Triode converters

A pentode power tube can be easily rewired to run as a triode. This reduces its power output substantially, and changes the sound. Some amps have a "low power" switch which does this.Rather than rewire any of my amps, I built these adapters that fit in between the chassis and the power tube. They make it possible to convert an amp without any permanent modification, and without opening it up. Two adapters are needed, one for each tube. If you have an amp with 4 power tubes, and are attempting to lower the amp's volume, pull two tubes, and use the adapters on the 2 remaining tubes.Running as a triode, the screens of the tubes are connected to the plates through a resistor. These adaptors house the resistor and make this connection. The diagram below is for 8 pin tubes (6L6, EL34, 6V6), but the same idea could work for 9 pin tubes.

The lower circle in the diagram is the plug, the top circle the socket. This plug is salvaged from a dead tube--carefully break the glass and unsolder the leads.Wire it up to a tube socket that you buy. Get clever about how you house the thing. I used some spare conduit that's used to bury electrical wiring because it fit the tube sockets I had.On 6L6 and 6V6 tubes, pin 1 and 6 aren't used. On EL34, only pin 6 isn't used. Pin 1 was missing on the plug that I had, and since pin 1 is grounded on EL34 tubes, I grounded it at the socket by jumpering to pin 8. This doesn't bother 6L6s, and made the adaptors more flexible in how they could be used.Here's a list of the pins:1: suppressor (EL34 only)

2,7 : heaters

3: plate

4:screen

5 : grid

6: no connection