Marshall Major 1967

[Willabe]

               

[tubenit]

Ok, edited and corrected. Thanks!  Two tube with OWM & PPIMV is what I personally would do.

And also the original with four KT88's.

With respect,  Tubenit

[Ritchie200]

Jeff,

I've played a lot of Marshalls and a few with KT-88's in place of the EL34's.  Nothing ever came close.  I'm sure your design would sound great, but in my humble opinion, I don't think it would replicate the original design.  Ed's description of the kt66 to kt88 was spot on.  At the same volume, the kt66 would scream, but the kt88 would kick you first - one of my favorite things! I also think the UL has a LOT to do with the final product.  And unlike Ed, every Major I had sounded better with the au7 (see my post on the Soundclip thread), but I was pushing it pretty hard.

There is a lot of misinformation going around about the Major.  The cause of all the original Major's issues comes from a VERY crappy Dagnall output tranny.  They used masking tape for "insulation" between the windings.  If set up properly there is ~620v B+ (always was).  The flyback condition produced 1800v spikes.  So blam across pins 2-3 or any connection close to a ground.  Later models came with double insulation for the high v runs, ceramic tube bases, and no sharp solder joints.  Eventually (always...) the Dagnall went poof.  Those still under warrantee in the States back then received a custom wound OP tranny from a guy named Otto in New York - a fantastic replacement.  Those custom trannies have lived in Ritchie Blackmore's Majors for years.  The original design of the Major was penned by the MO Valve company.  It is the only amp that Marshall produced that was not designed in house.  Marshall had built several "six gun" EL34 models in the wattage race with Hiwatt.  They were pushed to the limit and crappy components caused failure after failure.   So they called the main manufacturer of the KT88 for help.  They essentially gave them a HiFi amp. There were two distinct versions of the Major.  The Marshall 200, which was called the Pig and had active tone controls.  Other than Mick Ronson, everyone hated it.  The Major came next and it came in a Lead, Bass, and PA version.  Deep Purple had stacks and stacks of the Major PA to achieve their loudest band in the world designation back in the early 70's. There have been statements that due to parts and tube availability Marshall decided to quit making the Major after only about 300 were made.  That is also not true.  Warrantee costs were killing them, but were easily absorbed as a flagship loss leader.  What really put the Major out to pasture was the factory logistics.  In one shift a single woman could assemble 6 - 50watt, 4 - 100watt, or 1 - Major (with help due to the weight).  In the early to mid 70's they could not meet demand as it was, so....  Ritchie Blackmore's amp tech used to work for Macintosh.  He was the one who figured out what was wrong with the Major's design and helped them find a solution.  Many Marshall products were wrung out on the road with Deep Purple in those days.

Any new OP UL tranny will work in this amp.  Ed likes the Hammond, many Major owners have gone with the Heyboer replacement and have been really happy with no smoke issues.  I think it would be very easy to replicate the original tone without blowing out the windows.  Yes, speaker breakup and moving a lot of air contributes - as well as a tinge of KT88 distortion (the best!).  But the full body response of the UL KT88's working with this unique preamp is awesome at any volume.  You could run those tubes at 350v and have a great 60 watt amp with the OWM and PPIMV.  Just because a car will do 150 mph, doesn't mean you have to go that fast.  I've only found a few tube brands that work well in my amp.  With that plate voltage and screens only .001v behind (with the original screen resistors), they get beat up pretty bad.  Lower the B+ and just about anything out there will work.  Ed has done a LOT of KT tube swapping with his builds, so I would defer to him on anything new.  I'm still stuck on my =C=.

Hope this esplains it and debunks some myths.  This is great to see!  I have been beating the Major drum for years, it's good to see you guys running with it! 

Jim

[Ritchie200]

Jeff, I meant your OTHER design, not the one you just posted.

Jim

[jojokeo]

At the same volume, the kt66 would scream, but the kt88 would kick you first - one of my favorite things! I also think the UL has a LOT to do with the final product.  And unlike Ed, every Major I had sounded better with the au7 (see my post on the Soundclip thread), but I was pushing it pretty hard.

How the heck do you have any hearing left???

[jazbo8]

Ed likes the Hammond, many Major owners have gone with the Heyboer replacement and have been really happy with no smoke issues. 

Ed prefers the Dynaco more - "I prefer the Dynaco replacement UL over the one Hammond sells and I have used both."

