KT88 PP amp

[shooter]

fwiw info
Ed's       400-0-400 full wave rectifier 2 120's got 535 plate
I used a 280-0-280 full wave on 1 kt88          got 388 plate
I used a 350-0-350 full wave 2 el34's             got 402 plate

[uki]

For the power supply can this caps be used in place of 200uf/500 ?

[shooter]

if you're pretty sure they're good I don't see a problem

[DummyLoad]

http://el34world.com/Forum/index.php?topic=11329.msg104651#msg104651

that was an amp richard designed and i helped with - skip to the last of the thread, ver. 3

it was a very, very nice sounding amp. richard had limited resources available for the PS, so i attached a his plan with a modified PS that should work with the MKIII PT.

your winder should be able to reproduce the dynaco MKIII PT and OT. the choke is a hammond. i show 500uF for the main filters, however, your 330uF 400V parts will work fine.

--Pete

[shooter]

Pete, can you hear the 6SN7 whimper when you touch the power switch 

[uki]

http://el34world.com/Forum/index.php?topic=11329.msg104651#msg104651

that was an amp richard designed and i helped with - skip to the last of the thread, ver. 3

it was a very, very nice sounding amp. richard had limited resources available for the PS, so i attached a his plan with a modified PS that should work with the MKIII PT.

your winder should be able to reproduce the dynaco MKIII PT and OT. the choke is a hammond. i show 500uF for the main filters, however, your 330uF 400V parts will work fine.

--Pete

Thanks Pete!

I'll have to buy a few more parts, the big caps are very expensive, I did find 560uF/400v ... but not the 200uf/500v. Then I'll use the ones in post #51.

I got a questions about the OT and choke/PS , looking at the schematics presented so far there are 5k load in the primary, for the 100w major, for the Le Gourmet 3k for a 30-40w, and so on, the data I've attached in post 48 is correct to follow for the amp have about 70w, 4k load is the correct load?  Oh what kind of PI is the one in the schematic I'm putting together?(I'm no engineer just copying and pasting)

Do i need a choke for the PS? I got a 9H 200ma 140 Ohms choke. Planning for a PT with 360-0-360. how many amperes it will need?

[shooter]

here's a good read on your Cathodyne PI

http://www.valvewizard.co.uk/cathodyne.html

[DummyLoad]

Pete, can you hear the 6SN7 whimper when you touch the power switch 

????

[shooter]

I was just looking at 440v and 33k thinking they're running heavyfooted   

[DummyLoad]

rated at 450v. how's that a problem? 


--pete

[shooter]

I never have a problem with your boundary pushin 
you're design skills are pretty good to.

[DummyLoad]

http://el34world.com/Forum/index.php?topic=11329.msg104651#msg104651

that was an amp richard designed and i helped with - skip to the last of the thread, ver. 3

it was a very, very nice sounding amp. richard had limited resources available for the PS, so i attached a his plan with a modified PS that should work with the MKIII PT.

your winder should be able to reproduce the dynaco MKIII PT and OT. the choke is a hammond. i show 500uF for the main filters, however, your 330uF 400V parts will work fine.

--Pete

Thanks Pete!

I'll have to buy a few more parts, the big caps are very expensive, I did find 560uF/400v ... but not the 200uf/500v. Then I'll use the ones in post #51.

I got a questions about the OT and choke/PS , looking at the schematics presented so far there are 5k load in the primary, for the 100w major, for the Le Gourmet 3k for a 30-40w, and so on, the data I've attached in post 48 is correct to follow for the amp have about 70w, 4k load is the correct load?  Oh what kind of PI is the one in the schematic I'm putting together?(I'm no engineer just copying and pasting)

Do i need a choke for the PS? I got a 9H 200ma 140 Ohms choke. Planning for a PT with 360-0-360. how many amperes it will need?

have your winding shop copy the attached PT. 300mA should work nicely.

your 9H choke will work fine.


--pete

[PRR]

> 440v and 33k thinking they're running heavyfooted

440V supply, but what is the actual plate-cathode voltage?

Something like 157V, about 8.4mA, about 1.33 Watts Pdiss. Not a strain for 6SN7.

[DummyLoad]

B+ 440V - Vese of Ra for both anodes is about 130V - 80V on top of the tail R, so Va-k is about 220V. the whole system draws about 8mA.

like you said: loafing along. 


--pete

[shooter]

like you said: loafing along

that's why I'm trying to catch up with the smart kids, but sometimes I think it might be better spent with the fire extinguisher near by and lots of gator clips 

[uki]

your 9H choke will work fine.

