DIY Audio Projects Forum

So lately I have been working on two triode amps based on old television vertical deflection tubes. The first was my 6EM7 Vertical Amp discussed on this forum. Now I have finished the second one. It's a nice little low power stereo amp (1.3W/channel) based on the 6CY7. Here it is:
Here is it undergoing testing shortly after it was completed.
And here is a shot of the insides.
The amp uses a Hammond power transformer and chokes and a pair of Edcor XSE10-8-5K output transformers. I have to say that it sounds really nice. There is just something about triode amps that nothing can beat. The circuit was first prototyped here.

As soon as I get some free time I'll type up project pages for both amps.

So what do people think?

UPDATE (31 Jul 2016) - Added project page: http://diyaudioprojects.com/Tubes/6CY7-SET-Amplifier/

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Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog

Well done!

I love "useless TV tubes"; vertical outputs are fantastically linear. Looking great as well.

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-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design

Just a little more data on the amp. The peak clean power output is 1.3 watts RMS per channel (as determined from watching an oscilloscope). The 3dB frequency response is ≈48 Hz to 30 KHz. A plot of the end to end frequency response is included below with the lines indication the stated bandwidth of just the Edcor output transformers.This plot is from measured data taken with a signal generator (Zout=600Ω) and a fixed resistive load of 8Ω. The test setup is pictured in the first post. Below is the as built schematic (nearly).I say nearly because after finishing the amp and checking the plate dissipations, I found that the B+ voltages were running a little high. As such I added an appropriate dropping resistor in each B+ line to get the plate dissipations back under the maximum of 5.5 watts each. You can see the modification in this picture.They may not be in the most optimal position in the power supply, but with a nice constant current SET stage it works out just fine.

I still can't get over how good and how loud this amp sounds. It handles everything from classical, to blues, to choral music equally well. And the sound stage is awesome. I will never go back to building common power supply filters for both channels ever again.

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Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog

There are no "useless" tubes (well, some maybe like diodes and some other). When all "normal" tubes have been tested, some experimenting with "odd" tubes can be rewarding.

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Magnus

“If you don't know where you are going, any road will get you there.”
―Lewis Carroll

A little NFB will flatten that right out, if you wish to do so.

Or even local anode FB and draw the cathode of the output stage through the secondary, de-saturating it a tad will drop that low end to close to 20Hz

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-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design

Yes, but it will also greatly increase 3rd harmonic distortion which I cannot abide. Besides, it's only 4dB down at 40Hz and there is virtually nothing in music down that low. And even at 20Hz it's only ≈9dB down which is really not very much considering the variability in human hearing. I almost didn't include the frequency response characteristic because I knew that it would draw out the NFB comments.

I virtually never use NFB in my designs (with the exception of cathode degeneration) because I simply don't like the effects on the harmonic structure. I guess that's why I'm a SET (SE-UL) kind of guy. But to each, his own.

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Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog

Ok, there is one more thing I really like about this amp. It's one of those "tube things" that either you care about or you don't. These are all small base 9 pin miniature tubes. The heaters for these tubes are 6.3W for the 6CA4 and 4.7W each for the 6CY7s, for a total of 15.7W. This is compared to 1.9W for a typical 12A*7. What this means is that this amp REALLY GLOWS! In a dim room the glow from the amp really stands out.

You can call it the "Tube Geek" factor if you want, but I really like it.

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Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog

Nice set (pun intended), Matt!
I can't say that I'm surprised about the performance of the 6CY7. Many good quality amps have been made using various H-drive VTs, so why not a V-drive VT?



I do really like the layout, the cabinet AND the nice warm glow!

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The key to a successful build is to keep the smoke IN the circuit.
-Les

We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
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LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board

One of the best reasons I've ever heard for zero NFB

That gorgeous pic.. into the wallpaper folder it goes

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-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design

Yeah... the 6V6 Lacewood has a nice glow as well...

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Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog