Wanting to build a higher powered SE.

[DeathRex]

I have a 5 watt se amp, a 10 watt se amp, and several PP, but I would like to use some sort of impressive looking transmitting tube to make a SE amp. Something bigger than a 1625 and smaller than my living room. Around 25 watts so I could use an Edcor. Like to stay below 900 volts. Of course if anyone has a list of transmitting tubes for audio use that would be nice.

[kheper]

Some transmitting tubes, running in A2, would get to 25W @ below 900Vdc.

211 A2 SE 40W @ 1100Vdc amp, driven by a "chip-amp":
http://www.electra-print.com/techblog.php?blogid=7

This guy uses "zero-bias" transmitting tubes (811a, 100th, 838, etc.) at lowish voltages (less than 600Vdc) to achieve 20-35W. Look at his drive circuitry.
http://tubes.nekhbet.com/michimori.pdf

He also uses zero-bias transmitting tubes (801a, 8025a, etc.) in PSE.

A KT120 should hit 20W or so in A2 SE triode mode with the right driver.

[Geek]

Have an 845

http://geek.scorpiorising.ca/contrib/Ge ... 845_v2.png

PSU:
http://geek.scorpiorising.ca/contrib/Ge ... supply.png

The XPWR169 is no longer available, but there are Hammond alternatives.

22.5W clean SE per channel

Cheers!

[Shannon Parks]

Wowsers, Gregg. I hadn't seen this one.
I need to site suck all your schematics.

Shannon

[Geek]

Wasn't listed until this thread, Shannon

*goes to post finished unit pics*

Ha! I'll post the finished unit when my site comes back from maintenance

*edit*

Here ya go!

http://www.classicvalve.ca/images/slide ... tumblr.jpg

http://www.classicvalve.ca/images/slide ... tumblr.jpg

[Shannon Parks]

Gotta love those potato masher 5R4s!

Shannon

[soundbrigade]

Use "normal tubes" like KT120 or parallelled KT88, EL34, GU50.
I will soon start experimenting with GU-72 to get some 20+ W.

[DeathRex]

I have a 6P3S and GU-50 SE amps. Wanted something bigger.

I've been looking at 811, 845, 813, 814 and 828.

Wondering how well this 838 works at 673 volts?
Schematic looks doable, but 838s are kinda expensive, at least compared to 811s.

[kheper]

I have a 6P3S and GU-50 SE amps. Wanted something bigger.

I've been looking at 811, 845, 813, 814 and 828.

Wondering how well this 838 works at 673 volts?
Schematic looks doable, but 838s are kinda expensive, at least compared to 811s.

The 838 is a high amplification factor version of the 845. (50 vs. 5.3) Michimori is a wicked engineer. His schematics are very meticulous. He uses expensive iron, however.

Pete Millet's 813 amp runs at about 800Vdc, it uses a one pentode driver, and it is good for 22W. There are many other schematics for the 813. It is widely billed as being easy to drive, but I have my doubts about the certainty of these claims. Easier to drive than some rf tubes is more accurate.

http://www.pmillett.com/813_se_triode_amps.htm

[DeathRex]

Amount of cathode feedback depends on Mu of output tube and turns of 2nd or 3rd winding coils of OPT.
In my opinion, dumping factor of tube amp should be 1.0 at least.
My OPT has 36 ohm of 3rd winding coil which adapted to 838(Mu of 50) and gets dumping factor of 1.6 with only CFB.
If you don`t want using GNFB, you should use full of your 2nd winding, 16 ohm tap. May be you can get nearly 1.o of DF?
I learned that even CFB with OPT, too much amount of NFB is affects to the sound (too tight).
I have tried attached cathode feedback on my 811A SE amp.
An 811A has so high Mu(160) that 36 ohm of 3rd winding seems too much.
With out CFB, dumping factor was 0.2 and with 36 ohm of CFB DF become 2.0.
Schematic 14 shows added 50 ohm of resister in between cathode and 3rd winding coil, functioning current feedback and reduced
dumping factor from 2.0 to 1.5.
Schematic 15 shows using 4 ohm of 2nd winding coil and added
small amount of GNFB and get total DF of 1.0.

So he's saying you can, instead of having a dedicated tertiary winding, ground the 4 ohm connection and use the ground connection for CFB in his 811A schematics. For the 838 use the 16 ohm tap and ground the ground. But Edcor's only have one secondary tap.

[Geek]

Look again at my 845 schema how to do CFB with a single SE Edcor secondary.

Cheers!

[DeathRex]

Wow I totally missed that being feedback.
As the British would say "Brilliant!"

I'd like to use those 600V motor run capacitors, but I'd still need two.

[EWBrown]

My OPT has 36 ohm of 3rd winding coil which adapted to 838(Mu of 50) and gets dumping factor of 1.6 with only CFB.

Just watch out for that "dumping factor", it will get you every time!

/ed B

[EWBrown]

Update 8/10/16: Gary Kaufman's website on the-planet no longer exists, the server had a fatal crash several months ago,
and all that wonderful tube data has vanished

Nov 25, 2016: Note: some of his website has been partially restored, the info in "Links" is still valid, it has been adjusted to work with the restored files.

However I managed to save the schematic and a couple of photos of the completed amplifier, well before the crash, so I can e-mail it if anyone wants it.

Gary Kaufman had another Nobiru Shishido (sp?) SET design on his website, using an 826, driven by a 6EM7, with a Class B interstage transformer feeding the 826, which, in order to run in Class A2, requires a positive grid bias voltage of approx. 40 VDC. It does draw significant grid current, and a Hammond 124B won't cut the mustard here...

Note that the driver section is a more or less conventional 6EM7 SET design, so it furnishes 1.5 to 2W of drive in order to feed the somewhat power-hungry Class A2 826 grids.







I've seen and heard this one in person, several years ago. It is not very high powered, maybe 8 or 10 watts, but its design takes a different approach.
Basic info: B+ 260V, 826: VP = 250V, IP = 115 mA; 6EM7 consumes 35 mA total. For a stereo amp, 260VDC @ at least 300 mA continuous, which is easy to
produce with an isolation tranny with a FW voltage doubler, or a 120:240 step-up and a FWB.


826 data here: http://frank.pocnet.net/sheets/049/8/826.pdf

826 fits the common "Septar" socket, about same physical envelope size as the Russian 6C33C. Filaments are power-hungry, 7.5V @ 4 A
And they really need to have DC power to eliminate any 60 Hz hummm issues.

The 826 was intended a moderately high gain (mu of 31) Class C RF oscillator / Power amp, so it has to be "tricked" into behaving as a Class A2 device.


/ed B

[Geek]

Wow I totally missed that being feedback.
As the British would say "Brilliant!"

I'd like to use those 600V motor run capacitors, but I'd still need two.

Thanks!

You can run the cathode FB DC through the winding too, like this:
http://geek.scorpiorising.ca/contrib/Ge ... Amp_v1.png

The inverse DC field through the core de-saturates the transformer somewhat and increases bass response.

Cheers!