I'm deparately seeking comment from you experts so this project can begin NOW! After alot of research, and reading, and input here. I have decided once and for all on topology, and output power.
I should first state that i'm quite green, but have decent build skills, and some general idea how tube amps work. I am not able to design, and trouble shooting without hand holding would be very limited. I have one ST70 New build under my belt.
I have decided on what Eli had suggested. A modified mullard 5-20 LTP type driver with some type of CCS in the tail. Outputs will be 2 KT88's run Ultralinear, and output goal is about 60W. Builds will be constucted on custom mono block chassis. All parts will be new, and of good to better quality. The build should be as simple as possible while still offering quality equal you better than commercial offerings of the same class. Cost is not a concern within reason.
I'm looking at 3 options to get started, and would like the disscussion limited to those option. I'll just confuse myself otherwise.
Option 1
Was created by forum member Zafir 1983 by modifing an existing schematic with input from all the Gurus on this forum. IT meets all the requirement except complexity. I have no idea how to design a first class PS, or pick the transformers. A fully P2P project could be over my head. However, I know you guy's like the Schematic. Wavebourn said it was on of the best for PP he has ever seen! Another issue is that it has not been put on a scope and tested. Also there are no other proven builds for refference. This one sounds very risky for a newby to me Here it is.
404 Not Found
( Anyone willing to help with this one? that would mean a full PS schematic, and recommended Transformer model numbers!)
Option 2
would use a Mark III upgrade board from Diytube, and very loosely follow the rest of the MarkII schematic. . I used this build option with the ST 70, The results were great, and this may be more within my ability. Shannon has created a Modified 5-20 circuit that includes the CCS. The key here is I can use the Comlpete MarkII schematic as a great guide. Repro Trannies are availible, and the power supply could be upgrade, or replaced with a SDS upgrade board. Some here didn't like the driver tube choices (12ua7), but some limited options are availble (12BHt), and even some 6 volt options. This one is very doable for me.
Here's the schematic.
http://www.diytube.com/unidriver/poseidon.pdf
Option 3 would be the same as option 2 except using the Triode Mark III replacement board. This appears to also be a 5-20 type driver? I don't see where a CCS is used on this one but it does seem to have move driver tube options. I can't find a schematic, but here's the info.
Driver Boards for Dynaco Mark II and Mark III
Any comments keeping in mind that my design / electronic skills are limited?
I should first state that i'm quite green, but have decent build skills, and some general idea how tube amps work. I am not able to design, and trouble shooting without hand holding would be very limited. I have one ST70 New build under my belt.
I have decided on what Eli had suggested. A modified mullard 5-20 LTP type driver with some type of CCS in the tail. Outputs will be 2 KT88's run Ultralinear, and output goal is about 60W. Builds will be constucted on custom mono block chassis. All parts will be new, and of good to better quality. The build should be as simple as possible while still offering quality equal you better than commercial offerings of the same class. Cost is not a concern within reason.
I'm looking at 3 options to get started, and would like the disscussion limited to those option. I'll just confuse myself otherwise.
Option 1
Was created by forum member Zafir 1983 by modifing an existing schematic with input from all the Gurus on this forum. IT meets all the requirement except complexity. I have no idea how to design a first class PS, or pick the transformers. A fully P2P project could be over my head. However, I know you guy's like the Schematic. Wavebourn said it was on of the best for PP he has ever seen! Another issue is that it has not been put on a scope and tested. Also there are no other proven builds for refference. This one sounds very risky for a newby to me Here it is.
404 Not Found
( Anyone willing to help with this one? that would mean a full PS schematic, and recommended Transformer model numbers!)
Option 2
would use a Mark III upgrade board from Diytube, and very loosely follow the rest of the MarkII schematic. . I used this build option with the ST 70, The results were great, and this may be more within my ability. Shannon has created a Modified 5-20 circuit that includes the CCS. The key here is I can use the Comlpete MarkII schematic as a great guide. Repro Trannies are availible, and the power supply could be upgrade, or replaced with a SDS upgrade board. Some here didn't like the driver tube choices (12ua7), but some limited options are availble (12BHt), and even some 6 volt options. This one is very doable for me.