--pete

  The choke is open, no resistance ... gotta fix it.

The PS and Power section is from the Major-Minor, it doesn't have a choke; the preamp and PI is from Sluckey's Rocky-Ola, it does have a choke, should the choke be added ?

[sluckey]

Ugh, my Rocky does not have a choke.

[Willabe]

You might want to put a switch on the -FB loop to turn it off.

Some guys love a guitar amp that is UL without -FB.   

[VMS]

Related to the choke question for those who know better:

I have often wondered do UL amps need better filtering because screen supply is essentially same as plate supply?

[uki]

Ugh, my Rocky does not have a choke.

I was mistaken, is that a pot on the power supply?  1540 with CT

[sluckey]

No. It's just a power resistor with a fixed tap. Just consider it to be two resistors connected in series.

[Ed_Chambley]

ed, you should be making about 100W with that OT & PT combo even in UL mode. suspect with those values that your LTPI is not driving hard enough to do that. i guess that's what you want?

likely you're not capable of driving output stage into clipping with current LTPI.

bump B+ to 400V for the LTPI.

suggestion:
Ra1 = 82K (inv)
Ra2 = 91K (non-inv)
Rtail = 15K
Rbias = 1.2K @ 2.9mA
B+ = 400V
Vout ~90Vpk

Rdrop of B+A to B+B is = 75K now, lower to 33K-36K. so, change two resistors and you should get near to 100W and allow power amp to clip. the OT can take it since it's rated at 120W @ 30Hz

--pete

Of course, you are correct.  I have pushed the 12At7 and a 6SN7.  What happens is the amp with the KT120's gets stiff, but some of the GE6550A love it.  The attack changes and it is difficult to describe.  UL can have sort of an ebb and flow feel and you get some rich harmonics from the preamp.  It is the only amp I have where I can play Hollowbodies with flatwounds.  It is sort of a Western Swing amp.


It is also extremely HUGE sounding without any raw edge.  Very HiFi.  A lot like a Standel.  I could probably get a tad more, but I do like it.  Now back to work.  Seems my work is getting in the way of amp building.

[shooter]

Seems my work is getting in the way of amp building.

lack of it's getting in my way 
somedayz ya just gotta play guitar

[uki]

You might want to put a switch on the -FB loop to turn it off.

Some guys love a guitar amp that is UL without -FB.

I like clean tone amps, putting a switch for the -FB the amp will have distortion?
I've been thinking about to add a presence control, Trying to figure it out, I'm not sure how 

[Willabe]

I like clean tone amps, putting a switch for the -FB the amp will have distortion?

How loud do you play?

The UL tap's are a form of FB, helps keep it clean without a -FB loop. UL power amps with a -FB loop can often be too clean and cold sounding. Disconnecting the -FB loop warms them up. 

And with an amp with that much power, depending on how loud you play, it should still have plenty of clean volume with just running it in UL.

But that's why you use a switch, a small switch is fine, low voltage and low current there.

[sluckey]

You may be interested in a Sunn KT88 amp such as this Spectrum II...

     https://el34world.com/charts/Schematics/files/Sunn/Sunn_spectrum_ii.pdf

Simple, very clean with powerful punch.

Or step up to the Sceptre if you want the same amp with reverb and tremolo...

     http://sluckeyamps.com/sunn/sunn.htm

[Ed_Chambley]

You may be interested in a Sunn KT88 amp such as this Spectrum II...

     https://el34world.com/charts/Schematics/files/Sunn/Sunn_spectrum_ii.pdf

Simple, very clean with powerful punch.

Or step up to the Sceptre if you want the same amp with reverb and tremolo...

     http://sluckeyamps.com/sunn/sunn.htm

Or a Hampeg Gemovibe running 4, 6550's, but for me the one you built is the shiznit.  One day you will get tired of it and no I have done nothing with the the hammond 63 I have. Ever since Swart came out with their Stereo amp, here is a clip, http://swartamps.com/sound_samples/st-stereo_samples/swart_st-stereo-blues_redux.mp3


And Magnatone with theirs, everyone I know is drooling.  Why not just use 2 small amps?  I do not know.  Guitar players are strange.

[uki]

I like clean tone amps, putting a switch for the -FB the amp will have distortion?

How loud do you play?

The UL tap's are a form of FB, helps keep it clean without a -FB loop. UL power amps with a -FB loop can often be too clean and cold sounding. Disconnecting the -FB loop warms them up. 

And with an amp with that much power, depending on how loud you play, it should still have plenty of clean volume with just running it in UL.

