question about ef86 front end preamp

[wsaraceni]

when amps use an ef86 preamp, are they generally just the 1 tube in that channel. when i look at a matchless dc30, for example, i see that the ef86 goes into a rotary switch and then direct into the PI section. is that normal for an ef86 channel in most applications? are there any other amps with schematics that use this tube in a preamp?

thanks
bill

[Zippy]

Z-28 and Route 66.

[wsaraceni]

where can i find the schematics of them? im not looking into building one of them, but i wouldnt mind seeing how the circuit around it is built.

[Zippy]

See the topic "EF86 Wiring".

[klingo]

booooh!!!

[klingo]

I've made a RT77 version of this amp,with JJ's KT77, ~380v/-490v SS recto...but 22uf/120ohm/47uf before plates...big PT&OT(5K5 UL43%) from my favourite Toulousian Manufacturer (electra sud-ouest)...monster amp if your neightbors plays guitar, but my 18wlite is too loud most of the time.
sorry for sharing again!

[m.alexander]

I've made a RT77 version of this amp,with JJ's KT77, ~380v/-490v SS recto...but 22uf/120ohm/47uf before plates...big PT&OT(5K5 UL43%) from my favourite Toulousian Manufacturer (electra sud-ouest)...monster amp if your neightbors plays guitar, but my 18wlite is too loud most of the time.
sorry for sharing again!

I've made a RT6550

[klingo]

nice built Alexander!

mine took place in a MIG50 cab (tight fit)
IIRC you have a cathode/fixed bias switch , and i wonder if you find it really useful.
mine is fixed bias and about 60/70w, cathode bias will decrease power to ~35w and rise harmonic distortion
is there sufficient touch response difference between the two mode?
i worry about drilling & moding again a good amp but i love the way my 18wlite feel (ss recto,22uf/180 ohm/47uf, and cathode bias in a blues jr)

olivier

[klingo]

sorry Alexander!

in fact the double bias is fixed bias but individually adjustable!

just look at the inside pic now

[wsaraceni]

cool. thanks for sharing guys. what i would like to try is a tube rectified, ef86 into single ended 6v6. kinda like a matchless meets a champ. im not sure how it will sound, or if it will sound good. not quite sure how to even do that just yet. im looking at a bunch of schematics. i think first i need to figure out how to spec a transformer set to do what i want. any suggestions?

[klingo]

hi wsaraceni!

in this case you may need one more triode(or another ef86 wired as triode) between ef86 and 6v6.
the cascaded 12ax7 in champ has way more gain than the single pentode
(3000 vs 200), and high output impedance of the ef86 pentode mean it will not be my first choice to drive a power tube into guitar distortion.

i may be wrong again(i've just look into a kt66 quad schematic )

[bueller]

I completely agree, a single EF-86 is not enough gain to drive a PT. I've also tried one EF-86 with PI into a push-pull EL-84 sections, not enough.
My latest version is an EF-86 cascading into a paralleled 12AX7 section, then PI, EL-84 push-pull power. Almost as much gain as three 12AX7 stages.

Plus you don't have to follow what everyone's done on the EF-86. I've even used a 0.68 cathode cap for a brighter tone, and various plate and cathode resistors.

[klingo]

well i tried this 6av6 à la TW section http://www.nintendork.org/images/akai/akai.gif
my feedback voltage divider is 10k lin with a 1nf cap across the hot pin and the wiper, 6av6 is a single 12ax7,and it sound very good so it's going to stay in mig/RT 77
i've just need to twist the push-pull wires because of positive feedback
my RT77 was good for the clean side
now it could walk on the dark side

[m.alexander]

[dartanion]

Here's my layout for an 18watt EF86 Lite. It sounds pretty darn good to me without an extra gain stage.