Pete Millett's Engineers Amp

Well I made progress, she sings! Here is a crappy cell phone pic. Now I need to put a skirt on this lady!

Al
 

Attachments

  • 0309101751-00.jpg
    0309101751-00.jpg
    48.8 KB · Views: 217
I would put the better caps in from the srart.When you finish the amp. you are not going to want to go back in and start changing caps. when you could be sitting back and enjoying the fruits of your labor.
Dave
 
The more I read about it, the more I like this design. He's using the same technique that was used in the El Cheapo amp- picking offsetting non-linearities in the driver tube, to counter errors in the output tubes. We have seen lots of evidence, that this trick WORKS.

Though, with those output tubes, I'd still be inclined to go with the idea I espoused and Jaymanaa built... the Berning EA-230 design, using toroidal output transformers (the Antek toroids are CHEAP for the power rating, BTW). Screen drive, baby! It's a higher parts count (two 12AT7s, a 6SN7 and the outputs), but it's probably close to twice the power, with the same output tubes...

Regards,
Gordon.
 
You should see what George from tubelab has done with this board! He did some mods and changed tubes and got somewhere around 240 watts per channel!
 
Thanks,
I like it too. The plate was well wort the 50 bucks. Now they are selling for 45. With the number of holes the time it would have taken me, and the cost of the materials it was a no brainer! My lady bought the plate for me for Valentines day! What a gal!. :banana:
 
Here's mine:

4423018547_d2238798e9_b.jpg


One note: check your tube bias and balance on the power tubes after the first week or so - mine had drifted significantly as the tubes broke in.

Oh, and here's the obligatory nude shot (sans OPTs and additional wire organization and general cablegami):

4409092084_40c745dff8_b.jpg


-D
 
The "Red Board" rocks!

I'm another proud builder and owner of the Millett "Engineer's Amplifier" (DCPP).

I stuck pretty well to the BOM and details on Pete's website, only deviating on the chassis style. I also used 6JM6 (plate cap) Compactrons, mostly because I had lots of them. Pete made a good call spec'ing the Edcor iron; the value is excellent. The quality of the Millett PCB is very high and worth every cent Pete asks for it. It was an easy project given the well-designed layout of the board, and the great documentation available on petemillett.com.

This amplifier has the potential to embarrass factory-built gear costing much more. The sound is very dynamic, yet totally easy to listen to for long sessions. It appears to be making more than the 17wpc Pete claims. It is also dead quiet; a pleasant surprise compared to other tube amp projects I have built.

I have it currently driving a pair of Vandersteen 2Ci's. These speakers don't really like less than 40wpc, but are making great music in my average-sized room. The bass is astonishingly good with plenty of detail in the mid-range.

Considering the money spent, this design is a "giant killer". Build it and you won't be disappointed! Congratulations to Pete Millett for bringing it to the DIY community.
 

Attachments

  • IMG_2173_sm.jpg
    IMG_2173_sm.jpg
    44.6 KB · Views: 156
  • IMG_2167_sm.jpg
    IMG_2167_sm.jpg
    73.7 KB · Views: 122
Last edited:
This looks like a very interesting and rewarding project. I just had a look at
the designer's site at the link provided at the beginning of this thread. I am
surprised however that the second harmonic distortion product is nearly at
the same level as the third. Why would this happen with a push-pull design,
does anyone know?
 
Last edited:
I'm another proud builder and owner of the Millett "Engineer's Amplifier" (DCPP).

I stuck pretty well to the BOM and details on Pete's website, only deviating on the chassis style. I also used 6JM6 (plate cap) Compactrons, mostly because I had lots of them. Pete made a good call spec'ing the Edcor iron; the value is excellent. The quality of the Millett PCB is very high and worth every cent Pete asks for it. It was an easy project given the well-designed layout of the board, and the great documentation available on petemillett.com.

This amplifier has the potential to embarrass factory-built gear costing much more. The sound is very dynamic, yet totally easy to listen to for long sessions. It appears to be making more than the 17wpc Pete claims. It is also dead quiet; a pleasant surprise compared to other tube amp projects I have built.

I have it currently driving a pair of Vandersteen 2Ci's. These speakers don't really like less than 40wpc, but are making great music in my average-sized room. The bass is astonishingly good with plenty of detail in the mid-range.

Considering the money spent, this design is a "giant killer". Build it and you won't be disappointed! Congratulations to Pete Millett for bringing it to the DIY community.

Looks very nice, Neon! Don't forget to check the driver balance and the power tube bias after every 8 hours of use (or so) for the first week or two as they'll both drift a bit as the amp & tubes break in. Here's mine after staining and finishing the chassis:

4585163143_265db8d744_b.jpg


I still need to get a vented bottom plate milled by Front Panel Express (convenient that they're only a 1/2 hour drive from my house...although I need to wait until the back account is re-inflated post Fisher 800c restore) and get some Vibrapods or other feet, but for now, it's close enough.

-Derek
 
This looks like a very interesting and rewarding project. I just had a look at
the designer's site at the link provided at the beginning of this thread. I am
surprised however that the second harmonic distortion product is nearly at
the same level as the third. Why would this happen with a push-pull design,
does anyone know?

Well, Pete Millett would be the logical person to explain this question. E-mail him.

I do not own any test gear other than some DMM's, so measuring distortion etc. was not an option. However, I do have a decent set of ears, and this amp sounds very clean playing music at realistic levels. Initially, complicated musical passages on some recordings sounded a bit congested. Now, with around 50 hours on the amp, this characteristic has all but disappeared.

On his website, Pete mentions he tested some high-end OPT's which measured better than the Edcors. Could you hear enough difference to justify the larger expense? I bought 2 boards and might build another one using extra-premium components and iron. However, I suspect it will take a disproportionate amount of money to beat what I'm listening to now.
 
On his website, Pete mentions he tested some high-end OPT's which measured better than the Edcors. Could you hear enough difference to justify the larger expense? I bought 2 boards and might build another one using extra-premium components and iron. However, I suspect it will take a disproportionate amount of money to beat what I'm listening to now.

I think the Hashimoto HCW-30-8 or the James JS-6238H might fall into this category. Not exactly huge money for either.

Jeff
 
I think the Hashimoto HCW-30-8 or the James JS-6238H might fall into this category. Not exactly huge money for either.

Jeff

I dunno - I'd count just shy of $400 for a pair of Hashimoto OPTs (and ??? for a pair of 6238H transformers - nobody lists the price out there) as pretty large money compared to < $100 for a pair of Edcors.

-Derek
 
For what it's worth, if you have a variac (and even if you don't) and a meter you can determine the turns ratio of the transformer, and with that information we can calculate what impedance will be reflected back to the primary with any given load from the secondary. Here's a page with the maths: http://www.radioremembered.org/outimp.htm

DON"T use a variac except as a last ditch and then only with serious current limiting on BOTH SIDES. Much better to use an audio generator. If you have to use a Variac I would put a small 110 v light bulb with the hot side and then use a stepdown transformer with a series car bulb on that.
 
I'm another proud builder and owner of the Millett "Engineer's Amplifier" (DCPP).

I stuck pretty well to the BOM and details on Pete's website, only deviating on the chassis style. I also used 6JM6 (plate cap) Compactrons, mostly because I had lots of them. Pete made a good call spec'ing the Edcor iron; the value is excellent. The quality of the Millett PCB is very high and worth every cent Pete asks for it. It was an easy project given the well-designed layout of the board, and the great documentation available on petemillett.com.

I just am not that thrilled with PCBs in tube amps. It's actually cheaper to build on tagboards or point to point like God and Leo Fender (and some guys in Binghamton) intended.
 
I just am not that thrilled with PCBs in tube amps. It's actually cheaper to build on tagboards or point to point like God and Leo Fender (and some guys in Binghamton) intended.

So it's cheaper....does that make for great sound?

The DCPP could be quite difficult to build PTP, especially for a novice. That is why Pete did a PCB in the first place.

As far as "God" and "Leo Fender" are concerned, they can line up behind Mr. Pete Millett! The Engineer's Amplifier is a top-shelf design and project.
 
So it's cheaper....does that make for great sound?

The DCPP could be quite difficult to build PTP, especially for a novice. That is why Pete did a PCB in the first place.

As far as "God" and "Leo Fender" are concerned, they can line up behind Mr. Pete Millett! The Engineer's Amplifier is a top-shelf design and project.

Agreed. I'm sure if high-quality PCBs were readily available in the 1950s, Leo and God (whoever "God" refers to) would have used them. Theoretically, PTP has sonic advantages because you are able to work in 3-dimensions for the shortest signal path, but in practice I've found any differences negligable.

-Derek
 
Back
Top Bottom