Found this huge toroid for ~20 bucks on Tradera (Ebay, sort of):
800VA with 230 + 33 + 2x11,7v secondaries. Current rating of each winding is unknown but judging by the wire gauge it should be more than enough for output stage B+ and heaters.
300VDC is a bit on the high side for my application but with >60V dropped across the cathode resistors it might turn out just right.
With this beast in the power supply and the 120W-rated 1650T output transformers it would really be a shame not to use 4 x PL519 per channel and get 50-60W class A...!
800VA with 230 + 33 + 2x11,7v secondaries. Current rating of each winding is unknown but judging by the wire gauge it should be more than enough for output stage B+ and heaters.
300VDC is a bit on the high side for my application but with >60V dropped across the cathode resistors it might turn out just right.
With this beast in the power supply and the 120W-rated 1650T output transformers it would really be a shame not to use 4 x PL519 per channel and get 50-60W class A...!
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Move the cathodes to the end of the primary winding and ground the center tap and it might work..
dangerous stuff
and I have no clew what happens connecting OPT this way
better forget about it
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Hi
Somes news about this projet
I realized recently an amplifier with EL34 trioded and 5W output
The driver is a 6SJ7
I use a bootstrap installation to provide enough swing to EL34
This is a diagram of the 60s
Listening to this amp is nice with wide band Fostex or Lowther
Yan
Somes news about this projet
I realized recently an amplifier with EL34 trioded and 5W output
The driver is a 6SJ7
I use a bootstrap installation to provide enough swing to EL34
This is a diagram of the 60s
Listening to this amp is nice with wide band Fostex or Lowther
Yan
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Certainly not 20W, but I've been looking at this transformer coupled cathode follower thing for a low power amp (headphones or desktop speakers). Not sure if the 12AX7 would really be able to swing enough voltage (about 200V p-p) for a full watt output with only a 300V B+. Maybe a 12AT7 with a CCS around 5mA or a 6SL7 is a better choice.
Any thoughts or suggestions are appreciated.
Any thoughts or suggestions are appreciated.
Historical throwback time - this discussion made me remember a schematic.
About 25 years ago I had a collection of old Audio magazines - I remember this project, or something like it:
A Direct-Coupled Amplifier with Cathode Follower by Raymond H. Bates
I've always wanted to build it but getting primary resistance value (not impedance) was difficult back in the pre-internet days. And I was a poor college student
About 25 years ago I had a collection of old Audio magazines - I remember this project, or something like it:
A Direct-Coupled Amplifier with Cathode Follower by Raymond H. Bates
I've always wanted to build it but getting primary resistance value (not impedance) was difficult back in the pre-internet days. And I was a poor college student
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Here's another idea using two halves of a 6SN7 (choke loading the second) and a 6L6GC for a little more power:
Using a VR (could also be a 0C3 or a resistor) to drop some volts above to keep the 6SN7 plates in the second stage well below the 300V max. They will swing above that with signal but that's typical of transformer coupled output stages, so I'm hoping it isn't a problem here.
I wasn't really optimistic about the ability of the 12AX7 to swing a full 200V ptp with 300V B+ in the previous schematic.
Using a VR (could also be a 0C3 or a resistor) to drop some volts above to keep the 6SN7 plates in the second stage well below the 300V max. They will swing above that with signal but that's typical of transformer coupled output stages, so I'm hoping it isn't a problem here.
I wasn't really optimistic about the ability of the 12AX7 to swing a full 200V ptp with 300V B+ in the previous schematic.
Hi
I am delighted to see that the subject is still passionate.
For kstagger
I tried this circuit. I did not manage to make it run as is.
To get some swing volt (and watt output) I added an LC boostrap for the input penthode.
On the other hand I noticed that this circuit was very sensitive to the load
(Boostrap) which multiplies the initial value of the anode resistance of the penthode.
I now orient myself towards an intermediate transformer (LL1692A en 3.5/4) charging a penthode input
With a 6E6P and also for a distributed load 50 - 50 for the output transformer (decrease of the swing) .
This circuit in 2 stages remains simple (thanks to Yves Monmagnon)
I am currently testing the penthode and pseudo triode mounting for the power tube with a 6P36C (el500) and I get + - 5w
It remains for me to obtimize the impedance of charge of the 6P36C before going to 2 x 6P45S (EL519) in // and to obtain 20w easily
Stay tuned
Yann
I am delighted to see that the subject is still passionate.
