modifying kt88 pp ul amp

[iorga]

Hi guys, I m new to tubes
i ll have loads of questions, and I m still reading a lot.
But basically I plan to do a stereo tube amp in a single chassis based on the
Class A Ultra Linear (UL) 12SL7 SRPP / KT88 SIPP Tube Amp


in diyaudio projects.
with KT88 and 5751 tubes.
I have questions about the transfos, I think the 1605P from hammond should be ok for each channel but what about the output transfo? Is it some kind of 1650PP at 210 euros?!?



Now, and i know this is not the main question, anyway it s another necessary condition for me to go on with it, i plan to do a couple of mods, but i don t know if they are possible:

i ll do one chassis, for a single stereo (two of those blocks) system.
if i do 2 mono amps, and join their signals in an operational amp in addition mode, i would be able to have stereo, mono, left or right sound, am i stupid?


I plan to use an old amp chassis. Big, cute, nice pots and switches.

Can I easily connect its headphone jack to the circuitry?
How can I add inputs to the schematics?
(i don t think this is that hard)
How can I add 4 and 8 ohms for the speakers?
(i have def no clue here)

My old amp is 2x60W and has nice vu meters. Can I plug them easily to the schematics? Where?

I know I need to learn basics, but as I d like to do that greatly I must ask if these things are at one's reach. Is it just plugging?

The Power switch has a LED on it.
Is that complicated to make it work?

There s also a function "switch" (tuner, phono, tape): can I integrate it in those schematics? Would anyone have some example of such a union?

I won t need any of the other wheels, so I ll just let them there without connecting them.

If you have nice schematics it could be cool.


Many thanks and sorry for the messy character of this post!


Regards,
I.

 

[Herr Grau]

Hi guys, I m new to tubes
i ll have loads of questions, and I m still reading a lot.
But basically I plan to do a stereo tube amp in a single chassis based on the
Class A Ultra Linear (UL) 12SL7 SRPP / KT88 SIPP Tube Amp

I think KT88 are a good choice, as are PP and UL operation. But SRPPs are known to be bitchy and I would propably not build one without the knowledge (and time) how to polish it, should it not perform to your satfisfaction.

I'm currently putting the finishing touches on my UL PP KT88 Amp and have to tell you: By now I would already do a great many things differently. If I were you, I would try building this. Interstage transformers may seem expensive, but you save coupling caps, tubes and other parts + there is less to do wrong + I think they are excellent phase splitters.

I have questions about the transfos, I think the 1605P from hammond should be ok for each channel but what about the output transfo? Is it some kind of 1650PP at 210 euros?!?

Transformers in the signal path are always a bottle neck, so I think you should make shure to use good output transformers (and interstage, if you take my advice...). I don't know where you are from, so I can't give you local recommendations.

i ll do one chassis, for a single stereo (two of those blocks) system.
if i do 2 mono amps, and join their signals in an operational amp in addition mode, i would be able to have stereo, mono, left or right sound, am i stupid?

If you have a chassis and it's good, then use it. Not having to do the metal work is a major advantage.

Can I easily connect its headphone jack to the circuitry?
How can I add inputs to the schematics?
(i don t think this is that hard)
How can I add 4 and 8 ohms for the speakers?
(i have def no clue here)

For the headphones you just source the incoming signal directly behind the volume pot out again. High gain sources like CD Players can drive headphones themselves.
If you need 4 and 8 Ohm outputs, you have to choose an OPT with those outputs. After that it's as simple as connecting them to jacks.

My old amp is 2x60W and has nice vu meters. Can I plug them easily to the schematics? Where?

Depends on which range they measure in.

I know I need to learn basics, but as I d like to do that greatly I must ask if these things are at one's reach. Is it just plugging?

The Power switch has a LED on it.
Is that complicated to make it work?

Although I think everyone can build an amp if the schematic is good enough, you should ensure that your basics are straight, so you don't electricute yourself - the voltages in an tube amp are very dangerous. Don't take this lightly. High voltages can let the flexors of your fingers cramp, so that you can't let go of a once touched wire. Once a current of about 50mA runs across your heart in the relative refractory time, youre done for. So if you're not certain, don't do it. Otherwise: Go ahead and try! You might want to buy the books of Morgan Jones, those will solve most of the other questions thatll appear sooner or later in the project.

Getting LED to run is not that hard, just look under "LED" in wikipedia, the basics are all there.

There s also a function "switch" (tuner, phono, tape): can I integrate it in those schematics? Would anyone have some example of such a union?

If you have a source selector, thats a good thing. Just figure out where the output is and you can use it as-is.

