18Watt.com

So increasing the tail R will decrease the drive to the 6V6s... I'll have to try that .. Deductive reasoning would indicate that the awesome gain I hear is from the PI, since the "other 6SJ7 amps' didn't have anywhere near the gain this beastie' has... I'll never be able to use all the gain this thing has ,for what I'm playing... Oldies...I may just change back to the 56K and see what happens ...I'll still try out some other tubes as I can find them..The TeleF 12ax7 did sound good on 1...
Even at 9:00 it's still louder than any other amp we built (those amps)..Yes, Big you were right, it's not a Toy ...
Weird thing is all the microphonics ,strange noises, squealing has mysteriously vanished... just like yours... Strange !!!! Very quiet now ... I hope it holds out, planning on using it for the gig on Sat. Won't need any 3SBs for this one

Tried putting the amp in my old empty marshall head cab... just too small in there, seems lost ...Sigh!!! guess I'll have to build another cab for it... I'd better just toss that old cab or I'll get myself in more of a fix trying to build something to fill it...

Geezer,

You'll be able to go from clean to mean with your guitar volume control.

So much for logic... put the 56K in there and it didn't make much difference at all, except the sound became "grainy":... Ecch!!! Hated it!!! so I put back to 22KR.. sounds nice and sparkly now... That ZP has a good bag of tricks eh???
KY, That's what I'll have to do ...tried that and it does work very well..Thanks !!! have to get used to this one ...I'm used to turning up those "other amps"

Andrekp wrote:Gain-wise, a "normal" 18watt is not all that gainy in a modern sense. Don't know how much your choice of tubes causes so much gain, but I suspect it should still act normally. If you are hitting distortion just about 1 on the dial, chances are something is wrong.

18Ws have lots of good old fashioned voltage gain though, which is why they distort so much. And it usually gets pretty crazy with the extra gain of a pentode in the preamp. So this looks like pretty normal behavior to me.

GUITARmole wrote:You mean 220? The StarGeezers schematic has a 200 ohm resistor there now...

Whatever value will drop a few volts. But if he's using 6V6s, then there's no need to worry anyway.

bigbeck wrote: I think Geezer made a typo here. In another post he stated that his cathodes were 21.5V. His big voltage difference was between the two 6v6 control grids,pin 5.

Control grids have to be at 0 volts, whatever happens. If not, there's something seriously wrong, which needs to be fixed before anything else.

StarGeezers wrote:Big, not yet ... got a 12AU7 (old) I can plug that in and see the difference...got a 5751 too for somewhere in the middle ... we'll try them all... PI Cathode R is 820R....

So now you've got all that extra gain, why are you trying to throw it away? Repeat after me 10 times, "Gain is good, gain is good, gain is...."

bigbeck wrote: Try 12at7,12ay7 and 12au7. With at being highest and au being lowest.

Like I just said..... and I always thought you were the kind of guy who liked to fire up the barbecue...

kyoungsteadt wrote:You have to understand that ZP wants your amp to sound wild...

You bet!

StarGeezers wrote: Think restoring the tail R back to 56K would tame that wild PI??? 22K now as ZP suggested...

You need the lower value tail resistor, so that the PI can provide enough signal voltage to drive the 6V6s, which have a lot lower internal gain than EL84s.

bigbeck wrote: Edit: a 12at7 might be perfect for you,but might as well try raising the tail resistor to see what happens. Clean up to 9:00 sounds good as long as it's loud enough at that setting.

Actually, if it's breaking up at 9:00 (I assume you mean 9 o'clock on the dial), then that's pretty much like you'd expect from a regular 18W. It should then get progressively dirtier from there. I don't believe there would be a benefit in using a 12AT7, as AT7s will drive the power stage even harder due to their lower anode impedance. They also bias differently to AX7s. If you want to trim off a little more gain, you can reduce the power tubes' 470k grid reference resistors, say to 330k.

ZP it behaves and sounds really good now ..works as you have indicated..
"Control grids have to be at 0 volts, whatever happens. If not, there's something seriously wrong, which needs to be fixed before anything else. "
RUH ROH!!! My 6V6 Pin 5s were at varying Vs , from like 16V to manyVs... I couldn't get a consistent reading from time to time ...The Vs would rise and fall slowly ...???? Any idea of what it's doing... ??? doesn't seem to affect the tones , it does sound really good , and LOUD...

StarGeezers wrote: That ZP has a good bag of tricks eh???