Here's the schematic.
http://www.diytube.com/unidriver/poseidon.pdf
Option 3 would be the same as option 2 except using the Triode Mark III replacement board. This appears to also be a 5-20 type driver? I don't see where a CCS is used on this one but it does seem to have move driver tube options. I can't find a schematic, but here's the info.
Driver Boards for Dynaco Mark II and Mark III
Any comments keeping in mind that my design / electronic skills are limited?
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On the surface, Option 1 appears the best. I could quibble with some design elements, but it's basically solid. Option 2 has an input stage that is loaded poorly, compromising gain and linearity. It then has a driver stage using a tube with relatively high distortion. Option 3 is unknown, no schematic.
TM,
I agree with SY. Go option 1.
AnTek's model AN-4T550 torroidal power trafo seems suitable for B+ and heater power. Parallel the 2X 550 VAC windings and bridge rectify with 2X snubbed 1000 PIV PN diodes (on the ground side) and 2X 600 PIV Schottkys (on the "hot" side). Pseudo-choke I/P filter the "raw" B+. Not much capacitance will be needed in the "fudge factor" position to bring the rail in at the spec'd 520 V.
We'll work out the 2 negative voltages necessary later.
Edcor's model CXPP100-MS-3.3K will do nicely for the O/P trafo. Super premium "iron" in a Mullard circuit is nice, but it's not essential.
I suspect you don't have an o'scope. Getting CF (phase compensation) right without a scope is next to impossible. Instead, I suggest you use the brute force method for phase compensation. Use 50 KOhm inductive wirewound resistors as part of the 'T7 loads. Wire 1% tolerance 100 Ω resistors in series with the 50 KOhm parts. Connect 1 end of the assemblies to the tube and the other end of the assemblies to the ends of a linear taper 10 KOhm potentiometer. Wire the wiper of the pot. to B+. Either 100 Ω part serves as a test point for the DC balance adjustment the pot. provides. A 0.3 V. drop across either resistor means both 'T7 sections are "idling" at 3 mA. Adding inductance to the load peaks HF gain. All that remains to keep from biting off more than you can chew is to short the NFB loop out at approx. 2 octaves above the audio pass band. Making RF 560 Ω will feed back about 15% of the O/P voltage. 2.7 nF. of capacitance between the "hot" speaker terminal and ground takes care of shorting the GNFB loop out away from the audio band.
I agree with SY. Go option 1.
AnTek's model AN-4T550 torroidal power trafo seems suitable for B+ and heater power. Parallel the 2X 550 VAC windings and bridge rectify with 2X snubbed 1000 PIV PN diodes (on the ground side) and 2X 600 PIV Schottkys (on the "hot" side). Pseudo-choke I/P filter the "raw" B+. Not much capacitance will be needed in the "fudge factor" position to bring the rail in at the spec'd 520 V.
We'll work out the 2 negative voltages necessary later.
Edcor's model CXPP100-MS-3.3K will do nicely for the O/P trafo. Super premium "iron" in a Mullard circuit is nice, but it's not essential.
I suspect you don't have an o'scope. Getting CF (phase compensation) right without a scope is next to impossible. Instead, I suggest you use the brute force method for phase compensation. Use 50 KOhm inductive wirewound resistors as part of the 'T7 loads. Wire 1% tolerance 100 Ω resistors in series with the 50 KOhm parts. Connect 1 end of the assemblies to the tube and the other end of the assemblies to the ends of a linear taper 10 KOhm potentiometer. Wire the wiper of the pot. to B+. Either 100 Ω part serves as a test point for the DC balance adjustment the pot. provides. A 0.3 V. drop across either resistor means both 'T7 sections are "idling" at 3 mA. Adding inductance to the load peaks HF gain. All that remains to keep from biting off more than you can chew is to short the NFB loop out at approx. 2 octaves above the audio pass band. Making RF 560 Ω will feed back about 15% of the O/P voltage. 2.7 nF. of capacitance between the "hot" speaker terminal and ground takes care of shorting the GNFB loop out away from the audio band.
Looks like you've already got help picking the iron, and a good start on the PS. Given that you have some experience already, I don't think you should worry about diving into a P2P project. The entire schematic might look daunting, but work through bit by bit and you'll be fine.
Most tube amp projects consume considerable time and financial resources. Why choose compromised designs when you can build something great? If SY and Eli recommend "option 1", dive in. You'll figure it out and be happier in the end, even if you burn a couple of parts.
Paul
Wild Burro Audio Labs - DIY Full Range Speakers
Now were talking! I'm going with Option 1 I want the best. I
Eli, I have puchsed a new 30MHZ scope and low Dist. audio generator so I do have that.
Could I request another Ps trannie suggestion as these are going in the main room, and must look nice. I'd love standard verticle mount trannies in black if possible. Somethiong that "LOOKS" simular to the Mark III trannies would be nice. Cost is ok within reason, and if nessasary. I'm still reading but iit appears the B+ voltages were thought to be high, and Zafira1981 has lowered them, but the revised schematic is now missing. I think he finally went with 450V to the OP transformer. Not sure if he dropped any other voltages, as i'm still reading the thread. Here's the thread were additional changed were made. What I want to ask is if the required voltages should be reexamined first?
http://www.diyaudio.com/forums/tubes-valves/103494-help-amp-layout.html
He also changed the CCS a final time, and mentions going with a 12UA7 for some strange reason. I don't know whats up with that?
Eli, if you or anybody cares to help out with this, i'm ready to gather a BOM, and put in several orders as soon as everything could be determined.
Thanks everyone.
Eli, I have puchsed a new 30MHZ scope and low Dist. audio generator so I do have that.
Could I request another Ps trannie suggestion as these are going in the main room, and must look nice. I'd love standard verticle mount trannies in black if possible. Somethiong that "LOOKS" simular to the Mark III trannies would be nice. Cost is ok within reason, and if nessasary. I'm still reading but iit appears the B+ voltages were thought to be high, and Zafira1981 has lowered them, but the revised schematic is now missing. I think he finally went with 450V to the OP transformer. Not sure if he dropped any other voltages, as i'm still reading the thread. Here's the thread were additional changed were made. What I want to ask is if the required voltages should be reexamined first?
http://www.diyaudio.com/forums/tubes-valves/103494-help-amp-layout.html
He also changed the CCS a final time, and mentions going with a 12UA7 for some strange reason. I don't know whats up with that?
Eli, if you or anybody cares to help out with this, i'm ready to gather a BOM, and put in several orders as soon as everything could be determined.
Thanks everyone.
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Hi everybody, I'm jumping on this thread too, I have been thinking for some time to build my first tube amp and decided to go with KT88 PP, maybe the reason is they look good but they seem to be popular and the power output is quite on spot too for what I'm looking for.
I noticed that an Edcor transformer was suggested with 3,5k input, I have skimmed through a some KT88 PP schematics and most seem to be 5k transformers, can anyone tell what makes the difference, why some are higher input impedance while other lower? What does it mean in terms of power output and distortion and what else it could mean?
A second thing I noticed on the schematic by zafir1981 is the UL w typical 40% tap, but in his schematic its 43% and yesterday I went through Lundahls homepage and found a suitable transformer (think it was 1679) but it has a 37% tap and 4,5k input impedance instead, what's the difference and why?
Cheers Michael
I noticed that an Edcor transformer was suggested with 3,5k input, I have skimmed through a some KT88 PP schematics and most seem to be 5k transformers, can anyone tell what makes the difference, why some are higher input impedance while other lower? What does it mean in terms of power output and distortion and what else it could mean?
