Take a look at my ST-70 mods page, configured for Ultralinear operation this circuit can do 40Wrms per channel with the right iron. Use the stock dyna power supply circuit design or upgrade choke and capacitors for a stiffer supply.
http://www.kta-hifi.net/projects/amp_page/st70amp/st70.html
The schematics are in the old pcx format (I'll eventually get everything back up in pdf)
Use this great free graphics program to view, edit and print pcx, jpg, etc.
http://www.faststone.org/FSViewerDetail.htm
Note I have no affiliation with Faststone - just a happy user.
edit
http://www.kta-hifi.net/projects/amp_page/st70amp/st70.html
The schematics are in the old pcx format (I'll eventually get everything back up in pdf)
Use this great free graphics program to view, edit and print pcx, jpg, etc.
http://www.faststone.org/FSViewerDetail.htm
Note I have no affiliation with Faststone - just a happy user.
edit
Kevin,
thanks for pointing the Dynaco, yes I agree this brand is my first look and the only simplest schematic I found.
I only download and see the schematic only not the power supply schematic.. I miss something ?
I wonder how to configure in linear and triode mode ?
actually I'm looking for the Triode mode that can do 35Watt at least.
I don't think I can found the Dynaco Output transformer here, can I use other like lundahl or tango ? which model ?
or what's the specification of that Output transformer ?
other questions, how can I modify the bias into auto bias ? possible ?
Kevin, I don;t think I can modify the schematic my self, all I can do is build base on the schematic, if you can show me the final schematic like Triode mode (can you modify to 35W plus ?), auto bias and PSU Schematic.
regards
Cal
thanks for pointing the Dynaco, yes I agree this brand is my first look and the only simplest schematic I found.
I only download and see the schematic only not the power supply schematic.. I miss something ?
I wonder how to configure in linear and triode mode ?
actually I'm looking for the Triode mode that can do 35Watt at least.
I don't think I can found the Dynaco Output transformer here, can I use other like lundahl or tango ? which model ?
or what's the specification of that Output transformer ?
other questions, how can I modify the bias into auto bias ? possible ?
Kevin, I don;t think I can modify the schematic my self, all I can do is build base on the schematic, if you can show me the final schematic like Triode mode (can you modify to 35W plus ?), auto bias and PSU Schematic.
regards
Cal
Cal,
No way are you going to get 35 W. from a PP pair of triode wired EL34s. You'll be hard pressed to get 35 W. from a PP pair of triode wired KT88s. A near Class "B" operating point is necessary.
What sort of speakers are you planning on using? Honest 91 dB. efficient speakers need only 15 WPC, in most rooms.
Hi Calico88 ,
If you are looking for a simple , cheap and good quality
unit ,and an excellent cost / benefit ratio , try the following :
1st option : DYNACO STEREO 70
Uses one 7199 and two EL34 per channel and can
deliver 35 W / ch .
2nd option : If you don’t want to use the expensive and
hard to find 7199 tube , I suggest the DYNACO MARK II
Uses one 6AN8 and two EL34 per channel and can
deliver 35 W / ch .
3rd option : The MULLARD’S 520
Uses one EF86 ( hard to find , only Svetlana manufactures
it nowadays ) , BUT with “minor” changes in the resistors
values you can use the 6AU6 ( cheap and easy to find ) ,
yet uses one ECC83 (12AX7) and two EL34 per channel
and can deliver ( squeezed ) 30 W / ch of good quality sound .
Obviously , there is many , many more circuits that can
attend your previously specified characteristics , BUT the
3 examples above are simple , relatively cheap , the TRANS-
FORMERS are very , very easy to find , easy to build , and the
final result will surprise you .
NOTE : The 3 options above are ULTRALINEAR circuits , that
means , they are a good compromise between the pentode
power and the triode linearity , exactly what you are looking for .
Regards ,
Carlos
If you are looking for a simple , cheap and good quality
unit ,and an excellent cost / benefit ratio , try the following :
1st option : DYNACO STEREO 70
Uses one 7199 and two EL34 per channel and can
deliver 35 W / ch .
2nd option : If you don’t want to use the expensive and
hard to find 7199 tube , I suggest the DYNACO MARK II
Uses one 6AN8 and two EL34 per channel and can
deliver 35 W / ch .
