Bottlehead Forum
Bottlehead Kits => Reduction => Topic started by: Paul Birkeland on September 07, 2013, 12:55:03 PM

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

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?

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.

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