Hi Guys
Steve, as Nauta said, it is best to build and test incrementally AND to use the Power Limiting Safety Socket - the Mandatory Project in
TOT (Tonnes of Tone).
With that in mind, you build the
PSU-PRE Power Supply for Tube Preamp first, which you have the option to build in two steps since it really is two power supplies on one PCB. Suppose you make that incremental choice and build the high-voltage plate section first because it is simplest. Follow the assembly notes, wire the mains for your local voltage, then plug the PSU-PRE through the PLSS fitted with a low-wattage bulb (25-40W). You will see the bulb brighten then dim if everything is okay. There is no load yet and if you measure the DC voltage at the W2 output block it will be a couple of hundred volts - lower than the voltage with full mains voltage.
If everything is okay then you would stuff the heater supply and test its output voltage at W3.
Both W2 and W3 have the positive end of the supply on pn-1 and the negative end at pin-2. Once LNK8 is added, the heater supply is "programmed" to look like a negative supply where W3-1 is at ground and W3-2 is -12V (or -6V if that is how you've set it).
Remember to install LNK8 to join the DC grounds together.
Remember to add the chassis wire to CHS.
You can make the testing increments even smaller in the case of the
PSU-PRE. Were you to do the mains wiring and mount the transformers only, you could verify that mains wiring is correct by measuring the PT secondary AC voltage. You should see >200Vac out from T1 and >12Vac from T2 if LNK4 and LNK5 are in place for a 12V supply. You would measure these AC voltages by carefully probing the middle two holes of where the respective bridge rectifiers are mounted.
You mentioned that everything is assembled, so you can still test what you have WITHOUT TUBES first, using a low-watt lamp in the PLSS. making sure that all the appropriate links are in place for 12V heaters on both the PSU and
M-PRE British-Style Tube Preamp Kit, and for the mains voltage for your area, it is best to clip the black meter probe to ground using an alligator test lead. This lets you probe voltages with only one hand and the other on the power switch.
With the power 'off', you can do a resistance check to verify the ground connections are intact. The meter probe clip above should be on the circuit ground NOT the chassis as the ground-link-isolator on
PSU-PRE places a small resistance between these points. With the RED meter probe, check PSU W2-2, W3-1, M-PRE VP-2, and the sleeves of the jacks. All these should read zero, or as close to zero as your meter allows. As a reference, wipe the meter probes together to see what the lead resistance is prior to performing any resistance check.
Turn the power 'on' and see if there is high voltage at PSU W2 and then if this voltage is getting to M-PRE VP. Within M-PRE, you can follow the voltage along the string of 10ks (21,19,20) and see that those connections are intact by the presence of voltage.
Similarly, you can check for heater voltage on PSU W3 and follow this through to the tube sockets pins-4 and 5.
If voltage is not present at any of the points, turn the power 'off' and see why.
If everything is okay without tubes, add the tubes and change the lamp to 60W or so and power up. You'll see the lamp glow dim - if it is too bright try a 100W bulb. Voltages will be a bit low, so the -12V will look like say -10V and the +320V will be <300V. Still, you should now see voltage drops across M-PRE 's supply resistors (R19,20,21). You only have to probe one end of these Rs to see that the voltage is dropping as you move from VP to the input stage.
Ideally, if you have a sinewave generator and a scope you can do a signal test through the preamp and verify proper operation of all the controls. Without these pieces of test equipment, you can just go to an audible test.
An audio test should begin with the output level set to zero, or if you are using the plexi wiring, that the monitoring equipment has its input level set to zero to will avoid being surprised by any loud noises, buzz or hum.
Common errors would be solder bridges, reversed diodes, reversed bridges - should cause the PLSS bulb to light bright. It used to be that semiconductor packages had printed lettering on them - silk screened with ink or paint. The modern way is to burn the lettering in with a laser, which leaves very faint grey text on the usually black background, which is very difficult to see without bright light and rotating the part slightly to see the reflective difference. For this reason, it would be easy to reverse the flat BJTs (QN1-4) or the bridges.