It is surprising how loud one 1 6V6 (about 4 watts) can be in the Two Stroke. After my last post about using an attenuator, I looked around the web to see what might be available. I found a number of examples of guys simply adding an attenuation pot between the OT and the speaker. This is not a good solution as it does not deal with the issue of impedance mismatch that adding an additional load to the OT will create. Think of adding an attenuator as adding an additional speaker load that does not make sound. If you added a 4 ohm speaker in series with a 4 ohm speaker you would create a 8 ohm load, right? You would adjust the OT’s impedance output to see the 8 ohm load. The same is true when adding a power attenuator. It’s not difficult to do, but you need to account for the impedance load change.
Too much attenuation changes the output sound and when used in excess, can overload, overheat and fry an OT. Even commercially available examples of power attenuators can cause problems. Limiting attenuation to about 12 db is a good idea (-12 db is a very noticeable reduction in output). The plans for building a nice, simple, and inexpensive attenuator that works great are available in Gerald Weber’s book: All About Vacuum Tube Guitar Amplifiers. The instructions for building a one stage (-6db) and two stage (-12db) were original originally posted in Weber’s old monthly column in Vintage Guitar magazine. I’ve built both versions and can report that they work great.