Slightly OT, why did KOC referred to the differential amplifier as "paraphase", they aren't really the same thing, are they?

[DummyLoad]

something along the lines of what i'd build.

maybe the following as well:
a) up the values of the coupling and bypass caps on the ice-pick channel.
b) adding cathode fuses for each KT-88.
c) neg bias PS go/no-go mains lockout.

--pete




EDIT: current copies of schema in reply #82.

[tubenit]

Pete,  I always value your input and thoughts on stuff like this. THANKS for sharing your schematic. I am posting it in the SCH Library along with the others.

http://el34world.com/Forum/index.php?topic=17556.new#new

Jim,  great info about this!  You and Ed are a wealth of valuable insight and info on this amp.

I think this is a very interesting thread and discussion & I appreciate everyone's contributions. Cool stuff.

I don't plan on building this amp, but I was very intrigued by the design of it and loved the YouTube tone that Jim posted.  My hearing is not very good already.  I can not afford to play a really loud amp and lose what I have left.  Maybe someday, I'll get a chance to build this for a friend or a good local guitarist & get a chance to try out this design.  I'd love to have an amp like this if I could get that tone at about 15-20 watts, but that doesn't sound possibly.

I will post a layout for this by this wkend if not sooner.

Thanks, guys!  I enjoy the interaction and thoughts!                    With respect, Tubenit

[HotBluePlates]

diff-amp grid-leaks should be 270k? i'd use 470K. just because. :p

Oops, DL already said it. I thought I checked to make sure I wasn't repeating anyone, but I guess I need more sleep. 

Why not take it way on down? Maybe a pair of 6AQ5s? Call it Major Minor. 

Get it down to 7w. Then you could call it a "Minor Major 7". Perfect amp for your jazzy songs...

[SILVERGUN]

something along the lines of what i'd build.

maybe the following as well:
a) up the values of the coupling and bypass caps on the ice-pick channel.
b) adding cathode fuses for each KT-88.
c) neg bias PS go/no-go mains lockout.

--pete

That's a nice looking print Pete!

Is there a problem with the way you have the FWB on the bias winding? 
Looks like one of the AC legs is going to ground

Jeff, I definitely like his grid stopper on V2 pin 7

[Ritchie200]

Pete,

The top boost channel (your ice pick description!) is not bad at all.  Those values would not work well in a normal 50 watt!  I think it goes back to the overall design.  The normal channel has a very full body response - if even a little boomy.  I find the top boost very musical and manageable.

Jim

[Willabe]

Slightly OT, why did KOC referred to the differential amplifier as "paraphase", they aren't really the same thing, are they?

From TUT5, chapter 7, page 3;

"Since the UL connection reduces the effective gain or sensitivity of the tube, much more drive voltage is needed to get full output. Referring back to Mullard's own spec; in tetrode, -34V of bias on g1 with 67Vpp drive, versus -75V and 140Vpp in UL. To use the UL output stage will require something more than a Schmitt (LTPI) splitter.

The drive stage Marshall settled on was a paraphase stage. This is merely a differential amplifier that has differential drive all the time."


                    Brad        

[SILVERGUN]

Slightly OT, why did KOC referred to the differential amplifier as "paraphase", they aren't really the same thing, are they?

From TUT5, chapter 7, page 3;

"Since the UL connection reduces the effective gain or sensitivity of the tube, much more drive voltage is needed to get full output. Referring back to Mullard's own spec; in tetrode, -34V of bias on g1 with 67Vpp drive, versus -75V and 140Vpp in UL. To use the UL output stage will require something more than a Schmitt splitter.

The drive stage Marshall settled on was a paraphase stage. This is merely a differential amplifier that has differential drive all the time.


                    Brad     

Another very informative post...

I gotta sell a couple amps and get me some of dem dare books 

[Ed_Chambley]

Any new OP UL tranny will work in this amp.  Ed likes the Hammond, many Major owners have gone with the Heyboer replacement and have been really happy with no smoke issues.  I think it would be very easy to replicate the original tone without blowing out the windows.  Yes, speaker breakup and moving a lot of air contributes - as well as a tinge of KT88 distortion (the best!).  But the full body response of the UL KT88's working with this unique preamp is awesome at any volume.  You could run those tubes at 350v and have a great 60 watt amp with the OWM and PPIMV.  Just because a car will do 150 mph, doesn't mean you have to go that fast.  I've only found a few tube brands that work well in my amp.  With that plate voltage and screens only .001v behind (with the original screen resistors), they get beat up pretty bad.  Lower the B+ and just about anything out there will work.  Ed has done a LOT of KT tube swapping with his builds, so I would defer to him on anything new.  I'm still stuck on my =C=.

