6L6 15/7 watt PP amp?

[Ed_Chambley]

Here is a very good review on this amp.

&t=1050s


I actually played one last night.  I'll pass, but thanks.  It feels a little cheap and as many times as I have had a stage hand knock something over it probably would not last as a head.  If I did get one, I believe I would give it the Traynor Test.


Drop it off a 2 story building.  replace the tubes and jam.  Anyone ever seen this?  The PRS transformers would break off with those pot metal chinese screws.

[PRR]

Some posts Moved to
Other Topics
"The Bickersons"
You know why.

[DummyLoad]

some edits. LED polarity fix, added boost to clean channel, footswitch/front-panel channel switching, etc..

STILL no reverb & no tremelo. bah! u don need no stinking reverb & tremelo señor!

--pete

[jojokeo]

STILL no reverb & no tremelo. bah! u don need no stinking reverb & tremelo señor!

  Bah is right!    But now Jimbob isn’t going to have any help covering up all of his misfrets and wrong notes? 


You are the schematic king Pete! I only would like a bi-color single LED on my model please? 

[DummyLoad]

STILL no reverb & no tremelo. bah! u don need no stinking reverb & tremelo señor!

  Bah is right!    But now Jimbob isn’t going to have any help covering up all of his misfrets and wrong notes? 


You are the schematic king Pete! I only would like a bi-color single LED on my model please? 

you'll get single color LEDs mr. and you'll like it.    and no more    mr.!

thanks jo. i publish mostly trash that amuses self and possibly a few others.

thinking that the first second stage needs to be a paralleled pair of triodes. that satisfies the bottle count and won't be a total noise bomb. maybe. maybe not.

i get this sinking feeling that is amp is incomplete, at least without a spring reverb.



--pete

[SILVERGUN]

So Mr. Jim,
Now that we are 55 replies (plus another thread) deep into this...
A)What have you learned about how this amp can deliver 7/15 watts with 2 6L6GCs?

B)And what are you going to do about it?
 

[shooter]

plus another thread

ya, n tell me how that thread started with 33 reply's n 22 views 

[Ed_Chambley]

It appears Pete has figured out a way to build one helluva preamp there.  I like the slight bias difference in 2 of the stages on the lead channel.


Anyway, as a preamp it could be very handy to me as I have a few lower voltage amps.  Thanks for the time to share your thoughts and drawings.

[Ritchie200]

Well, SG, thanks to the people who actually CONTRIBUTED, I do have some ahhdeas… 


1. I think with all the info available for a 5 tube cascaded preamp ( ), it would be pretty interesting and easy to replicate the front end.  Although, MT has a different odd scooped sound that I have not heard from the mainstream metal guys or their amps, I don't know if I would like to be stuck there.  It would need some flexibility which I think could be obtained as it is developed.  I would definitely go high gain with effects loop.



2. I am still having a hard time with the 6L6's.  Along with the 6550, it ranks up there with my least fav tubes.  If I were to build this...… And guess what?  I am seriously thinking about doing just that.  Now where did I put my soldering iron.... Anyway, I would put a PP UL KT88 output on it.  Obviously not replicating the MT15 but I really like the ideas that have come out of this analysis.  Lets keep a decent B+ and throttle them back to 20'ish watts.  Then add a triode switch for half power and maybe a different flavor.  I don't think I've ever heard a KT88 slammed in true triode mode.  Heck, I am almost there with the UL on my Major - maybe that is the secret sauce I am hearing when I crank and really let her run?  I think it would be a cool project.


3. Pete is awesome. 

Jim


ps, just kidding SG, thanks for all the photos and info you posted

[shooter]

I don't think I've ever heard a KT88 slammed in true triode mode.

I can hear the audiophile types cringing across the world 

[DummyLoad]

I don't think I've ever heard a KT88 slammed in true triode mode.

I can hear the audiophile types cringing across the world 

oh, no worries sniffer types, we won't use NOS KT88 in a guitar amp... no sir, no way.

i lie like a cheap rug. 

--pete

[DummyLoad]

probably too much overall gain. trying to get the major's concertina and buffer amps in the mix for the KT88 drive - may have to scrap the 12AU7 buffer amps and drive KT88s with the concertina.

another option is to lose the concertina, the FX recovery amp, the buffer amps and go with LTPI for the FX recovery and KT88 drive and that would reduce 9pin bottle count by 2. with as much overall gain, i'd like to see a choke in the mix for the preamps & buffer amps - 10-15H. may add that yet.

all this would be better built on a PCB - not as complex as some of the new ultra-high gain stuff, but given the complexity and bottle count, a PCB would make the overall chassis size much more manageable.

jim, i still have the major minor II's mutant bastard child on the breadboard, i'll give the triode/pentode switch a test drive. oh, wait! sorry, that was built with EL34's... wahwahwah...   

thoughts? insults? flamage? comments? h-e-l-p!   

