF86, CF to tone stack, PI to KT77's this spring, very nice and a fair (!) bit of gain.

[imaradiostar]

Hi Jamie,
I did a 12Ax7 driving an EF86, CF to tone stack, PI to KT77's this spring, very nice and a fair (!) bit of gain.

Awesome. Did you do any bass rolloff before the EF86? I've thought about putting an Orange/Matchless style switch with multiple tone caps in my prototype.

Does it do that neat pentode compressed edge of distortion sound? I'd like to be able to hit the pentode hard enough to not have to overdrive the phase inverter and maintain better volume control.

jamie

[clyde1]

Hmm, looking at my schematic, I have a .001 coupling cap, 6.8k cathode resistor on the 12AX7 with a bypass cap, but no value for the cap-????? It definitely sounds fuller than the 12AX7 circuit and my guy plays in a punk band so he wanted lots of gain, probably more than you're designing for. I also have a PPIMV on the amp.