THANKS to everyone who helped, amp schem finished

[jimmy]

thanks to all the people who helped my put this together. in theory, we should have a fairly solid amp here. as promised, i will bug you no more with tube amp questions (hopefully).

unfortunately, i will be building this one over a long period of time, since i have very little cash on hand, but i will definitely get back to you with some pics.

here it is:
http://img78.photobucket.com/albums/v323/jm121088/schems/?action=view¤t=superanarchistschem.gif

the Super Anarchist thing is a bit of a personal joke... i called my FireFly the Rebel Jr. its kinda hard to explain.

thanks again
Jim

[AdamOn6thStreet]

Hey your album (photobucket) is password protected.  Share it with us!  i wanna see!

[jimmy]

:!:  im sorry, i didnt know!!! fixed and fixed. again sorry about that...

cheers
Jim

[Mark Hammer]

First, kudos!  Second, nice drawing.  Third, shouldn't there be a feedback resistor from the transformer to the presence control or does this one work different?

[Alpha579]

That looks really good! Should be a great wee crunch rocker...
I dont think its vital to have a resistor from the presence control, but i think the output may drop without one...

Btw, and the diodes from plate to ground on the el34's nessecary?

[jimmy]

the diodes are part of a voltage spike eater that stops voltage spikes wrecking your tubes. its not necessary, just a safety measure.

as for the feedback resistor, i didnt even notice that. ill stick one in for good measure.

thanks all!

btw, the drawing credit goes to Philip Ruetz. it was his schematic i started with, and it looked alot prettier than mine, so i decided to go with that. his site is //www.diyguitaramp.com check it out.

cheers
Jim

[Arn C.]

Jimmy,
    What size resistor are you putting in between the transofrmer and the presence control(feedback)?

Thanks!
Arn C.

ps  Great Job!

[jimmy]

47k - i got that value from the Marshall Super Lead schem. is that alright?

its in the updated schem, and uploaded.

thanks
Jim

[Arn C.]

Thanks!!!!
Peace!
Arn C.

[Peter Snowberg]

Two more small changes....

1) The protection diodes on the plates need to be polarity flipped so that if power trys to flow tre opposite way through the power tubes it gets shunted by the diode. While this is a truly optional circuit addition (along with the MOV), you'll find it standard in some of the very best amps out there.  I've seen a couple of different schematic symbols for MOVs. One fairly common one is the same symbol used by the diac witch looks just like a triac symbol but without the gate lead. I like your colored boxes schematic style too!

2) The feedback loop needs a little change. Check out how Fender does it in the Super Reverb. They use a resistive divider (820R/100R) to trim off roughly 1/8th of the signal from the speaker jack and they feed that into the grounded grid side of the PI which has a 100 ohm impedance to ground. Marshall does it a bit differently. Look at this 1959 re-issue. Here they provide a presence control. The speaker signal gets trimmed down to 1/20th by a resistive divider (100K/4K7) and then the presence control provides an AC bypass around the 4K7 that removes the feedback signal from the PI cathodes and the grounded grid by shunting it to ground. The grounded grid sees the low impedance of two 0.1uF caps in series if the presence is turned all the way down and the impedance raises as you turn it up (all the way to around 4K). In the Fender design you can just replace the 820R with a pot to add series resistance to the feedback signal and get a presence control. The impedance to ground on the grounded grid side of the PI stays constant there at 100R.

The approach you choose is totally up to your personal taste. There are lots of other ways to provide feedback too. I've seen one Hi-Fi approach where the speaker output is used as the power tube cathode connection (the power tubes are still run at fixed bias) and no other loops were present. Good things were said about that approach but I don't recall any of it now.

Iron these two things out and you're ready to enter the building/refining stage.

Take care,
-Peter

[Chill]

It does look like a good amp...why the 470pF across the PI plates rather than 47pF?

And have you considered a post PI master?  That would make it look a fair bit like the Orange AD series schematics.  You'll probably get more clipping with the extra PI stage before your MV.

[Peter Snowberg]

Hmmmm.... I was thinking about your presence contgrol more and it should work as you've drawn it and work differently from the standard controls out there but in wiring things that way you'll also need to make sure you use insulated speaker jacks becuase the speaker ground and the circuit ground would need to be different. If you did build it that way I would lower the value of the 22K to maybe 10K-15K on the cathode of the PI to bias things decently. Who knows.... this style of presence might sound really great.

Other than that, everything looks really solid. It looks like a neat little head that might have a great tone for jazz when played straight and should be a great rock-n-roll amp with the addition of a pedal or ROG amp sim (!) or a Super Screamer.

I can't wait to hear some sound clips. I hope the parts find their way to you quickly.

Keep in mind that you could add four more resistors and the sockets and run a quad of EL84s too.

[jimmy]

thanks for the suggestions!

the 470pF in the PI was there when i started, so i just left it in.

ive heard several opinions on the post PI master volume and they were all mixed, so i decided that since *most* marshall amps had the pre PI master volume id just stick with that.

yeah those prescence controls confused me  :?  so i just kept it as simple as i could understand.

arrrrgh, i had those diodes the right way round the FIRST time. all fixed.

the vision i had for this amp was it would be really clean, or maybe a little crunchy at full gain, and if you wanted distortion, you could hammer the tubes with boost cicuits. looks like itll do the job.

Peter, i see youve discovered the Super Screamer   , i mentioned that on here ages ago, when i was going through my SRV phase. im going to have to revisit that though. yesterday i watched my SRV & double trouble Live at the El Mocambo dvd again, and ive been abusing my firefly with Pride and Joy non-stop haha.

thanks again
Jim

[Boofhead]

The protection diodes on the plates need to be polarity flipped so that if power trys to flow tre opposite way through the power tubes it gets shunted by the diode.

I'm pretty sure they are correct as is (well as of today in case the drawing has been changed at some point).  Flipping will short the op tx across the supply through the diodes.

Any particular reason for the 12AU7 and 22nF caps between the 12AU7 and the power tubes?

[jimmy]

the 12AU7 is there for a bit lower gain, keeping everything a tad cleaner. the 22nF caps are there because the marshall super lead has them. i have no idea why  

cheers
Jim

[Lonestarjohnny]

the .022 cap's are there to keep the DC out and only allow the A.C. signal into the power tube's, they can be called coupling cap's or Blocking Cap's, because they do both job's, with out them you get nodda but Noise !, the 470 PF cap is to help stop feedback and parisetic induction Batween the 2 leg's of your phase inverter, it's supposed to help clean the tone somewhat.
JD

[Boofhead]

Thanks Jimmy,  so you are basing that part of the design on the Marshall super lead.  (Some amps use larger values like 47n and 100n...maybe you can play around with them).

[jimmy]

actually, that bit was based on the Z20. thats where the 470pF in the PI came from as well. and yep i sure do intend to play around with the values a bit once i got it up and running, but god only knows when thatll be   :?

cheers
Jim