Biasing Express / cathode resistors

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eazilyled
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Joined: Sat Jan 17, 2009 9:24 pm
Location: Buxton, UK

Biasing Express / cathode resistors

Post by eazilyled »

I was reading ahead to the section about biasing in the Express build guide, and have a couple of questions regarding the use of 1 ohm resistors.

The guide says to remove the jumper between pins 1 and 8 and install precision 1 ohm resistors between pin 8 and ground for each EL34. I would rather not have to desolder / resolder components when biasing, so:

1) Is it OK to leave the 1 ohm resistors in the circuit after biasing? I have done a search on the forum about this and people have said 'yes' to this, but I'd thought I may as well ask this again.

2) Would it be OK to make these 1 ohm resistors switchable to take them out of the circuit after biasing? That way you could return the circuit to its original form without have to warm up that soldering iron.

3) Is it really necessary to untie pins 1 and 8 before installing the resistor between pin 1 and ground? I was thinking that it would be OK to leave them tied because all it would mean would be that the cathode and suppressor grid would be at the same potential - which is what you would want anyway? <Assumption alert! :D >

Sorry if these questions come across as a bit noobish. I'm really appreciating the wealth of knowledge shared here.

Cheers,
Rick
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martin manning
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Re: Biasing Express / cathode resistors

Post by martin manning »

eazilyled wrote:1) Is it OK to leave the 1 ohm resistors in the circuit after biasing?
Absolutely.
eazilyled wrote:2) Would it be OK to make these 1 ohm resistors switchable to take them out of the circuit after biasing?
No need to.
eazilyled wrote:3) Is it really necessary to untie pins 1 and 8 before installing the resistor between pin 1 and ground?
No. 6L6 sockets are often done that way so that either 6L6 or EL34 types can be used without rewiring.
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eazilyled
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Location: Buxton, UK

Re: Biasing Express / cathode resistors

Post by eazilyled »

Great, I'll leave the resistors in. Thanks, Martin!
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