Author Topic: Kay Tremolo voltages and info  (Read 1821 times)

Brett Clark

Kay Tremolo voltages and info
« on: December 14, 2003, 06:13:08 PM »
I actually have one of the almost-famous Kay T-1 tremolos. At Nightingale's request, I measured some voltages and did some general poking around to help out those of you that are cloning this thing.

Voltages - measured with 8.22V battery voltage and oscillator disabled (by breaking the connection between the 33 Ohm resistor and the caps)

Q1 E=0V  B=0.697V  C=7.09V

Q2 E=0.028V  B=0.541V  C=0.029V

Q3 E=0V  B=0.548V  C=0.029V

Q4 E=0V  B=0.697V  C=1.20V

SOME VERY IMPORTANT NOTES:

1. The transistors are 2SC828R, which have pinouts of E-C-B (left-to-right, looking at label). The GGG layout is for transistors with a E-B-C layout (such as 2N5088, etc.)! 2SC828 (or NTE199) will not work in the GGG board unless you twist the leads around!

2. I don't have an original datasheet for the 2SC828, but the NTE199 (it's substitute) is a high-beta (>400) part. So the 2N5088 may be a good sub that works directly in the GGG layout. HOWEVER, the actual betas of the transistors in my unit seem to be in the 100-200 range, based on the measured voltages. It might be worth checking out some lower-beta transistors as well and see what works better.

3. There is an error in the GGG schematic. The control pot is not a 1K unit - it's 5K (labelled and measured). I am the original owner of this unit, and it has not been changed. Using a 1K would give only the faster range of speeds. However, the oscillation cuts out if the pot is set above about 4.2K. So, you could put a 33K resistor in parallel with the pot to limit the resistance. In the original pedal, the pot rotation is constrained by the mechanical design of the pedal. By the way, the schematic label on the unit identifies the pot as "1Kx5" , which is a strange notation and the probable source of the error.

SOME MOD SUGGESTIONS: The first stage is not well-designed, as it is not stable with beta and temperature. It needs a bypassed emitter resistor to stabilize the bias point. Try a 390 or 470 Ohm in parallel with a 22uF cap, and then adjust the value of the 470K resistor to set the collector voltage to about 4.5V.
The bass response is weak - increasing the 0.1uF input cap to 0.47uF and the 0.01uF to 0.1uF might help, but I haven't tried it.