Hi people,
it's been a while since I've built my last project and needed your help.
But at last I managed to build my Loesch-style Phono-pre.
Now it's time for a 'real' amp and after hours and hours of research I finaly setteled for this design:
Franz Wichlas KT88 UL PP Amp "Red Hot"
Schematic
Schematic PSU
Firstoff: Does anyone see anything that should be done differently?
Then I got me some stupid questions (since propably noone will remember: I can build a circuit, but I merely understand the basics of electronics):
1. How much power do the unmarked resistors have to be able to tolerate? 0,5W? 1W?
2. I would like to use tubes for rectification (because of the 'inbuild' slow start and the so called "soft PSU" resulting from rec tubes) and build the amp as mono blocks, too. Other than the fact that I'll only need one 6,4V-lane per transformer: Can someone please re-write me the PSU-scheme?
(I just read at Emission Labs (here) that choke load should be preferred to capacitor load with rec tubes. If that's true, perhaps it's worth mentioning/implementing?)
I searched all over the net, but I couldnt find an explaination of how to calculate a filter circuit for a PSU. If you have something like that or could explain it, so that even I could understand, that would propably do it, too. But I guess, that'd be even more work...
Thanks in advance guys,
regards from Germany,
Herr Grau
(P.S. whoever helps me earns free drinks whenever in my reach...
)
it's been a while since I've built my last project and needed your help.
But at last I managed to build my Loesch-style Phono-pre.
Now it's time for a 'real' amp and after hours and hours of research I finaly setteled for this design:
Franz Wichlas KT88 UL PP Amp "Red Hot"
Schematic
Schematic PSU
Firstoff: Does anyone see anything that should be done differently?
Then I got me some stupid questions (since propably noone will remember: I can build a circuit, but I merely understand the basics of electronics):
1. How much power do the unmarked resistors have to be able to tolerate? 0,5W? 1W?
2. I would like to use tubes for rectification (because of the 'inbuild' slow start and the so called "soft PSU" resulting from rec tubes) and build the amp as mono blocks, too. Other than the fact that I'll only need one 6,4V-lane per transformer: Can someone please re-write me the PSU-scheme?
(I just read at Emission Labs (here) that choke load should be preferred to capacitor load with rec tubes. If that's true, perhaps it's worth mentioning/implementing?)
I searched all over the net, but I couldnt find an explaination of how to calculate a filter circuit for a PSU. If you have something like that or could explain it, so that even I could understand, that would propably do it, too. But I guess, that'd be even more work...
Thanks in advance guys,
regards from Germany,
Herr Grau
(P.S. whoever helps me earns free drinks whenever in my reach...
)
Which design would you recommend?
I'm searching for the definite amp for the next many years, so I'm more than willing to consider every option, of course searching for the best value. I just need a complete, working schematic which I can 'cook' the amp from.
If you don't think the design is 'the thing', than the PSU-work isn't necessary now.
I don't have too many wishes, I want a KT88 PP Amp with non-rare pre-tubes (personaly I do like the 6SN7, but thats not so important)(yeah, it shouldn't need an external pre-amp...) and tube rectification. It would be most terrific if the design would work with one of the standard supplied Sowter OPTs...
I'm searching for the definite amp for the next many years, so I'm more than willing to consider every option, of course searching for the best value. I just need a complete, working schematic which I can 'cook' the amp from.
If you don't think the design is 'the thing', than the PSU-work isn't necessary now.
I don't have too many wishes, I want a KT88 PP Amp with non-rare pre-tubes (personaly I do like the 6SN7, but thats not so important)(yeah, it shouldn't need an external pre-amp...) and tube rectification. It would be most terrific if the design would work with one of the standard supplied Sowter OPTs...
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The 6SN7 is a fine tube for an input stage, as long as you run it the way it wants to be run for high swing. With this topology, the first stage has to swing the entire drive amount because the phase splitter is unity gain.
One thing to be aware of- if you have an ultralinear output stage with no feedback, the source impedance will be rather high. Some speakers are fine with that, some aren't.
I'm not terribly familiar with published diy designs, but I'd start by checking out Pete Millett's site and tubelab.com.
One thing to be aware of- if you have an ultralinear output stage with no feedback, the source impedance will be rather high. Some speakers are fine with that, some aren't.
I'm not terribly familiar with published diy designs, but I'd start by checking out Pete Millett's site and tubelab.com.
I had checked the before mentioned sites, I checked jogis-roehrenbude.de too and googled quite a bit.
I found this one, but its a Williamson Circuit and I've read more than one post of you describing its immanent problems. So I threw that one out, too.
And of course I've stumbled across the Quad II which generaly was considered a very good amp. What about that one? How complicated would it be changing the circuit from KT66 and GZ32 to KT88, GZ34 and a senseful OPT? (schematic)
I found this one, but its a Williamson Circuit and I've read more than one post of you describing its immanent problems. So I threw that one out, too.
