I think I am inclining towards building a new ST-70. I found a few 'mods' or versions of the driver boards on the web and here are some of them -
Triode Electronics http://store.yahoo.com/triodeel/st70boards.html
SDS Labs http://www.quadesl.com/
Curcio Audio http://www.curcioaudio.com/
Welbourne Labs http://www.welbornelabs.com/st70.htm
(any other ??)
Triode Electronics and SDS Labs versions appear to be very close to the original. They differ from the original in the sense that they use seperate tubes (a triode and a pentode) instead of both in one envelope like the 7199. Looks like the idea is to be able to use better audio tubes. Both TE & SDS use EF86 and 12AU7, whereas SDS has one more version also using a 6AU6, instead of EF86.
Curcio and Welbourne are a bit different. Curcio has two versions both are 'all triode' but one with a CCDA (constant current differential amplifier).
Welbourne Labs also makes a very different type of driver.
Other than this, I dont have much information based on which I can decide what is good, better or best. So here's where I need your help. If anyone can provide some more information or insight on this, it would be very helpful. Especially who have built and used any of these or better yet had a chance to compare!
Looks like SDS would be the most economical way to go.
Secondly, I noticed that all the mods that are out there are related to the driver board only, none for the power stage. Is it because modifying would call for replacing the OPT which is considered to be a very good opt, or there really arn't any great mods that can be applied and its probably best left as is ? I am asking because the option for a different transformer(different from a Dynaco opt clone) is open for me since I would anyway have to buy transformers so if there is a mod for the power stage do let me know.
Triode Electronics http://store.yahoo.com/triodeel/st70boards.html
SDS Labs http://www.quadesl.com/
Curcio Audio http://www.curcioaudio.com/
Welbourne Labs http://www.welbornelabs.com/st70.htm
(any other ??)
Triode Electronics and SDS Labs versions appear to be very close to the original. They differ from the original in the sense that they use seperate tubes (a triode and a pentode) instead of both in one envelope like the 7199. Looks like the idea is to be able to use better audio tubes. Both TE & SDS use EF86 and 12AU7, whereas SDS has one more version also using a 6AU6, instead of EF86.
Curcio and Welbourne are a bit different. Curcio has two versions both are 'all triode' but one with a CCDA (constant current differential amplifier).
Welbourne Labs also makes a very different type of driver.
Other than this, I dont have much information based on which I can decide what is good, better or best. So here's where I need your help. If anyone can provide some more information or insight on this, it would be very helpful. Especially who have built and used any of these or better yet had a chance to compare!
Looks like SDS would be the most economical way to go.
Secondly, I noticed that all the mods that are out there are related to the driver board only, none for the power stage. Is it because modifying would call for replacing the OPT which is considered to be a very good opt, or there really arn't any great mods that can be applied and its probably best left as is ? I am asking because the option for a different transformer(different from a Dynaco opt clone) is open for me since I would anyway have to buy transformers so if there is a mod for the power stage do let me know.
if building from new parts...
I'd not replicate an ST-70. Historically, the ST-70 is an ingenious case
study on doing something good on the cheap. It is an artful balance
of tradeoffs to achieve a particular price point, a particular package
footprint and be easy for people to build. It's not worth replicating those
design criteria if you are coming up from new parts because you can
do better for not much more money.
That said, a 6600CT output transformer rated around 50W gives you
alot of flexibility. You can opt in for 6550, KT88, 6L6 as well as EL34s.
There's a myriad of good PP output transformers with these specs.
Next, plan for a stiff 450V power supply. Again, there are plenty of
good new Power Transformers that meet these specification. If you
build one of these - you will essentially have what is out there on the
market (Quicksilver, Rogue, Conrad, et cetera). It will be flexible for
changes and it will last forever so dont flinch at dropping $1000 in
parts to do the project right if you are so inclined. I might add you should
be able to get all the parts you need for less than that.
You can still buy driver boards if you are not comfortable hardwiring
from schematics. Uncle Ned's boards a great. His boards are great
and I've heard a renovated ST70 - with the board equipped with
12AU7s and a 12BH7 which i donated.
-- Jim
I'd not replicate an ST-70. Historically, the ST-70 is an ingenious case
study on doing something good on the cheap. It is an artful balance
of tradeoffs to achieve a particular price point, a particular package
footprint and be easy for people to build. It's not worth replicating those
design criteria if you are coming up from new parts because you can
do better for not much more money.
That said, a 6600CT output transformer rated around 50W gives you
alot of flexibility. You can opt in for 6550, KT88, 6L6 as well as EL34s.