--pete

[jojokeo]

Well, SG, thanks to the people who actually CONTRIBUTED, I do have some ahhdeas…

[/l]

Uh err NO! Porn doesn't count. Those are fantasies kimosabee Turtle! And SG asked to be left out of them!

[/q]

I think with all the info available for a 5 tube cascaded preamp ( ), it would be pretty interesting and easy to replicate the front end.

[/l]

Bah! NO! Anyone with experience knows that cascading even a couple tubes can bring about parasitic oscillations and other hypersonic animals buzzing around one's head driving it's unwitting creators batty enough to eat snakes from the bush meat market! Flexibility? You?! Says the man with a need for only two sounds on a switch: Blackmore & Trower modes.

[/q]

I am still having a hard time with the 6L6's.  Along with the 6550, it ranks up there with my least fav tubes.  If I were to build this...… And guess what?  I am seriously thinking about doing just that.

[/l]

Again bagging on great sounding poor 6L6s like they are your red headed step children just because you have 88s being all snooty on top of the hill looking down at everyone wearing that ungodly ugly witches' hat or Abraham Lincoln stove pipe model... you may want to take them off once in a while, oxygen and sunlight are good things!

[/q]

Now where did I put my soldering iron....  

[/l]

I think SG could tell you?  But if you can't feel it? One would think that you'd step on the chord every once in a while? Oh what a good boy takes on a whole 'nother meaning now?

I'm suddenly hearing a banjo far off in the distance...

? 

[/q]

Then add a triode switch for half power and maybe a different flavor.  I don't think I've ever heard a KT88 slammed in true triode mode.  Heck, I am almost there with the UL on my Major - maybe that is the secret sauce I am hearing when I crank and really let her run?

[/l]


Oh brother - "normal" triode mode is NOT half power and if you made use of that soldering iron (for it's intended purpose) you just might know this? Your flavor and secret sauce fantasies are disturbing


Stick to Blackmore & Trower modes... you can thank me later,
Yer pal jojo

[tubenit]

Pete,

THANKS for your contributions to the forum and on this thread!  IF you still have the SCH version of this proposed Jim-Bob Special with 6L6's and KT88's, can you post them on this thread OR in the ExpressSCH Library, please?  If you post them on this thread, I'll move them over and be sure to note that it's your work.

http://el34world.com/Forum/index.php?board=12.0

Even if Jim doesn't build this amp, there may be someone down the line interested enough to pursue it.

Thanks, Tubenit

[shooter]

Bah! NO! Anyone with experience knows that cascading even a couple tubes can bring about parasitic oscillations and other hypersonic animals buzzing around one's head driving it's unwitting creators batty enough to eat snakes from the bush meat market!

 
have you EVER listened to Jim's music, that's THE SOUND an EFFECT on the audience!!!

[SILVERGUN]

If I were to build this...… And guess what?  I am seriously thinking about doing just that.  Now where did I put my soldering iron....

NOBODY would want to try to help you troubleshoot this nightmare.

It's probably best if you start out with something like a Champ build before you get too far over your head.

I think you could possibly handle this one but I have no idea what your experience level is...

[Ed_Chambley]

I don't think I've ever heard a KT88 slammed in true triode mode.

I can hear the audiophile types cringing across the world 

oh, no worries sniffer types, we won't use NOS KT88 in a guitar amp... no sir, no way.

i lie like a cheap rug. 

--pete

Once I considered posting a photo of just my =C=, not even any GEC's.  Then I remembered Silvergun built 2 amps that needs one each.  One is not THAT expensive unless you want real ones and he seems to want real ones.  So I decided not to poot them so he couldn't download the photo.  Look closely at the glass to find a familiar reflection.  Search the image with google search and drive from yankee town and borrow some.


I do not like the awkward comments about audiophiles simply because I listen to a Triode Strapped Dual Single Ended stereo.  It used to have 2 Mullard Rectifiers Tubes, but Ebay wanted them too bad.  I tested 2 Amperex Rectifier tubes and just couldn't hear any difference so I guess I fail the Audiophile test, but wait.  Did you know 4 real =C= 6550's strapped in triode mode sound the same as GEC Gold Loins NOS and =C= KT88's.