 

[iorga]

Thanks!!
I m in Barcelona, Spain
I ll hav a closer look at what you suggest;
right now i m concerned of the reusable or not chassis:
i can just unplug the function switch and provided i plug where it should be plugged, i can just use it as it is?

that s good news isn t it?


As for the security concerns, i ve read so far the 11 first pages of the sticky post and i m still reading! wow
i know it is dangerous
A friend of mine, experienced with such devices (he built a couple, that s enough for me), and both having read the warnings list, I think it could be the minimum necessary things to do...

You suggested me another scheme, why?
Why is there a concern with SRPP? Can t i just get rid of it then?

Thanks again!

 

[iorga]

The scheme you suggested, did you try it?

Actually, i d like
a PP UL class A with KT88 tube amp.

Then for the extras, i d like 4 inputs, 0-4-8 ohms, headphone jack, power led and vu meters usable, and the Mono left, Mono Right, Stereophonic modes available too.

(N.B.: The speaker i m planning to get are the supravox 215 RTF 64 BIC or 215 signature Bic, in TQWT boxes, respectively 96 or 93 dB.)

Cause I listened to such an amp, and enjoyed a lot. So if I keep the scheme similar (no access to the scheme, sadly), i would have same sound...

If possible, i read that nowadays we can do SE benefits in PP operation mode, without having SE disadantages. I don t know how one can perform this. I d be glad I had such schematics in my hand for the amp i d like to have.
Does anyone have such a scheme?


When you refer to transfos as the bottleneck, .. i ve seen a lot of designs identical, so... are you saying this way is not good?



btw, what OPT stands for? (operational amp?)?

 

[Herr Grau]

Spain is Europe, that's good. We have some very good transformer makers here.
You might want to look at AE Europe, Tribute, Lundahl (e.g. here), Amplimo and IG Präzisions-Wickeltechnik.

Regarding SRPP, I just quote from frihu.com (translation included):

SRPP is nothing for a quicky and wants to be 'raised' (means: optimized). Only very seldomly the circuit will work just like that with the given source, output stage and speaker combo. Either the amplification is too low or too high, either the output impedance is right or not, either the tube is within it's working point or not. A tini-tiny wrong turn at the input can turn the high end SRPP into a noise generator. Last but not least you're on with termic shifting. Ergo: Either youre a designated SRPP-freak with masochistic tendecys - or not.

Just 'removing' it doesn't do the job, you have to come up with something to substitute it with. And without experience in the circuit design department, that's gonna be al little tricky.
I would tell you to stick with a working schematic without bells and whistles. And since it seems to be your first project, you might want to look for simplicity. Not always is 'more complicated = more better', sometimes you find the best results in pure, simple things. The schematics always look far more easy then the wires in real life

right now i m concerned of the reusable or not chassis:
i can just unplug the function switch and provided i plug where it should be plugged, i can just use it as it is?

Sorry, I don't understand what you mean.

 

[iorga]

i ve been reading a bit more.
it s been SO helpful
The howtos in this web are really cool.

I hae a doubt on the layout of the 2 mono layouts in a single stereo chassis: how can i join them together in terms of power supply (2 plugs?).
Will I have the space in a 42x35x15 chassis?

What I asked was for the input selector pot: the old amp already has one.
But only 3 inputs. I plan 4 inputs. Maybe 5.
I figured out roughly where those inputs ought to be, as well as the 0 4 8 ohms speakers imped.

The thing I am concerned also is about the physical position of inputs: must be far away from power.
In a dual monoblocks config, I m afraid that distance won t be that big.

Isn t it easier to have one main power input? How can I do this?

OPT = output transformer.

The 5751 are the rectifier ones from the driver stage? Am I wrong?

 

[Herr Grau]

i ve been reading a bit more.
it s been SO helpful
The howtos in this web are really cool.

I hae a doubt on the layout of the 2 mono layouts in a single stereo chassis: how can i join them together in terms of power supply (2 plugs?).
Will I have the space in a 42x35x15 chassis?

The chassis is big enough. But to give you hints on how to do it, I'd have to see it. If you make fotos, we can suggest where to put what and how to lay out.

What I asked was for the input selector pot: the old amp already has one.
But only 3 inputs. I plan 4 inputs. Maybe 5.
I figured out roughly where those inputs ought to be, as well as the 0 4 8 ohms speakers imped.

The thing I am concerned also is about the physical position of inputs: must be far away from power.
In a dual monoblocks config, I m afraid that distance won t be that big.

Isn t it easier to have one main power input? How can I do this?

