# Has anyone read the R. Kuehnel Soldano SLO book (2021)?

#### 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!

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#### Tom Kamphuys

##### Tele-Holic
No real answers (yet?), but some remarks:

The number 287 _is_ just a number. The units of the formula are [1/s]*[C/V]*[V/A] = [1/s]*[As/V]*[V/A] = [-], so no units.

Valvewizard also has a page on power supply design that might give you a different view and might give you some insight into your actual question, or maybe not?

I have seen the image before, but I don't know where that was...

Edit: Found it! Guitar Amplifier Power Amps by Richard Kuehnel. Now I only have to answer the original question.

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#### YellowBoots

##### Friend of Leo's
I don’t have an answer for the first question.

Second question answer is that 287 is the x-axis value of his red dot. The gotcha is that the logarithmic scale is demarked into 20 divisions instead of the customary 10.

My personal question is how does he calculate 0.2 for %Rs/Rl?

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• Snfoilhat and Tom Kamphuys

#### Tom Kamphuys

##### Tele-Holic
Ok, here we go:

The description of the figure is: "It shows the power supply output voltage as a percentage of the peak secondary voltage as a function of 2pifCR, .... Each curve is for a different ratio of power supply resistance to load resistance."

the value of 2pifCR = 287. That is the x axis of the graph. In the text it is stated that the load ratio is 0.2%. So we have to go up from the x axis value 287 until we cross the (missing) 0.2% load ratio line. We don't end up at the red dot, that is a bit problematic. I don't do this on a daily basis ;-) , so you might want to think this through yourself. But because the line is nearly flat is doesn't matter that much. The y-axis value will be around 98%, giving 509 V * 98% = 498.8V (is nearly 497V).

I'm not 100% sure I interpret the little bit of text below the graph correctly, as not all is shown.

• YellowBoots and Snfoilhat

#### Tom Kamphuys

##### Tele-Holic
• YellowBoots and Snfoilhat

#### Snfoilhat

##### Tele-Afflicted
Ah thanks very much! Sure looked like a lot of lines for a log scale but I 'knew' they had to be 10 • YellowBoots