For kstagger
I tried this circuit. I did not manage to make it run as is.
To get some swing volt (and watt output) I added an LC boostrap for the input penthode.
On the other hand I noticed that this circuit was very sensitive to the load
(Boostrap) which multiplies the initial value of the anode resistance of the penthode.
I now orient myself towards an intermediate transformer (LL1692A en 3.5/4) charging a penthode input
With a 6E6P and also for a distributed load 50 - 50 for the output transformer (decrease of the swing) .
This circuit in 2 stages remains simple (thanks to Yves Monmagnon)
I am currently testing the penthode and pseudo triode mounting for the power tube with a 6P36C (el500) and I get + - 5w
It remains for me to obtimize the impedance of charge of the 6P36C before going to 2 x 6P45S (EL519) in // and to obtain 20w easily
Stay tuned
Yann
Hi
Some news about this uthopic projet..
I spent a lot of time with the 6P36C with an SE and a Cr Cathode schema by Patrick Turner
I get 6,5w very clean with 20w to the plate
Back on this project
Here is the schema used
I have distributed the load 50/50 because my output transformer allows it and
the drive is just for a full charge on the cathode.
I get 13.5w with 30w to the plate.
The G2 feed is floating and I am currently testing the reaction rate on the G2 "Ultraline" between 0, 15 and 25%.
I'm looking for design a new output transfo to allow different ration beetwin plate and cathode like 20 / 80 or 30 / 70
Yan
Some news about this uthopic projet..
I spent a lot of time with the 6P36C with an SE and a Cr Cathode schema by Patrick Turner
I get 6,5w very clean with 20w to the plate
Back on this project
Here is the schema used
I have distributed the load 50/50 because my output transformer allows it and
the drive is just for a full charge on the cathode.
I get 13.5w with 30w to the plate.
The G2 feed is floating and I am currently testing the reaction rate on the G2 "Ultraline" between 0, 15 and 25%.
I'm looking for design a new output transfo to allow different ration beetwin plate and cathode like 20 / 80 or 30 / 70
Yan
Attachments
In 2008 Tubelab created a very impressive cathode follower power amp. It is extraordinary that it produces 25W from 550V at 100mA, achieving 50% plate efficiency!! It is on his website as 'Minitron' and is a masterpiece of modern design here:
Cathode Follower | Tubelab
He used a dissimilar triode, 6EM7 as first and second stage, and a large TV sweep tube (6LW6) using a 600:8 OPT.
Personally, this is the best cathode follower power amp I've ever seen, and it uses some modern IXYS CCS chips which operate at very high voltage with efficiency and reliability.
George has done some wonderful amps over the years, and is incredibly passionate about his work. I hope he continues with this work in his retirement!
HD
Cathode Follower | Tubelab
He used a dissimilar triode, 6EM7 as first and second stage, and a large TV sweep tube (6LW6) using a 600:8 OPT.
Personally, this is the best cathode follower power amp I've ever seen, and it uses some modern IXYS CCS chips which operate at very high voltage with efficiency and reliability.
George has done some wonderful amps over the years, and is incredibly passionate about his work. I hope he continues with this work in his retirement!
HD
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Still at it, albeit with a rather slow start. I had to move everything about 1200 miles, and we got 3 weeks notice to move, so about half of my stuff was sold, given away, or tossed. What did go with us was hastily tossed randomly into unmarked boxes. There are still things I can't find after two moves and two years, and I'm not sure if they ever got moved. I did however find that cathode follower amp PCB pretty much intact, so it will see some power sooner or later. I did learn however that the 6LW6 doesn't like being triode wired on anything over 350 volts of B+. It will work for a while then run away and melt.
After seeing a few high powered tube audio amps, I decided that I needed to quit talking about building one and get to it. Preliminary work has begun and it will be a sweep tube (36LW6) amp of about 500 WPC.
My initial plans were to make a BIG cathode follower amp, but the drive voltages needed for 500 watt cathode follower are extreme to say the least. I have decided to make the big amp using a conventional drive scheme initially and experiment with a lower powered push pull cathode follower before building the monster cathode follower.
The trials, smoke and tribulations of both amps will be posted in a new thread on this forum sometime soon........I got a new 4K video camera to capture those melting tubes.
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