Hope this esplains it and debunks some myths.  This is great to see!  I have been beating the Major drum for years, it's good to see you guys running with it! 

Jim, just a couple of corrections.
I prefer the UL OT from Triode.  As a matter of fact on the last build (the best one yet) I simply used the whole set, PT, Choke and OT.  The whole deal is $260 which may seem high until you get them.  Lot of iron.


The Hammond feels tighter.  In the amp I used the 1650N, which is 60 watt iron.  It will get a little hot when cranking, but to me has a better feel than the Hammond 1650R which is really overkill for 2 tubes and the thing 10lbs.  All things considered the A431S Dynaco to me worked best.


Now on the 12Au7 as the driver.  Like I mentioned, the preamp is much different in the Route 66 and that is what I have used.  I believe if I raise the voltage some in the preamp, I would not need much gain at the driver. 


The Major is one of the few Popular amps I have never owned or spent much time with, but I am very familiar with the tone.  I would think if you design from the prospective of reducing the ma on the PT and get voltage in the high for 2 tubes and copy the rest of the Major, it should sound very close.


I am not sure if lowering the voltage is a good idea, but I don't know for sure.  The only comparison I have is between an amp out of a Leslie 147 I converted to run KT88 cathode bias.  The difference is that it is not punchy.  IMO the only reason to use KT88 is the punch.  Sure the distortion is nice, but it is this punch I find in KT88's that I have not found in other tubes.  To me this is the difference between 6550 and KT.  The 6550 is really not a replacement for the tube as some say.


This thread caught my attention because I have been wanting to build a 2 tube Major myself, but I have been concerned if it can be done with 2 tubes.  Like you said, it doesn't have to be turned up all the way all the time.  I question it because a Marshall 4 tube EL34 IMO sounds better than 2 EL34.

Edit; Fixed quote, Willabe/Brad.

[jazbo8]

Slightly OT, why did KOC referred to the differential amplifier as "paraphase", they aren't really the same thing, are they?

From TUT5, chapter 7, page 3;

"Since the UL connection reduces the effective gain or sensitivity of the tube, much more drive voltage is needed to get full output. Referring back to Mullard's own spec; in tetrode, -34V of bias on g1 with 67Vpp drive, versus -75V and 140Vpp in UL. To use the UL output stage will require something more than a Schmitt (LTPI) splitter.

The drive stage Marshall settled on was a paraphase stage. This is merely a differential amplifier that has differential drive all the time."


                    Brad     

Interesting background story for sure, alas, the use of "paraphase" to describe the differential amplifier used in the Major is an oversight... The paraphase or "see-saw" circuit has a distinctive feature, with one half of the differential pair getting its input from the output of the other half, as shown in the diagram below, whereas in the Major, each of the differential pair's inputs are driven from the previous cathodyne stage. 

[Willabe]

This thread caught my attention because I have been wanting to build a 2 tube Major myself, but I have been concerned if it can be done with 2 tubes.  Like you said, it doesn't have to be turned up all the way all the time.  I question it because a Marshall 4 tube EL34 IMO sounds better than 2 EL34.

And that could be the hitch in the giddy up right there.

From KOC's TUT3, chapter 7 (Plexi) page 5;

"A 100W model has 4 tubes contributing to the class-A region, and the transition to class-B is higher in power and slightly higher on the loudness scale. Some players feel they must have this articulation available, even though they can never hope to use 100W.

Other players find the sound of the 50W amp at reasonable-to-loud volumes is more "present". Although they do not know it, they are playing above the transition point to class-B operation. In this part of the transfer curve, the harmonics imparted to the signal by the output tubes is different than when the tubes are in class-A. We have a higher level of odd-order-harmonics which in small quantities contribute a sense of "attack', "crispness" or "fast response". Too many, of course, this will sound harsh."

