12 series distorts early

Jeremy1283 · Post by **Jeremy1283** » Fri Oct 10, 2014 3:31 am

I have a 12 series i built and was wondering if anyone else has had distortion happen early(6) on vol1. If I push it anymore it gets bassy and woofy sounding. The highest i can go is 6. Am i missing something or is that normal?

neikeel · Post by **neikeel** » Fri Oct 10, 2014 9:07 am

Jeremy1283 wrote:I have a 12 series i built and was wondering if anyone else has had distortion happen early(6) on vol1. If I push it anymore it gets bassy and woofy sounding. The highest i can go is 6. Am i missing something or is that normal?

spec. ??

Jeremy1283 · Post by **Jeremy1283** » Fri Oct 10, 2014 11:16 am

I have all mustards in it. Here is the exact spec i am using.
Split cathode V1a 250uF/820,V1b .68/820
All coupling caps are 0.022uF
Bright channel coupling cap is 0.0022uF

470k mixer resistors
560pf mixer bypass cap
Bypass cap on V2a is .68uF and a 330
33k/560pF lemco tone stack combo
47k NFB resistor at 4 ohm tap
0.1 uF cap on presence control
.022uf output couplers
Speakers are 6402 celestions. tubes are eh6ca7 and sylvania v1 v2 RCA v3 7027.
filtering 100 mians
screens 32 in series
two 32 on the board.

Strat78 · Post by **Strat78** » Fri Oct 10, 2014 11:33 am

Get rid of the fat cap over the .68, that's a slop inducer. Use the 16ohm with the 47k NFB. Try a 100uf for the PI filter cap. You can also experiment with the bright cap, start with 500pf and work your way up to 5600, but there will always be a sweet spot on Vol#1 and it's different in every amp. Use a fast diode (Fred) next to the bias resistor and even try fast diodes for the rectifier (though the slow ones are nice there). Mess around with different pre amp tubes. Don't throw out the baby with the bath water, these amps take a lot of skill to control the tone and it is mainly done with the picking hand. They are bright and unforgiving but oh what a glorious noise they make!

neikeel · Post by **neikeel** » Fri Oct 10, 2014 11:42 am

Strat78 wrote:Get rid of the fat cap over the .68, that's a slop inducer. Use the 16ohm with the 47k NFB. Try a 100uf for the PI filter cap.................

They are bright and unforgiving but oh what a glorious noise they make!

Yes, ditch the fat cap as it loses focus and precision for me (ok for legato only

) and upping the NFB to either the 8ohm or 16ohm tap tightens things up considerably, I always use a 4700 to 5000pF cap on V1, have to confess I've not experimented with higher values.

I like 48-50uF in the PI but Strat78 is right it can help keep things together. Then of course you have to crank it to 7-8 on the volume pot to get things working

Jeremy1283 · Post by **Jeremy1283** » Fri Oct 10, 2014 11:43 am

I forgot bright cap 4700 on vol pot.

Jeremy1283 · Post by **Jeremy1283** » Fri Oct 10, 2014 11:45 am

neikeel wrote:
Strat78 wrote:Get rid of the fat cap over the .68, that's a slop inducer. Use the 16ohm with the 47k NFB. Try a 100uf for the PI filter cap.................

They are bright and unforgiving but oh what a glorious noise they make!
Yes, ditch the fat cap as it loses focus and precision for me (ok for legato only ) and upping the NFB to either the 8ohm or 16ohm tap tightens things up considerably, I always use a 4700 to 5000pF cap on V1, have to confess I've not experimented with higher values.

I like 48-50uF in the PI but Strat78 is right it can help keep things together. Then of course you have to crank it to 7-8 on the volume pot to get things working

Oh. So the higher filtering on the pi (100) would let me crank the amp more?

Jeremy1283 · Post by **Jeremy1283** » Fri Oct 10, 2014 12:07 pm

I have the dual 32 f and t in my amp presently. Any thoughts on what brand to go with?

stef · Post by **stef** » Fri Oct 10, 2014 1:32 pm

I like:
V1b - 2k7/.68uf (tighter bass, more mids than 820R)
47k - 16 NFB (tighter bass)
50uf mains filtering (stock Daly)
32 - screens (F&T)
32 - preamp (F&T)
50 - PI (100 is even tighter bass and somewhat cleaner and bigger sounding) - Daly

2k7 vs 820 is probably the most audible change, then NFB, filtering...

Jeremy1283 · Post by **Jeremy1283** » Fri Oct 10, 2014 1:42 pm

stef wrote:I like:
V1b - 2k7/.68uf (tighter bass, more mids than 820R)
47k - 16 NFB (tighter bass)
50uf mains filtering (stock Daly)
32 - screens (F&T)
32 - preamp (F&T)
50 - PI (100 is even tighter bass and somewhat cleaner and bigger sounding) - Daly

2k7 vs 820 is probably the most audible change, then NFB, filtering…

thanks for your input stef.. Yea I am just trying to clean up the tone abit. it falls apart above 6 on the vol. I cant wait to try the 100uf in the phase inverter.

Strat78 · Post by **Strat78** » Fri Oct 10, 2014 2:11 pm

Do you have a 3H choke in there? I've struggled with the 2.7k vs. the 820ohm question. For VH1 I always go back to the 820, though 2.7k is an over all richer and well rounded tone. Ha ha, don't go too crazy with this stuff, your amp probably sounds better than Ed's 12series at this point!

Jeremy1283 · Post by **Jeremy1283** » Fri Oct 10, 2014 2:14 pm

Strat78 wrote:Do you have a 3H choke in there? I've struggled with the 2.7k vs. the 820ohm question. For VH1 I always go back to the 820, though 2.7k is an over all richer and well rounded tone. Ha ha, don't go too crazy with this stuff, your amp probably sounds better than Ed's 12series at this point!

haha. I already am. It has become an obsession.

I do have the 3H choke in there strat. should I change it out for the 7H?

Jeremy1283 · Post by **Jeremy1283** » Fri Oct 10, 2014 2:22 pm

This is what it sounds like slaves and with the vol. On 6
http://www.soundclick.com/bands/page_so ... D=12933815

stef · Post by **stef** » Fri Oct 10, 2014 2:40 pm

In my amp 820 is very overdriven, bassy and very bright sounding. 2.7k is fuller in the mids, high and low mids, tighter (or less) bass and much cleaner. I liked 1k very much, it's in the middle tone-wise between these two. Marshall put that resistor (1k piher) as stock in my 70's amp

Jeremy1283 · Post by **Jeremy1283** » Fri Oct 10, 2014 3:17 pm

Im going up to jnews place next week again so we can tweak some more. Gonna do some non attenuated clips also. Good can always get better. Lol

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12 series distorts early

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