I am looking for a Proven high powered diy tube amp of 50+watts. Something comparable to a Citation ii or a McIntosh mc75. Preferably a 6550 design but kt88's or kt120's are welcome.
Not looking for an amp in kit form. Cannot be a SET design as my speakers are 87db sensitivity. And when I say proven I mean something like the DCB1 preamp in quality but for a tube amp.
Thanks!
Not looking for an amp in kit form. Cannot be a SET design as my speakers are 87db sensitivity. And when I say proven I mean something like the DCB1 preamp in quality but for a tube amp.
Thanks!
Last edited:
The Cit. 2 and MC275 have very special O/P transformer requirements. "Cloning" either of these 2 will be difficult.
Get the best O/P transformers you can afford and employ either Mullard or Williamson style circuitry. Use current production, "reissue", Gold Lion KT88s, which have a reputation for being the best big beam power tetrode in production. I've seen the KT120 data sheet and the curves are non-linear and ugly.
Dig into the archives for Modern Mullard. Lots of good info. there.
The Heath W6M (schematic uploaded) is an interesting Class "AB2" Williamson setup, which might be reviewed. FWIW, I'd change the small signal complement to: "improve" gain structure, increase open loop linearity, and boost gm.
Get the best O/P transformers you can afford and employ either Mullard or Williamson style circuitry. Use current production, "reissue", Gold Lion KT88s, which have a reputation for being the best big beam power tetrode in production. I've seen the KT120 data sheet and the curves are non-linear and ugly.
Dig into the archives for Modern Mullard. Lots of good info. there.
The Heath W6M (schematic uploaded) is an interesting Class "AB2" Williamson setup, which might be reviewed. FWIW, I'd change the small signal complement to: "improve" gain structure, increase open loop linearity, and boost gm.
Attachments
Conrad-Johnson mv75 will do it https://sites.google.com/site/httpstubeamp/home/conrad-johnson-mv75-leak
One I tested easily provided 55W. But it is harsh on tubes - takes them to a limit and some more.
One I tested easily provided 55W. But it is harsh on tubes - takes them to a limit and some more.
Thanks. What are peoples opinions of swapping out the output transformers on a Dynaco mkiii and upgrading the pcb board? I Understand that they are a good value but they are not what people consider a no compromise design. How easy are they to upgrade to something that can hang with the big dogs?
Why you would mod Dynaco MkIII but wouldn't consider kits? There are Dynaco MkIII kits available with modded circuitry, which can be easier to get better final results than modding old MkIII.
This is because kits often cost more. It is rare that a person just pays 'only' for the price of parts when in kit form. Also, since my cousin is in metal working and has a c&c machine I can create the cab/enclusure for very cheap. Also, this lets me shop around for parts that I want and get good deals.
I mentioned the Dynaco because there is so much info/mods. Although determining sound quality vs TOTL is difficult because of all the nastalgia some people have.
I mentioned the Dynaco because there is so much info/mods. Although determining sound quality vs TOTL is difficult because of all the nastalgia some people have.
Dynaco transformers are pretty good; they aren't the problem with that amp. The driver board is. It was implemented for cost cutting reasons, and the amp really suffers for it. There are many driver board upgrade kits for the Mark III that really make that amp stand out. Stay away from configuring it as ultralinear; a well designed pentode output stage will out perform ultrallinear.
red board, some large-ish TV deflection tubes, decent iron, solid PSU. Job done. Lets all move on.
Alternatively, follow the thread on Chris' AB2 design and build. Cant remember the name of the thread, but its large and almost the primer on this stuff.
Interesting that you suggest SET is no good because of your speakers. For me, SET @ 50w would be no good because I like to look my bank manager in the eye and we only have a 50A line supply.
Alternatively, follow the thread on Chris' AB2 design and build. Cant remember the name of the thread, but its large and almost the primer on this stuff.
Interesting that you suggest SET is no good because of your speakers. For me, SET @ 50w would be no good because I like to look my bank manager in the eye and we only have a 50A line supply.
I have built Mullard and Williamson (including improved version) in the past. However, my schematic of preference is floating paraphase - differential - push pull.
Please find schematic attached, you can search for whole article on the net if you wish, its really insightful and comprehensive.
I have changed cathode bias to fixed bias, and 12AX7 to 6N2P-EV.
Please note grid leak resistors R1/R10, as well as R8/R9 need to be 470K instead of 1M, B+ voltage 460 - 490V. Output power is 60W with 3.3 - 3.9K output transformer.
Unlike Williamson, and some Mullard 520 variants, this design doesn't suffer from so bad instability/oscillation problems, and have very low distortions.
Another issue you may encounter is an output stage oscillation under certain circumstances related to the quality of output transformer. It is not specific to this schematic, its a common issue of all UL amplifiers.
Disconnect global NFB (R11), and drive your amp into overload with 8 Ohm wirewound resistor at output terminal in 20Hz - 25KHz range. If you see oscilloscope diagrams as attached, it means that output transformer is decent quality, and you will need anode - grid2 snubbers (usually 0.01uF capacitor + several KOhm resistor, exact values to be determined individually with particular transformer). With snubbers, RC HF networks C3/R12, C6/R13 should be deleted, and global NFB resistor need to bt paralleled with 50 - 150 pF capacitor in order to suppress transformer ringing.
Please find schematic attached, you can search for whole article on the net if you wish, its really insightful and comprehensive.
I have changed cathode bias to fixed bias, and 12AX7 to 6N2P-EV.
Please note grid leak resistors R1/R10, as well as R8/R9 need to be 470K instead of 1M, B+ voltage 460 - 490V. Output power is 60W with 3.3 - 3.9K output transformer.