But that's why you use a switch, a small switch is fine, low voltage and low current there.

How loud I play?! Depends on the place where the gig is happening, but usually the volume is around 3-5, that with my Fender 6G8, now at home for practice just at 1.

How about a pot instead of a switch for the -FB ?

[Willabe]

How about a pot instead of a switch for the -FB ?

Yes, you could use a pot.

[sluckey]

If clean is your goal I'd leave the NFB alone. That also includes no presence control.

[uki]

If clean is your goal I'd leave the NFB alone. That also includes no presence control.

I use the presence pot of the 6G8 at 3, gives a very smooth saturation in combination with my Paramount OD pedal which is more like a booster(it only give some noticeable drive at 7) the drive control is usually at like 3-4, just to warm up the tone a little bit without distortion, so I can play loud with 95% clean tone, for the rhythm cords, but for the solo I got a Distortion Purple Plexi 800 and another OD that saturate a lot the HBE Power Screamer.

This kind of clean tone is what I want !
I like a lot the tone of the 1st amp of those tree. I think it does have octal pre amp tubes.

[shooter]

as long as your TS doesn't eat too much gain, you might be able to leave a pedel or 2 behind 

have a few 2.2 - 10uf Ecaps on hand for tuning your preamp sound.  I've found the 25uf is to much for most builds I've done.

pretty sure you'll be smiling when she gets about 7 for volume

[uki]

Is the presence placed correctly ?

[sluckey]

That's where I'd try to put it. I would not use that 1.5K though.

[shooter]

what he said.

If you look, the 1.5k is always in || with the 3.9k, which gives you an effective Rk of ~~ 1.1k instead of the happy 3.9k

[uki]

Something worth mentioning... I changed over to 6SL7s soon after converting Rocky. I think those KTs will like the extra gain also.

... I switched to a LTPI because I couldn't quite get satisfactory output from a Concertina.  The LTPI got me there no problem...

So I decide to do a major modification. I'm not sure about that 1m resistor between the v1 and v2.

[sluckey]

It's not necessary. Same goes for the .022 cap.

[uki]

It's not necessary. Same goes for the .022 cap.

Thanks Sluckey !  In your AB763 Lite there is 3 components in that same spot, what they do ?

[PRR]

> In your AB763 Lite there is 3 components

Looks like he had "too much gain", at least for his mild style(?), so added a knock-down.

Your plan, 6SN7 with a James, is not a lot of gain, maybe not enough, depending on your style and fingers. I bet you don't want any knock-down.

[uki]

> In your AB763 Lite there is 3 components

Looks like he had "too much gain", at least for his mild style(?), so added a knock-down.

Your plan, 6SN7 with a James, is not a lot of gain, maybe not enough, depending on your style and fingers. I bet you don't want any knock-down.

Oh I forgot to change V1 tube name it is a 6SL7.

What is a James? Tone stack?

[sluckey]

Thanks Sluckey !  In your AB763 Lite there is 3 components in that same spot, what they do ?

Those components simulate the loading that was present before the VIBRATO channel was stripped away.

[uki]

I think the schematic is done, is it all correct?
Also i got the transformers schematic.

[PRR]

Fixed resistor next to Presence pot needs a value.

[uki]

Fixed resistor next to Presence pot needs a value.

Thanks PRR !
Fixed that.
Which phase inverter does more output, cathodyne or Long Tail ?

[sluckey]

Cathodyne has a gain of less than one. LTP has gobs of gain.

[uki]

Cathodyne has a gain of less than one. LTP has gobs of gain.

Goblins?    

You mean lots ?

[Willabe]

Cathodyne has a gain of less than one. LTP has gobs of gain.

Goblins?    

You mean lots ?

Yes he means lots of gain. 

[Ritchie200]

I think that was a relevant question:

"a lump or clot of a slimy or viscous substance" - like a beer at Wrigley Field....


The goblins show up when you first power up!

Jim 

[PRR]

> Which phase inverter does more output, cathodyne or Long Tail ?

Yes. (Either can do very very well.)

Sluckey's point compares a one-triode cathodyne to the two-triode LTP. However at the same tube count, cathodyne has another triode which can be a gain stage. Total gain can be significant higher than LTP. With care, both can deliver more voltage than any of our usual power tubes can swallow.

However getting more than so-much gain in the driver leads to compromise. If you need big gain, get it in the small stages.

[uki]

How about a pot instead of a switch for the -FB ?

Yes, you could use a pot.

What value the pot should be 20k , 25k ?