How to Convert your PP amp to Triode mode
Ever wonder why idiots like me rave about Pentode Push Pull amps in Triode mode? Don't you hate idiots like me as your amp is only wired for Ultra Linear (or *gasp* Pentode mode) and Triode mode now becomes the sweet tasty Forbidden Fruit everyone raves about but you can't taste?
Oscar Wilde said the only way to get rid of temptation is to yield to it. And if you know which end to hold the soldering iron, read on.
Shown here is a Jadis Orchestra amp.
Close up for you near-sighted folks.
OK. See the yellow and orange wires? The yellow ones are wired to pins 3 of EL34 while the orange ones are wired to pins 4.
To convert to triode mode is a piece of cake. Just wire a resistor between anode and grid2 pins, meaning between pins 3 and 4. Leave out the ultra linear tap on the output trans. See below.
That's all it takes! Easy huh? Most common values of this resistor is 47ohm or 100ohm. Either one will work fine. Leak/Mullard claims one is better than the other, but you can't go wrong with either. Although 1/2W is usable, go for 1W or higher.
A DIYer did the above to his Jadis and these are his exact words.
Hi yeo, fire up the jadis yesterday and wow yes there is a major difference. On the penthode the sound was a bit forward and fatter but on the triode the forwardness is pulled back and the mid/hi is more sparkle and more open leaving more space between the different instruments. Bass was not as heavy as penthode but more in control. Overall 1st listening is good but not to say that in ultralinear is bad just difference in characteristic. In triode mode it is more refine but in penthode you get the sunday live jazz lounge ambience with big chesty vocal( can be a bit fat) with a lot of air in the vocal range but the instrucments is a bit gluey.
Personally I find that triode mode has more realism but please bear in mind one very important point. Going from UL to Triode mode, you lose about half the power. If you have 40W in UL, now you have 20W in Triode. Not a problem for my 97dB sensitive speakers but if your speakers aren't efficient enough and need all that juice, then for sure your experience with Triode mode won't be positive.
That's all for now!