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RE: 2A3 Direct Coupled VS. Capacitor coupled

Posted by 91derlust (A) on February 16, 2019 at 17:36:31

In Reply to: 2A3 Direct Coupled VS. Capacitor coupled posted by audiophilewannabe on February 16, 2019 at 03:14:47:

Responses that follow are based on my experience of building and running capacitor-coupled and direct-coupled amps using the same signal tubes (but other components are different).

> > > Can somebody explain to me the difference and the reason why it's done that way?

CB has covered this well, as usual. Capacitor-coupling is cost effective, suitable for use with a wide range of driver tubes, and is relatively easy to implement a safe, stable amplifier.

> > > Is one actually better than the other?

This is difficult to say. I think direct-coupling has an advantage in sound quality; however, this will be more obvious in some designs and may come down to personal preferences and design goals. I think if you know what you are doing and your goal is transparency (reflected in tube and component selection) and perhaps agility and coherence, then direct-coupling is worth considering.

> > > Are there any other way it can be done besides these 2 ways?

• Capacitor-coupling with grid-leak resistor
  
• Capacitor-coupling with grid-leak choke - popular in DIY circles a decade or so ago
  
• Transformer-coupling - dependent on transformer quality
  
• Direct-coupling variants - Loftin-White, monkey variants (free lunch, DRD et al), and "simplified"
  

> > > How do big name well known companies do their SETs?

It varies, but I think capacitor-coupling with grid-leak resistor is most common.

I run a pentode direct-coupled to a 2A3 using a simplified approach (no monkey or Loftin-White). It demands a progressive switch-on sequence and occasional checking of driver current (I have external test points) - and generates a bit of heat. Now rock-solid in operation, but it took some work to get it there.

Next time, I'll go all-DHT, either with monkey style direct-couple or transformer-couple.

Cheers,
91

"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein

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