Why?

[philipbarrett]

...do diodes have 5V heaters rather than the typical 6.3 or 12? Enquiring minds want to know.

Philip

 

[Colt45]

So that Idiots dont use the 6.3v supply for other heaters as the supply for the diode's filament, therefore making all the heaters biased at +400v


Nah.. 5U4, 5Y3, etc are very old designs, back when most tubes used a 5v filament supply. I think.

I you get a diode with a cathode (damper for example) they use 6.3v heaters.

 

[anatech]

Hey Colt45,
I like your first answer the best. Knowing your average human, you could be right! Just think how many tubes and lives were saved due to the difference.
Still, they make 5AQ5A's and the like.

-Chris

 

[Eli Duttman]

5AQ5s, 3AU6s, 7DJ8s, etc. were used in TVs with series heater strings. A bunch of tubes with the same heater current draw whose heater voltages totalled to 120 V. were wired together.

AMOF, the "A" seen in 7 and 9 pin mini type designations (6AU6A, etc.) indicates controlled heater warmup time. The "A" types are for series heater string service. Profit matters, you know. Save the expense of filament windings in the power trafo. Never mind that when any given heater fails, the whole string goes dark.

 

[anatech]

Hi Eli,
Yes, and they are used in other things as well. Point is, a 5V heater may be waiting to make someone famous, posthumously. That's what Colt45 was poking fun at I think. There is always some truth in a joke, no?
I think I saw 5AQ5A's used on a computer based amp. Cool and scary at the same time. Computer guy + a couple hundred volts. Wow.

-Chris