Bottlehead Forum

General Category => General Discussion => Topic started by: RPMac on March 15, 2013, 02:10:05 AM

Title: Direct Coupled 300b
Post by: RPMac on March 15, 2013, 02:10:05 AM: Why are direct coupled 300b set so rare?
Title: Re: Direct Coupled 300b
Post by: Paul Birkeland 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).
Title: Re: Direct Coupled 300b
Post by: RPMac 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.
Title: Re: Direct Coupled 300b
Post by: 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.
Title: Re: Direct Coupled 300b
Post by: Hank Murrow 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
Title: Re: Direct Coupled 300b
Post by: Tickwomp 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
Title: Re: Direct Coupled 300b
Post by: RPMac 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?
Title: Re: Direct Coupled 300b
Post by: Paul Birkeland 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.
Title: Re: Direct Coupled 300b
Post by: RPMac on March 20, 2013, 05:10:01 AM: The pre will be a BeePre. Interstage iron could be a second choice.
Title: Re: Direct Coupled 300b
Post by: Paul Birkeland 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.
Title: Re: Direct Coupled 300b
Post by: braubeat on March 20, 2013, 08:14:25 AM: How about these bad boys.

http://www.ebay.com/itm/PAIR-NEW-SVETLANA-SV572-160-TUBES-/400308738641?pt=LH_DefaultDomain_0&hash=item5d34429a51

Michael
Title: Re: Direct Coupled 300b
Post by: Paul Birkeland 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)
Title: Re: Direct Coupled 300b
Post by: RPMac 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.