Which EML 2A3... if any?

About the Emission Labs tubes and how to use them.

Which EML 2A3... if any?

Postby Docere » Sat Jul 12, 2014 9:35 am

Hi all,

I would like to know which EML2A3 is most suitable for my amplifier, if any.

Details of the amplifier output stage as follows:
  • Output stage run single-ended
  • Measured operating points: 47.5mA and 265V plate to grid (grid -47.5V)
  • Measured filament voltage (with JJ 2A3): 2.49V
  • Cathode bias
  • B+ has slow start-up via thermistor on transformer primary (~15 sec to full power)
  • Filaments are AC using separate transformers, with no slow start-up (filaments are powered before B+ reaches full)
  • 0.22uF new design Jupiter coupling capacitor (alu foil and wax) - not PIO and no reported issues with new design
  • 330K grid leak R
Is this amplifier suitable for EML tubes? Which 2A3 would you recommend - I'd like to try mesh, but have concerns regarding sound, tube-life and reliability in an unsuitable amplifier? I have submitted a quote for the 2A3-S, but would change if mesh is suitable.

On a slightly different topic: for my next build, I would like to DC filaments - do you have a list of approved designs suitable for EML tubes?

Thank you for any assistance you can provide.

Posts: 2
Joined: Sat Jul 12, 2014 9:06 am

Re: Which EML 2A3... if any?

Postby Jac19 » Sun Jul 13, 2014 9:08 am

Hello Raymond,

sure what you write looks all ok to me for any 2A3 also EML.

For DC heating there is no list for how to do that, but generally we advise against electronic regulators. You have some risk on higher voltage output by mistake, while experimenting. It sounds kind of stupid, but regulators are the #1 error source.

Best is to use a filament choke. Check for the "CMR" circuit here. This is described for the HV power supply, but a heater power supply is not made any different.

http://www.emissionlabs.com/Articles/AP ... PPLIES.htm

Or, just use passive stabilasation with a plain C-R-C circuit. With the "R" you can adapt nicely the 2.5V needed, and ripple is lower as you need to make the tubes dead quiet.

Best regards,
Posts: 21
Joined: Sun Dec 29, 2013 10:54 pm

Re: Which EML 2A3... if any?

Postby Docere » Sun Jul 13, 2014 9:37 pm

Hello again Jac,

Thank you - your response clarifies things nicely. Open and informative. I will review my order.

Posts: 2
Joined: Sat Jul 12, 2014 9:06 am

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