These in turn sound NOTHING like a 300B.  And yes, I finally broke down and added a Crown SS amp for 150 hz and below.


Guys, seriously be careful of my feeling.  I have some KT88's in a 1987 Plexiglas Build currently.  It's called punishment Gurls.

[DummyLoad]

y'all are gonna get us upgraded to the bitchersons.

jimbob - baby steps. build the champ first. 

--pete

[Ed_Chambley]

y'all are gonna get us upgraded to the bitchersons.

jimbob - baby steps. build the champ first. 

--pete

Damn, we are trying.  Where is PRR?

[shooter]

jimbob - baby steps. build the champ first. 

agreed!, I even build one with a KT88!!
didn't know what I was doing then so it was all noisy, but I lern't how to fix that here 

[DummyLoad]

Pete,

THANKS for your contributions to the forum and on this thread!  IF you still have the SCH version of this proposed Jim-Bob Special with 6L6's and KT88's, can you post them on this thread OR in the ExpressSCH Library, please?  If you post them on this thread, I'll move them over and be sure to note that it's your work.

http://el34world.com/Forum/index.php?board=12.0

Even if Jim doesn't build this amp, there may be someone down the line interested enough to pursue it.

Thanks, Tubenit

tubenit, schematic(s) not finished and do not have part reference designations. will push editable versions later.

thanks!

--pete

[tubenit]

Thanks, Pete!  I appreciate your contributions to the forum. 

[shooter]

Ok, I’ll participate,
Because I appreciate Mid-west reality in a field of costal weeblees I will meet you ½ way with my last build. should be a cornfield in IL 

The pre can produce a square wave at ~70Vacrms, (with HOT guitar).  the bias is set to sweat the 88 at ~41W so don’t roll in any family heirlooms without tweaking Rk 
It even has some stole ideas from Marshall, DCCF and a sucky TS (CCW 9 3 CW)

Put a switch on G2 and hear triode mode, cut your boat anchor pre-out into the 88’s coupler and you have a 18W screamer WITH a triode switch
And use your stack (amp is 4/8ohm switchable)

There!
Batter up 

[DummyLoad]

shooter - that thing has more than 2 tubes, not so sure that's a good "starter" amp. 


--pete

[DummyLoad]

con·trap·tion
/kənˈtrapSH(ə)n/
noun
a machine or device that appears strange or unnecessarily complicated, and often badly made or unsafe.

schema done. ref. des. for parts added (that was a b!^ch!). so with 70 resistors, 40 capacitors, 13 diodes 8 tubes, 3 relays and 2 transformers, the definition of the quoted above comes to mind.

--pete

[66Strat]

Ok, I’ll participate,
Because I appreciate Mid-west reality in a field of costal weeblees I will meet you ½ way with my last build. should be a cornfield in IL 

The pre can produce a square wave at ~70Vacrms, (with HOT guitar).  the bias is set to sweat the 88 at ~41W so don’t roll in any family heirlooms without tweaking Rk 
It even has some stole ideas from Marshall, DCCF and a sucky TS (CCW 9 3 CW)

Put a switch on G2 and hear triode mode, cut your boat anchor pre-out into the 88’s coupler and you have a 18W screamer WITH a triode switch
And use your stack (amp is 4/8ohm switchable)

There!
Batter up 

Nice!

Is that a copper chassis?

[shooter]

that thing has more than 2 tubes

ya but they're already soldered so a switch is all that's needed to start, well a guitar, someone that can play it.........

It's copper foil, scraped from an old RF room 

[Ed_Chambley]

Well Pete, I just looked closely at the Job-Bob Shredder.  Very tempting, that is all I have to say. That is a lot of tubes to make 25 watts, but I like Monster Trucks too.  Very nice, but JoJo has a valid point.  Better be on point with a layout.

[shooter]

but I like Monster Trucks too.

what, with a 2.5L eco-boost 

violating the KISS principal with MANY tubes is the best invitation for forehead slapping, parts smoking gremlins 

[DummyLoad]

Well Pete, I just looked closely at the Job-Bob Shredder.  Very tempting, that is all I have to say. That is a lot of tubes to make 25 watts, but I like Monster Trucks too.  Very nice, but JoJo has a valid point.  Better be on point with a layout.

thanks! - it's the JIMBOB shredder. we need to show jim some respect. JOEBOB is just too...southern?

do you think jim will ever come to the light side and buy a tele? 