1. Ok, I realy think that you don't have the whole monoblock/stereo thing out correctly. Monoblocks mean that you build two seperate chassis, each with their own power supply. The only difference in a stereo build is, that you build the two circuits into one chassis and possibly let them share a power supply. If you already have the chassis, take it and build stereo!

2. If the input selector works - take it. If it has to few positions - dont take it. I would rather settle for one input less than to fit a new input selector in it. It is expensive and takes time and metal work skill.

3. Yes, you should always try to keep away the signal path from the power supply, more acuratly electromagnetic fields produced by the power transformer and every wire that carries AC. This 'keeping away' can be done by isolating the two things with a sheet of iron connected to ground or by distance, since the intensity of an electromagnetic wave decreases with r².

The 5751 are the rectifier ones from the driver stage? Am I wrong?

Yes, you are wrong. The 5751 ARE the drivers. Rectification is in your mentioned project done via solid state.


If you have help building the amp, you'll propably be fine. But you might realy want to learn a little more. Try reading the pages of Boozhound and Valve Wizard. You should know how the basic stuff works and most importantly get your grounding right. Otherwise you'll end up with an expensive hum generator. I want to strongly advise you once again not to build that OddWatt Project. You are better of not using an SRPP and not trying to build something too complicated.

 

[iorga]

great!

TFYH!
I understood the mono blocks had 2 separate PSU and what i thought was that a stereo one is basically 2 monoblocks in the same chassis sharing the same power unit. If I ask it is because my aim is just to try to insert a Mono / stereo / mono left / mono right switch and i don t know exactly how to do this.

As for reading: you re absolutely right. Yes I do need to read more, and I m on it. And yes I want to learn more. I read those pages, they re on my computer now, it s really pedagogic. I am still at the beginning...
About the rectifier: ok. It s not properly exxplained how it rectifies, that s hy.
Sin wave -> abs(sin) is done by the rectifier. Ok; these can be tube or solide devices. Then the CRC or CLC (Pi thing) is there to make the signal as flat as possible (i don t have the terms): the camel back done by the rectifier is not good enough, we d like something DC perfect. So CLC.
Well, i still have NO schematics. The one you suggested me, did you try it? Or is it just the one you think would be perfect?


I m still studying a lot the way things work. I have to read a lot.

About the chassis: the input selector switch has 3 positions. It s supposed to work.
Is it THAT hard to put another switch? I mean: the hole is done, the knob is there, shouldn t it be fine to put another switch whose diameter is compatible with the knob?
Too hard? (Then I would follo your advice)


The pics: i have something in my mind, but that is not mine yet. I d rather keep discrete until it is, so please forgive me not putting right no the pics.


You would go for a tube rectifier?
And for the transfos? I need one output transfo (hammond or another) per channel, and I also need the "main" one, the one that gives the power. This one is not clear in its characteristics, cause i haven t found yet any schematics of a ultra linear class A stereo kt88 push pull.

Night and thanks!
I began this. When my mind is set, full and ready, I ll gather parts. Then I ll see my friend. This is going to be long...
Please be patient...

 

[iorga]

sorry you must become crazy:
I meant
Yes i d like to share the power supply between the 2 "blocks", but with 1/ possibility to choose the stereophonic /mono mode, and 2/ i have no idea of which transformer use here (and i knew monoblock meant 2 chassis; but i used that term even if then i was thinking on stereo= 2 mono blocks on same chassis)

Again, sorry: the tube is not the rectifier, the tube is the DRIVER.
(what does rectification then? this absolute value? it s not said in the how to page)

Night!

 

[Herr Grau]

I understood the mono blocks had 2 separate PSU and what i thought was that a stereo one is basically 2 monoblocks in the same chassis sharing the same power unit. If I ask it is because my aim is just to try to insert a Mono / stereo / mono left / mono right switch and i don t know exactly how to do this.
[...]
I meant
Yes i d like to share the power supply between the 2 "blocks", but with 1/ possibility to choose the stereophonic /mono mode, and 2/ i have no idea of which transformer use here (and i knew monoblock meant 2 chassis; but i used that term even if then i was thinking on stereo= 2 mono blocks on same chassis)

If I understand correctly, you want to build a stereo amplifier (two channels, one power supply) with the option to make it a bridged mono amplifier. I hope that's what you mean because otherwise I have no idea what youre talking about and why.
So I drew up the basic way to do this with a 2-position 3-way switch:

An externally hosted image should be here but it was not working when we last tested it.

In position 1 of the switch you get standard stereo operation, in position 2 only the upper input is used and the outputs are bridged together on the upper speaker.

