EL34 > Interstage > PPKT88 Project

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stephenl
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EL34 > Interstage > PPKT88 Project

Post by stephenl »

My latest project
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Steve
Stevem
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Re: EL34 > Interstage > PPKT88 Project

Post by Stevem »

What made you want your house eith AB2 class?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
davebolden44
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Re: EL34 > Interstage > PPKT88 Project

Post by davebolden44 »

Question, i know the interstage transformer would be dc blocking, and the bias voltage would be negative, but would you still need dc blocking caps before the grids of the kt88s due to tbe bias voltage?
stephenl
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Re: EL34 > Interstage > PPKT88 Project

Post by stephenl »

The PA is pretty much an experiment for me. I lifted the design elements from a HiFi design and something I found in KOC's poweramp book.

I liked the idea of the el34 interstage driver feeding the PP PA without coupling caps - removing the mechanism for blocking distortion. Coupling caps could be added, of course, but are not needed.

Stevem, I wasn't specifically interested in AB2 for extra power but yes, it can

I'm anxious to hear how it sounds - hopefully good :)

If for whatever reason it doesn't work out, I'll drop in a 6S*7 for a more conventional gain stage>cathodyne.
Steve
davebolden44
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Re: EL34 > Interstage > PPKT88 Project

Post by davebolden44 »

seems fascinating, I hope it works out and sounds cool. I have often wondered about other uses for power tubes like this. Eager to hear about your findings.
stephenl
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Re: EL34 > Interstage > PPKT88 Project

Post by stephenl »

I'll post as I progress. It takes me a while to build an amp - it's strictly a spare time thing.
Steve
stephenl
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Re: EL34 > Interstage > PPKT88 Project PROGRESS PICS

Post by stephenl »

I made a little progress on this
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pdf64
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Re: EL34 > Interstage > PPKT88 Project

Post by pdf64 »

Interesting project!
Won't the interstage secondary require a 5k load in order for the intended load to be reflected back to the primary?
What's the idea with the power tube cathode circuit / feedback from plate?
stephenl
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Re: EL34 > Interstage > PPKT88 Project

Post by stephenl »

I took the interstage/PA design from a hifi design, and I honestly don't understand it's design completely... My thoughts were similar, the grids of the power tubes don't really reflect any load back to the primary.

If anyone has a good understanding of how the interstage splitter works in terms of impedence/reflected load, I'd appreciate the education.

As for the A-K resistor connection, my understanding is that it acts as a snubber for transients caused by Speaker inductive kickback.
Last edited by stephenl on Tue Apr 25, 2017 12:59 am, edited 1 time in total.
Steve
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M Fowler
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Re: EL34 > Interstage > PPKT88 Project

Post by M Fowler »

Anyone using Front Panel Express know how to put numbers or anything around the volume, TMB controls?

I couldn't figure it out so I used the * symbol at noon position to help know where your at.

You can import certain types of files and instead of ingraving they now have a graphics option.
strelok
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Re: EL34 > Interstage > PPKT88 Project

Post by strelok »

stephenl wrote: Mon Apr 24, 2017 10:47 pm I took the interstage/PA design from a hifi design, and I honestly don't understand it's design completely... My thoughts were similar, the grids of the power tubes don't really reflect any load back to the primary.

If anyone has a good understanding of how the interstage splitter works in terms of impedence/reflected load, I'd appreciate the education.

As for the A-K resistor connection, my understanding is that it acts as a snubber for transients caused by OT inductive kickback.
They won't present any load so long as the grid voltage remains well below zero. Usually the grids will start conducting somewhere between -1 and 0v. Depending on how much drive you have available and how you bias the amp will determine whether or not you cross into AB2 operation. If you do then the grids will be drawing current and the input impedance to the tube drops dramatically. So you'll want to have an output impedance for the driver that can match or be below that value if you want the amp to run into AB2, otherwise you'll just get the usual grid clamping effect seen in most other designs, which is not necessairly a bad thing. Just depends on what you're going for. Whether or not 2.5k is low enough for this particular application I couldn't say, but I suspect it would be.
stephenl
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Re: EL34 > Interstage > PPKT88 Project

Post by stephenl »

Here's the preamp:
PREAMP.pdf
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Steve
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