trinityamps.com

First off, I've made the 1M grid resisitor change.

As I've been playing the amp, it seems that over time the input get weaker. That is, at first all is well. Plenty of volume and crunch. Then,I notice the gain (grit/crunch) seems to get lower, then the volume gets lower, until eventually it feels like the amp is barely audible. This seems to happen over about a 10 minute period.

Any ideas on what could be happening?

There is a problem somewhere in the build - notthe design. This is not typical of the Tramp.
Be sure that 1M is soldered in well on boith ends. Measure the voltages as the volume fades, over time. That might provide a clue. Check to see if some component is heating up or any obviuos signs of heat or component degradation.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

OK. Which voltages to check? Voltage across 1M resistor?

Measure all the voltages as on the layout and create a table of voltages over time.
Specially B+, 6V6 Cathode & plate Voltage, cathode & plate voltages in 12AX7.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Well, I'm not getting any crunch right now. I took readings every 2 minutes. Settings Vol 9, Bass 6, Treble 9, Master 4, Power Max. Both push pull pots in (tweed mode, non-fat mode). I was getting some nice crunch the other day with these settings.

The only reading that looks way off is the nominal 2.3 voltage reading.

Nominal Voltages from Layout
Time min 400 29 340 191 203 2.3 1.7
0 432 30 330 182 194 1.66 1.69
2 405 30 332 183 195 1.72 1.66
4 407 30 338 183 196 1.72 1.67

All the voltages are good. Something else has changed. The volume should not change over time with those. Those are pretty solid.
If it is changing I suspect tube or external gear..

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps