Using 7DJ8's in the Reduction

[Paul Birkeland]

One possibilty that exists with this new design is using 7V tubes.  The stock circuit regulates the heaters to 6V, in order to get to 7.5V, I would do the following:

1.  Replace 1N5430's with 1N5343BG's.
2.  Remove each pair of 22 Ohm resistors, replace each pair with a 6 Ohm 5 Watt resistor.

This will set your heater voltage to 7.5V, with 200mA of Zener current and 300mA of tube heater current.

-PB

 

[Chris65]

Hi Paul,

Are there any advantages (sonic) to using these tubes? There is a cost advantage (I bought a pair for a $1), but I assume that they would perform the same/similar as it's only the heater difference, would that be correct?

 

[Paul Joppa]

The disadvantage is greater sensitivity to power line voltage variations. This is always a problem with shunt regulation ... Since the original was designed for +/-10%, and you change 11 ohms to 6 ohms, you'll want to keep the variation to +/-5% from 120v.

 

[Chris65]

OK, thanks 'other' Paul for clarifying that. I'm in a 230V area & variation is definitely more than 5%.