Yes indeed!

gain is good......gain is good.....gain is good I may be treading on thin ice here, but you can even attenuate more with 220K grid leaks.

What am i thinking? Just put 6l6's in there and you'll be looking for ways to "increase" the crunch. That stayed clean up to about 2:00. The distortion above that was not as nice as a 6v6 breaking up,though.

This is 18 watt land. Light the fire and let'er rip... Geezer you wanted more gain and you got it. Turn your guitar volume down and it will clean up. Now you'll have to join an AC/DC cover band

AC/DC...at my age,. more like "Intermittent Potential"...

Played the amp for 4 hours , so we know it'll make it through the gig... still worried about the 6V6 input grid V thingie'...all though there appears to be no ill effects.. yet...
Tried the amp through 1/12 open back cab, was very bright , then plugged it in my 4/12 closed back cab... NICE, with Thump...Just right!!!! Now if only I had some Hair...and roadies

ZP, I can't help obsessing over your statement..."Control grids have to be at 0 volts, whatever happens. If not, there's something seriously wrong, which needs to be fixed before anything else. "... Checked everything out... the amp works fine ....as Big would say ...WTF???????
I was reading DC,which could account for the erratic readings ,but I can only see the pin 5 V source as a bad coupling(blocking) cap from the PI....???? I'll have to take some more readings ...Maybe it fixed itself ... Right!!!!

Man, you just can't trust an old Geezer.... Re-read the Vs, everything was fine until I noticed the 6V6 Pin 5 voltages were in mV... 61mV on one , 141 mV on the other... This seems much better...not exactly 0, but not as scary....My Bad!!!...

The amp sounds really Great ,Killer tones , stable and quiet now...can't wait for the Sozos to "form"...
I guess this about wraps this project ... once again , my infinite gratitude to all who helped get us through this amp build... THANKS !!!!!!!!
We'll make a cab for this , take some pics and get back when we're done...Thanks again!!!!

Just an update... I was able to put the amp in an old Marshall 100w head (SS) that I'd been saving for 10 years...waiting for a suitable project. Saved a lot of woodworking!!! All I had to make was a new front faceplate for the cab. Since I was using the BN Flex chassis (backwards) the front has some rather large holes , so I made a whole faceplate (cab) and just cut out the area where the input jack, Volume and Tweed TC was...used 1/4" Masonite, easy to work ,and painted it with a rough textured Gloss Black latex house paint...looks remarkably like Tolex... Put five 1" holes across the top for ventilation ...and can look in and see if the tubes are glowing... no power lamp...After all ,it is an Absolute Minimum!!!!!!!... ready for the gig...

Rock on, Geezer.

Tried out the amp at the gig, got GREAT TONES, more than enough volume , and the approval of my band mates...Couldn't be happier... With the wonderful sound of this amp , we didn't even need or want any "effects", ran straight into the amp, used the guitar V for controlling the volume and dirt.... (as prescribed by KY)....KILLER TONE, Holy Grail stuff, no BS!!!! Best of all , spent less than $225.00 USD on the whole thing... I already had a cab for it...FREEBIE
I can't see a sane reason , for any amp louder than this one ...I could have easily overpowered the entire band, drums included...
I just might have to build another for a "spare", and to incorporate some new ideas to make assembly even easier...I Love this amp !!! 18Watt Rules!!! Hoo Hah!!!

Having trouble posting the pix here, you can see the amp at http://www.sewatt.com/node/17435?page=36 towards the bottom of the page...

Congrats on getting amp working! That sure is one fugly amp though. At least no one will want to steal it.

zaphod_phil wrote:Congrats on getting amp working! That sure is one fugly amp though. At least no one will want to steal it.

I like it! One man's sunrise is another man's fried egg.

jake

Geezer, just wants the tone. The looks are irrelevant

Thanks KY... !!! I'd rather have a fugly amp that sounds really good than a pretty amp that sounds like all the rest...Not trying to impress anybody with flashy appearances or clones of famous amps ...nobody really cares except me anyway......right??? For as good as this amp sounds ,I'd have put it in an apple crate, if I had to...Killer TONE is why we came here, and why we stayed...

Yes, it's the tone that matters - and it seems you've nailed that real good.

So, just to summarize, you've built a minimalistic 18W, with a 6SJ7 (OctalOne) preamp and 6V6 power tubes. Is that right?

Geezer used one of those Red Special 6SJ7's. I think they have a different number just to confuse us.