Direct Coupled 300b

RPMac · 4995

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Offline RPMac

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on: March 15, 2013, 02:10:05 AM
Why are direct coupled 300b set so rare?


Offline Paul Birkeland

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Reply #1 on: March 15, 2013, 02:52:00 AM
I believe it's mostly that the voltages are quite high (maybe 550V on the 300B plates, so maybe 575V in the power supply).


Paul "PB" Birkeland

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Offline RPMac

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Reply #2 on: March 18, 2013, 08:54:21 AM
PJ said in the 2a3 paramount or paraglow, we could rewire the transformer for 5 volt output filaments and use a 300b. Other than giving up max power from the 300b, what would be the consequences?
The paraglow would have a 2.5k OPT.


Offline Grainger49

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Reply #3 on: March 18, 2013, 11:24:16 AM
IIRC the JJ 2A3-40 is a 2A3 heater in a 300B tube.  Jim Rebman, in whose ears I trust, really likes them.  And now that I am more flush with cash they will be on the purchase list.


Offline Hank Murrow

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Reply #4 on: March 19, 2013, 05:38:17 AM
My 2A3 Custom BH amp built by PB is not direct-coupled, but the JJ 2A3-40 tubes I rolled in a month ago from "Eurotubes" in Portland OR really sing sweetly and produce thunderous bass. Huge stage, and do remind me of the 300B somewhat in their presentation. I hope they last a long time, as i would hate to change them back to NOS GE's or National Union. Eurotubes offers a 6 month guarantee.

Cheers, Hank in Eugene
« Last Edit: March 19, 2013, 05:42:36 AM by Hank Murrow »


Offline Tickwomp

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Reply #5 on: March 19, 2013, 10:00:17 AM
Quote from: Grainger49 on March 18, 2013, 11:24:16 AM
IIRC the JJ 2A3-40 is a 2A3 heater in a 300B tube.  Jim Rebman, in whose ears I trust, really likes them.  And now that I am more flush with cash they will be on the purchase list.

You saying these JJ 2A3-40 are a direct replacement when the Paramounts are setup for 2a3?  Anyone compare them directly to the EML 2a3?

TIA,

Tick

Mach2 Mac Mini->Amarra Mini-> Chronos Athena USB Cable->Audio Note 4.1LE DAC->24ga Ag w/WBT0101ag ICs-> Audio Note L4 Remote->24ga Ag w/WBT0102Ag ICs-> Paramounts w/MQ Nickel Opts and EML 2a3 Mesh Plates->16ga Ag Bi Wire->Klipsch RF-7 w/DeanG Mods

Offline RPMac

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Reply #6 on: March 20, 2013, 04:23:12 AM
Grainger, the JJ 2A3-40 is on my short list, but what has my interest is direct coupling...more so with a DHT driver. Only schematic I could find with Mr. Google was Gary Pimm's 26/300b.
Maybe I should try to modify my Parabee into a Blues Master?


Offline Paul Birkeland

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Reply #7 on: March 20, 2013, 04:44:27 AM
For an all DHT 300B amp, the EML 30A is going to be one of the few driver tubes that will get the job done.  To get full output from the 26/300B combination without any interstage iron, you'll need an unusually high amount of output from your preamp, and I'd expect there to be some noise issues with that configuration. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline RPMac

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Reply #8 on: March 20, 2013, 05:10:01 AM
The pre will be a BeePre.  Interstage iron could be a second choice.


Offline Paul Birkeland

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Reply #9 on: March 20, 2013, 07:32:35 AM
I'd recommend building with the EML30A instead, an amplifier with an input sensitivity of 10V will only bring frustration.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline braubeat

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Reply #10 on: March 20, 2013, 08:14:25 AM


Offline Paul Birkeland

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Reply #11 on: March 20, 2013, 05:35:47 PM
Heck yeah! Oh wait, have a look at the curves for those, yikes!  (I have some SV572-10's sitting around somewhere with similar issues)

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline RPMac

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Reply #12 on: March 22, 2013, 07:21:16 AM
Quote from: Caucasian Blackplate on March 20, 2013, 07:32:35 AM
I'd recommend building with the EML30A instead, an amplifier with an input sensitivity of 10V will only bring frustration.
I know my limitation and I know I'm not able to design an amp.
I believe I could build from a proven schematic, which is what I was looking for.
Thanks for your help.


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