Sprague cap Question....

[kevrockitt]

First time builder almost done with 100w kit- Super lead version....checking and double checking my work. Referencing the circuit board section of the new instruction manual.... In the instruction manual photo, the first piece installed on the board is a black sprague cap. The instruction manual photos clearly show the same cap on both the super lead and super bass boards (labeled 330uf). The illustrated diagrams call for a different cap to be used on each... the Super lead a 250 and the Super bass a 330. What is correct and how do you tell them apart as the supplied chart doesn't specify.

Thanks
Kevrockitt

[Roe]

first the difference is hardly audible at all. and 250uf caps often read around 300uf

[thousandshirts]

The Super lead a 250 and the Super bass a 330. What is correct and how do you tell them apart as the supplied chart doesn't specify.

You can use either. Order both, and try for yourself. They are cheap!

That being said, 330uf with a 820 ohm resistor in spit cathode setup is going to give you a -6db rolloff point of 0.6 Hz - far under the human hearing range. Everything above 0.6 Hz will be full gain. With the 250uf cap and a 820 ohm resistor in split cathode setup, you're again going to get a -6db rolloff point that is far below the human hearing range: 0.8 Hz. Again, everything above 0.8 Hz will be full gain.

If you are using shared cathode, the 820 ohm resistor is spread across both halves of the tube, so it functionally acts as somewhere close to twice the resistance. So we'd see 330uf with an 820 ohm resistor actually as 330uf with, say, a 1640 ohm resistor, which works out to a rolloff point of 0.3 Hz, and 0.4 Hz with a 250uf cap.