I am putting my Thunderfunk 500B up for sale.
It has recently come back from Dave in february and it received all the available upgrades for this model. That includes a modified power section, with 6 filter caps giving the amp more headroom, and opening up the lows quite a bit. This also received improved heat-sinking. Dave said this would make the amp 2 ohm capable, though as you can read in many threads, it was designed for optimal 4 ohm operation.
I should note that the original reason the amp went to dave was a broken power switch (physical break/ not electrical) and a bent volume knob. They were replaced at the time of the upgrades.
The upgrades and repair totaled $295 with return shipping. Here they are as Dave put them on the receipt...
TFB550-B Upgrade 2
In-Rush Current Limiting
Part Value Changes providing stronger drive, lower DI-2 Output, Less DC Offset on DI-2
Six Transistor Upgrade
Automatic Fan Thermostat
Current Limiting Adjustment for 2-Ohm Drive
Service and return freight
Pics to follow
Asking $850 Shipped o.b.oSOLD for $800