major minor III r1.2

[DummyLoad]

built this on the breadboard yesterday. sounds very close to a major (based on youtube clips). not nearly as loud as major - duh! does dial in VERY brite like a major. it's very quiet (yes, even on the breadboard) and will push into a crunchy overdrive with a lot of push from single coil strat PU. overall some great clean and crunch tones. won't push to metal levels like a 2203/4. perhaps with a 12AT7 for the final driver set it might. i did NOT install the cathode bypass caps, that will help push OD some, but i don't believe as much as i'd like to be able to dial in.

would like to see B+ up around 430V-440V, however, the hammond 373HX has a max. theoretical at 420V +/-. have a hammond 260J PT on the way that should get closer to that 430V-440V target.

PS rail R & C values subbed for lower volt PS. the NFB loop is still being tweaked.

schema attached with as-built telemetry - i fully expect that jim-bob will disown pete and disavow any knowledge of such shenanigans. 

--pete

EDIT: fixed voltage table entry error - V4 and V5 plate V and g2 V were in wrong fields.

[Ritchie200]

I see many extra unnecessary parts and what's up with C18 and C19?  V1 and V2, bah.  Chain them.  Are you sure you don't want a PPIMV?  I think you will be disappointed with anything BUT a AU7 in the driver.  Take care of your 88's.  If you chain V1 you will not have to worry about needing any more drive.  This isn't a Major, it's a buck private at this point.  Who are you anyway?

Jim

[DummyLoad]

jim, have a 5814A in V3 hole. sounds really nice. no, don't want PPIMV. probably going to ditch the 2203/4 MV arrangement as well.

C18-C19 - it's cathode bias for 50W of cathode biased goodness.

Who are you anyway?
i am nobody. :p

--pete

[tubenit]

Pete, 

I always appreciate your contribution to the forum and the well thought out amp designs!  Thanks!

Pete was generous enough to post his SCH version of the schematic here:
http://el34world.com/Forum/index.php?topic=17556.0

With respect,  Tubenit

[SILVERGUN]

Take care of your 88's. 

Who are you?...the first boy to join The Girl Scouts?

Spank the piss out of those 88s or build a Firefly.

If the cops don't show up it must be in standby.

[Ritchie200]

Says the Brownie Scout with a SE 88....  That's exactly what I mean.  Let the AU7 swing the current, something an AT7 can not do.  Things change when you have more than ONE cylinder.

Again, what's up with C18 and C19?  That's just not right.

Tubenit, yeah yeah yeah...  Pete's a nice guy.  But change is NOT good!!!

Jim

[shooter]

Again, what's up with C18 and C19?  That's just not right.

I woulda used 100v, but that's just me 

change is NOT good!!!

agreed, they look at you funny when you pay for groceries in change, but sadly the Benjamin's are hard to come by 

[DummyLoad]

Again, what's up with C18 and C19?  That's just not right.

the rating text was askew a bit. fixed now... thnx for pointing that out. 

--pete

[DummyLoad]

swapped PT to increase B+. installed hammond 290CX. rev. 1.3 attached.

pushed B+ from 410V to 450V. that added some more headroom and sounds a bit brighter.

in case anyone was wondering; in this experiment i am using Sovtek KT88.   

--pete


EDIT: fixed voltage chart - had residual values from r1.2 experiment.

[Ritchie200]

So when will the official p2p build happen? Head or combo? Soundclip? Again, C18 and C19 does not contribute to "goodness" ..... (See original schemo for additional detail and instructions)

Jim

[shooter]

does not contribute to "goodness"

you're just sour grapes that we of cathode caps can sound JUST as good without having 3 roadies luggin the luggage 

[Ritchie200]

 


Jim

[DummyLoad]

So when will the official p2p build happen? Head or combo? Soundclip? Again, C18 and C19 does not contribute to "goodness" ..... (See original schemo for additional detail and instructions)

Jim

with C19 and C18 installed they cause LF motorboatin' when MV is 90-100%. C19 & C18 are being cantankerous like jim-bob!    PRR will say: "so don't do that!" iffftt! 

[DummyLoad]

hey jim-bob! no mo moterboatin! - helps to have the right value cap in the NFB loop!     i had 220nF for C8 - calls for 680nF. changed C8 to 680nF and presence now works much better. NFB loop R11 is 33K. 

reinstalled the bypass caps C19 & C18. the KT88's are pushing harder when dimed. now it feeds back with the guitar and MV dimed.

also, tested with alternate PT: a hammond 273BX  - 700VCT @ 201mA pushes about 442-ish V at node A.   

--pete

[DummyLoad]

attached is what's currently on the BB.

trying a different PT - this one is upright mounted (X mount). r1.4 makes use of a hammond 373BX; 700VCT @ 201mA.

--pete

[Ritchie200]

"now it feeds back with the guitar and master volume dimed"??????

I would expect it to feed back sooner than dimed?  What have you done to my amp?!?!?!?!

Jim

[DummyLoad]

a bit more hacking on this: sounds somewhat better without the 2203/4 style MV. i tune vol1  & vol2, then use the guitar as the MV. that seems to work best with this amp. lesser load of the 1M MV in || to TS bumped gain up a bit.

for the next experiment i'm going to bump the B+ to 470-ish V. hammond 274BX on the way.

non-believers and skeptics take note...it still sounds like a 50W major.   

--pete

[shooter]

use the guitar as the MV

 
I been trying to convince strummers "your  guitar has knobs USE THEM ", or pay me stupid money to add amp knobs 

[DummyLoad]

<< I would expect it to feed back sooner than dimed?  What have you done to my amp?!?!?!?! >>

[Ritchie200]

Jim

[shooter]

Just got back from couple miles hiking, hour fishing and Jim goes and reminds me WHY I'm happily retired 

thanks!!!

[DummyLoad]

hey jim-bob, on your major, did you cascade the triodes of V1, or are they still in tandem?


TIA, jim!


--pete

[Ritchie200]

She is as god made her - perfect in every way.  ANY deviation from this excellence in design and application is reckless foolishness, sacrilegious, and is punishable by a Strat whipping.  You have been warned....

Jim

[DummyLoad]

i'm not much a fan on having a tone stack wrapped inside of a NFB loop, so i came up with this. probably NOT the first time someone has thought of mods to the major topology, but me it is.

i cascaded V1 triodes a la 2204 and i added a MV of sorts. killer tone! not really a major, but a mean sounding amp nonetheless.

schema attached.

--pete 

[Ritchie200]

I believe that is Michael R/T’s exact mod.  You don’t like the tone stack location?  When the design is perfect you don’t need no knob twisting!  Actually the presence control is the biggest tone control. The others don’t do too much.  When will we hear this killer tone?


Jim