I'm building an amplifier

First test amplifier:

I have been desiring a new audio amplifier for some time now but had not settled on the details.

After years of collecting parts, the design that appealed to me was a single ended (one main tube) style the operated in a class A mode. That means simple circuitry but inefficient operation. Still if I realized half of the main tubes power capability, I could have a 65 Watt version.

It didn't turn out that way! the highest power output was 22 Watts. OK for an efficient speaker system but not my Bose 901's.

Second version:

I always admired McIntosh equipment but knew they were out of easy reach. The tube models were legendary in their operating fame and while I do own some Mac equipment, the MC-275 was out of reach with a price tag of $3000.00. That would be the used model I found at Audio Classics in Vestal. Truly a beautiful (and heavy) but it was not in the budget.

Audio amplifiers are easy to build but good amplifiers tike lots of design time and effort to perfect. The second attempt was modeled after the MC-275 in terms of power and style but the design is typical of a straight forward effort.

This initial test version wired up in a few sessions wi th a few more to debug and tune. The result was good... maybe great. so far, 72 Watts of audio and low distortion. Tripple that because I have stereo with a rear channel. 225 Watts of body rattling sound five feet away from the listener.

Well it

doesn't look pretty yet. I wanted to be sure I understood the basics before I committed to making the near final version. This little beauty has a 500 Volt power supply with fixed bias, featuring push p ull design after one conventional stage of preamplification, 10DB of global negative feedback with other features throughout to ensure stable performance. It looks like a promising basis. After all, this is just a prototype...

Third version:

I laid out a few of the tubes and the transformers just to see what the finished product might look like. It turns out I need at least another of the smaller tubes though... maybe even two for adequate preamplifier gain.

Mom says that it feels good to see me 'inventing' again!