Again, sorry: the tube is not the rectifier, the tube is the DRIVER.
(what does rectification then? this absolute value? it s not said in the how to page)

About the rectifier: ok. It s not properly exxplained how it rectifies, that s hy.
Sin wave -> abs(sin) is done by the rectifier. Ok; these can be tube or solide devices. Then the CRC or CLC (Pi thing) is there to make the signal as flat as possible (i don t have the terms): the camel back done by the rectifier is not good enough, we d like something DC perfect. So CLC.

Let's take the schematic I suggested and I'll explain it along.

The upper circuit is only the amplification unit. Power is only inserted at two points: The center tap of the OPT and the primary of the interstage transformer. This inserted voltage is generated and filtered in the lower circuit, the PSU. In this case, the power transformer generates 230V which are then rectified by a bridge rectifier consisting of four diodes. What that does is basicly inverting one of the half waves into positive, so that you have a pulsed DC. To smooth that out, you have a LCL filter for the output stage and another RC-filter for the input. In the end you have a more or less smoothe DC to run your amp with.

You would go for a tube rectifier?

Yes, I definitly would. This is a matter of disagreement though within the tube fan community. Personaly I like tube rectifiers and will always use them.

And for the transfos? I need one output transfo (hammond or another) per channel, and I also need the "main" one, the one that gives the power.
This one is not clear in its characteristics, cause i haven t found yet any schematics of a ultra linear class A stereo kt88 push pull.

You need one main transformer if you build a community PSU (which I think you should and want to do). The quality of this is not completely unimportant, but not that critical. I would try finding a toroid winder localy. If you don't find one, the german ones surely ship to spain. What you want to look at very carefuly are the OPTs. Their quality basicly determines the quality of the amp. So I strongly disagree with Hammonds and point to the manufactorers I mentioned earlier.

Well, i still have NO schematics. The one you suggested me, did you try it? Or is it just the one you think would be perfect?

No, I have not tried it. But I plan to build some varity of it. I'm currently playing with the schematic changing it to my taste. But I'll have quite some time to think about it, since I've got no money for another build at the moment. I can show you, what I've come up with so far, adapted to UL and tube rectification (and - for you very important - with a complete grounding scheme):

An externally hosted image should be here but it was not working when we last tested it.

I can't account for the PSU to be perfect though.

About the chassis: the input selector switch has 3 positions. It s supposed to work.
Is it THAT hard to put another switch? I mean: the hole is done, the knob is there, shouldn t it be fine to put another switch whose diameter is compatible with the knob?
Too hard? (Then I would follo your advice)

I can't tell you that without having seen it. Those things have a habbit of not being standard interchangeable parts. The main thing is that a good input selector costs real money. The cheap stuff will drive you crazy. Look for ELMA, they cost around 50€.

]I began this. When my mind is set, full and ready, I ll gather parts. Then I ll see my friend. This is going to be long...

That's good. Take your time, don't rush it. That helps avoiding mistakes.

 

[iorga]

If I understand correctly, you want to build a stereo amplifier (two channels, one power supply) with the option to make it a bridged mono amplifier. I hope that's what you mean because otherwise I have no idea what youre talking about and why.
So I drew up the basic way to do this with a 2-position 3-way switch:

Yes that s it!

OK;
for the other hints and theory, ... great. A lot to read.
I m looking at the lundhal transformers, as you seem (and everyone out there) to say the OPT are KEY (bottleneck) in scheme: there s a lot a lot a lot of things.
I also saw the Amity and Aurora from Olsen page (nutshell) (are they good? i think i remember they need, NEED, a pre amp -that was not my idea : too expensive and too long and too ambitious maybe as a first project (am i wrong?)

Also these (one of them being the one you suggested )
Push-Pull Amplifier
Push-Pull Amplifier

The ones you suggest use the Lundhal OPT and more over they seem to be nice OPTs... I think this would be a nice beginning.

You enlightenmed me with the initial switch and the common PSU. I guess I should begin there.

(oh: and i don t need any kind of LED in the power switch: the tubes glowing would be enough).
I also read that there are some mods done to let the tubes warm properly: some kind of security for not shortening their lifetime. Is this hard to implement?

I keep reading.
Thanks for your support.
I have a huge amount of things to breathe before going further.
And I promise you: once I have the chassis, I post pics and pics and pics for you to advise me.
But first things first:
1/ schematics and theory (PSU and main AMP part, DRIVER, tubes, cathode bias or fixed bias or whatever (still no idea of the pros and cons and theory underneath)
2/ mental thinking of the layout once the chassis is here (and still theory)
5/ last mods of the scheme and slowly material gathering (once i m sure of the scheme) and theory
4/ security post read and read again
3/ scheme being checked just in case, by more experts.
6/ once everything is settled on, small series of soldering (I d love this being done in August, but I think this could be easier for December, i ll have more time then) with the supervision of an experimented guy. Anyway: I think the key fact is here NOT to fix any kind of deadline: it will done when it is done. If you fix a deadline you are probably fixing a deadtime...