There's a myriad of good PP output transformers with these specs.
Next, plan for a stiff 450V power supply. Again, there are plenty of
good new Power Transformers that meet these specification. If you
build one of these - you will essentially have what is out there on the
market (Quicksilver, Rogue, Conrad, et cetera). It will be flexible for
changes and it will last forever so dont flinch at dropping $1000 in
parts to do the project right if you are so inclined. I might add you should
be able to get all the parts you need for less than that.
You can still buy driver boards if you are not comfortable hardwiring
from schematics. Uncle Ned's boards a great. His boards are great
and I've heard a renovated ST70 - with the board equipped with
12AU7s and a 12BH7 which i donated.
-- Jim
Off this page @ vacuumstate.com....
This is the direction i'm going with mine...
dave
An externally hosted image should be here but it was not working when we last tested it.
This is the direction i'm going with mine...
dave
This is worth what it's costing you:
I have the Curcio full-blown mod with regulated power supply and CCDA driver stage. WIth "garden variety" type tubes (6922 Sovteks, Siemens EL34 (one pair marked "Made in E Germany", the other "Made in Germany") I was extremely happy on first power-up in 1995, and am still happy (and still using the same tube set after 4 - 5,000 hours).
The image I get out of this amp is un-believable (front to back and side to side). When I first powered it up I was using a Sonny portable CD player (1987 vintage) on the input side, and a "sacrificial lamb" (Jensen Duette's, late '50s) pair of speakers. After about 30 minutes of smelling closely and looking for flames I shut it down and connected ADS L1090's.
I cannot describe how good it sounded. While finishing the amp I had been listening to a Hafler DH-220 (certainly no slouch) and the ST-70 was miles better.
Some of the things you may want to think about are:
1. Curcio is the only one who looks at the whole picture - power supply, driver stage, and output. If you still need a tube rectifier, you are still in trouble. Have you priced real 5AR4/GZ34's lately? Look at a tube manual, add up the current draw for 4 EL34's and compare that with a GZ34 can supply. Then consider that the Fisher EL34 stereo amp had 2 GZ34's. The GZ34 supplying 4 EL34's is right at it's limit.
2. I personally don't care for pentodes in driver stages (you may not care).
3. Support for Curcio is great - he has a forum on AudioAsylum, and he's got a bucketload of troubleshooting documentation on his web-site. Welborne also has a forum on AudioAsylum, but no other documentation that I am aware of.
4. The A470 output transformes are 4300 ohms (not 6600), which is also good for 6550, KT88, 6L6, and I think the Sovtek 6B4G's can also take the 425V B+ of the modified unit. I would think you would have this option with any of the mods (after taking care of bias, etc.).
From the length of this it looks like I got on my soapbox.
Fire away.
I have the Curcio full-blown mod with regulated power supply and CCDA driver stage. WIth "garden variety" type tubes (6922 Sovteks, Siemens EL34 (one pair marked "Made in E Germany", the other "Made in Germany") I was extremely happy on first power-up in 1995, and am still happy (and still using the same tube set after 4 - 5,000 hours).
The image I get out of this amp is un-believable (front to back and side to side). When I first powered it up I was using a Sonny portable CD player (1987 vintage) on the input side, and a "sacrificial lamb" (Jensen Duette's, late '50s) pair of speakers. After about 30 minutes of smelling closely and looking for flames I shut it down and connected ADS L1090's.
I cannot describe how good it sounded. While finishing the amp I had been listening to a Hafler DH-220 (certainly no slouch) and the ST-70 was miles better.
Some of the things you may want to think about are:
1. Curcio is the only one who looks at the whole picture - power supply, driver stage, and output. If you still need a tube rectifier, you are still in trouble. Have you priced real 5AR4/GZ34's lately? Look at a tube manual, add up the current draw for 4 EL34's and compare that with a GZ34 can supply. Then consider that the Fisher EL34 stereo amp had 2 GZ34's. The GZ34 supplying 4 EL34's is right at it's limit.
2. I personally don't care for pentodes in driver stages (you may not care).
3. Support for Curcio is great - he has a forum on AudioAsylum, and he's got a bucketload of troubleshooting documentation on his web-site. Welborne also has a forum on AudioAsylum, but no other documentation that I am aware of.
4. The A470 output transformes are 4300 ohms (not 6600), which is also good for 6550, KT88, 6L6, and I think the Sovtek 6B4G's can also take the 425V B+ of the modified unit. I would think you would have this option with any of the mods (after taking care of bias, etc.).
