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6S41S WCF OTL Design
Mar 26, 2020 at 9:17 AM Post #16 of 38
I think I got the final schematic figured out. Going with 6S3P input tube.
 

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Mar 26, 2020 at 5:14 PM Post #17 of 38
I guess I am still not understanding the point behind the 6S19P stage.

I would think the 6S3P stage should be able to drive the output stage directly. If you are concerned about output impedance, why not double up your 6S3P tubes to make a mu follower?

It would save you a lot of money on the plate choke, and if my math is right, it should give you a lower output impedance than the 6S19P.

Maybe I am missing something though.
 
Mar 26, 2020 at 11:03 PM Post #18 of 38
I'm using the 6s19p tubes because I have them on hand (been dying to use em) and to be honest, they look cool and I've already drilled the holes. I also already have the plate chokes (I am fortunate to have shelves full of transformers). I like your idea about doubling up on the 6s3p, but will have an empty socket. I could keep the 6s19p but use 6n1p mu follower for input?
 
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Mar 27, 2020 at 2:28 AM Post #19 of 38
Type26 said:
I'm using the 6s19p tubes because I have them on hand (been dying to use em) and to be honest, they look cool and I've already drilled the holes. I also already have the plate chokes (I am fortunate to have shelves full of transformers). I like your idea about doubling up on the 6s3p, but will have an empty socket. I could keep the 6s19p but use 6n1p mu follower for input?
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Thats fair. I was concerned that you were going through all the work of having a 3rd stage simply to get double the gain when you didn't need it.

I will say that the 6S19P is an interesting tube and could make a capable OTL amp on its own. I just wish we had better triode curves for it. That is always my main gripe about russian tubes. Their data sheets are pretty lack luster.
 
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Mar 27, 2020 at 7:20 AM Post #20 of 38
Yeah, the Russian datasheets leave much to be desired for sure. I will say that every time I have built an amp with Russian tubes, I have been more than happy with the sound!

I have decided to drop the choke loaded input stage because I have ran out of room under the chassis and I am afraid of the choke picking up hum in close quarters with everything else. I think at this point, I'm going to put another SRPP stage in front of the 6C19P with either 6N1P or 6N3P. I hope it works because I haven't seen anyone do a double SRPP driver stage before, but I'm thinking I can get away with it since the 6C19P gain is so low.
 
Mar 27, 2020 at 2:24 PM Post #21 of 38
Type26 said:
Yeah, the Russian datasheets leave much to be desired for sure. I will say that every time I have built an amp with Russian tubes, I have been more than happy with the sound!

I have decided to drop the choke loaded input stage because I have ran out of room under the chassis and I am afraid of the choke picking up hum in close quarters with everything else. I think at this point, I'm going to put another SRPP stage in front of the 6C19P with either 6N1P or 6N3P. I hope it works because I haven't seen anyone do a double SRPP driver stage before, but I'm thinking I can get away with it since the 6C19P gain is so low.
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Just use a mu follower instead. It is kind of similar to SRPP however it has even lower distortion. Morgan jones talks about it in his book, and tube cad has more than a few articles on it.
 
Apr 8, 2020 at 2:08 PM Post #27 of 38
Tjj226 Angel said:
If the voltages and currents all look correct, but the choke is humming for seemingly no reason, throw a clamp on it and see if the lamination are loose.
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Unfortunately, they are sealed transformers. I may redo the power supply with SS bridge into parallel 6D22S (for slow turn on) then use current limiting resistors. Im not 100% sure the buzz was from choke as I turned off the amp pretty quickly. Could be the toroidal power transformers. I was originally going to add current inrush limiter resistors, bit figured the 6d22 would limit due to slow start up.
 
Apr 8, 2020 at 4:52 PM Post #28 of 38
Type26 said:
Unfortunately, they are sealed transformers. I may redo the power supply with SS bridge into parallel 6D22S (for slow turn on) then use current limiting resistors. Im not 100% sure the buzz was from choke as I turned off the amp pretty quickly. Could be the toroidal power transformers. I was originally going to add current inrush limiter resistors, bit figured the 6d22 would limit due to slow start up.
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Test it with just the SS bridge and leave the 6D22S out of it to see if the tube itself isn't causing some issue. You don't even need slow turn on in this circuit anyways nor would I worry about inrush current on something like this.

For testing purposes, run the amp as bare bones as possible and then work backwards to figure out where the issue is coming from.
 
Apr 8, 2020 at 6:44 PM Post #29 of 38
Tjj226 Angel said:
Test it with just the SS bridge and leave the 6D22S out of it to see if the tube itself isn't causing some issue. You don't even need slow turn on in this circuit anyways nor would I worry about inrush current on something like this.

For testing purposes, run the amp as bare bones as possible and then work backwards to figure out where the issue is coming from.
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Good idea. Im going to run the amp with only the rectifiers and no other tubes and see what happens. I tried it with the tubes and no rectifiers and there was no issue.
 
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