Monday, December 3, 2012

New project: Heathkit W-2 tube amplifier rebuild

Things are never quiet here at the 6th Street Bridge.  Having just finished up the 1625 amplifier, I decided yet another project was worth pursuing.  This time it's yet another rebuild of a vintage piece of gear - the Heathkit W-2.  This was a fairly popular "20W" mono amplifier made in the early to mid-1950s.  It uses the classic Williamson circuit with 6SN7 driver tubes, 5881 output tubes, and Peerless output iron - running in Ultralinear.  Another special thing to note is the separate chassis for power supply and the signal which is a great way to reduce hum.

The W-2  I received was in pretty good condition.  Popping the hood and the resistors and capacitors look to be in mint condition.  But sadly, the amplifier didn't work.  Not a single hum, burp, or anything out of the test speaker.  A quick diagnoses with the multimeter and it appears that the original builder had neglected to ground the two chassis together via the umbilical cord!  A short length of wire, two solder joints, and music was coming out the speakers.  It makes me wonder if I was the first to ever hear this particular amplifier.  Very weird to say the least.

Anyway, the sound - with almost 60 year old passive parts - was rather lifeless: undynamic with some treble roll-off..  Here's hoping that some coupling and power supply capacitor upgrades will bring this old amp up a couple of notches.  Of course I also need to score another unit so I can listen to stereo.


Freelance said...

If you can't get that singing, let me know. I have a single too, and recently was sniped on ebay for my much awaited mate, but the first block I bought, the seller was a pro techie and did some re-designing, thru in all q's, and changed a couple values, and it sounds as good as a WA-1, and close to a very well redone W3. From what I've read, it seems in good hands, but if you want his schematic changes I can try to scan and upload it. He even put what he found to be the best feedback values per OPT ohm tap.

Freelance said...

Oh, I forgot to mention the most important part. An old timer told me that the W2 OPT is the same as the WA-1 except for the UL taps. So, you can wire it exactly as a WA-1 and run 807's or my favorite ATS-25's in them very easily and it also has no feedback in the circuit. You could also use 5933wa's, or if you don't like the anode cap, I've found the 5932's are very nice as well. I had no idea that the OPT's just changed numbers and added two taps, but were basically one and the same. That was the whole "gilding the lily" term they talked about in the WA-1 and W2 maneuls. Btw, I grew up the G.R. area, you might know some of my audio buddies back there. Very nice blog; I enjoy reading innovative and refreshingly new perspectives in the tube world.

DividebyTube said...

I love 807s, so that would be a worthwhile upgrade. I would also love to see the alternative schematic you mentioned.

The "old audio" crew here in GR isn't the same as it used to be. However, I still hang out with one of them to check out stereo gear.

Freelance said...

I'll see if I can dig up the schematic the seller sent me along with the amplifier. He took a W2 Schematic and wrote the changes in pencil over the stock schematic. In the meantime, using Google Chrome translator, I found this humorous, yet informative history of Heathkit Co., along with the line up of 807 varients (5933 types, ATS-25(my favorite), verses the 5881, and later KT66's).
Here's the link in an older Chinese dialect. But the chrome translater does a fairly good job. I particularly like the authors change in the position of the feedback loop, shaving off several inches of un-needed circuit wire. His 5933wa commentary is very good, although he fails to even mention the Cossor ATS-25's with the 350a W.E. like rounded black plates unlike the VT-100's or later 807's square rectangle shape.

As to the audiophile scene in the Pacific Northwest, the record buying is awesome- no LP's are picked through. Conversely, that's because I only know 3 audiophiles in my area. I still buy tubes from Andy of Vintage Tube Services and from telephone conversations, he seems to be the same old person I remember.
Unfortunately, I've lost touch with most of my friends in the greater G.R. area. In Michigan, people would drive 45 minutes to have a "listening session." Out here, people lack the will to drive a WHOLE 6 miles to the nearest city of say, 10 thousand people, just to talk tubes and listen to a new amplifier. Six of one, half dozen of the other, as they say.
Don't miss the snow much, but miss knowing 20 people who were audiophiles "at heart." After all, what's music, if it's always an audience of one. :)
Keep up the nice blog. I emjoy reading critical, accurate, and detailed analysis of both the 'world of new tubes' and your 'flashbacks' to the past world of amplifiers that inspired hundreds of thousands to become interested in tubes in the past, and now if the present yet again. When the schematic reveals its hidden location to me from the W2 seller who did an amazing W1 retro-mod not only using all old PIO Q's or Hyrels, but also gave perfect feedback values for every ohm tap, and included the way to connect the W2 transformer taps to match up with the W1 layout. This person REALLY knew what he was doing. I believe he included square and sine wave pictures from it as well. It's been a couple years since I bought it, and I just recently acquired a 2nd W2 that I wish to use and copy his modifications onto it.
Another "Old-Timer" told me that the W2 OPT by Peerless was basically a prototype akin to the W1 except as you know with UL taps, (what they referred to as 'Gilding the Lily' in the Original W-2 kit manual's later 'one-page publication update' found inserted into the manuals printed just before the end of the W2 run as they transistioned into the massive commercial run of the W-3 grey chasis version). Hope that helps for now. You'll get a few chuckles out of the Chinese translation, but it's well worth reading several times until the semantics overlap. Warning- the process may leave you feeling as if your in a different 'zip code' by the time you've parsed it!