From the length of this it looks like I got on my soapbox.
Fire away.
PP1C
Hello ,
The driver stage is excellent , highly recommended IMO
If you only need to swing 30-40V P-P and have B+ >350V this should provide enough gain to only require a volume pot in front of it . Currently working on a more substantial version using 6H30 to drive GM70 , maybe using cathode followers
cheers
316a
planet10 said:
Hello ,
The driver stage is excellent , highly recommended IMO
If you only need to swing 30-40V P-P and have B+ >350V this should provide enough gain to only require a volume pot in front of it . Currently working on a more substantial version using 6H30 to drive GM70 , maybe using cathode followers cheers
316a
Re: PP1C
For both the cascode and the pentode drivers, you want a nice clean PS of course, but I'm sure I'm not telling you anything you didn't already know.
+1!! especially if 10W or so is enough. I've built a couple of these and they're truly excellent, much better than any standard ST70 or clone.planet10 said:
Before you add a CF into such a nice sounding circuit, take a look at Pete Millett's pentode driver designs. Built a few of these too, and they were the best drivers I found for the 813 trioded and the GM70. I don't have my notes in front of me, and the actual amp is in storage 800km away, but iirc, I used 12HG7's in the end.316a said:The driver stage is excellent , highly recommended IMO
cheers
316a
For both the cascode and the pentode drivers, you want a nice clean PS of course, but I'm sure I'm not telling you anything you didn't already know.
Having heard good things about it on the forum I did seriously consider the PP-1C. I believe its rated at 4W, and I confess it is the main reason I did not consider this and a few nice SE projects also(I hope I dont start a war here. if you feel I need to be educated on how much power is realistically needed please fire away). But do note that atleast for a start I wont be having any great speakers. Efficiency maybe 87-89db range.
One reason for choosing the st-70 was there is a lot of support available. Many people have built it. This is important as it will be my first time building a tube amp(other than a tube school project few years ago). From whatever I have come across so far, I felt that st-70 is a nice balance between complexity, cost and power. I might be wrong as I have not yet seen enough.
I am open for other designs that are not too complex. Availibity of boards will be an advantage, if otherwise its not a major obstacle.
Thanks!
One reason for choosing the st-70 was there is a lot of support available. Many people have built it. This is important as it will be my first time building a tube amp(other than a tube school project few years ago). From whatever I have come across so far, I felt that st-70 is a nice balance between complexity, cost and power. I might be wrong as I have not yet seen enough.
I am open for other designs that are not too complex. Availibity of boards will be an advantage, if otherwise its not a major obstacle.
Thanks!
If you're looking in the 'get my feet wet' area,
look at http://www.diytube.com.
They have an ST-35 board, and Eico HF-89 board.
Won't sound as good, but, both are well documented, and the ST-35 would be about half the price of a 70.
look at http://www.diytube.com.
They have an ST-35 board, and Eico HF-89 board.
Won't sound as good, but, both are well documented, and the ST-35 would be about half the price of a 70.
The PP-1C looks very interesting. For those who've built it, did you also use the suggested power supply? What mains transformer did you use? I'm having a devil of a time finding one with both 6.3V and 12V taps. Also, did you add any additional filtering (e.g. a choke)? Has anyone tried converting it to use KT88s for more power?
I've been down the same road. This is something I'd do differently if buiding Curcio's CCDA option again: Use (leave) plenty of slack in the wires connecting the board to the rest of the amp. Some resistors may need values changed in order to get voltages adjusted just right. Removal and replacement of this board several times was a B**CH.
Joe Curcio was very responsive with help in getting me my through my first tube project. He knows this one very well.
Joe Curcio was very responsive with help in getting me my through my first tube project. He knows this one very well.
Wodgy said:
No. Used my own LCLC and CLCLC supplies, later with a Superreg on the front end. Mainly because it's proven itself to my ears to be the best sounding, and definitely the quietest especially with damper diodes and lots of H's in there. However, I have no doubt that Allen's design works well.
I don't recall, as I buy a lot of surplus and have maybe 1 metric ton of iron.
So? Use a seperate TX for the heaters anyway. LV stuff is cheap as, but I'd be surprised if there wasn't a Hammond, Lundahl or the One-Electron mains TX that has it all.
See above.. Look for archived posts of mine on this, as I don't recall the exact specs and my notebooks aren't here. I went through a bit of an amp building spree for a year or so and all the details blur from this distance. Allan currently uses an LC filter for the PP2C.