I keep on reading.
Thanks for sharing the mods of the scheme you suggested, this will be useful -one day-!

 

[iorga]

I have a doubt: I read in jacmusic.com the following:



When measuring the plate current of a tube, it is generally not desired that the signal path will go through the ampere meter. Reason is, that Ampere meter has a coil inside, and any Audio signals should go through this. This is to prevent frequency dependent effects, and other kind of distortion. Besides not all low cost meters will indicate precise.
Yamamoto has found a nice solution for this. The meter is connected in parallel to the cathode resistor, and the meter has a high impedance. The nice part is, the impedance of the meter is choosen very convenient for the end-user. It is choosen in such a way, that the series resistor you need is exactly 100x the Cathode resistor of the amplifier. Like this you need to make no special calculations, and the meter is always calibrated correct.



Well, I plan to get an old chassis of a 2x60 amp. to reuse the vumeters, the pots etc.
But what if the vumeters can t be properly plugged? What if the input elector or the main volume wheel is cracking?
I mean: i ll have to change them... Is it worth paying the chassis? Will I be able to reuse it? I m not qualified enough to see whether I should buy it...
It s sold 100 euros... Is it expensive? (i mean: nice vu meters, nice potentiometer like those found at jacmusic.com, and chassis, laser painting, and blablabla... this will be expensive too, won t it? How much would you pay (it s said to be in perfect condition but it s almost 30 years old)

 

[iorga]

another thing:
I previously asked about the Amity and Aurora: correct me if i m wrong, but after deeper reading, i think they re also using some kind of SRPP. (shunt regulation). Right?

I asked for the input function selector and the old amp chassis reusing: you told me "ELMA" and I saw at jacmusic that YES they're freaking expensive, 75€ a nice pot!
You say a switch could be 50. I may be reuse then the old chassis PROVIDED those buttons work.

One last:
the circuit you show is 20W. This is not that much (it s much much much) but I mean: i thougt KT88 in PP were between 45 and 60W. Is that due to a possible Class A operation of the circuit you gave me?
The outcome is about the vumeters of the old amp, supposedly 2x60 RMS (doubts): will they show something if it is only 20W? By the way, what i wrote about the vus, do you think it s not worth/ advisable to use them?

No need to answer for the A class operation, cause this is just an assumption, and i know by reading more and more that i ll get that answer by myself.

Thanks again for your help.

I have calculated the total price of my chassis and the main parts (no cables, banana plugs, silver wire): 1100 euros!
2 output transfos + pcb and 1 power transformer, 4 paired matched KT88 gold lion, 1 EC887 from Philips; my chassis...
This is a lot! Isn t it?
Am i wrong somewhere?

PSU:
Electronics 9 for more info.
I read more about the PSU: transformer rectifier filter regulator. this page is EASY and clear:THE BASIC POWER SUPPLY

I read that tube rectifier are not efficient. You prefer them. I don t really care: this is a very first project.
I never heard a sold state rectified. And I liked the tube rectifier one I listened to. A redson amp. So no need to go back.
I don t get that "half EC887" thing. I need one of these for the stereo amp? Or do I need one per channel? I don t get out I could take half of it. I guess more and more reading

I d also like to put in that amp some kind of tube protection (a time delay for the tubes to be fully operative).
Is that hard to do? I m afraid I m not that clear. I ll try to send you the exact terms of what I mean.



I think i ll reach at some point a WONDERFUL scheme. Thanks to you. I m learning SO much, this is funny. Finally applied electronics (not those I studied 11 years ago without the experience and distance). I can go back to my classes then. Funny funny funny.

Once the scheme is there, well, I ll buy the parts. First, the chassis - then getting scheme and theory. If i get it, i ll probably try to find a local transformator provider/maker here in Barcelona, but i bet i ll finally buy the whole bunch of stuff from jacmusic, in Germany.

Cheers!



EDIT:
http://www.lh-electric.4t.com/tbprimer.html -> i got now how the valve RECTIFIES the AC current! Coooool. The diode
As for Class A operation:http://www.lh-electric.4t.com/vt_primer5.html but this is still out of my reach. I guess I m tired. Next week.
Any suggestions for the scheme provided in the other post is welcome.

 

[Herr Grau]

I m looking at the lundhal transformers, as you seem (and everyone out there) to say the OPT are KEY (bottleneck) in scheme: there s a lot a lot a lot of things.