3rd option : The MULLARD’S 520
Uses one EF86 ( hard to find , only Svetlana manufactures
it nowadays ) , BUT with “minor” changes in the resistors
values you can use the 6AU6 ( cheap and easy to find ) ,
yet uses one ECC83 (12AX7) and two EL34 per channel
and can deliver ( squeezed ) 30 W / ch of good quality sound .
Obviously , there is many , many more circuits that can
attend your previously specified characteristics , BUT the
3 examples above are simple , relatively cheap , the TRANS-
FORMERS are very , very easy to find , easy to build , and the
final result will surprise you .
NOTE : The 3 options above are ULTRALINEAR circuits , that
means , they are a good compromise between the pentode
power and the triode linearity , exactly what you are looking for .
Regards ,
Carlos
Hi,
I posted earlier a link to this amp. If you read the building instructions you will find 5-20 (page 16) schematics as well.
I posted earlier a link to this amp. If you read the building instructions you will find 5-20 (page 16) schematics as well.
I have built this amp and recommend it highly. Very similar to the original Mullard 5-20.
http://www.arrakis.es/~igapop/iga6550.htm
Very very nice sound, Class A operation, simple cathode bias, and will work with 6550 or KT88. KT90 will yield more power. JJ KT77 can be used as well but will yield just slightly less power at less cost. Will give a KT90-like sound with EL34 power. I don't think that EL34 will plug it due to slightly different pin-out.
http://www.arrakis.es/~igapop/iga6550.htm
Very very nice sound, Class A operation, simple cathode bias, and will work with 6550 or KT88. KT90 will yield more power. JJ KT77 can be used as well but will yield just slightly less power at less cost. Will give a KT90-like sound with EL34 power. I don't think that EL34 will plug it due to slightly different pin-out.
Why use triode mode ???.........rocketting power supply costing(!)
A simple way is to (examine) parallel upgrade the o/p stage of the Williamson. The 6SN7 driver can supply the goods, But I don't agree to the moral of having to do this.
Question: Does it really have to be triode operation ?? Some 50 years ago Hafler and Keroes found a better way....-> UL and most listeners can be fooled into believing they are listening to either without any difference. Parallel p-p o/p stages soon put SE aside.
richj
A simple way is to (examine) parallel upgrade the o/p stage of the Williamson. The 6SN7 driver can supply the goods, But I don't agree to the moral of having to do this.
Question: Does it really have to be triode operation ?? Some 50 years ago Hafler and Keroes found a better way....-> UL and most listeners can be fooled into believing they are listening to either without any difference. Parallel p-p o/p stages soon put SE aside.
richj
base on my knowledge... which is little knowledge .. 
triode is better than the ultra linear, but some people say it's very close.
I have VTL 35Watt Mono block long time ago, and it has triode and pentode switch mode, of course that VTL better in Triode mode.
maybe the technology are improving now for UL. let me know
I have the 6550 SE 50W using hammond 1640SE, 12ax7 and 12at7 in my hand (priciple of power book)
this catch my mind to build one.
conider the cost is quite high on this thing, I wonder if there is a cheaper version but using the same topology or even better.
I agree that Triode mode will sky rocketing the Power SUpply cost, this is the input I would like to hear from the expereince tube amp designer or expert.
thank you.
then I'll go with UL, but what do you think of my 6550 SE 50W, is this Ultra linear ? any good ? I can not understand wheter the design is good or not.
cal
triode is better than the ultra linear, but some people say it's very close.
I have VTL 35Watt Mono block long time ago, and it has triode and pentode switch mode, of course that VTL better in Triode mode.
maybe the technology are improving now for UL. let me know
I have the 6550 SE 50W using hammond 1640SE, 12ax7 and 12at7 in my hand (priciple of power book)
this catch my mind to build one.
conider the cost is quite high on this thing, I wonder if there is a cheaper version but using the same topology or even better.
I agree that Triode mode will sky rocketing the Power SUpply cost, this is the input I would like to hear from the expereince tube amp designer or expert.
thank you.
then I'll go with UL, but what do you think of my 6550 SE 50W, is this Ultra linear ? any good ? I can not understand wheter the design is good or not.
cal
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.