This interesting little amp is based on one of my favorite small pentodes, the 6197. It was inspired by similar "spud" amps I have seen around the internet. I have covered the 6197 pentode in great detail on another page, but had to remove it due to space limitations. I will re-post it if someone in interested. Look for more projects using this tube in the future.

The dimunitive chassis is less than 9" wide and 8" deep. I used a pair of Telefunken (or perhaps Grundig) output trannys obtained off eBay. These ugly trannys are beyond asthetics for top mounting, so they are hidden inside.

Design The design was straight forward and simple. Direct input via the volume control to the grid of the 6197. Other than the power supply, the amp consists of only the self bias resistor, a bypass cap for that resistor, and the output transformer. The tranny is run at about 12K, although 10K would work fine also. Tranny's much lower take away some of the pentode's gain. The power supply uses a 5Y3 feeding into the usual CRCRC type filter. A bleeder resistor at the end of the chain also performs the function of stabilizing the screen grid voltage; always a good practice generally and required in such a simple design. Each screen grid is stood off from this supply with a 1K5 resistor. How does it sound? I used this as a monitor amp on my bench for some time before finishing the construction. I always enjoy listening to it. While the bass is not very deep, the rest of the audio spectrum is clean and clear. The 6197 is a low distortion pentode, and you can tell that when you hear it. Image is very detailed and has good depth. My CD player (and I expect most CD players) drive this thing plenty loud, but not into clipping. The true net power in on the order of 2.2W per channel, so there is plenty of headroom. I can turn the volume control all the way up and the amp easily fills my 12x15 room with sound. It never sounds strained. jef Click Here for schematic. Click Here for text file.