The ones you suggest use the Lundhal OPT and more over they seem to be nice OPTs... I think this would be a nice beginning.

I think it's pretty safe to assume that Lundahl makes outstanding transformers. I would recommend though not to buy the power transformer and the chokes out of their sortiment. They are very expensive and do the same thing as their cheaper brothers.

I also saw the Amity and Aurora from Olsen page (nutshell) (are they good? i think i remember they need, NEED, a pre amp -that was not my idea : too expensive and too long and too ambitious maybe as a first project (am i wrong?)

Those are 300B Amps with a lot of iron to them. That's gonna be roughly a 1000€ extra. I think, this'll propably disqualify them. If you should like the Olsen approach, then do it right, he just copied from Sakuma as far as I can tell.

Also these (one of them being the one you suggested )
Push-Pull Amplifier
Push-Pull Amplifier

The second one lacks all the quality I like in the first one. If you need to build a capacitor coupled amp with tube phase splitter, try one of the circuits of the Mullard 5-20 topology currently discussed in this very forum.

I also read that there are some mods done to let the tubes warm properly: some kind of security for not shortening their lifetime. Is this hard to implement?

No, it can be done with a simple switch, but using a directly heated tube rectifier, you don't need it at all.

I have a doubt: I read in jacmusic.com the following:
[...ad text...]

Yeah, they have to sell their products too. Bias voltage is in most cases measured across the cathode resistor. But this too is only necessary at all if you use fixed bias, which is technicaly better, but requires a complete own PSU instead of on resistor and one capacitor. So I wouldnt worry about the VU meters, build a cathode bias amp and maybe later attach the meter to the PSU or something, just for laughs and giggles.

Well, I plan to get an old chassis of a 2x60 amp. to reuse the vumeters, the pots etc.
But what if the vumeters can t be properly plugged? What if the input elector or the main volume wheel is cracking?
I mean: i ll have to change them... Is it worth paying the chassis? Will I be able to reuse it? I m not qualified enough to see whether I should buy it...
It s sold 100 euros... Is it expensive? (i mean: nice vu meters, nice potentiometer like those found at jacmusic.com, and chassis, laser painting, and blablabla... this will be expensive too, won t it? How much would you pay (it s said to be in perfect condition but it s almost 30 years old)

It's as if you ask me again and again "I can buy a car! Should I?"
Without seeing it or trying the parts, I can't tell you anything.

another thing:
I previously asked about the Amity and Aurora: correct me if i m wrong, but after deeper reading, i think they re also using some kind of SRPP. (shunt regulation). Right?

The SRPP mentioned doesn't stand for shunt regulated, but series regulated. It's a circuit topology. And it's not used by Olsen.

I asked for the input function selector and the old amp chassis reusing: you told me "ELMA" and I saw at jacmusic that YES they're freaking expensive, 75€ a nice pot!
You say a switch could be 50. I may be reuse then the old chassis PROVIDED those buttons work.

Trust me, you don't want cheap ****. If you need a new selector, stick to ELMA.

One last:
the circuit you show is 20W. This is not that much (it s much much much) but I mean: i thougt KT88 in PP were between 45 and 60W. Is that due to a possible Class A operation of the circuit you gave me?

I don't think so, it's propably due to the single triode driver stage and very likely to the triode connection of the output tubes (which I already changed in my schematic to UL, which should give you some more power). I think 20W should be more than enough to drive most speakers. But it does depend on your speakers. If they are less efficient than, say, 87dB, it could be to little. I'm guessing a little bit on the numbers here though. But most people can drive their speakers with a <5W SE amp.

I have calculated the total price of my chassis and the main parts (no cables, banana plugs, silver wire): 1100 euros!
2 output transfos + pcb and 1 power transformer, 4 paired matched KT88 gold lion, 1 EC887 from Philips; my chassis...
This is a lot! Isn t it?
Am i wrong somewhere?

You could say so. You don't need silver wire. You don't need Gold Lion tubes.
If silver wire makes any difference at all is very questionable. Gold Lion tubes are made by Relektor Russia and most likely very much alike to the Electro Harmonix tube from the same manufactorer. Save the money and invest in good OPT.
But other than that: No, you're not wrong. There is a price tag on a good quality PP amp and it's somewhere around 1000€. The iron and tubes alone just cost money.

What do you mean by PCB? Where do you see a EC887? I'm confused.

I don t get that "half EC887" thing. I need one of these for the stereo amp? Or do I need one per channel? I don t get out I could take half of it. I guess more and more reading

Many small tubes are twin triodes, meaning that they have two complete triode systems inside. You just use one for each channel.

 

[iorga]

Quote:

"What do you mean by PCB? Where do you see a EC887? I'm confused."

