
Hello all & happy labor day -
I just posted the design of a new power amp that I've been working on for some time.
This is a push-pull amp pentode using sweep tubes. Not screen driven (sorry SY) but pentode mode, with plate-to-grid feedback. Using 6JN6 or 6JM6/6GV5 tubes it does about 18W. Works with no global feedback, or with 6dB of feedback.
Drivers are also pentodes. The amp is set up to cancel some distortion between the driver and output stages (yes, it really does work!)
My goal was a practical and affordable amp. The total BOM cost is about $325.
Details are here:
http://www.pmillett.com/DCPP.htm
Pete
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6GV5's are still listed on the dollar menu at ESRC, so for a buck, I would be tempted to dial up a bit more B+, OK a lot more B+ but that is just my MO. I got a bunch of these when they first went on the dollar menu. I think that I have several hundred 6CB6's and a bunch of other IF tubes with the same pinout. If I ever get some time, I might put one together.
The Edcor power transformer looks like a good choice for the Simple P-P, so I may get one of these.
The Edcor power transformer looks like a good choice for the Simple P-P, so I may get one of these.
Nice use of Compactrons and 7-pins😉.
Calculated the Zout of each output tube to ca 1k and Zin to ca 7k with inverse feedback applied.
This looks great!
Calculated the Zout of each output tube to ca 1k and Zin to ca 7k with inverse feedback applied.
This looks great!
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Hi Pete,
No compactron this side of the ocean !
Who may disagree with such design ?
Pentodes LTP, local FB, stabilized G2, no
UL ! I love it.
Just a question, did you try to balance the driver (or even the pwr stage) by adjusting screen voltage ?
This affects transconductance and seems to be a way to match tubes "dynamically".
Not yet checked, work in progress ....
CUSOON, I hope.
Yves.
No compactron this side of the ocean !
Who may disagree with such design ?
Pentodes LTP, local FB, stabilized G2, no

Just a question, did you try to balance the driver (or even the pwr stage) by adjusting screen voltage ?
This affects transconductance and seems to be a way to match tubes "dynamically".
Not yet checked, work in progress ....
CUSOON, I hope.
Yves.
Pete,
Great looking design and beautiful execution. I can tell by the design elements and the thoughtfull layout that your truly an engineer. Form clearly follows function and the use of these traditional TV tubes and the feedback scheme makes the design unique. Very cool. From one engineer to another, Job Well Done!
Doug S. (aka Mickeystan)
Great looking design and beautiful execution. I can tell by the design elements and the thoughtfull layout that your truly an engineer. Form clearly follows function and the use of these traditional TV tubes and the feedback scheme makes the design unique. Very cool. From one engineer to another, Job Well Done!
Doug S. (aka Mickeystan)
Are those 12 pins tube sockets still available??
Search our favorite auction site and you'll find the ceramic pcb version.
Jeff
Nice one, Pete, despite the lack of screen drive.😀 Looks like you've got some new software to replace AudioTester- what is it?
Nice one, Pete, despite the lack of screen drive.😀 Looks like you've got some new software to replace AudioTester- what is it?
Just posted it... here:
http://www.pmillett.com/hp_8903_software.htm
Home-grown!
I figure I'd whoop up one of these cause I've got almost all the parts already, and then plenty extra for tinkering with Tubelab's screen drive design too. I've already got 6GV5's, and some iffy 6CB6's wanting for action.
Are there any complications or limitations in using higher uF caps in positions C3, C6, C25, ,C27?
Are there any complications or limitations in using higher uF caps in positions C3, C6, C25, ,C27?
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Hi Pete,
Using stabilized G2 voltage with unstabilized bias voltage may cause significant bias current variation if mains voltage varies. Wouldn't it be safer to use stabilized bias as well ? (incremental complexity and power dissipation in bias regulator can be very small)
Using stabilized G2 voltage with unstabilized bias voltage may cause significant bias current variation if mains voltage varies. Wouldn't it be safer to use stabilized bias as well ? (incremental complexity and power dissipation in bias regulator can be very small)
Are there any complications or limitations in using higher uF caps in positions C3, C6, C25, ,C27?
I don't thinks so, should be fine.
Pete
Hi Pete,
Using stabilized G2 voltage with unstabilized bias voltage may cause significant bias current variation if mains voltage varies. Wouldn't it be safer to use stabilized bias as well ? (incremental complexity and power dissipation in bias regulator can be very small)
Maybe so. I did think about it but decided to leave it unregulated.
The benefit of keeping it unregulated is that if the line voltage goes up, bias gets more negative so plate current drops... so you don't risk exceeding the plate dissipation rating. That allows you to more safely bias it close to the limits.
Pete
Hi Pete,
No compactron this side of the ocean !
Should I bring a big box full to ETF?
Seriously, I could... they are cheap!
Pete
I've dug through the great box of parts and I'm doing pretty well. I've got a burning question though. Why 1k carbon composition? I've got a mess of 1k's but are all metal film, but only 2 CC 1k's from "the shack".
Why 1k carbon composition?
The CC's are grid stoppers. Their purpose is to be lossy (resistive) all the way from audio up to high (RF) frequencies - most metal film resistors are inductive, and can actually form a tuned circuit and promote oscillation at HF.
The CC's are grid stoppers. Their purpose is to be lossy (resistive) all the way from audio up to high (RF) frequencies - most metal film resistors are inductive, and can actually form a tuned circuit and promote oscillation at HF.
Carbon films are less noisy and I've measured 1.2:1 SWR at 470MHz with a 2-watter. More than enough HF range for audio 😉
Metal oxides (the Matsushita power types) are pretty good too.

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