HM in the Netherlands shared a beautiful Muchedumbre XL build with me recently. He adapted his build to use a pair of Telefunken ECC83s (jealous). My notes on tweaks from our emails:
“In the Muchedumbre XL, adapting for different tubes is not so difficult (compared to resistor loads). A tweak to optimize for a 12AX7 in this circuit would be to lower the Rseries value a bit (1k5 in the original schematic). For a 12AX7, a value closer to 1k is optimal but this also depends on the amplifier you’re driving. I would not say this value is too critical unless you have a very low input impedance on your amplifier.
The other value to tweak is the cathode resistor (300 in the schematic for 12AU7). A 12AX7 may be happier with a higher value here. Something around 1k-1k5 gives you more signal swing before grid current which is generally a good thing.”
He also includes a 45 second bypass relay based on the NE555 to save his powered speakers on power on and off.
Beautiful build, HM!
Additional pictures of wiring and testing: