New Build with KT-88's

[W5FH]

Built on Super Reverb blank steel chassis. Pair of KT-88's into an O'Netics A-431 level #1 output (not using UL taps). Modified Astroverb preamp, HiWatt fixed bias phase inverter/presence circuit, Sluckey Tremonator vibrato and Jensen line-out circuit per application bulletin. The little JT-11 transformer is housed in a small tin plate box to shield it from filament wiring runs, however this may not be necessary and next build I am going to leave out box. Hammond 291EBZ power transformer with heater elevation. I started using tin plate strips to shield power supply section away from preamp area. This amp is very quiet. Using the Blencowe standby circuit with 47K series resisto, I like this much better than just switching B+ on/off. KT-88's have 1K/10 watt screen resistors, 120K bias feed and 1.5K grid stopper resistors. Using combination of polyester and polycarbonate film caps (total 70 ufd) for active mixer cathode bypass. All other cathode bypasses are polyester film. These film caps give the amp a really sweet unique tone. Beefed up reverb (from original Astroverb) using parallel 12AT7 driver into the MPS reverb driver transformer. The MPS is a really nice one with bigger core. Sozo tone capacitors throughout except using Jupiters after phase inverter. Plate current of each KT-88 can be read on tip jacks (1.0 ohm resistor), have bias set and bias balance pots.

kt88 topside.jpg

kt88 underside.jpg

[xtian]

Wow! Your P-t-P-FU is a knockout!

[maxkracht]

Nice looking build! Can't tell from the picture if you have already done something to remedy this, but might want to add some insulation between the rectifier and the mounting hole. I could see myself fumbling with the chassis bolts and getting zapped if they don't go in perfectly straight.