Marshall 9004 Rackmount Preamp Negative Voltage Supply

[g1]

Sorry to belabour the point, I'm still not clear whether you were on AC or DC range for those voltages you denoted with ~, or whether you meant the symbol to denote "approx." ?
The reason being, if you were on AC range, your meter does not differentiate between AC and DC properly, which is common with lower end meters. In this case you should use a blocking cap on your meter probe when measuring AC where there is any DC present.

[bobloblaws]

Sorry to belabour the point, I'm still not clear whether you were on AC or DC range for those voltages you denoted with ~, or whether you meant the symbol to denote "approx." ?
The reason being, if you were on AC range, your meter does not differentiate between AC and DC properly, which is common with lower end meters. In this case you should use a blocking cap on your meter probe when measuring AC where there is any DC present.

Ahhhh, now I see what you meant and how I compounded the SNAFU by using that symbol. Yes, I originally used that symbol to mean "approximately". I was using the DC range exclusively. In hindsight it stands to reason I should have been expecting AC voltage on the power supply side but for whatever reason I wasn't thinking in terms of the diodes being using used for rectification, I was just thinking in terms of reversing the orientation of the D2 to change the polarity from positive to negative. Thanks for the tip about the blocking cap. But I have a Fluke 175 so it's relatively high end.