Curious_George

Decware definitely is saving a few pennies by omitting a few very inexpensive components. The shared cathode resistor/cap is a surprise. Especially when the ultimate sound quality is touted with this amp. $0.75 more could have bought you separate channels for this. The input tube grid if referenced to ground through the volume potentiometer, not a bad design. Definitely cost effective. Nothing wrong here unless the wiper arm opens and then you have no input reference to ground. Possible, but highly unlikely. Power supply could have used at least one choke for the money you pay, in my opinion.

The one for $350 indicated the OPT's used Z11, which I believe is Hi-B orient core. So those cores would/could be smaller compared to M6.

What’s better is that it ships from LA.

https://www.ebay.com/itm/133632180413?hash=item1f1d1940bd:g:4NQAAOSwfSFhwp0o&amdata=enc%3AAQAHAAAA4CO52824qSrpF%2BJiz5BSwO2sD4d%2FnsKBCB%2BBaD2O0Oq3O66njSr044tLaqohnfWzQvYVDxGPRC2qF4nzO%2BWTjRLze0SvemBsRagtJHkU0H3SvmPWWsgQ%2F6gTb0IeA6CrM7b72r0ucEhK74JamEgFJ%2B1csvj3uFnRS%2BpKlDbYXcPSxN5XFmBccCe9prtXpw6kmW%2FQRuXgwMT0EXfo%2F1EGI2yIkMV2GG1%2ByXxCBGOmj7BUJJoXYPboOSu4fav%2Fe95xRHcqoYcQDnvtI1YNVd8WG5LWSaMlDSKocmhCRz0JyY3o|tkp%3ABFBMyMSgyNtg This one may be the one to get. $350 including shipping.

It could still be a “deal” if one wanted to do minimal chassis work. $550 for a nice EL34 amp is not bad.

I did not plot a load line for the 6L6. I figured I would just plug one in and see how it biased up. The Chinese OPT in the amp calculated out as 3.8k, but it was probably designed to be 3.5k.

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Awesome! A breadboard. Those James OPT's were/are great.

Yep, I was just trying to keep it straight for the ones following along. I think due to Philips/Mullards patent, nobody could mention a fifth element.

1625's are fairly rugged too. Price keeps creaping up on them, but still reasonable.

For clarification, when Cappy says "pentode wired", he is referring to applying a voltage to the screen for a certain mode of operation. The 807 is a beam tetrode, not a pentode. PM me the PDF.

After all the holes are drilled in the chassis, that is when the fun starts.

What speakers and preamp do you have 51?

I agree to a point Henry, but when I listen to my ported Heresy's, I need a bit more power and one pair does not have a sub in my particular listening area and more power is needed to get some bottom end that I like.

Another great book for audio amps is the GEC An Approach To Audio Frequency Amplifier Design. This is geared more toward pentode mode and offers a huge selection of amps and building guidance. http://www.tubebooks.org/Books/GEC_approach.pdf

Such as the EL84. Any brand of EL84 would make a great amp in my opinion unless you just got a hold of a real dawg.

If anyone wants the PDF of the Mullard "Circuits for Audio Amplifiers" here it is. It is a trove of DIY building knowledge. This book was geared toward Mullard getting people attracted to their tubes and encouraged DIY. https://archive.org/details/19400164MullardCircuitsForAudioAmplifiers

I think those suggestions would make an excellent DIY amp. It would make the Zen sound like a function generator...

Here is the Mullard SE EL84 amp. It probably has too much input sensitivity in its original form, but we could tame that down easily. This is spec'ed at 3 watts.

I think the biggest challenge is finding a SE output transformer that has good bandwidth (and other specs) for a DIY project that are reasonable priced. Sure, they are out there, but prices are super high. James Audio Transformers were the best kept secret. Very similar to Tango and Hashimoto transformers. Supposedly, they share the same DNA if you will. If we could find a company (maybe Matt @ musical power supplies) to make a line of nice transformers with Hi-B core material, decent inductance and wide frequency repsonse, similar to what James was offering in there JS-6112HS or JS-6113HS we would be in business with some serious DIY amp builds. I have a set of James JS-6112HS and they are easily my favorite transformers in the 10 watt range.

As a matter of history, if my memory serves me correctly, back when the original Zen amp came out, I believe it was Nelson Pass who coined the term unofficially. Around exactly the same time, Deckert used the name and I remember Nelson mentioning in a forum post how someone "used" that name too and he was a bit upset about it, but let it go.

We could redesign the Little Sweetie to match the power output of the Zen. A new name could be BAMF. I'm not into eastern religions nor western religions for that matter. I'm sure everyone can figure out my acronym.

When Pentodes or Tetrodes are wired in triode mode, there is less of a sonic signature in my opinion. Not a bad thing, but just making an observation. You could use JJ EL84 or NOS EL84's and probably not notice much difference. Except for the JJ5AR4, I've had good luck with a lot of their tubes and the price is nominal.

Yep. Even parts for a mid-quality 300B build will run $1k and that is with a Hammond chassis w/ wood side panels. But, considering the alternative, DIY is much less expensive than buying a completed unit.