Unlike Williamson, and some Mullard 520 variants, this design doesn't suffer from so bad instability/oscillation problems, and have very low distortions.
Another issue you may encounter is an output stage oscillation under certain circumstances related to the quality of output transformer. It is not specific to this schematic, its a common issue of all UL amplifiers.
Disconnect global NFB (R11), and drive your amp into overload with 8 Ohm wirewound resistor at output terminal in 20Hz - 25KHz range. If you see oscilloscope diagrams as attached, it means that output transformer is decent quality, and you will need anode - grid2 snubbers (usually 0.01uF capacitor + several KOhm resistor, exact values to be determined individually with particular transformer). With snubbers, RC HF networks C3/R12, C6/R13 should be deleted, and global NFB resistor need to bt paralleled with 50 - 150 pF capacitor in order to suppress transformer ringing.
Attachments
Yes...fine design, and the easiest way to make 100+ WPC without a whole lot of thinking since most of the hard stuff is already done. The thread is about Pete's 18 WPC TV sweep tube amp. Read through the thread to see how to get up to 250 WPC. I wouldn't recommend any build over 125 WPC though. A dozen or so 125 WPC versions are out there that I know about, probably more. Reliable? Mine has been left at full power pounding out rock music for hours several times. No issues. I plug a guitar preamp into it and really annoy my neighbors with the amp driven well into clipping. Again no issues
http://www.diyaudio.com/forums/tube...p-p-power-amp-design.html?highlight=6l6gc+ab2
Alternatively, follow the thread on Chris' AB2 design and build. Cant remember the name of the thread, but its large and almost the primer on this stuff.
An exercise in remote amp design. I proposed amp circuits and tested a few of them Chris designed the power supply and built it. He has a nice amp, I have a breadboard for amp design and testing, everybody gets the design details and schematics. It is a nice no compromise design but no "easy build PCB's are available....yet.
http://www.diyaudio.com/forums/tubes-valves/133034-6l6gc-ab2-amp.html?highlight=6l6gc+ab2
Only 50 amps, you guys have 240 volts, that's about 12 kilowatts.....A 50 WPC SET should be easy. I have a 40 WPC SET using 845's in A2. It does consume about 500 watts and was rather unusable in Florida since about 499 of those watts goes out the top of the amp as heat under normal listening conditions. Now that I have moved to a cold climate it will likely get hooked back up this winter.
At full tilt it will push my 87db Yamahas around on the table....loud, yes!
Hey! Check out my thread!
http://www.diyaudio.com/forums/tubes-valves/276840-choosing-tube-amplifier-build-help-needed.html
http://www.diyaudio.com/forums/tubes-valves/276840-choosing-tube-amplifier-build-help-needed.html
No! Check out our thread ;-}
http://www.diyaudio.com/forums/tubes-valves/156699-mullard-5-20-kt88-pp-blocks.html
I've been listening to Steve Brown's version for 2 weeks and to me, it sounds like my DHT-SET 45 amp but with all the weight and headroom necessary to convey the sense of a Mahler-sized orchestra. Most of the big names here participated in the design and, despite so many cooks 😀, it's a wonderful sounding amp.
Guys,
The OP started by mentioning the "Deuce" and "Mac". Those amps make the cut, in the best ever competition. While a good value, Dyna MK3 O/P "iron" is not up to the challenge.
There several rational signal topologies that can be employed. To achieve the superior performance desired, the OP will have to spend quite a bit in obtaining the very high quality O/P transformers necessary. The "iron" makes or breaks the amp. Only a little can be done "with smoke and mirrors".
The OP started by mentioning the "Deuce" and "Mac". Those amps make the cut, in the best ever competition. While a good value, Dyna MK3 O/P "iron" is not up to the challenge.
There several rational signal topologies that can be employed. To achieve the superior performance desired, the OP will have to spend quite a bit in obtaining the very high quality O/P transformers necessary. The "iron" makes or breaks the amp. Only a little can be done "with smoke and mirrors".
It's OK and nothing more. It is no better than mediocre, when compared to the "iron" in a Cit. 2, MC275, or W6M.
The consensus seems to be, of the Dyna O/P transformers, that the Z565 (used with "12" W. tubes) is the best of the bunch. The Z565 is definitely a price/performance champion.
I've read in a few forums the Hammond 1650R (not the easy wire RA version)
is a really nice Output Trans. for the money and better than many more expensive ones. Maybe someone here has some experience.
is a really nice Output Trans. for the money and better than many more expensive ones. Maybe someone here has some experience.
I have decided to I like the tube amps located tube-amps.net . I really like that I can run el34's or kt88's with minimal modification.
EL34 Push-Pull
Hashimoto KT-88 UL Push Pull
The problem is that I am having trouble finding a suitable power transformer. The Hashimoto power tranformer has:
20V-0-360V-720mA AC (450mA DC;Bridge rectifier) 75V-0-75V-0.15A、6.3V-4A(×2)、6.3V-2A(×2)
What is the going rate for a custom power transformer in the USA? How much more for a static and/or magnetic shield?
EL34 Push-Pull
Hashimoto KT-88 UL Push Pull
The problem is that I am having trouble finding a suitable power transformer. The Hashimoto power tranformer has:
20V-0-360V-720mA AC (450mA DC;Bridge rectifier) 75V-0-75V-0.15A、6.3V-4A(×2)、6.3V-2A(×2)
What is the going rate for a custom power transformer in the USA? How much more for a static and/or magnetic shield?
Last edited:
- Status
- Not open for further replies.