Difference berween 5Y3 and 5U4 tubes

Just look at the voltage and current ratings.

If you have a table radio that has maybe a two watt output you don't need a ll that much power. Therefore the extra expense and space of a 5U4 is not w arranted when the lesser 5Y3 would do just fine. (and more filament current )

Accounting is part of engineering. I do not need the five buck cap in this circuit, the 25 cent job will do. However in THIS circuit I do need the fiv e buck job. (like in reactive scanning CRT monitors and TVs) It is your job to know when you need the expensive part or if the elcheapo will work just fine.

Sure, you have the spec sheet, ESR, ESL, ripple current tolerance, temperat ure range, all kinds of things, and somewhere in there is the price. That i s the one that starts with a "$" and that is the one your bosses are concer ned about.

Would you use a pair of KT88s at 200 volts on the plate into 25K load to pr oduce something like 2 watts to a speaker ? Hell no, you would just use a 6 AQ5. Why ? Because you just did with three bucks what could have costed fif ty, even back then KT88s were not all that cheap, and the dollars were diff erent.

The 5U4 is a higher powered rectifier, 1550 PIV, 800 mA peak current, 44V voltage drop. The 5Y3 has 1400 PIV, 375 mA peak current, 60V voltage drop.

Get the tube datasheets at

Dave M