trinityamps.com

viewtopic.php?f=14&t=3264 Might give you a starting point and maybe PM Coco if no one else replies.

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"The only problem with being retired is you never get a day off"

zaphod wrote:
+! to kurtlives' comments.

Basically, the VRM/power scaling concept doesn't really work well with Hiwatt type amps. These aren't Marshalls. When developing the Triwatt, which is based very closely on classic Hiwatt designs, it became very clear that there was a specific voltage sweet spot for the right classic Hiwatt tone. If you went much above that, it started to sound shrill. If you went below, it got mushy and lost definition. Just use the built-in MV. If you wanted to add anything to that, you could also install a post-PI MV, which a few folks have tried with regular Hiwatts and appeared to work well.

Sorry, thought Zaphod's comment about a volume pot after the phase inverter might work for you.

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"The only problem with being retired is you never get a day off"

matt_garman, as for PPIMV controls, if you're not familiar with them, google, the different types of PPIMV controls. There's an amp guy that wrote some "pages" and in them is contained different types. (Not sure if I'm allowed to say who wrote them of the name of them, I'm not familiar on copy-write.) Specifically do some research on Type 3 master volumes. There are a few different types and they all have pros and cons. I've modified a "presence" control in an amp that I had, which was basically a cut control from old voxes. Turned it into a type-3 master volume. It's very similar to (and may actually also be called) a crossline master volume. Check out the schematic for the TC15, I think it uses this type of master as well.

Matt: Yes, there are various ways to do PPIMV. Most of them use a dual gang pot to vary the two signals coming out of the phase inverter before they get to the output tubes.

The resistor mod you proposed sounds feasible. It would be easy to test the mod out to see if it does what you want. Just remove the wire going to the master volume control and clip in a resistor. If that doesn't work you can experiment with PPIMV.

Yes, it's definitely possible to add a "bedroom mode" switch to your Triwatt to limit the volume ceiling. Essentially, you would be adding a fixed resistor in parallel with the master volume pot to reduce its sensitivity.
phrazle

That's a lot more sophisticated than what I'm proposing, which has nothing to do with variable-voltage regulation (VVR). From what I can see, VVR allows the power tubes to be operated at a lower voltage, which not only lowers the overall volume but also keeps power tube breakup/distortion within reasonable bounds. To put it simply, Hiwatt-style amplifiers aren't well-suited to the VRM/power-scaling concept.
mini crossword

Adding a resistor with a switch to control the volume in your tube guitar amp is a feasible idea and can be done retro bowl unblocked

Your idea sounds quite interesting and could work if done properly. Using a resistor to reduce the input voltage of an amplifier is a way to reduce the amount of volume, creating a lower sound level. fnf

It appears that the VRM/power scaling concept may not be suitable for replicating the classic Hiwatt tone due to voltage sensitivity. Utilizing the built-in MV or post-PI MV could be preferable. Stay solar!

The mod reduces the amp’s output power, allowing you to achieve the same level of saturation and bandle overdrive at a much lower volume. This is usually done by re-biasing the tubes or using an attenuator circuit within the amp.

Finding and maintaining that voltage sweet spot is crucial for anyone looking to achieve that classic Hiwatt Slope Unblocked tone, especially in designs like the Triwatt, where the goal is to replicate those vintage sounds as closely as possible.