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I know they are supposed to be subtle, but at any volume I cannot tell if my mid and treble knobs do *anything*, from one end of the sweep to the other. The bass and presence work as I would expect. I had an old Hiwatt Custom 50, on that amp you could definitely hear changes as the treb/mid pots were swept.

Can you hear audible differences on yours?

I had a tech look over my build, he said he found a piece of solder inside the treble pot, cleaned it out, and gave it a clean bill of health. Still, I'm wondering if it's defective - to the point that I'm debating pulling it apart and redoing the entire tone stack.

I have a good meter, but do not know where I should be checking - any recommendations if I want to check it all first?

Yes the EQ section is a bit more subdued than your typical FMV tonestack. It's a completely different design than the tonestacks you are used to.

I found the Treble control is subtle like you say but I can defiantly notice the change as I sweep the pot through its' rotation. Listen to the clarity of a big open chord going from min to max on the treble control.

I find setting all the EQ knobs at noon gets you a pretty good tone, don't need to deviate too much from there.

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So, thank you Stephen for emailing me the schem - I didn't realize I could find it here under resources. After looking at schems of old ones, I agree the values are good.

I still say there's something wrong with my amp. Whether it's user error or a bad part somewhere, I don't know. I had an '81 DR504 and, as I stated above, the treb and mid pots definitely did *something*, whereas on my Triwatt I hear *nothing*.

Here are some photo's of the tone section. See any user errors?







Given how many users talk about the subtlety of the treb + mid, and I hate to say it but I'll ask anyways, there's no chance there's an error in the layout? Though I can read schem my brain cannot translate to a layout this complex so I just followed what I see on the supplied layout.

Hi Keto

The layout is correct. This is the same tone stack that DR504's used so it should work the way you remember.

Looks like you missed a jumper between lugs 1 and 2 on the Bass pot. Without that, the tone stack won't work properly.

I haven't built a Triwatt, but I did build a DR504 clone and a 6V6 version. All three tone pots definitely do something.

That should do it! Thanks, Mitch! I did miss that.

Yeah, that was it. Just tested at very low vol just now, clearly the treb + mid work after bridging the bass pot. It seems to lessen the depth of sweep of the bass knob, but that's fine (subject to testing at volume tonight).

Different question, re: biasing. Mine has never got high enough in 6V6 position - maxes out around 15-16. So, I turned the pot all the way down and flipped it to the other position, where it gave me a starting range around 14.5 and I turned it up around 20. Seeing 430v on the tubes using a bias-rite. There's no risk of harming any other components (PT, etc.) I assume, the changed circuit is still just a function of supplying voltage to the power tubes?

If that's all it is, I can't be bothered trying to track down the problem.

Glad you got the tone stack working. The way the layout is done, the 47n and 1n caps aren't connected properly without that jumper on the bass pot. The whole tone stack wasn't working properly. Bass had too much range and Treble and Mid did nothing.

For the bias issue, most DPDT toggle switches work backwards to how you might think, so there might be some confusion as to how the 6V6/KT66 switch operates. In the 6V6 position the center terminals should make contact with the outer terminals that have no wiring attached.

If you wired the switch according to the layout, the 6V6 position is with the switch's paddle flipped so it's closest to the power transformer. Rjohnson in the post below this one had a similar problem. He thought he had the switch in the 6V6 position and he was only getting 16mA cathode current with the bias pot maxed. But he actually had the switch in the KT66 position. When he flipped it the other way the bias pot had enough range for the 6V6's.