I mean that can be read there:
Push-Pull Amplifier
which is:
Components All the audio transformers used in this project are Lundahl products:

• LL1623/PP + PCB_B Output transformer
• LL1649 Power supply transformer
• LL1638/4H 500mA Power supply choke
• LL1660/10mA Interstage transformers

it seemsto be some kind of 0-4-8 ohms "adapter/adjuster"

Quote:

"You don't need Gold Lion tubes."

I was first going for EH but I read in Bruce's posts that he had many many problems pairing them and making them work perfectly together. And this was only happening with EH. Not with others. He tried, as others, many tubes, and a lot of guys agree the KT88 from JJ or Gold Lion are great ones.
Honestly, this is not the whole money: the transformers are expensive:
About this, you say

"I would recommend though not to buy the power transformer and the chokes out of their sortiment. They are very expensive and do the same thing as their cheaper brothers."

i don t get what do you mean by this. And I read on the pp3 page that I needed

• LL1623/PP + PCB_B Output transformer
• LL1649 Power supply transformer
• LL1638/4H 500mA Power supply choke
• LL1660/10mA Interstage transformers

* LL1623/PP + PCB_B (pour 0 4 8) Output transformer 195 € X 2!!
* LL1649 Power supply transformer -> 154 €
* LL1638/4H 500mA Power supply choke 85,43 €
* LL1660/10mA Interstage transformers 92 € How many of them?

What chokes/power transfos are you speaking about? Are they in this list?

Which are according to you a bit too expensive?





The EC887 thing... oops
EC887: the tube rectifier Bruce uses in his dual monoblock kt88 push pull amp. I meant E187CC SORRY!!!!!


pp3 or pp1 scheme: pp3 is better than pp1. And you took pp3 and added UL. So i ll part from what you gently suggested. And this is great if this gives extra power. Again, this is not needed (speakers planned: supravox 215 Bicone, Signature or RTF64 - 93 or 96 db) in terms of speaker efficiency. It IS in terms of vumeter possibly (and probably useless utility) from the other amp rated 2x60. (don t think so - anyway, not the big point here)
Plugging it will be some kind of "funnytoy" more than the fundamentals of the circuitry.


as for the switch, thanks for pointing that DHT rectifiers don t need such a protection (didn t know).

About the Olsen design: ah ah ah 1000€ is already hard. So 2000 won t do. You guessed right I forgot it asa you mentioned it thanks again for your expertise and feedback. Heartidly welcome.

Last one

build a cathode bias amp and maybe later attach the meter to the PSU or something, just for laughs and giggles.

Great! I didn t really know what to choose for the BIAS.

Types of Grid Biasing.
There are two main types of biasing - Fixed and Self. In a tube circuit that uses Fixed-Bias, the bias
voltage is supplied from a separate power source shown in Fig.2-1

An externally hosted image should be here but it was not working when we last tested it.

The most common type of biasing is called Self-Biasing.
There are two methods of self-bias: Cathode Biasing and Grid-Leak Biasing.

Cathode Bias.
In this type of biasing, a cathode resistor is used. Grid voltage is kept at ground potential with a high value
Rg resistor. A voltage drop across the cathode resistor Rk makes the cathode go POSITIVE relative to the grid.
[FONT=Arial, Geneva]
The same effect as making the grid NEGATIVE. Fig.2-2 shows cathode biasing method.

An externally hosted image should be here but it was not working when we last tested it.

[/FONT]

[FONT=Arial, Geneva]
seen here: Vacuum Tube Theory - Tube Biasing[/FONT]
Thanks, thanks, thanks.

 

[Herr Grau]

Quote:
I mean that can be read there:
[...]
What chokes/power transfos are you speaking about? Are they in this list?

Which are according to you a bit too expensive?

Ah, I see. Didn't know that the Lundahls need special PCBs.

I think you are making about the same mistake I did when I started and stick very intensly to the exact components listed. That's not necessary.

Although I strongly recommend that you use the described interstage transformer, you can choose a different OPT as long as it is specified to about 5k to 5,5k Raa and cathode bias. If I were you, I would start looking for something with Ultralinear taps in the range of 40 to 43% and not 33 like the suggested Lundahl. That didn't matter to the designer when he specified the LL1663, because he planned it only using triode mode. And for the power transformer and chokes you are really free to buy anything that fits the same specifications (VA rating, secondarys). And I would, because Lundahl chokes are very expensive (about three times what I pay for a choke). The power transformers aren't that expensive, but still no bargain. I'd rather choose a toroid from Rondo-Müller (sourcable via askjanfirst.com), they have a higher efficiency, are more compact and have far less magnetic stray field AND are wound to your exact specifications without being any more expensive.