The chapter has a build in it that Kevin calls the "5100" which is a 50w Marshall type amp that has 4xEL34's but only the power of a 50w amp. Pull 2xEL34 tubes and you have a 50w 2xEL34 Marshall clone, leave all 4xEL34 tubes in and you have the 'sound/feel' of a 100w Marshall but only at 50w because of the iron set.

IIRC, it was a very popular build over at his Power Scaling forum.


                   Brad   

[Willabe]

Interesting background story for sure, alas, the use of "paraphase" to describe the differential amplifier used in the Major is an oversight... The paraphase or "see-saw" circuit has a distinctive feature, with one half of the differential pair getting its input from the output of the other half, as shown in the diagram below, whereas in the Major, each of the differential pair's inputs are driven from the previous cathodyne stage. 

Kevin's a pretty sharp guy and I'd be very surprised that he would miss-name a simple circuit. He must have a good reason he referred to it as he did.

A further explanation is probably in 1 of his other TUT books somewhere but I'd have to go through 7 volumes and 100's of pages to find it.   

                    Brad     

[jazbo8]

Kevin's a pretty sharp guy and I'd be very surprised that he would miss-name a simple circuit. He must have a good reason he referred to it as he did.

A further explanation is probably in 1 of his other TUT books somewhere but I'd have to go through 7 volumes and 100's of pages to find it.   

                    Brad     

KOC is really knowledgeable, that's why I seached through old books and papers to see where that reference came from, and I couldn't find any... Don't mind me, just geeking out a bit...

[SILVERGUN]

Kevin's a pretty sharp guy and I'd be very surprised that he would miss-name a simple circuit. He must have a good reason he referred to it as he did.

A further explanation is probably in 1 of his other TUT books somewhere but I'd have to go through 7 volumes and 100's of pages to find it.   

                    Brad     

KOC is really knowledgeable, that's why I seached through old books and papers to see where that reference came from, and I couldn't find any... Don't mind me, just geeking out a bit...

Maybe it's just in the wording....
It's not a paraphrase inverter that we're looking it....(because it's not the phase inverter)

But the driver section that it refers to 'could' be described as a paraphase amplifier?....maybe?

[Willabe]

Maybe it's just in the wording....
It's not a paraphrase inverter that we're looking it....(because it's not the phase inverter)

But the driver section that it refers to 'could' be described as a paraphase amplifier?....maybe?

Ahhhhh..... maybe.


                  Brad   

[jazbo8]

Try to pull a fast one, eh?!    No, KOC call the driver stage "concertina" which is what it is. Here is what Brad posted:

KOC, TUT5, 7-6 , Marshall Major chapter;
"Note that placing the (MV) dual pot between the concertina and the paraphase (driver triodes) stages is no different than the single-section pot at the input of the concertina (in place of the grid leak R). This is because the concertina is not a gain stage and should not be considered as such.

[Willabe]

No, read my quote again, "between the concertina and the paraphase (driver triodes) stages", concertina 'feeds' the paraphase 'driver' stage'.

I left out the part where Kevin says the PI is a concertina to feed the paraphase.

I'm thinking SG's correct on this, it's a 'paraphase amplifier' not a 'paraphase PI'.


              Brad   

[SILVERGUN]

Try to pull a fast one, eh?!    No, KOC call the driver stage "concertina" which is what it is. Here is what Brad posted:

KOC, TUT5, 7-6 , Marshall Major chapter;
"Note that placing the (MV) dual pot between the concertina and the paraphase (driver triodes) stages is no different than the single-section pot at the input of the concertina (in place of the grid leak R). This is because the concertina is not a gain stage and should not be considered as such.

No, KOC call the driver stage "concertina" which is what it is.
?
Maybe we're having a misunderstanding...
In this amp:
Phase inverter = concertina
Post phase inverter driver stage = paraphase  (paraphase amplifier?)

[SILVERGUN]

Don't mind me...
I just want to have a new acronym that I can use:
PPIPD

 

[jazbo8]

Maybe we're having a misunderstanding...
In this amp:
Phase inverter = concertina
Post phase inverter driver stage = paraphase  (paraphase amplifier?)

You may be right, that he was simply using "paraphase" as a generic term to describe a differential amplifier, but that's rather unorthodox, as paraphase is usually associated with "phase splitter" - doing the duty of phase splitting and not just an "amplifier". See this definition for example.


