Tubes!

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!

Outdoor Stereo

How about something different for a Saturday afternoon? Let's talk stereos.

Since it's warming up a bit here in lovely NW NJ, I've taken my summer/oudoors system out of hibernation.

They say there are two kinds of stereo guys: amplifier guys and speaker guys. In my heart, I tend toward the former. The guts of the system are a tube amp and preamp:

My favorite tube is the 300B, but at 8W, the 300B just won't cut it for outdoor use. This amp, an Assemblage ST-40, is a stereo amp that uses EL34 tubes hooked up in pentode and puts out probably 35W. It was the first amp I ever put together, made from a kit sold by a company called The Parts Connection, which was the parts-and-kits arm of the old Sonic Frontiers. Every time I plug this amp in, I'm amazed how good it sounds. I love it.

The preamp is a Foreplay clone, jazzed up with some tweaks and some "designer" parts, such as the caps. I've also added twin stepped attenuators, assembled from Welborne Labs kits. Very pricey, but I just hate potentiometers.

Finally, here are the speakers. They are based on Pi Speakers Tower 2 kits. The boxes are MDF, veneered in ash with cherry borders. Frankly, I'm not wild about the ash look, but it was worth experimenting. Whatever they look like, I know the boxes are well-made. There are two layers of MDF on the front faces, almost 1 1/2 inches worth, and they're well-braced inside. The Tower 2s mate extremely well with tube equipment.

City Stereo

It's been a long time since I've told you that I love low-power tube amps and high-efficiency single-driver speakers, so I'll tell you again: I love low-power tube amps and high-efficiency single-driver speakers.

My setup in my small city apartment is simple: Lynn Karik-Numerik CD/DAC, conrad-johnson tube preamp, Audionote 300B stereo kit amp (8W), and small DIY speakers with Fostex drivers. The picture above was taken years ago, but it will give you the idea. Not ideal for Wagner or Mahler, but then again I'd be tossed out if I really cranked it up anyway.

Playing now is Tom Rapp's (Pearls Before Swine) The Use of Ashes, from the recently-released Jewels Were The Stars collection. I've had Tom Rapp's albums for over thirty-five years (yikes!) and play them at my weekend house, where I have a setup that includes a Rega turntable. It's about friggin' time that these albums have come out on CD.