A second thing I noticed on the schematic by zafir1981 is the UL w typical 40% tap, but in his schematic its 43% and yesterday I went through Lundahls homepage and found a suitable transformer (think it was 1679) but it has a 37% tap and 4,5k input impedance instead, what's the difference and why?
Cheers Michael
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Wow, I had all those same questions!
Please do join me in this build. It will make things easier I believe... I've spend a year researching, and believe this is the topology to go with for a "standard" KT88 PP amp. I also thought some good arguments were made for the driver tube choices. As for the schematic, i'm still unsure of the various stage voltages, (there was some debate over 520v), and if the CCS needs altering (cascode mosfet). I think all this was later changed by Zanfir, but the later schemetic is missing? If the 520v is needed for 60W output, i'd be inclined to stay with it.
Please do join me in this build. It will make things easier I believe... I've spend a year researching, and believe this is the topology to go with for a "standard" KT88 PP amp. I also thought some good arguments were made for the driver tube choices. As for the schematic, i'm still unsure of the various stage voltages, (there was some debate over 520v), and if the CCS needs altering (cascode mosfet). I think all this was later changed by Zanfir, but the later schemetic is missing? If the 520v is needed for 60W output, i'd be inclined to stay with it.
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hey-Hey!!!,
I'd suggest the Hammond 1650R 5k a-a output TX for starters. Very nice output, and in comparison to *MANY* custom and vintage units it came out ahead...let alone it isn't very expensive...
I'd also suggest dropping the power a few Watts to 45-50 and cut B+ to ~400V. It is much better to run the KT88 at 80-85 mA/tube without getting so close to maximum ratings the higher B+ would expose them to.
cheers,
Douglas
I'd suggest the Hammond 1650R 5k a-a output TX for starters. Very nice output, and in comparison to *MANY* custom and vintage units it came out ahead...let alone it isn't very expensive...
I'd also suggest dropping the power a few Watts to 45-50 and cut B+ to ~400V. It is much better to run the KT88 at 80-85 mA/tube without getting so close to maximum ratings the higher B+ would expose them to.
cheers,
Douglas
TM,
If you use any sort of choke I/P filtration, true or pseudo, you will have 2 big inductors on the topside of the chassis. Mount the toroidal power trafo on the underside of the top plate, where it can't be seen. An "acorn" nut makes things attractive, "upstairs".
A very easy way to bring the B+ rail voltage down somewhat is employing a true choke I/P filter and FWCT rectification with a pair of damper diodes. ESRC is selling 19AU4s for $1 each. You'll have to buy 10 (big deal). Wire the heaters in series and energize them with an AnTek model AN-1236.
The 1st inductor in a choke I/P filter gets the snot badly beaten out. HEFT is the order of the day. The 21 lb. Hammond model 193Q should do. "Ordinary" stuff is fine for the 2nd inductor.
If you use any sort of choke I/P filtration, true or pseudo, you will have 2 big inductors on the topside of the chassis. Mount the toroidal power trafo on the underside of the top plate, where it can't be seen. An "acorn" nut makes things attractive, "upstairs".
A very easy way to bring the B+ rail voltage down somewhat is employing a true choke I/P filter and FWCT rectification with a pair of damper diodes. ESRC is selling 19AU4s for $1 each. You'll have to buy 10 (big deal). Wire the heaters in series and energize them with an AnTek model AN-1236.
