Wounded B&K Components ST1400 Power Amplifier is Back from the Dead! Dynaco A25XL Speakers Driven.

 April 3, 2025

#509

Gentle reader,

I've been enjoying the hobby of home entertainment in the form of listening to recorded music with the most realism my budget can afford since 1976.

This image shows the 1970's Dynaco A25XL speakers I scored via eBay years ago for only $99. In front of them is my once electronically wounded B&K Components ST1400 stereo power amplifier. How I came to own one of the now-out-of-business American audio companies fine pieces of equipment can be read here: The Robb Collections: 30-year-old Panor-era Dynaco ST-200 Power Amp loses Left Channel. Meet the B&K Components ST1400 Replacement Amp!

This image shows it installed into my system prior to my going crazy buying replacements for ALL of my wiring with WBC (Worlds Best Cables) cables.

Matching pre and power amp side by side. The WBC XLR cables I bought were too short to reach the power amplifier if it was all the way to the left. MY OCD really did not like that!

You too may have suffered from this type of logic: "Well, I really like this __________, so, I might as well buy the matching_____________________." Which I did by buying the matching B&K Components PRO10 preamplifier which has an external power supply made of Unobtanium. "Why is that the case?" you may be thinking. 

My theory is this: Some of percentage of what is sold via eBay are things which the seller's parents once owned. There were three PRO10 units on eBay when I went looking. Only this one included the power supply. The likely scenario is: said adult children of late-parents carted all the stuff they wanted from Mom/Dad's house to a storage locker having decided to see what they could get some money out of by putting things on eBay, Facebook Marketplace, or wherever. By the time they got to their Dad's stereo stuff, they had no idea what this unmarked little metal box with a cable coming out of it was for. They put the preamp up for sale to those looking for a PRO10. I myself, did not know the situation separate power supply situation, but the seller of the one I bought said in the description: "..WITH power supply." That's what this article is about. The Robb Collections: Panor-era Dynaco PAT-6 in Reserve, Made-in-the-USA B&K Components: PRO10 Sonata Preamplifier and ST1400 Power Amplifier

So, everything is going along swimmingly as far as wonderful sounding music and I was proud that B&K Components were designed and built right here in the US. The trouble is, they are also from the 1990's as are the Panor-era Dynaco PAT-6 Preamp/tuner and ST-200 power amplifier were. One day, the left channel was very low volume and crackly!

Like the late 1990's Dynaco, B&K Components went out of business a few years ago and they shut down their website too. I could find ZERO service information on their products. 

I worked on things with electronics for a little longer than I have been in this hobby, starting in 1973 as a new-car dealership auto mechanic for nine years, switching in 1982 to working on the nation's capitol's Subway cars for an additional 35 years, then retiring. So, I know much about electronics, but without a schematic, I don't know where to look for the problem with an ohm meter.

Fellow vintage electronics lovers are always talking about "recapping" their receivers and amplifiers. So, I took the amp far enough apart to be able to read the information on the four large power capacitors. I found exact ((looking) replacements and bought two. 

Once the board which attaches to the two large capacitors was out of the way, I decided to remove the amplifier board and heat sink to take a closer look. That is when I spied the four glass BUSS AGC 4 amp fuses. B&K had wrapped a thin yellow piece of tape around each, perhaps to make them more visible. I began to look closely with a LED flashlight. That is when I saw one fuse had "blown". "Ah-hah!", I said. I looked through my supply of glass fuses and had five 3 amp ones and one 5 amp. Fuses open (and circuit breakers too) because there is a problem somewhere. Putting a larger (higher capacity) fuse in to replace an open one is a BAD and potentially dangerous idea. DO NOT DO THAT!

Since I had already bought and installed a new Marantz power amplifier. The Robb Collections: Review of Marantz MM7025, their Last Two Channel Power Amplifier. I thought, "I have nothing to lose, it's already broken, try the 5 amp fuse."

Some time ago, a fellow reader of this blog, and now my actual friend, Bob Berne, had sent another fellow reader, and also now actual friend, Bruce Woodrow and myself a kit to build a tiny Chinese tube buffer amplifier. After messing with those for a while, I bought two other Chinese, but factory built and better quality, tube preamplifiers to see if it would make an audible improvement in my systems. 

Using my SONY CAR Discman as a source and the last of my Monster Cables pink speaker wire driving my 1970's Dynaco A25XL speakers, I fired everything up and waited....perfect sound!!!

I was SO happy! I went on eBay to find genuine BUSS 4 amp AGC fuses and ordered ten of them. Once they arrived, I replace all four 32-year-old fuses with new ones. I put the cover back on and retested it. Still perfect. 

Since my also now-one-channel (and now residing in Bob Berne's Dynaco Museum) Dynaco ST-200 power amplifier had TWO sets of outputs and the B&K Components and Marantz MM7025 only have ONE set of speaker outputs, I have not been able to enjoy my 1970's Dynaco A25XL speakers. FYI: They are 3dB more efficient than the standard A25 speakers, and thus take half the power to produce the same level of sound.

The thick power cable (shown) I am using for the ST1400 is from a dead PURE|AV power conditioner. It is made by Belkin from their famous 19364 shielded power cable. In the past, I had replaced factory power cords with this cable on many power amps and receivers. 

When something electronic dies, I disassemble it putting the PC components and transformers in a box for transporting to the county's Hazmat/Electronics recycler facility. I recycle the metal parts as well.  If it was driven by a "wall wart" power supply, I keep it, just in case... Sadly they only accept #1 and #2 plastics for recycling.

I decided to use the now-revived ST1400 power amplifier to drive them. 

See the matching stands under the Dynaco A25XL speakers? I came up with an inexpensive alternative to factory-built speakers stands. Many of which are made from inferior particle board or MDF covered in black vinyl or paper: Bamboo stools. The Robb Collections: Wooden Speaker Stands and Risers too Expensive? Try Bamboo Stools. How-To Guide. I first found a perfect pair which matched and replaced the falling apart bases from my Klipsch KG4 speakers. They too perfectly matched. The secret to keep the stands firmly attached to the speakers is revealed in the article linked above.

The system in 2018. Klipsch KG4 on the left with bamboo stool for a stand.

The B&K Components PRO10 preamplifier has THREE stereo outputs (below). Two sets of RCA terminals and one pair of balanced XLR outputs. 

So, now I have the ability to listen to the Cerwin-Vega! LS-12 speakers driven by the Marantz MM7025 in stereo, or in pseudo-quadraphonic with my Dynaco QD-2 supplying the pair of Tannoy C-88 tower speakers behind my listening chair with ambiance and sometimes individual instrument sounds.

It does a marvelous job of making me feel like I am on stage with the band or orchestra. Truly a marvelous passive device. Unlike it's QD-1 brethren, it has three-way binding/banana terminals on the back rather than the cheap spring terminals.

And, if I really want to be blasted, I can once again drive all six speakers at the same time, but now with two separate power amplifiers.

And that, my dear readers, is the end of this saga. I am SO glad that I took the time to try and figure out why the left channel of the ST1400 was failing. There are four fuses, two for each channel. I do not know enough about complex electronics to understand why any sound was being produced in one channel with an open fuse, nor do I care. I am just VERY happy that it is fixed and all is well in my audio world.

Thank you SO much for taking the time to read my humble blog. I began writing many years ago just for something to do. Little did I know that so many people would be interested in what I have to say! Feel free to comment below or via Facebook.

Also, every (all 508!) article is below this one, at least on a PC it is. Happy listening!

Scott Robb

April 3, 2025

#509