PPIPD is a real PITA

[sluckey]

as paraphase is usually associated with "phase splitter"

That's true in our small room of electronics. But when you open the door to the rest of the electronics industry, paraphase has a much broader definition. Still generally applies to the idea of two signals that are phase shifted by 180°.

As a side bar google "tube differential amplifier".

[Ed_Chambley]

Don't mind me...
I just want to have a new acronym that I can use:
PPIPD

 

Got your PPIPD, PPMIV, MV, LTPI, PT, PA, OT, oddly enough we are still typing Choke which is guess is short for Inductor.  What is PPPI?  Maybe we can come up with enough where it looks like we are typing in code.

[tubenit]

Got your PPIPD, PPMIV, MV, LTPI, PT, PA, OT, oddly enough we are still typing Choke which is guess is short for Inductor.  What is PPPI?  Maybe we can come up with enough where it looks like we are typing in code.

That's "A OK" with me! 10/4 good buddy!

 

Tubenit

[Ed_Chambley]

Got your PPIPD, PPMIV, MV, LTPI, PT, PA, OT, oddly enough we are still typing Choke which is guess is short for Inductor.  What is PPPI?  Maybe we can come up with enough where it looks like we are typing in code.

That's "A OK" with me! 10/4 good buddy!

 

Tubenit

Breaker 19, Jeff you got your ears on?  Be back gotta go 10/100, or maybe 10/200.  Heres hoping.

[SILVERGUN]

This amp has turned into a :
'67, lite, OWM, TMB, CPI, PPIPD, PPIMV, CB (for tubenit), FB (for me), 2- KT88, UL OT @ 500+ into 4.2K
Edit: I left out 2 : SS + FWB

Sometimes, when I read DL's (and others) posts, I have to stop and think about what the abbreviations mean,,,,and I feel like a dummy 

We should probably create a chart...

I needed one of these when I started texting with my kids :

[Willabe]

 

[Willabe]

Sometimes, when I read DL's (and others) posts, I have to stop and think about what the abbreviations mean,,,,and I feel like a dummy 

Join the club my friend.   

We should probably create a chart... I needed one of these when I started texting with my kids

Meh, texting, my wife does it with her kids and the other nurses at work. I got no use for it. 

Wanna talk, call me on the phone!!!!!!! (Web site forum is different.)

And don't get me started on face book.      

                     Brad       

[DummyLoad]

something along the lines of what i'd build.

maybe the following as well:
a) up the values of the coupling and bypass caps on the ice-pick channel.
b) adding cathode fuses for each KT-88.
c) neg bias PS go/no-go mains lockout.

--pete

That's a nice looking print Pete!

Is there a problem with the way you have the FWB on the bias winding? 
Looks like one of the AC legs is going to ground

Jeff, I definitely like his grid stopper on V2 pin 7

fixed! thanks guys. i don't know why i make that mistake when drawing a bridge. i just do if over and over again! ugh! :-)


--pete

[DummyLoad]

the concertina is feeding a differential pair, sometimes called the long tail pair. IIRC this is one of the traits of the williamson design.


in this amp the tail is passive. audiofools like to add an active tail. they tend to make things far more complex than they need to be. that's just my opinion, not fact.


--pete

[DummyLoad]

Pete,

The top boost channel (your ice pick description!) is not bad at all.  Those values would not work well in a normal 50 watt!  I think it goes back to the overall design.  The normal channel has a very full body response - if even a little boomy.  I find the top boost very musical and manageable.

Jim

thanks, for the feedback jim. it is appreciated very much. this is an intriguing design.

do know of anyone who has tried the hammond 1650WA that i specified in my schema? sim shows PS will make about 550V B+ with the hammond 379WX.  a well matched quad of =C= should be able to hold that back. i'd probably just use the quad of phillips branded GE 6550s i just acquired. i can't find anyone who stocks the heyboer marshall major 200W PT/OT sets. they must be custom order?

i plan on buying a couple of quad sets of the =C= before they dry up. after that, who knows what'll work...kind of feels like the 80's again; when US companies dumped tube mfg.

--pete

[Ed_Chambley]

Pete,

The top boost channel (your ice pick description!) is not bad at all.  Those values would not work well in a normal 50 watt!  I think it goes back to the overall design.  The normal channel has a very full body response - if even a little boomy.  I find the top boost very musical and manageable.