The 1st inductor in a choke I/P filter gets the snot badly beaten out. HEFT is the order of the day. The 21 lb. Hammond model 193Q should do. "Ordinary" stuff is fine for the 2nd inductor.
hey-Hey!!!,
On the choke input choke, there are vintage swinger chokes to be had in the usual markets, but they're a bit rare. I've designed a swinger with standard E-I lams that should work well in this service w/o the nasty saturation buzz. The gap is a wedge, longer at one end of the E than the other to give a slow and gradual saturation of the core as flux( both AC and C ) increases.
cheers,
Douglas
On the choke input choke, there are vintage swinger chokes to be had in the usual markets, but they're a bit rare. I've designed a swinger with standard E-I lams that should work well in this service w/o the nasty saturation buzz. The gap is a wedge, longer at one end of the E than the other to give a slow and gradual saturation of the core as flux( both AC and C ) increases.
cheers,
Douglas
hey-Hey!!!,
I'd suggest the Hammond 1650R 5k a-a output TX for starters. Very nice output, and in comparison to *MANY* custom and vintage units it came out ahead...let alone it isn't very expensive...
I'd also suggest dropping the power a few Watts to 45-50 and cut B+ to ~400V. It is much better to run the KT88 at 80-85 mA/tube without getting so close to maximum ratings the higher B+ would expose them to.
cheers,
Douglas
Well I didn't expect the Hammond recommendation! Hmmm. Excluding cost, would this Hammond be a better preforming choice than a standard Electraprint with the same specs? I won't be buying Super expensive outputs from Japan, but as these will be my main amps for the long haul, I'm fine with spending a little extra on such an important componet.
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yes.
That particular Hammond is *THAT* good. Totally put the brakes on building clones of the Peerless S-271-S I acquired and had torn down( shuddering while remembering the cost involved with that exercise ).
cheers,
Douglas
hey-Hey!!!,
I'd also suggest a different circuit...but check out Dave's post here:
Tube DIY Asylum - Hammond 1650R - Salectric - December 11, 2009 at 04:08:37
He's built an amp with them and could tell you how it worked for him. Straying from your current design is not what I am suggesting, at least not yet...
cheers,
Douglas
I'd also suggest a different circuit...but check out Dave's post here:
Tube DIY Asylum - Hammond 1650R - Salectric - December 11, 2009 at 04:08:37
He's built an amp with them and could tell you how it worked for him. Straying from your current design is not what I am suggesting, at least not yet...
cheers,
Douglas
Hey TubeMack,
ok I'm in too, let's build the nicest KT88 PP around!
Reread your first post and the goals for the project is quite similar for what I have lined out in my thoughts, even been thinking of mono-blocks here too!
I didn't aim for so high power with these tubes though it's probably not impossible but I would like to not run them so hot, I guess I would be happy if I get even lowish 30-40 Watts but maybe 50 is quite a sensible compromise and it's just 1 dB here or there and isn't really hearable.
Transformers,
agree we should go for something good but as you also said within reasonable costs as some are very expensive, but still the transformer is a very big part of the sound quality so should be high on priority as it's something one doesnt swap out after the amp is built.
I would prefer toroids through-out for several reasons because of the great bandwidth with toroids and that it's very easy to get (ironically though!) even with standard winding teqniques, the other reason is very low magnetic stray field meaning surrounding components will pick up less hum especially good thing in the power supply transformer but yet good magnetic connection between primary and secondary meaning less stray inductance especially important for the OPT. OTOH toroids doesn't have the "vintage sexiness" as ol' EI cores but square shaped cans can be found of course which is what I will go for if I use toroids.
Found one supplier of toroidal OPT's
Antek - Your reliable source of transformers, power supplies, and more.
eBay Store - Antek inc: Transformers, Enclosures, Power Supply
but they have very few models which is pity as they have a 70 Watt and 8 lb model which would have been on spot but it has a very low primary input impedance of around 2k and that's way too low I guess as I haven't seen anything near when it comes to KT88 PP amps, well I sent an e-mail inquiry about higher input impedance to them but just recently read from the very few post on DiyAudio regarding Antek that some have not had any good luck communicating with them. A Polish maker replied today they don't make output transformers, I truied to tell them I can give the winding specification but it seems the message didn't went through.
