Design ?

[shooter]

I've found about an even mix of the two diferent ways to hook up the plate and screen on SE units.  Is there a "prefered" version.  I built the 2nd style a couple times but the 1st method havn't tryed.  I do know in the 1st examble B+ is below max plate/screen volts, where the one I built, the 2nd method, B+ was above max plate/screen ratings.  Both examples are using EL84's. 
Thanks

dave

[kagliostro]

One is Pentode the other is a Pentode triode strapped

K

[sluckey]

The first one is feeding the screen and plate from the same B+ node and is more likely to be found in cheap amps. The second one offers a separate B+ node for the screen and also offers a screen resistor. I prefer the second one.

[shooter]

I searched "triode strapped pentode" and got skooled!!! but I failed! a paraphrased quote, "in triode mode the screen "feels" the plates signal..."  That made sense, but I can't see how the screen "feels" the plates signal in either examples, the first is locked to B+, the second it's locked to B+ - rail drop resistors.   I can see how it would be a "cheaper" design and the second being better for controling the screen volts better. my B+ will only be 250.  I'm using a bridge rectifier, a CLC pi, then just a 10k tap for a 6snl pre.  the last builds have all been 50's style tube rectifiers, so this is more of a "so can the guy behind the curtian tell".  I'm a visual artist, not musical, i still can't figure out why you guys like the fat string on top!!!  Anyway, thanks, i like the way this site trys to "raise the bar" instead of bumbing me down!

[sluckey]

but I can't see how the screen "feels" the plates signal in either examples

Neither of those circuits are strapped for triode operation.

[kagliostro]

Neither of those circuits are strapped for triode operation.

My fault 

K

[PRR]

> i still can't figure out why you guys like the fat string on top!!!

Me neither.

> I'm a visual artist

Then you know painting.

Where signal comes in, at the guitar jack, it is very small. Think Rapidograph technical pen. This has to be used on VERY smooth surface. Fine smooth paper.

Where signal goes out, Power stage, it is very big. Think whitewash brush. This works fine on ROUGH surface. Barn-board. Brick wall.

And foot-for-foot, brick is a lot cheaper than fine paper.

The power tube plate takes a lot of power. But it can be really rough power.

The power tube screen takes less power but it has to be smoother.

So in a highly optimized design, the first filter cap is just big enough to supply a lot of rough power to the plate, a second filter (resistor and capacitor) delivers a lesser amount of smoother power to the screen. Rough brick for your 20 foot mural with one slick brick for your signature.

OTOH, sometimes it is simpler, maybe cheaper, to go ahead and clean all the power big enough for the plate yet smooth-enough for the screen. Canvas or plaster the brick wall so you can mural and sign all on the same stuff.

> the 1st method havn't tryed.  I do know in the 1st examble B+ is below max plate/screen volts

If you have not tried it, how do you know where the B+ will end up?

> a CLC pi

For a ONE power-tube amp, like the plans you show, you can go C-R-C. Rectifier to 40uFd, then 1K 10W, then another 40uFd. Take both your plate and screen from the _second_ cap. This will be plenty clean. And the 1K resistor will drop about 40V, lowering the B+ to the tube.

> above max plate/screen ratings

Don't sweat the ratings on 6V6 or EL84 too close. The 1957 ratings were to give good life in your grandmother's tube radio, so she would not have to pay a radio guy to replace her tubes. Also so broadcasters and other pro users got good long service without unexpected and costly breakdowns. (If a radio station can't put the ads on the air they don't get paid.) We rockers have other goals. We like it loud. Yet light. We get paid (paying gigs or self-enjoyment). We can lug amps around, and we can learn to replace our own tubes without paying a guy. Guitar amps always over-volt their power tubes. Reputable g-amp tube suppliers sell tubes which can take such over-voltage for hundreds of gigs.

[shooter]

Thanks all, even the guy that sent me lookin for strapped triodes, now I know what they are, not sure the why, unless you just have a bunch laying around.  My build is actually a quad SE el84 driven by a 6sn7, no knobs.  I gave my musicial son the last 5 builds, He even gigs with a couple.  He's got his amp guy workin a couple kinks outta my stereo KT88.  He likes the idea of always having a spare amp! so now i'm stuck listenen to music through a 2 watt computer amp. 

Again thanks, maybe 30years of solidstate computer knowledge i've got will be replaced by something fun!

[sluckey]

My build is actually a quad SE el84 driven by a 6sn7, no knobs.

We would love to see some pics and a schematic.