HappyCat wrote:Well, I've just finished a TB, and I'm suffering a pair of troubles that are getting me crazy. It's a TB MKii, with a DPDT switch to change between MK1.5 and MKII modes. The wiring of the switch is verified, and I tested in other buildings succesfully. I followed the well-known schematic for the OC75 version, traced (I think) by Electric Warrior:
[ Image ]
In this case, I mounted GT308b russian germanium transistors. Gains are specified below. Leakage zero, are usually happens with these old soviet germs. At the same time, I mounted an external bias pot (100k) for Q2 collector, and an internal trimmer (20k) for Q3. Let's see what happens...
The sound in MK1.5 mode is acceptable, even with the wild voltages for Q3. In MkII the sound is very noisy, hissy, and a bit gated. With extreme settings in the bias pot an trimmer, the sound can be avoid, but the sound is not very acceptable. I tried different transistors, and the result is the same.
About the readings:
Q1: Hfe around 45
Q2: Gain 59
Q3: nearly 70
Users browsing this forum: No registered users and 2 guests