Hammond 1650R was mentioned, of some reason I got a feeling Hammond is not the pick from the very little I have read, like this thread: http://www.diyaudio.com/forums/tubes-valves/156545-japan-vs-us-output-tx.html read post #15. The good part is I found out I can get these locally to a reasonable price, but would still like to get more FB on Hammonds. Douglas link looks promissing so will have an eye how that thread develops.
Well, there's some food for thoughts for now, even if we wouldn't agree on all details I think we should still stick together and make it through, this is going to be a great thing and I think I won't build so many tube amps in my life(?) so this one is going to be something extra so I will for sure beside building an excellent amp also add som bling-bling as well to its aesthetical appeal. Oh, and don't worry about electronics/electricals and such things, I am a 'toob-noob' too but have some knowledge of electronics and I would be happy to give a helping hand as much as I can and I'm sure we will get lot more help from the forum members too.
EDIT: oh, and for the record if I didn't say it Option 1 looks like a great base to build on and I'm sure we can eventually add some further goodies and improvements!
Cheers Michael
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Any comments on the smaller Hammond 1650N? I've read good things about it, but never tried one myself.
Here are the related threads if you want to read up.
http://www.diyaudio.com/forums/tubes-valves/97002-help-modifiying-schematic.html
http://www.diyaudio.com/forums/tubes-valves/88070-my-new-project-2-x-kt88-60w-amp.html
http://www.diyaudio.com/forums/tubes-valves/103494-help-amp-layout.html
After reading more, I would like to lower the B+ to the KT88's to 460V. Also, I think I'd rather stick with traditional vertical Trannies @ this time. As soon as at can get the Specs nailed, i'll purchase, or order custom from Electraprint.
As to the PS, I'd really love to keep it straight foward, and simple. I.E. diode bridge, single choke, caps, and resistors. As long as it performs well, i don't want to get too involved here. I'd therefore like to size the PS trans, just right to achieve this. Ultima Thule, How do you feel about 460V?
http://www.diyaudio.com/forums/tubes-valves/97002-help-modifiying-schematic.html
http://www.diyaudio.com/forums/tubes-valves/88070-my-new-project-2-x-kt88-60w-amp.html
http://www.diyaudio.com/forums/tubes-valves/103494-help-amp-layout.html
After reading more, I would like to lower the B+ to the KT88's to 460V. Also, I think I'd rather stick with traditional vertical Trannies @ this time. As soon as at can get the Specs nailed, i'll purchase, or order custom from Electraprint.
As to the PS, I'd really love to keep it straight foward, and simple. I.E. diode bridge, single choke, caps, and resistors. As long as it performs well, i don't want to get too involved here. I'd therefore like to size the PS trans, just right to achieve this. Ultima Thule, How do you feel about 460V?
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TM,
For a PSU with CLC filtration, you will not get a better value than the AnTek model AN-4T360. The rail will be in the 450 to 475 V. range, which is just fine for KT88s.
Be sure to use a CL150 inrush current limiter between the rectifier bridge and the 1st filter capacitor. 100% SS rectification allows the use of a large cap. in the 1st filter position. You can kill ripple freq. overtones such a large cap. generates ("hash") by inserting a LC section made of a high current RF choke and a 1000 pF. NPO ceramic or mica cap. between the large 1st filter cap. and the main filter choke. The RF component filter blackens the background nicely.
For a PSU with CLC filtration, you will not get a better value than the AnTek model AN-4T360. The rail will be in the 450 to 475 V. range, which is just fine for KT88s.
Be sure to use a CL150 inrush current limiter between the rectifier bridge and the 1st filter capacitor. 100% SS rectification allows the use of a large cap. in the 1st filter position. You can kill ripple freq. overtones such a large cap. generates ("hash") by inserting a LC section made of a high current RF choke and a 1000 pF. NPO ceramic or mica cap. between the large 1st filter cap. and the main filter choke. The RF component filter blackens the background nicely.