And of course I've stumbled across the Quad II which generaly was considered a very good amp. What about that one? How complicated would it be changing the circuit from KT66 and GZ32 to KT88, GZ34 and a senseful OPT? (schematic)
For a KT88 there is also "Bill" from the Triode Dick's Page website.
look at the menu on the right for the TD's translation pages or something simailar for English. There is also a mono bloc version called (Trumpets blaring now) Mono Bill.
I have not heard it so cannot say what it sounds like but its 6SN7 input to ECC99 drivers
There are literally cazillions of circuits out there for KT88 PP (don't use Google Image search, you have been warned) but if you suffer from procrastination as I do, I would suggest only looking at perhaps half a dozen and then decide otherwise you will be forever comparing them against one another.
Good Luck
look at the menu on the right for the TD's translation pages or something simailar for English. There is also a mono bloc version called (Trumpets blaring now) Mono Bill.
I have not heard it so cannot say what it sounds like but its 6SN7 input to ECC99 drivers
There are literally cazillions of circuits out there for KT88 PP (don't use Google Image search, you have been warned) but if you suffer from procrastination as I do, I would suggest only looking at perhaps half a dozen and then decide otherwise you will be forever comparing them against one another.
Good Luck
While I don't think this is what Sy was suggesting it may be of some help nevertheless.
Williamson amplifier
An Ultra-Linear amplifier by David Hafler & Herbert I Keroes
see also
Audio amplifier with improved stability - Patent 4066975
Williamson amplifier
An Ultra-Linear amplifier by David Hafler & Herbert I Keroes
see also
Audio amplifier with improved stability - Patent 4066975
I know and after about ten or twenty hours of research in the last few days I feel like I've seen all of em. I basicaly excluded everything that used tubes too rare, everything that used only one split tube in the pre-stage, everything that I spontaniously disliked of some other reason...
Thanks.
(Regarding the Quad, I just read that the design only plays out its great cards if hooked up to a very specificaly designed OPT.. So screw that too.
)I believe it is Sowter in the U.K that made a duplicate or perhaps Woodside, in any case I remember a reproduction transformer being manufactured for the Quad II and also an anniversary and or a reissue amp. Sorry I cannot be more specific as this is all from memory. The only thing I remember is the primary was 10K and it was quite a special wind.
If I can find any further info I will let you know.
If I can find any further info I will let you know.
Both of these do Quad II replacement OPT's.
Woodside Electronics
Telephone/Fax: +44 (0) 1758 741026
Email: m.davis@virgin.net
Sowter Audio Transformers
E. A. Sowter Ltd, PO BOX 36, Ipswitch. IP1 2EL, England, UK.
Telephone: +44 (0) 1962 620135
Fax: +44 (0) 1962 870299
Email: techsupport@sowter.co.uk
Web: SOWTER AUDIO TRANSFORMERS
Quad output is model 8778
Woodside Electronics
Telephone/Fax: +44 (0) 1758 741026
Email: m.davis@virgin.net
Sowter Audio Transformers
E. A. Sowter Ltd, PO BOX 36, Ipswitch. IP1 2EL, England, UK.
Telephone: +44 (0) 1962 620135
Fax: +44 (0) 1962 870299
Email: techsupport@sowter.co.uk
Web: SOWTER AUDIO TRANSFORMERS
Quad output is model 8778
Franz-Wichlas-Red-Hot-PP-UL/Red-Hot-PP-UL.htm
Absolute minimum bits & spec, as per German schrift (great lingo). Amp is a reasonable start but later can be massively improved apon....Comment 4 on the handworking: < my woman is quite helpful with tasks around the bench> Rather fun and comical for a matched pair:-(More than mine is...)
I'm ingrained with Williamson, lock-stop-and-barrel. No change.
richy
Absolute minimum bits & spec, as per German schrift (great lingo). Amp is a reasonable start but later can be massively improved apon....Comment 4 on the handworking: < my woman is quite helpful with tasks around the bench> Rather fun and comical for a matched pair:-(More than mine is...)
I'm ingrained with Williamson, lock-stop-and-barrel. No change.
richy
Well, if there are no rudimental objections against Williamson...
Then the new favourite design is the so called 'Ultimate' Amp.
Let's wait for SY's article before deciding anything about changes.
Is there any problems with transfering the PSU of a Dynaco Mk III (schematic) into this one?
(I found most KT88-PP-Amps working with less plate voltage then this one, the MK III too. Since I do not know what that changes exactly, I ask before I do something (most likely stupid).)
If so, a choke of which specs would you recommend?
Second question is if I can replace the OPT (Pliton 4142) with a Sowter U070 since it has 4,5kOhm instead of 4k. Or would you have to adjust some things?
Well, that's that for today... Its 3:46am over here, propably bed time...
Then the new favourite design is the so called 'Ultimate' Amp.
Let's wait for SY's article before deciding anything about changes.
Is there any problems with transfering the PSU of a Dynaco Mk III (schematic) into this one?
(I found most KT88-PP-Amps working with less plate voltage then this one, the MK III too. Since I do not know what that changes exactly, I ask before I do something (most likely stupid).)