--pete

[shooter]

do you think jim

I'm holding out hope for the weather to break, then Jim can grab his banjo n go sit by the big river. 

[DummyLoad]

ok, back the tech stuff... some feedback from jim result in rev1a - see attached. thinking we'll need a grid stopper tacked to V2 pin2 & perhaps deleting C19 perhaps make it a switched option. also, a 12AU7 for the F/X loop to keep overall system gain manageable.


--pete

[Ed_Chambley]

Well Pete, I just looked closely at the Job-Bob Shredder.  Very tempting, that is all I have to say. That is a lot of tubes to make 25 watts, but I like Monster Trucks too.  Very nice, but JoJo has a valid point.  Better be on point with a layout.

thanks! - it's the JIMBOB shredder. we need to show jim some respect. JOEBOB is just too...southern?

do you think jim will ever come to the light side and buy a tele? 

--pete

I know he wouldn't EVER admit to having one.  How could he?  I called it the Job-Bob, typo.    The Jim-Bob Sherdder for those who shredded their diapers when baby and have reached the age to begun doing it again!


I am not sure how Jimbob got so against Telecasters and John 5, but he also thinks the Japanese made a Deep Purple record, the 3rd largest live album of all time.  Made in Japan.


Wasn't the big hit from that album called "I Want You to Want Me?", or is that just a better song I remember from some other Japanese Vinyl?

[SnickSound]

some edits. LED polarity fix, added boost to clean channel, footswitch/front-panel channel switching, etc..

STILL no reverb & no tremelo. bah! u don need no stinking reverb & tremelo señor!

--pete

I'm curious, and maybe the answer is somewhere in the thread but I missed it: is this sort of your own interpretation of what the MT15 probably is, or is this based on the actual circuit?

Just curious. I see a hot-rodded Marshall type of preamp here (looks like some AFD-esque mods that add an extra tube to a JCM800), but to my hear the MT15 is more mid-scooped and not as bright as this would sound. I'm guessing a smaller treble cap and bigger slope resistor, and perhaps some fixed resonance boost by way of a cap in the NFB loop. But to be fair, I haven't actually played the MT15, just watched some demos.

Now, based on my experience building high gain channel switchers, if I was to build this I would change the switching scheme a little:
- Keep both input stages connected at all time, prevents loud pops and doesn't have any ill effect except for:
- Ground the grid of the 3rd stage of the high gain side when in clean mode (in my experience, this doesn't pop and the clean channel is clean as a whistle)
- Use that same relay to connect the Presence control to ground (or actually, insert a high value resistor between the cap and ground and bypass it with this relay) so the Presence control only works in high gain mode (Fender cleans don't use presence boost)

e.g., I've attached a WIP schematic of a new version of a successful build. The original did not have a tone stack for the clean channel, and now I have this crazy idea to have a clean tone stack WITHOUT needing an extra tube. Anyway, very different circuit, but it implements the switching scheme I've described above (RLY1 either grounds V2a' grid or the Presence control, Clean channel shares the input tube but uses a MOSFET to drive a tone stack without loading down the input stage). Also, it has a "Deep" switch for a resonance boost, and a Solo boosts that partially bypasses the tone stack.

[jojokeo]

Well Pete, I just looked closely at the Job-Bob Shredder.  Very tempting, that is all I have to say. That is a lot of tubes to make 25 watts, but I like Monster Trucks too.  Very nice, but JoJo has a valid point.  Better be on point with a layout.

thanks! - it's the JIMBOB shredder. we need to show jim some respect. JOEBOB is just too...southern?

do you think jim will ever come to the light side and buy a tele? 

--pete

I know he wouldn't EVER admit to having one.  How could he?  I called it the Job-Bob, typo.    The Jim-Bob Sherdder for those who shredded their diapers when baby and have reached the age to begun doing it again!


I am not sure how Jimbob got so against Telecasters and John 5, but he also thinks the Japanese made a Deep Purple record, the 3rd largest live album of all time.  Made in Japan.


Wasn't the big hit from that album called "I Want You to Want Me?", or is that just a better song I remember from some other Japanese Vinyl?

Hi Ed, you know as well as I do that there's no one more stuck in the mud err their ways than the St Lou babba loo boy himself! If there's one thing that could possibly be more consistent than the Big Ben it would be Big Jim and he aint shy to let us all know about it. And not just the Tele but his prized '88s too as all should be well aware of by now. How long's it been like 20 years now? 

