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March 24, 2019, 06:17:08 am

Author Topic: Using 7DJ8's in the Reduction  (Read 2711 times)

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Offline Paul Birkeland

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Using 7DJ8's in the Reduction
« 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
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Chris65

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Re: Using 7DJ8's in the Reduction
« Reply #1 on: March 02, 2014, 04:42:02 pm »
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?

Offline Paul Joppa

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Re: Using 7DJ8's in the Reduction
« Reply #2 on: March 02, 2014, 05:43:05 pm »
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.
Paul Joppa

Offline Chris65

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Re: Using 7DJ8's in the Reduction
« Reply #3 on: March 03, 2014, 06:13:08 am »
OK, thanks 'other' Paul for clarifying that. I'm in a 230V area & variation is definitely more than 5%.