Jim

thanks, for the feedback jim. it is appreciated very much. this is an intriguing design.

do know of anyone who has tried the hammond 1650WA that i specified in my schema? sim shows PS will make about 550V B+ with the hammond 379WX.  a well matched quad of =C= should be able to hold that back. i'd probably just use the quad of phillips branded GE 6550s i just acquired. i can't find anyone who stocks the heyboer marshall major 200W PT/OT sets. they must be custom order?

i plan on buying a couple of quad sets of the =C= before they dry up. after that, who knows what'll work...kind of feels like the 80's again; when US companies dumped tube mfg.

--pete

A 20lb OT and 28lb PT.  WOW.  No, I have not tried them.  Sounds like fun, but I would need someone to help me get the things on my bench.

Man you could build a 2 12 combo like a twin with 8 6L6 in it.  Add a couple of JBL's and you would have one cool grab and go amp.

[DummyLoad]

Pete,

The top boost channel (your ice pick description!) is not bad at all.  Those values would not work well in a normal 50 watt!  I think it goes back to the overall design.  The normal channel has a very full body response - if even a little boomy.  I find the top boost very musical and manageable.

Jim

thanks, for the feedback jim. it is appreciated very much. this is an intriguing design.

do know of anyone who has tried the hammond 1650WA that i specified in my schema? sim shows PS will make about 550V B+ with the hammond 379WX.  a well matched quad of =C= should be able to hold that back. i'd probably just use the quad of phillips branded GE 6550s i just acquired. i can't find anyone who stocks the heyboer marshall major 200W PT/OT sets. they must be custom order?

i plan on buying a couple of quad sets of the =C= before they dry up. after that, who knows what'll work...kind of feels like the 80's again; when US companies dumped tube mfg.

--pete

A 20lb OT and 28lb PT.  WOW.  No, I have not tried them.  Sounds like fun, but I would need someone to help me get the things on my bench.

Man you could build a 2 12 combo like a twin with 8 6L6 in it.  Add a couple of JBL's and you would have one cool grab and go amp.

it would be of interest to know what reproduction iron weighs... ya 48Lb in transformer alone kind of makes me think about spinach and the gym...
--pete

[Ritchie200]

I could be wrong, but I don't think running a KT88 at 600v is necessary to reproduce what we are trying to achieve.  Iron for a project like that is VERY high dollar.  Run em at 350v and call it a day.  We don't need the dB's or the wear and tear on the tubes and ears.  I think the KT88 is one of the most beautiful sounding tubes when driven hard.  If we starve them, we will get there sooner - but it should retain it's other characteristics I'm seeing at 600v.  Cheaper iron and components.  The KT88's are a big part of the overall mojo which is why I think the Park 75 sounds better than a Marshall 50 (same except for KT88's in place of the EL34's).  However, the other half of the mojo is the preamp/phase inverter/driver interaction.  I think this is very doable with some safe voltages and cheaper parts.

Jim

SG, you got this thing breadboarded yet!

[DummyLoad]

I could be wrong, but I don't think running a KT88 at 600v is necessary to reproduce what we are trying to achieve.

my thoughts are just the opposite but i do concur of the 600V B+. not with modern tubes. 500-550V is doable with modern tubes and i think that'll get us closer to the mojo of the major [is that a book title?]. new FLA - MOTM.
perhaps it would be frugal to build a 100W version, however, i'm of the opinion that the KT-88 pushed hard in UL is a significant part of the overall sound and that part of that "hits you in the chest" you describe is the probably acoustic wave of a 200W amp and there's no other way to replicate that. hot rodder's have an old saying; "there's no substitute for cubic inches". in this case, there's no substitute for wattage.

all this is just blather speak, so please flame away!

--pete

https://www.youtube.com/watch?v=Xc1PHk9FhIk

[DummyLoad]

major minor  - steve, i stole the name! ;-)


100W version. using the bias tap for the bias supply wasn't getting it done on the sim. added T2 - a 10VCT/120V xformer with FWB bias supply.


ok, i'll be quiet now.


---pete

[SILVERGUN]

Jeff,
On your schematic of a 2- KT88 version, you can reduce the value of that 10 amp mains input fuse significantly (maybe half)

The final value will be based off of what B+ you wind up with, so maybe just leave the value blank and leave it up to the builder....?

