Anticipation Debug Notes

Use Extreme Caution when conducting these tests. Lethal voltages are present.
The Anticipation is the CCS (Constant Current Source) upgrade to the Bottlehead Foreplay PreAmp

First note:         The plastic side of the larger transistor faces the LEDs on both the VA and CF models.
Second note:    The LEDs do not light until the tubes warm up.
Third note:        If the LEDs are extremely bright, turn the power off. The large transistor is probably the wrong part.
Forth note:       Check the part values and LED direction before applying power.
Fifth note:         Make sure the Foreplay worked with the original resistors before putting in the Anticipation in.
Sixth note:        For a Sonic treat, I'd prefer to install the VA board first and then the CF board. For debug ease, I'd install the CF board first. You are less likely to smoke a resistor with the CF board installed first.

                        If you didn't get the Foreplay to work with the original resistors first, say "OUCH!," take the Anticipation out and put the resistors in.

Safer Anticipation Testing

    You can stack two 9V batteries for a cheap 18V power supply. Put a 1K resistor in series with the B connection and tie the other end of the resistor to the C connection. You should see the LEDs light dimly in this method. I estimate that the node voltages (other than the A, B and C connection) will be about 10% low with 18V from A to C instead of 155V from A to C. The voltages across the 1K resistors are estimates (guesses).  Someday, I'll take apart my Foreplay to get actual readings.

    For CF, attach C to the + connection. (Slightly visible LED.) Expect about 1.7V across 1K resistor.
    For VA, attach C to the - connection. (Visible in a dimly lit room LED.) Expect about 0.8V across 1K resistor.

CF

The flat area on the LEDs face towards A and the small transistor.
CF1 through CF6 are just made up names to make the measurements easy to reference.
These DC voltages are from a working unit in a Foreplay with power applied,
Black lead to ground (the A connection). The probing is done with the Red lead:

CF1    1.02V     across resistor next to the A connection
CF2    1.65V     connection between the two LEDs
CF3    3.30V     "B side" of the resistor that attaches to C
CF4    2.72V     Case of smaller transistor
CF5    48V        B connection
CF6    155V      C connection

If the 3.30V is less than 0.4V, suspect the resistor that attaches to C.
If the 3.30V is about 1.5V, suspect the B connection.
If the 3.30V is near 140V,  suspect the A connection.

VA

Be extra careful, the RED lead will have 155V on it when it is not attached to anything.
The flat area on the LEDs face away from A and away from the small transistor.
CF1 through CF6 are just made up names to make the measurements easy to reference.
The VA leds are dimmer than the CF LEDs.
These DC voltages are from a working unit in a Foreplay with power applied,
BLACK lead to B+ (the A connection). The probing is done with the RED lead:

VA1    -0.98V     across resistor next to the A connection
VA2    -1.59V     connection between the two LEDs
VA3    -3.18V     "B side" of the resistor that attaches to C
VA4    -2.64V     Case of smaller transistor
VA5    -111V      B connection
VA6    -155V      C connection

If the -3.18V is less than -0.4V, suspect the resistor that attaches to C.
If the -3.18V is about -1.5V, suspect the B connection.
If the -3.18V is near -140V,  suspect the A connection. 

Notes:
1. If VA3 reads about -111V and both VA4/ VA5 read about 0.5V to 1V higher than VA3, the LED between Q1 and Q2 is not soldered or is broken. The 2N2907A is in avalanche and has been degraded. Fix the LED and check to see if the circuit now works. If it does, buy a new 2N2907A in a week or so and replace the degraded one. It may be working now, but the degraded 2N2907A may fail at any time.
2. Before applying power, check the smaller metal can transistors to see if any of the leads are touching the case or each other. I've seen this happen with small metal can parts more than once. Caution: The exposed case metal of both transistors is electrically live and attached to the collector of the respective transistor. (2-Jun-01) 



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First edition about 9/26/00. Last update 02/15/01. 
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