If so, a choke of which specs would you recommend?
Second question is if I can replace the OPT (Pliton 4142) with a Sowter U070 since it has 4,5kOhm instead of 4k. Or would you have to adjust some things?
Well, that's that for today... Its 3:46am over here, propably bed time...
"Ultralinear Operation of the Williamson Amplifier," Hafler and Keroes, Audio Engineering, June 1952. It's reprinted in "Audio Anthology, Vol 2" from Old Colony. There's things that one might do differently these days (e.g, power supply regulation), but built as drawn, this is a classic circuit which will do well for you. The original used 6L6-type tubes, but with KT88, 4-5k plate-to-plate, and 450V on the output stage plates, you should be good for a solid 40 watts. The amp schematic you link to is taken from this article almost part for part, but for the output stage. It looks like a good direction to go in.
"The low frequency time constants of the original circuit's interstage coupling networks were the same for both networks. This is not particularly desirable in a feedback amplifier since a given frequency loss is accompanied by maximum phase shift. Separation of the time constants permits less phase shift for the same frequency loss. Increasing one pair of coupling capacitors from .05uF to .25uF gives a five-to-one ratio of time constant for the two pairs of networks and increases the low frequency stability margin at nominal increase in cost."
"The low frequency time constants of the original circuit's interstage coupling networks were the same for both networks. This is not particularly desirable in a feedback amplifier since a given frequency loss is accompanied by maximum phase shift. Separation of the time constants permits less phase shift for the same frequency loss. Increasing one pair of coupling capacitors from .05uF to .25uF gives a five-to-one ratio of time constant for the two pairs of networks and increases the low frequency stability margin at nominal increase in cost."
Langford-Smith (...the guy behind the Radiotron Designers handbook...) colaborated on a redesign of the Williamson: http://www.mif.pg.gda.pl/homepages/jasiu/eka/wil/williamson-807.pdf
(Note: the page / pdf file sometimes does not load, and you may have to 'refresh / F5' it in your internet browser to get it to load).
The amp is rated to 15W, but regard it as a 10W amp and it seems very clean. Their notes state very low and consistent distortion from 1 to 10W.
(Note: the page / pdf file sometimes does not load, and you may have to 'refresh / F5' it in your internet browser to get it to load).
The amp is rated to 15W, but regard it as a 10W amp and it seems very clean. Their notes state very low and consistent distortion from 1 to 10W.
Sy, are you suggesting to change the low frequency time constant in the "Ultimate Amp or leave it the way it is?" The feedback in this circuit is accomplished with a 39k ohm resistor.
I posted a thread last week on this exact amp. It's the most appealing circuit I've seen for a DIY 6SN7/KT88 PP amp capable of producing >25W.
http://www.diyaudio.com/forums/tubes-valves/153496-vtv-push-pull-6sn7-kt88-amp-diy-china.html
Eli D. pointed out that the Williamson circuit requires top notch transformers to prevent unstable phase shift oscillation. He says that the Mullard circuit is more stable in this regard. Unfortunately, I lost my Mullard Circuits book that I bought from Parts Express, so I can't access any schematics.
Furthermore, a set of Plitron transformers alone in the VTV Ultimate Amp is around $800. I was even considering buying an integrated amp from China and modifying it for less money than a DIY project, but then again, that wouldn't be the point. I've thought about using the Edcor CXPP60-8-4.2K for the OPT which has a 4.2k ohm primary (very close to 4k ohm). It's $62 vs $316!
Let us know how the build turns out...
I posted a thread last week on this exact amp. It's the most appealing circuit I've seen for a DIY 6SN7/KT88 PP amp capable of producing >25W.
http://www.diyaudio.com/forums/tubes-valves/153496-vtv-push-pull-6sn7-kt88-amp-diy-china.html
Eli D. pointed out that the Williamson circuit requires top notch transformers to prevent unstable phase shift oscillation. He says that the Mullard circuit is more stable in this regard. Unfortunately, I lost my Mullard Circuits book that I bought from Parts Express, so I can't access any schematics.
Furthermore, a set of Plitron transformers alone in the VTV Ultimate Amp is around $800. I was even considering buying an integrated amp from China and modifying it for less money than a DIY project, but then again, that wouldn't be the point. I've thought about using the Edcor CXPP60-8-4.2K for the OPT which has a 4.2k ohm primary (very close to 4k ohm). It's $62 vs $316!
Let us know how the build turns out...
Second question is if I can replace the OPT (Pliton 4142) with a Sowter U070 since it has 4,5kOhm instead of 4k. Or would you have to adjust some things?
Well, that's that for today... Its 3:46am over here, propably bed time...
The Plitron is a gapless core: the Sowter is conventional E&I. Swapping to the Plitron in a Williamson can be done but one effectively alters the Bode map so the loop gains when global nfb is used have to be re-worked to avoid LF instability. Reminds me of the Eckland amp:may be worth examination.
richy
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