And if you plan on using a tube rectifier, then you need a 5V heater winding anyway which the specified Lundahl doesn't have.

The EC887 thing... oops
EC887: the tube rectifier Bruce uses in his dual monoblock kt88 push pull amp. I meant E187CC SORRY!!!!!

I think you mean E182CC

pp3 or pp1 scheme: pp3 is better than pp1. And you took pp3 and added UL. So i ll part from what you gently suggested. And this is great if this gives extra power. Again, this is not needed (speakers planned: supravox 215 Bicone, Signature or RTF64 - 93 or 96 db) in terms of speaker efficiency.

You'll part from my suggestion? Did you use that word incorrectly or didn't I understand the sentence?

However, I currently would prefer UL over triode based on what I read published by Stanly White:

The problem is that loudspeakers (the intended load of the output transformer) are not a resistive load at most of the used frequencies of a loudspeaker. When a loudspeaker is attached to an output transformer instead of a resistive load, the load line of the output tubes goes crazy, whether the tubes are triode or pentode connected. Neither triode or pentode mode operate well with loudspeakers. This is why all performance tests are carried out with resistive loads.
Keroes and Hafler invented the tapped screen mode of operation of output tubes. By connecting the output tube screens to a tap at an appropriate winding location, the output tubes put out constant power into a load, rather than either constant voltage or constant current.
Distributed inductances and capacitances in the speaker circuit cause the varying impedance of a loudspeaker over the used range (see: Acoustical Engineering--Harry Olson, Chief Engineer, Audio, RCA. Harry also taught acoustics at Columbia University when his book was written.) Olson's book is the bible of the audio industry to this day). As is easily shown, inductances and capacitances are reactive in nature. They generate what is known as reactive power. You cannot hear reactive power. What you hear with reactive power is phase shift, which in stereo blurs the stereo effect.
By operating in a constant power mode, the output REAL power from a loudspeaker is more constant. The frequency response is more linear. It is obvious that "ultra-linear" (constant power out) is a better mode of tube operation than either constant voltage or constant current.

thanks again for your expertise and feedback. Heartidly welcome.

I'm just sharing what I very recently learned (and still do) by building my amp and am quite lucky that your questions are still within the range of what I do know. Still, that hardly makes me an expert.

 

[iorga]

You'll part from my suggestion? Did you use that word incorrectly or didn't I understand the sentence?

I mean: i ll take it as a starting point...


As for the chokes and prices, and every thing...

WOW
this is great. i ll have to look properly then, cause the lundhal are crazily expensive and blow the budget, and as you say, need a pcb and for the other arguments, ... i need to read more to get them
So, good night and thanks again!

btw i don t think my questions will make you hesitate, cause i don t plan going too deep: i know from experience that this is a vice, this is dangerous,this is a non ending story, and this is ALWAYS too expensive. i just cant. So I want to get the basics, the ideas, the reasons of the choices, understand what is being done and why i ll be happy for the choices and money and time spent and implication, but no need to dig further... cause i ll end spending loads of money and don t want to enter in the frustration never ending cycle...
And i m sure you ll know all my doubts

 

[Herr Grau]

Feel free to ask away. I'll tell you when I don't know something.

Crazily expensive you say? Hehe, ohhh there is more...
I advised you not to take the Lundahls because I consider the UL taps not ideal, not because I found them too expensive. I just said: Save money with the chokes and power transformer and rather put that money into good OPTs.

Here are some suggestions:
Amplimo Toroidal OPT (Menno van der Veen's transformers)
Sowter (you'd have to ask for that one with UL taps, won't be a problem)
Tribute (no idea how much they'll cost)
AE Europe(no idea about prices either)
IG Präzisionswickeltechnik (formaly Shinrock transformers)
Highend Series from Welter Electronic
Majestic Inc.
etc etc.....

And if you are willing to go outside europe, there is Tamura and Hashimoto from Japan (they have local dealers) and O/Netics from Washington, USA, who I have bought my OPTs from.

 

[iorga]

Hi,
me again.
I have a question: what do you personnally think about the Edcor opt?

Another one: for a toroidal power trannie, do you have some favourites?
Thanks!

 

[Herr Grau]

If you want to build something that works for 200$, Edcor is a valid choice. But they are realy low end iron, so if you are planning on keeping the amp for indefinite time, invest in good OPTs (I say it again and again) and not the budget stuff.
I personaly like (and therefore use exclusivley) the toroids made by Rondo-Müller, supplied by Jan Wüsten. They are custom wound to your specifications. Theyre no bargain, but very affordable.