Triode mode question

[RobertWStephens]

Hello! I want to try triode mode on my tube rectified ST-35. If I understand the manual correctly, I can just attach 1W 100 ohm resistors across pins 1 & 2 on J2-J5 and pull C20 & C21. It says to not attach any UL taps to pin 2. I am using the Hammond 1650F's. Do I just disconnect the wires going to pin 2 and terminate them with a wire nut? What kind of changes in the sound can I expect? Thanks for any input! Peace. Robert

[TomMcNally]

You're correct. I can't tell you what it will sound like, but it's a 10 minute change, give it a try. Use 100 ohm 1 or 2 watt resistors.

[mesherm]

For EL84s I use 200 to 250 ohm resistors.

[RobertWStephens]

Thanks! What does that change the output wattage to? What is triode referring to and why is it desireable? Peace. Robert

[mesherm]

Tying the screen grid to the anode to run in "triode" mode will typically cut your output power by 1/3 to 1/2. In my EL34 triode connected amps I have used a UF4007 diode in series with the 100 ohm resistor with the resistor attached to the anode and the banded end of diode attached to the screen grid pin. This seems to help restore some of the lost power. I am in the process of building a PPP EL84 triode connected amp now so most of my experience hase been with EL34 and similar higher power pentodes and been tetrodes.
Triode operation is explained on many sites on the web.
Here is one.
http://www.webace.com.au/~electron/tubes/triode.htm

I can attest that the sound is definitley better to MY ears.
The soundstage is just as open but the lows, mids and highs seem to be better defined. I loaned a JJ EL34 triode connected amp to a friend here at work who I built a stock ST70 for and he wants to buy the new one from me now. He noticed the difference right away.
Triode connected JJ EL34s sound great as do JJ KT77s and EH6CA7s....I have a set of EHKT88s though that do not sound as good when subsituted in the same amp so tube some rolling is worthwhile.
It is not to much trouble to install a 4pdt switch so your amp has dual capability. Its a good bet you will need to rebias the tubes when switching modes (turning off the amp of course).

[RobertWStephens]

I can't imagine that I will be backing out the triode mode I just hooked up! Thanks for keeping this fun!!! Peace. Robert