Thank you for such a nice review! It's humbling to read the efforts and results of builders like you!
BTW - I was able to find four of the tubes we spoke about in 12FM6 (RCA grey plates) and they'll be shipped out tomorrow. Unfortunately, the 12FM6 has reached a point of scarcity that there's very little to pick from. AFAIK, Beezar has the largest stock anywhere, and it's not much - perhaps about 150 at this point in time.
Just a couple of comments -
- 0.22uf Vitamin Q's are still in stock at Beezar, but they may not last long. I have a few dozen, but no more. The MiniMAX was originally based on the 0.18uf Vitamin Q's because they will fit on the PCB with the custom Beezar case, whereas the 0.22uf won't. I still sell what I have remaining mainly for the MOSFET-MAX which doesn't have a custom case and leaves all options open.
- There is a revised headphone relay-delay that we (cetoole and I) applied to the MOSFET-MAX. It uses a 24VDC regulator and relay, and deletes the zener diode altogether. Testing was done on the MiniMAX, so it's very easy to retrofit. The advantage is that the higher voltage regulator and relay actuate much quicker. The turn on phase is almost devoid of transient spikes and the turn-off phase is so much quicker that transients are minimized in that regime as well. I recently updated the MOSFET-MAX website with details of the new relay scheme (MOSFET-MAX Relay-Delay) and it shows a photo of a MiniMAX PCB with the parts and their mounting particulars:
As can be seen in the photo above, the mods are fairly simple - the biggest change is the use of a 78L24 TO-92 regulator in place of the BD-139. The middle lead of the 78L24 goes to the left pad at DM1. DM1 and RM1 are deleted completely. It would be best to use a transient suppressor in place of DM2, but it's not strictly necessary if you want to try it out. Also, CM3 should be rated at 35V, but I've never experienced a failure with the standard MiniMAX caps as specified. Replacing DM2 with an SA48C may promote a longer life for the relay and perhaps reduces the transients even more than the diode. It's something fairly easy to try anyway.
P.S. I socketed the relay as shown in the pic. You have to snip off some of the pins to make it work and even two DIP-8 sockets work as well (as shown in the pic).
Edited by tomb - 7/28/13 at 4:40pm