Circe! Circe!

In the summer, I use a separate stereo system geared for outdoor use. But when the cold drives me indoors, I turn back to my indoor system. For the past several years, that system has centered on 8 Watt Welborne Labs Laurel amplifiers driving a pair of Pi Speakers 4 Pi Studio loudspeakers.

For this winter, I thought it was time for a change: a little more power would be nice. I decided to hook up my old Parts Connection Assemblage ST-40 amp, the first amplifier I built from a kit, sometime in the late '90s. For those of you who don't know it, the ST-40 is a 40 Watt push-pull design built around EL34s, and it's one beautiful amp (if I do say so myself). I have not used it all that much in recent years, but every time I plug it in I'm amazed at how great it sounds.

Then, as I have documented in earlier posts, last winter the amp started blowing fuses. In a series of emails, Chris Johnson, the President of PartsConnexion (the unofficial successor to the old Parts Connection) diagnosed the problem as a shorted power transformer. I bought a new one, installed it (and cleaned up some sloppy wiring – remember, this amp had been my first effort), and Voila! Good as new!

So, last weekend I decided that my old, neglected but refurbished ST-40 should re-assume its rightful position. Right now it's paired with a Welborne Reveille preamp and drives the Pi Studio 4 speakers. Sources are a crappy CEC CD player (working on that) and a Rega 3 turntable (the latter accompanied by an Audio Electronic Supply phono preamp).

The ST-40 and the Studio 4s are a wonderful match. With 40 “tube Watts”, the ST-40 has plenty of power to begin with. Mated with the sensitive Pi Studio 4s (97 or 98 dB, if I recall correctly), the ST-40 can easily handle orchestral crescendos – or Eminem. After a long layoff, the ST-40 was grainy at first, but after a few hours it settled in and began displaying the clear, smooth lushness that makes it such a wonderful amp.

Firing up the system tonight, the first thing I noticed was that ST-40 is dead quiet. Even with the Reveille volume three-quarters of the way up (stepped attenuators!), when I put my ear to the Pi drivers I heard . . . nothing. Not even a trace of tube hiss. I must be a re-wiring genius!

Then I decided to put the amp to the acid test: Richard Strauss. First up, the second disc of the Rudolf Kempe Ariadne auf Naxos on EMI with Gundula Janowitz and James King. Both the glory and the difficulty of the recording is that it is miked very close. If your stereo is bad, you'll know it; but with a good system, the beauty of the voices makes the hair on the back of your head stand up – as mine is doing now.

Next up, the the third act of mono version of the Karajan Der Rosenkavalier, with Elizabeth Schwartzkopf, Christa Ludwig and Teresa Stich-Randall. You can quibble all you want about whether this is the finest version of the opera as a whole, but there's not a doubt in my mind that the trio is unsurpassed. And on the ST-40 it's spine-tingling. Sounds like its going to be a good winter!

The pictures were taken in low light and without flash to try to capture the tube glow, so forgive the fuzziness.

When Good Amps Go Bad IVb

Here is the second half of the Parts Connection Assemblage ST-40 Power Amplifier Construction and Operation Manual (pages 14 through 24):

When Good Amps Go Bad IVa

On the theory that someone, somewhere, some day, may need to refer to the old Parts Connection Assemblage ST-40 Power Amplifier Construction and Operation Manual, here it is. This post contains images of pages 1 and 3 through 13 (page 2 is blank). The following post contains images of pages 14 through 24.

When Good Amps Go Bad III

I hope you haven’t been holding your breath waiting for the next installment of the story of my attempt to repair my Assemblage ST-40 amplifier. It’s been a while. Earlier posts are here and here.

Briefly, after determining that my problem was a shorted power transformer, I contacted PartsConnexion (PCX), the de facto (but not de jure) successor to the old Parts Connection, which had marketed and sold the kit. In a series of emails, the president, Chris Johnson, told me that the transformer had been custom-made by Hammond. Chris said that the price that Hammond would charge for new units would be prohibitive unless he purchased a number of them (I forget how many). He said that several others had committed to purchase units if PCX ordered them, and asked whether I would commit as well. After checking with Hammond (which confirmed that the model was custom-made and that the price of a single unit would be an order of magnitude greater than the price Chris mentioned), I agreed.

Presumably Chris gathered the minimum number of orders he felt he needed and placed the order with Hammond, which then manufactured the new batch of transformers. Last week I received word that PCX had shipped the transformer, and it arrived the other day.

Now, unfortunately, you may have to bear with me again. Although I’m chomping at the bit, we have houseguests this weekend. It’s therefore uncertain whether I’ll have time to get to the project. We’ll see. In the meantime, you can look at the pretty picture of the new transformer at the top of this post.

When Good Amps Go Bad III

When we last visted this topic, I had emailed PartsConnexion to find out what power transformer I needed to replace the transformer that went bad in my ST-40.

The bad news: PartsConnexion doesn't stock it.

The good news: I exchanged some very nice emails with Chris Johnson, the president of PartsConnexion. They've contacted Hammond to see about pricing and availability.

The picture: Canada reminds me of winter . . . and snow . . .

When Good Amps Go Bad II

I previously explained that my Assemblage ST-40 power amplifier recently started blowing fuses. I have no idea how many ST-40s are still out there and in use, but I figured that I would post periodically on my progress, just in case others encounter the same problem and are looking for help.

The manufacturer or assembler of the old ST-40 kit was a Canadian company called The Parts Connection. TPC was, I believe, the original kit and parts company that later also made retail audio equipment under the name Sonic Frontiers. TPC fell on hard times, and the assets were sold to some of the old employees (and perhaps founders), who reopened the parts business under the name PartsConnexion. The website is at http://www.partconnexion.com. Although the new company is not formally the successor of the old one, there is I believe continuity of technical expertise.

For this reason, when I encountered my problem and was unable to figure it out, I emailed PartsConnexion. Within 24 hours, I received an email back that boiled down to the following: if the fuse still blows with all tubes removed, then the power transformer is shorted; if not, then one of the tubes is causing the problem.

Unfortunately, when I retested with all tubes removed, the fuse still blew. Looks like I need a new power transformer.

The power transformer in the amp is a Hammond H300338. Hammond is still in business, and PartsConnexion sells their transformers, but all the numbers seem to have changed. I've therefore emailed PartsConnexion for their advice on what I need. We'll see what they come up with.

The inside of the amp is pictured above. The underside of the power transformer is visible at the bottom center. You can click on the photo to enlarge. Note the tremendously bad wiring job, done by someone who at the time didn't know a resistor from a capacitor. Now I'll get to remove it and do it better.

When Good Amps Go Bad

I turned on my "summer" amp this morning -- and nothing. Dead as a doornail. Seemed like it must be a fuse, so I opened it up, and sure enough the fuse was blown. The amp is an Assemblage ST-40 EL34 tube amp, the first amp I ever built, and it's worked flawlessly for years. I'm not sure I've ever opened it up since I built it. I figured that, after eight or more years (I think I put it together circa '98-'99), the fuse had simply died, much as light bulbs eventually do.

Wrong. I put in a new fuse -- and it promptly blew. I have no idea why. Is the switch bad? Is there a short somewhere? Why? Where? I haven't the foggiest, and troubleshooting is not my area of expertise.

To assuage my frustration, I put a good solid state amp, a 100W AKSA built from a partial kit, into the system and am blasting Lauritz Melchior. The picture above is of the AKSA in action. Poor Floyd the Farmer is in the field getting blasting by Lauritz singing "Vesti la giubba" -- in German, no less! He probably thinks I'm insane!