If someone unknowingly builds it with a 10 amp fuse in there (just because your schematic has it on there), it won't provide the protection it was designed for....
...just a thought
 

[SILVERGUN]

SG, you got this thing breadboarded yet!

The good news is that my big board is clear.
The bad news is that I've got an amp that won't get off my bench, that is a must, for a guy who is waiting patiently.
I'm trading a sluckey TDR'ish for a PRS guitar 

Sooooo, the suspense will have to continue......

I have been shopping for OT's because I think there might be something to the UL hookup..

I'm leaning towards the Hammond 1650N for a 2-KT build @ about 500V'ish (similar to Ed's)
DL, how do you like 4.3K @ 500V?

Anyone want to donate a couple used 88's to a good cause?

[SILVERGUN]

using the bias tap for the bias supply wasn't getting it done on the sim. added T2 - a 10VCT/120V xformer with FWB bias supply.

I'm thinking about using this PT for 2 tuber

The 60V bias winding with FWB should get me there....right?

http://www.classictone.net/40-18069.pdf

500mA HT should be enough for the 4 tube build....?
You could put one(or both) of the 15V windings in series with the bias winding to beef it up.....if necessary...?

[DummyLoad]

using the bias tap for the bias supply wasn't getting it done on the sim. added T2 - a 10VCT/120V xformer with FWB bias supply.

I'm thinking about using this PT for 2 tuber

The 60V bias winding with FWB should get me there....right?

http://www.classictone.net/40-18069.pdf


it'll work nicely.

500mA HT should be enough for the 4 tube build....?

probably. it'll be choking at max power. you'll need around 630mA at full power.

You could put one(or both) of the 15V windings in series with the bias winding to beef it up.....if necessary...?

one would be enough, likely not needed since you have a separate winding for the bias on the classictone PT - use a delon FW doubler if needed. bias will need to be about -75V at 550V B+.

[DummyLoad]

SG, you got this thing breadboarded yet!

The good news is that my big board is clear.
The bad news is that I've got an amp that won't get off my bench, that is a must, for a guy who is waiting patiently.
I'm trading a sluckey TDR'ish for a PRS guitar 

Sooooo, the suspense will have to continue......

I have been shopping for OT's because I think there might be something to the UL hookup..

I'm leaning towards the Hammond 1650N for a 2-KT build @ about 500V'ish (similar to Ed's)
DL, how do you like 4.3K @ 500V?

that will work fine. anything from 4-5K for 2-tube or 1900-2200 for 4 tube, @ 500-550V. 2 tube OT will need to carry ~300mA/side. get the 1650NA not the 1650N - the non A suffix part has a convoluted secondary wiring scheme.

Anyone want to donate a couple used 88's to a good cause?

[SILVERGUN]

Cool..
THANKS DL!...I'll BB it first and see what's up...
At least I feel like we've demystified xfmr selection for anyone else who might be playing along

Down the line,,I'm thinking bout adding a tube loop, which will serve as my pre-PI master (yes Jim, I just said that  )....no PPIMV

We'll see how it goes 

[tubenit]

Thanks for the continued interest and info on this thread!   I am working on a layout and will have that done by end of the wkend.

10A fuse issue noted.  Thanks.

I personally like the idea of a two KT88 design idea with a UL OT and 400 or less volts on the tubes.

With respect, Tubenit

[PRR]

I don't think it is a Paraphase.

It is a lower-level phase splitter (cathodyne/concertina) driving push-pull voltage amplifiers (no long-tail under). Well known from Williamson. For hi-fi usually you use lower-gain tubes for supersonic bandwidth (for intense NFB for hi-fi) and slap another gain stage before the cathodyne for enuff total gain and a place to put that NFB.

Also I don't see how Schmitt's name got on the long-tail pair. (There IS a Schmitt Trigger which uses long-tail connection, but that's different from an audio amplifier.)

I think Kevin is more of a good, smart, and enthusiastic technician than a painstaking historian. Go by the circuits, not by names that were invented (and often confused!) before he was born.

[DummyLoad]

drawing depicts PT and OT discussed thus far in this forum.


for the major-minor, i'll run with the dynaco A-431-S OT and the CT 40-18069


for the major-major, i'll run with the hammond 1650WA OT and the hammond 379WX PT


--pete

[Ritchie200]

V3 - 12au7?

http://el34world.com/Forum/index.php?topic=17530.0

Jim