Yep, but I used a lower voltage secondary PS to run the KT88's down around 330V/100mA as they sound better there, but this arrangement doesn't produce any more power then the std EL34 setup. But I liked how it sounded better.
Ok so out of two people who have responsed and done the mods, both used the Curcio CCDA version.
I think I like the Welborne Labs version because it does have a regulated bias, beefier PS filtering, uses the constant current technique, and I feel its more simple than Curcio's.
Cost analysis shows the Welborne's will be more cost effective to make by just purchasing the boards and then parts seperately.
I think I like the Welborne Labs version because it does have a regulated bias, beefier PS filtering, uses the constant current technique, and I feel its more simple than Curcio's.
Cost analysis shows the Welborne's will be more cost effective to make by just purchasing the boards and then parts seperately.
ST70 modifications
For what it's worth, here are my two cents:
I've done two of the mentioned modifications on two different
ST70, the Curcio one and the other with the same topology
as the original, but with different tubes...
The latter one is my main amp to drive my electrostatics, whereas
I sold the Curcio. Why?
Because I found the original circuit more pleasant with the EF86
and 12AU7 even tough the Curcio circuit with the regulators
on the plates and grids, also very good quality, exibits one
peculiarity very subjective that doesn't do justice to the otherwise
excellent design.
If you ask what, I reallly can't tell you, may be a little harsh in
the treble, may be some other phenomenon I really can't explain,
the truth is I had to sell one of them so I decided to sell the
Curcio even though it was with some hard thinking, if I had my
way I would keep both, but.....
On the other hand I'm very, very happy with the Mr Ed and
Sheldon mod, I think it suits my needs in driving the ESL, with
excellent sound stage, very smooth and above all, all the power
I need even though I don't need tooo much to drive the ESL.
This was a Very nice experience for me, rebuilding the ST70.
For what it's worth, here are my two cents:
I've done two of the mentioned modifications on two different
ST70, the Curcio one and the other with the same topology
as the original, but with different tubes...
The latter one is my main amp to drive my electrostatics, whereas
I sold the Curcio. Why?
Because I found the original circuit more pleasant with the EF86
and 12AU7 even tough the Curcio circuit with the regulators
on the plates and grids, also very good quality, exibits one
peculiarity very subjective that doesn't do justice to the otherwise
excellent design.
If you ask what, I reallly can't tell you, may be a little harsh in
the treble, may be some other phenomenon I really can't explain,
the truth is I had to sell one of them so I decided to sell the
Curcio even though it was with some hard thinking, if I had my
way I would keep both, but.....
On the other hand I'm very, very happy with the Mr Ed and
Sheldon mod, I think it suits my needs in driving the ESL, with
excellent sound stage, very smooth and above all, all the power
I need even though I don't need tooo much to drive the ESL.
This was a Very nice experience for me, rebuilding the ST70.
For the guy in NJ who sold his Curcio:
Swapping 6CG7/6FQ7 for 6DJ8/6922 get's rid of that un-settling quality you describe (in my experience).
I neglected to mention that I tend to swap those out depending on the high-end of the speaker being used (I've used the amp with 3 different pairs). What I have found is that if the speaker 'hot' at the high-end, the 6CG7's sound better to me, else, the 6922's are OK.
Swapping 6CG7/6FQ7 for 6DJ8/6922 get's rid of that un-settling quality you describe (in my experience).
I neglected to mention that I tend to swap those out depending on the high-end of the speaker being used (I've used the amp with 3 different pairs). What I have found is that if the speaker 'hot' at the high-end, the 6CG7's sound better to me, else, the 6922's are OK.
6FQ7
Interesting idea. I'll have to try that.
My big tube roll was to use 6KN8s as the top tube in the cascode. It bumps the open loop gain up a bit, dropping distortion. The circuit as-is can often use a little bit of tweaking as far as the feedback loop is concerned; stock, there was a bit more ringing on square waves than I'm comfortable with, correctable by a small cap across the feedback resistor or, if you can squeeze a bit more gain out of the driver, an RC network between the plates of the driver tubes to set a dominant pole.
Like I said, nice platform to do some experimentation.
Interesting idea. I'll have to try that.
My big tube roll was to use 6KN8s as the top tube in the cascode. It bumps the open loop gain up a bit, dropping distortion. The circuit as-is can often use a little bit of tweaking as far as the feedback loop is concerned; stock, there was a bit more ringing on square waves than I'm comfortable with, correctable by a small cap across the feedback resistor or, if you can squeeze a bit more gain out of the driver, an RC network between the plates of the driver tubes to set a dominant pole.
Like I said, nice platform to do some experimentation.
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