[Stapsy]

Not likely. 
 
Also my mk4 uses the 5842.  If you want to use the 6C45 you will need an adapter.  I have no idea if the newer ones are using 6C45, but they have a different pin structure from the 5842/417A.  I have some extra 5842 that I will be trying so I can update you on whether they make a change or not.

 

[Crashem]

Hmm I am just looking at description on website on 2a3 mkIV and it makes reference to the 6c45.  Maybe things have changed.

 

[Stapsy]

Yep you are right.  I think it was going back and forth in development but when they found the 6C45 to 5842 adapters they went with 5842.  5842, 417A and 6C45pi are all interchangeable.  From what I know 6C45 is just the Russian version.  Just check with Craig to be sure for the new run.  Worst case scenario is you pick up some 6C45 and need to get an adapter off ebay.
 
The ones I really have my eye on are the Western Electric 417A but they are pricey.  Raytheon 5842 is what I got stock and I just picked up a pair of Amperex gold pin 5842 to try.  The problem is I am loving the NOS RCA's so much I don't want to stop and change out the 5842s.

 

[Crashem]

Any of you guys know if EC 2A3x4 has any tube bias setting or is it automatic or is it set and set at what?

 

[Stapsy]

I am 99% sure it is auto-bias based on a couple of recent conversations about tubes I have had with Craig.  I don't exactly know what auto-bias means though so perhaps it is best just to ask him.
 
Also I take back what I said before about the driver tubes.  After rolling the 5842's I think they will have an effect. It will be more subtle than changing the 2A3s, however it may be worth it for final tuning.  The Amperex gold pins have been the final treble taming tweak with the HD800s that really sets the 2A3mk4 into another world compared with the BA I heard last weekend.  It may be a slight roll of in the quality of bass, but I really can't be sure without doing some more testing.  I would put the driver tube rolling slightly ahead of cables in the tweaking hierarchy.  I will try to pick up all the 5842, 417A, 6C45 that I can to test out the effects.

 

[Radio_head]

Its auto-bias.

 

[Frihed89]

  I am 99% sure it is auto-bias based on a couple of recent conversations about tubes I have had with Craig.  I don't exactly know what auto-bias means though so perhaps it is best just to ask him.
 
Also I take back what I said before about the driver tubes.  After rolling the 5842's I think they will have an effect. It will be more subtle than changing the 2A3s, however it may be worth it for final tuning.  The Amperex gold pins have been the final treble taming tweak with the HD800s that really sets the 2A3mk4 into another world compared with the BA I heard last weekend.  It may be a slight roll of in the quality of bass, but I really can't be sure without doing some more testing.  I would put the driver tube rolling slightly ahead of cables in the tweaking hierarchy.  I will try to pick up all the 5842, 417A, 6C45 that I can to test out the effects.

Basically, cathode bias (no adjustments necessary) means that the tubes operating point is determined by the voltage dropped across a resistor located between its cathode and circuit ground (as opposed to a separate fixed bias voltage source applied to a tubes control grid). One drawback is that in a cathode biased amp tends to exhibit more compression than a fixed bias (adjustable bias) amp because the bias changes with the input signal.

 

[tremolo]

Are these stock or did either of you upgraded components?

 

[Stapsy]

There aren't really a whole lot of upgrade options unless you are talking about tubes.  I got the P&G pot because I was slightly worried that I would need to listen at very low levels due to the power, however the amp has the perfect amount of gain with the HD800 (10-12 o'clock).  If you have very sensitive cans then maybe that makes sense.
 
I would save the $300 and put it into tubes

 

[tremolo]

Great! Thanks

 

[GalaxyGuy]

Are these stock or did either of you upgraded components?

I had Craig upgrade, or at least change, the stock output transformers on my amp.  I'm not sure how much of a difference it makes, but there it is.  My amp has ElectraPrint OT with silver secondary coils.  The stock OTs are Hammonds, I think.

 

[tremolo]

Thanks GalaxyGuy. I think if I order one, I will stay with the Hammonds. In any case, the base price is about the max that I could afford. It is one of those things that I am looking for some re-assurance that I would be getting a great amp in stock form.

 

[Stapsy]

I am pretty sure you can't order with the ElectroPrint OPTs which is why I didn't mention it.  I don't think you can go wrong with the Hammond's, though there is always the option to roll the transformer's if you feel like creating a Tango transformer leviathan.  The ElectroPrint's may be more resolving but are said to be less impressive than the Hammond's in timbral accuracy.

 

[GalaxyGuy]

At the NorCal meet last month when I picked up the amp, Craig told me that the guy that makes ElectraPrints is not longer in business, or perhaps it was that he is no longer making OPTs.  Either way, I agree with Stapsy:  they are not longer available, to the best of my understanding.

 

[Radio_head]

Jack is always right.  That's the problem.