Your journey with lower-watt tube amps -- Can a kit be good enough?

What are your thoughts on reducing the bias a bit on the voltage?

@rankaudio The power tubes can handle it well enough. But that will affect the distortion signature of the amp but by how much is hard to say.

my tech and I will be adding a switch so it can run in triode mode.

@hilde45 Doing so will change the feedback since the loop gain of the amp will be reduced. You may actually wind up with higher distortion; partially because the EL84 is normally an easy tube to drive; as a triode it will be harder so the driver circuit is likely to make more distortion of its own on this account.

The ST35 employs ultra-linear operation in its output transformers, which allows the power tubes to have linearity approaching that of triodes (and in some cases, having exactly the linearity of triodes). So my thoughts are this will be detrimental. 

If you really want to find out what the EL84s and the Dynaco transformers can do I recommend getting a different chassis like this one and building up a different circuit on that. If I were to do something like that I'd arrange a 12AT7 as a differential amplifier to drive the power tubes instead, with possibly a constant current source for the power tubes as well as one for the input tube. 

@atmasphere I'll convey that to Mike and see what he says. Thank you.

@atmasphere Here's what Mike said: "It will almost certainty raise both the harmonic and intermodulation distortion in triode mode and drastically reduce the power, but it may be pleasant distortion."

It will be switchable, so if it doesn't sound nice on the speakers, we'll switch it back. Gotta experiment, right?

@hilde45 I applaud your interest in experimentation. Triodes will give a pleasant distortion. But if you want to maintain the feedback you'll need another stage of gain. 

Another consideration is the tube in triode mode will want to see a different plate load for which the transformer isn't designed. 

@atmasphere My tech said this about the ST-35 mods we're discussing:

"The datasheet lists a 10k plate-to-plate load for the tubes in triode mode and 8k plate-to-plate in ultra linear, so it's not that far off. Per the Mullard datasheet, power drops to about 5W, which is expected. Full power distortion is ~2.5% vs 1.17, but probably lower at lower power levels. Required grid voltage is about the same, so the feedback probably won't be completely borked. As for more gain, short of building a new amp on a new chassis, that is not an option and of course it would no longer be an st-35."