[Ritchie200]

SnickSound


Thank you for sharing your channel switching schematic with us!


As far as the schematic Pete posted, that is his interpretation of what we have been talking about.  Unfortunately we don't have the MT15 schematic.  We only have some gut shots and transformer specs - more later.


So, this is what I have been able gather from numerous reviews and interviews with Mark: Mark had been using the PRS Archon which Mark describes as very similar to his old Bogner Uberchall with 6L6's.  This amp is run alongside his old Rev. F Boogie.  Mark said the combination of the two is perfect for the tone he is looking for.  He also said he sent the MT15 prototypes back several times before they dialed it in to his taste.  He used it on his Tremonti solo album and also on the new Alter Bridge album so he is obviously pleased with the results.  PRS is building a 100watt signature amp for him as the MT15 isn't loud enough to play out with (Although some of the reviews would disagree!).  However I can see his point on a big stage where you want some guitar/speaker interaction.  His 100watt signature amp has been in the works for months so I would have to think it is a departure from the Archon, otherwise he would be using it and it would be out by now. 


Back to Pete's schematic.  As some have alluded to here....I am a KT88 fan so that explains the switch from 6L6's.  I talked to Pete about Marks scooped/dark tone but said I didn't know if I wanted to be locked into that so it would be nice if we had some flexibility.  We also talked about the clean channel being a Mini Major since I had also asked for UL operation and cathodyne/driver circuit - why not!  So that is why we have the presence on both.  The clean channel is not Fender derived.  This schematic is pretty much using the ideas we have tossed around along with my selfish desires!    What brought about this thread is I thought it was interesting how they were using big B+ and big bottles and reining them back to 15watts (or 25watts from that review). A 7watt switch that appears to be for triode operation.  The price point is crazy low for the parts and build quality - and yes I realize where it comes from.  Reviews have all been very positive. 

My geek mind wanted to know more!

So "hear" we are!

Jim

[sds1]

I have a PRS Sonzera 20 here. Incidentally, it belongs to MT's touring bass player.

Some insight with respect to this thread, this amp runs 2x Ruby 6L6GCMS. Plate voltage 283VDC.

Similar to the MT-15, the Sonzera 20 user manual instructs you to use bias jacks and adjust to 30mA. Oh but look they are using 2R bias test points...

From the manual for both amps:

Bias Jacks and Pot: These jacks measure the power tube current draw in milliVolts.
1mV=1mA.

Umm, nope.

So, biased just below 60%.

I scoped a legit 20W at the 16R output jack.

As an aside, it's interesting this amp has no choke but you do find a 120R 25W between standby and OT CT. Weird or just me?

[SILVERGUN]

As an aside, it's interesting this amp has no choke but you do find a 120R 25W between standby and OT CT. Weird or just me?

This is the design element I wasn't thinking of. With a resistor in place of a choke but placed before the first filter node it will act as a full wave-choke input rectifier design.
This means that you take the secondary voltage and multiply it .45, so in our case (approx.)610VAC x .45 = 274.5 VDC. These are design numbers and there will be some variance based on actual input voltage/ load conditions/ actual PT max current rating.
Also, if we are drawing approx. 130mA thru that 120ohm resistor then that is also dropping an additional 15V. From a static design point that puts us around 260VDC B+ for the MT-15.
Not a far stretch from that 283V your seeing.

Thanks for the info.



EDITED - struck falsities from the record so no one reads this in 2030 and thinks it makes sense.

[sluckey]

This is the design element I wasn't thinking of. With a resistor in place of a choke but placed before the first filter node it will act as a full wave-choke input rectifier design.
This means that you take the secondary voltage and multiply it .45

I don't think so?

[SILVERGUN]

This is the design element I wasn't thinking of. With a resistor in place of a choke but placed before the first filter node it will act as a full wave-choke input rectifier design.
This means that you take the secondary voltage and multiply it .45

I don't think so?

Awwwww  crap   

[shooter]

Did someone "FIX" the errors on that example sheet? can't find anything in my notes, and I'm not quite sharp enough to guess 

[SILVERGUN]

Googled it - strike 2
Tried to simulate in Duncans PSUD2 - strike 3

Figured it was time to go cut the grass.

[DummyLoad]

no. for full wave rectifier with CT an RC filter input is still 1.414 x 1/2 primary RMS less Vdrop across the resistor. just for comparison, i added a sim with 125R reduced to 10%. 

is the attached similar to what you guys see based on interior shots of the amp?


--pete