Philips Model 922 Tube Radio Video #1 - Checkout and Power Up

[@randomsteve4288]

38:40 There is a reason Philips opted to make the first capacitor after the 35W4 tube 30uF and not 40uF or 47uF, like Jim intends to. And the reason is the inrush current and repeated peak in charge current near the top of the AC wave. It is a common misconception that this only affects the initial inrush current on a uncharged cap. As a matter of fact the choice of capacity also determines where in the raising edge of the sine wave the recharge of the filter cap sets in. A too high value cap pushes the recharge point toward the peak tip of ur sinewave, meaning that only a very short timeframe (small phase angle) remains to fill the cap up to full peak voltage. And that means a high current needs to flow to achieve that. And again, this peak current is not a one shot event, but repeats with every wave - be it half or full wave depending on ur rectifier design. So choosing the value of the first cap after a rectifier - tube or semiconductor - is walking a fine line between reducing the repetative peak charge current versus ripple reduction. You can easily watch that effect of too high of a filter cap by simulating it in Pspice/LTspice! And even if you are of a less theoretical approach, tube datasheets specify the max capacity of the first filter cap after the tube. In the case of 35W4 it is 40uF. So philips opted for a 30uF as the first cap to stay well below that limit value and thereby reduce peak charge current to ensure a longer tube life. A more knowledgeable and more dilligent tech would have opted to replace the old 30uF with a 33uF one, and at least go for 200V not 160V.

An engineering sample is a prototype unit for the engineering department. Cool!

[@randomsteve4288]

46:37 seeing this wire wrapped mess of capacitors and later them flapping in the breeze with no mechanical tie points, makes one wonder why others like M.Caldeira or Robert Anderson bother with restuffing caps, relocating caps, putting in terminal strips or even going to the length of buying adapt-a-cap PCB boards... Oh wait i know why; they want to do a good job for the paying customers not just a "it will work until it is off my bench" job... I dont know what canadian law is on this, but in most civilized countries Jim, being the last one to service this radio, would be the sole one responsible for the electrical safety of this appliance. I am anxious to see what he does about the elephant in the room; the missing back cover on a hot chassis....

[@hestheMaster]

Oh brother!

[@hestheMaster]

Oh brother.