Snfoilhat
Tele-Afflicted
I ran into a hitch following part of the reverse-engineering of the OEM Soldano SLO 100 power transformer that is done in chapter 2 of the book. I'm missing a step in the logic*. That and a typo or two got me wondering if there is an errata page posted anywhere. When I got my copy of Blencowe's preamp book, I was able to immediately page through it with a pencil and fix a few mistakes. I can't find anything like that on the ampbooks site, but maybe someone here knows of a page on another site where there's an informal collection of fixes being discussed?
*if anyone wants to take a swing at the specific problem I ran into, here is a summary:
The author sets out that his initial guess for a high voltage winding on the PT is 360-0-360 Vrms, then says let's check and see. It's been worked out in the prior pages that the total DC load is around "132 mA" at "497 V" (±20% he emphasizes). Then uses Ohm's law to calculate a total load resistance given those two figures, 497 V / 132 mA = 3.8k Ω.
Then the part I don't get. He references a formula from the Radio Designer's Handbook 4th ed to calculate DC output voltage given a capacitor input filter and power line frequency (60 Hz), capacitor value (200 µF), and load resistance (calculated in the previous step, 3.8k Ω).
= 2π(60 Hz)(200 µF)(3.8k Ω) = 287
He doesn't show the units for that 287 figure, but i presume from the text that it's volts. Then, where I'm lost, is that this 287 never comes back. He goes immediately on to if we assume a winding that's 360-0-360 Vrms, then calculates peak voltage (= 509 V), then applies the calculated peak to the initially estimated "total" voltage (the 497 V from the start), using a figure from the same part of the Radio Designer's Handbook that has an X-axis that looks like it is using the same formula (ωCRL). But I don't see the 287 anywhere. Just the 497 and the 519. So what was the point of bringing in that calculation?
Any insights y'all may have to the 1st question (errata/discussion) or 2nd question, above, would be really welcome. Thanks!
*if anyone wants to take a swing at the specific problem I ran into, here is a summary:
The author sets out that his initial guess for a high voltage winding on the PT is 360-0-360 Vrms, then says let's check and see. It's been worked out in the prior pages that the total DC load is around "132 mA" at "497 V" (±20% he emphasizes). Then uses Ohm's law to calculate a total load resistance given those two figures, 497 V / 132 mA = 3.8k Ω.
Then the part I don't get. He references a formula from the Radio Designer's Handbook 4th ed to calculate DC output voltage given a capacitor input filter and power line frequency (60 Hz), capacitor value (200 µF), and load resistance (calculated in the previous step, 3.8k Ω).
= 2π(60 Hz)(200 µF)(3.8k Ω) = 287
He doesn't show the units for that 287 figure, but i presume from the text that it's volts. Then, where I'm lost, is that this 287 never comes back. He goes immediately on to if we assume a winding that's 360-0-360 Vrms, then calculates peak voltage (= 509 V), then applies the calculated peak to the initially estimated "total" voltage (the 497 V from the start), using a figure from the same part of the Radio Designer's Handbook that has an X-axis that looks like it is using the same formula (ωCRL). But I don't see the 287 anywhere. Just the 497 and the 519. So what was the point of bringing in that calculation?
Any insights y'all may have to the 1st question (errata/discussion) or 2nd question, above, would be really welcome. Thanks!
Last edited:
