OT - Octal Fatness Build Report

[Paul Marossy]

OK you Firefly builders: If you like the Firefly, you should give the Octal Fatness a try!

Anyhow, I finally have it done, and I think it sounds great! A wide range of tones is possible from this amp, and as Doug noted, it does have a lot of sustain. Everything worked out pretty well as far as my chassis layout goes, which is amazing since I have a lot of things stuffed in a pretty small chassis. Noise level is pretty low, except for a little heater hum when I crank everything up, but I assume that is normal for a higher gain circuit like this one.

For testing, I ran it thru my Celestion Sidewinder (which is in my Seymour Duncan Convertible), and used a 6V6 which is biased at 23mA, I think. I have no experience with 6V6s, anyone know what they normally would bias at (being cathode biased)?

Oh, and here is the B+ voltages with tubes installed, measured at the filter caps:

At rectifier diodes - 356V
B+1 - 348V
B+2 - 291V
B+3 - 247V
B+4 - 238V

To see a picture essay on it: http://www.diyguitarist.com/GuitarAmps/OctalFatness.htm

[Lonestarjohnny]

Nice Paul,
Great lookin build, I love the tone outa Doug's Octal, let us hear yours when ya get a chance,
Super Cool  
JD

[Paul Marossy]

Thanks JD.  

I learned how to figure out how many watts I'm dissipating. I'm well below the maximum specified on the 6V6 data sheet for Class A operation. It looks like I've got 34mA on the cathode current and I'm dissipating 11 watts.

I'll try to get a soundclip recorded of it sometime in the near future. I know some people also want to hear my Matchless Spitfire clone as well.

[Gringo]

Hey Paul, if that amp sounds half as good as it looks, it'll have a tone to die for. I hope some day i can build something that good looking...(probably when hell freezes)  

[Paul Marossy]

Hi Gringo,

Oh, you could do it, if you're determined enough.  :wink:
I know the high voltages are kind of scary, but with proper safety precautions, it's not so bad. Making the cabinet is the easiest part of the whole process. I guess I've always been good with my hands...

Anyhow, I was just thinking that I forgot to mention how great it sounds in a little more detail. This amp does have tone to die for! Beautiful tube amp distortion! I honestly don't care for that many tube amp distortions, but this one really does sound nice. I think it something to do with the 6SJ7 metal can pentode on the input (you can get them for about $5 a pop on ebay). I can tweak the EQ to get a very "acoustic" sound and by playing with the master, volume and drive controls, I can a very wide range of sounds ranging from pretty clean to almost metal kinda sounds. A lot depends on your guitar and what kind of pickups it has in it, too. That switcheable bypass cap mod on the 6SJ7 adds a little more grit to the mix, too. Not a huge difference, subtle, but it is noticeable.

Thanks for sharing your projects with us Doug.  

PS: Whoever it was from this forum that sent me the chassis I used for this project, thanks! Sorry, I forgot who it was.  :oops:

[Lonestarjohnny]

Paul, I knew I had a chart around here somewhere on bais, I'm so use to settin them by ear I very seldom look at a chart but this was a very good one when it was written, I got it from Gerald Weber,
6V6 Power tubes
at 350 v. class AB = 21.3 ma, high AB = 25 ma, class A = 32.6 ma
at 340 v. class AB = 21.9 ma, high AB = 26.5 ma, class A = 33.5 ma

this will give you some spec's to compare yours with.
the chart I got covers most of the popular power tubes so anybody need's to know what ma thier tube bias at, just ask, i'll copy this chart and put it in the archives if aron wants it.
JD

[Paul Marossy]

That sounds like a useful chart JD. I would like to see that chart. In fact, I could convert that the .html and post that at my site...

[Lonestarjohnny]

I'll scan it tomorrow for ya, my Scanner don't like window's XP, my son will fix that for me in the morn, then I'll be able to scan again.
JD

[Paul Marossy]

Cool.  

[Kleber AG]

Hello JD,
I'd like to see that chart too, please.
You're gonna post it or send by email?

Thanks
Kleber AG

[Lonestarjohnny]

check your PM Kleber,
JD

[Paul Marossy]

Uh, what about me?!?  

[Kleber AG]

OK, I sent...
Thanks JD

Kleber AG

[Kleber AG]

Relax Paul  

He just asked my email address for now

heheheee
Kleber AG

[Lonestarjohnny]

Paul, send me a email,
JD
jd@lonestaramps.com

[Paul Marossy]

JD, check your PM.