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Looking for 300B or 2A3 design suggestions......gearing up for a new project

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jmillerdoc

jmillerdoc

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Joined 2009
#1
Hi,

I have been thinking of building a big tube SET amplifier for some time now. I am looking for some suggestions on good, proven designs.

Would love to get some input from a few of you out there who have built and know of some excellent performing amp designs using the 300B or 2A3 (or variants) or similar "big power" tubes.

Thanks!
Jeff
Lawton, USA:cloud9:
 
#2
The type of SET design I use constantly is a three stage design with all DHTs. There are several variations. Input tube can be 26, 01A, 30sp, or even 10Y, driver can be 31, 71A, 46 or 10Y. Output is 300b normally. Any of those variations will give you superb transparency, timbre and realism and a really delicate and detailed treble. I think this sound is a trademark of DHTs in general so I use them all the way through, not just the output.

Couple these how you like - transformer, good russian teflon cap etc. I usually use a wirewound resistor on the cathode - others use battery grid bias which is probably better. I went off red LEDs though did give them a go. Plate load can be an active IXYS cascode or a choke. Or just start with a resistor to get it going.

Filaments are just Schottky diodes, big cap like 15,000uF and LM1084 ccs. But you need a filament supply for each tube, so that's 6 supplies. least hungry are 30sp into 31, and that's cheap and a very good sound. 30sp (VT67) is less microphonic than the plain 30. 01A into 71A is better still and still not so hungry. 26 into 10Y is getting seriously good, but filament supplies start to need big heat sinks. Given the 6 filament supplies, it's a pretty easy decision to use a seperate box for the power supply. That leaves you with choices for umbilicals. I use Amphenol AP 4 pin for HT and earth and XLRs (4 pin mostly) for filaments, or Speakon 8 pin connector for drivers and outputs and XLR for inputs.

Lots of information about this in the current 26 preamp thread.

andy
 
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#4
jmillerdoc said:
Andy,
Thanks for the great advice. I am not quite to the point where I can create a design de novo.....you wouldn't know of any good schematics that are proven would you?
Thanks,
Jeff
Click to expand...

Katelelo by Ciro Marzio is an excellent 300B amp. The circuit is shown here (post #6): http://www.diyaudio.com/forums/tubes-valves/152480-katelelo.html
For some reason the original article has been removed from the net.
You can use the 26 instead of the rare PT8 as input triode. The driver options are: 71a, 45 and 2A3. Also, as suggested by Andy, the 31, 46 and 10Y are excellent drivers, too.
The 4-300BLX was a special titanium plate 300B made by Golden Dragon and was discontinued a long time ago.
The original OPT's, chokes and supply transformer are available. However you can use other similar types for you own realization.
Cheers,
45
 
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#12
I built a variation of the 300b DRD from Jack Eliano that was recommended earlier by dsavitsk. It is my primary amp and I love the sound, although it may be a bit laid back for some-- especially since I'm running some TJ meshplates.

Circuit, my layout and authentic Kofi Screwups (TM) can be found here:

http://www.diyaudio.com/forums/tubes-valves/101759-kofi-annan-kofi-makes-300b-drd-you-get-help.html

Jack's original design pushes much more out of the 300b (I think right up to maximum dissipation), so you'll get more watts his way.

Good luck!

Kofi
 
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#13
Very nice!

88Man,
I love this design. This will definitely be my next project. It seems to be a well proven design with many fine examples of completed projects on the webpage you referred to. Wow, those are some incredible works of art! I am going to have to step it up a notch with this one.

I noticed on several of these builds (examples on the page here: Worldwide builders ) they used brass plates for the top plate of the amps. Does anybody know where to source this stuff? I have checked around my usual sources here in SW Oklahoma and come up empty handed. I have used aluminum on all of my projects thus far but really love the look of the brass and want to try this.

Another question about construction....I have heard and read many times about using "punches" to get the perfect holes in these projects. Exactly what are we talking about here? Is this a big shop tool with a hydraulic press, some giant piece of machinery? Or can one get these punches in a more portable type of tool? I am unfamiliar with the punch type tool people have spoken about. Can somebody refer me to a source for a metal punch tool that I might be able to acquisition at home?

Thanks!
Jeff
 
#15
Hi Jeff, there may be others sites, but here is a good start for brass tops: Speedy Metals - Plate
For more sites, just do a search for "brass plate." If you call them, the will custom cut for you. For sure, brass will definitely be harder to work with than aluminum, but the polish will be most impressive at the end. You can have other components anodized or plated with gold, chrome, copper, brass, etc.

Jeff, I agree, the builds on Derek Walton's site are truly an inspiration and a great reason to elevate this great hobby to an art form. What do you think, is it OK to use the James 6123HS OPT instead of the Hammond or Plitron the 300B amp?...
 
#16
I have personally never used James OPTs but I understand the are some of the better ones available. I am pretty sure they are going to set you back a little more than the Hammonds too. In the end though I think you wouldn't be making any sort of mistake by using the James. I say go for it if you have the means. If price is no concern however, you might want to give some serious consideration to Electrprints products. And if price is of absolutely no concern then I would go with their partial silver OPTs.
 
#17
Thanks, Jeff. I actually bought the James 6123HS for the SE KT88 amp that I am currently building. That's why I was curious to see if it would work in the 300B MkI. I think they were a good investment because they have multiple primaries @ 2.5k, 3.5k, and 5k ohm - it's like having 3 transformers in one - definitely a workhorse for most SET amps.

My first build ever will be the SE KT88. If I am successful, then I'll build the 300B. Let us know how your build comes along...
 
#18
Jeff,

These look interesting,

Google: YAWE91B300BA It's a WE91B 300B Amp (6SJ7 can replace 310A), plus links to more diyaudio threads on 300B

Also triodedick.com pdf files for Classic One preamp to go with Ceasar II 300B amp

I'm just reading and learning now, to later build. Great info on this site!

Thanks Very Much!

Randy
 
#19
I just spoke with (emailed with) Jack at Electra-print about soucing all of the iron from him for these MKI amps. His reponse to me was he thinks this amp will hum. I asked him why but have not yet heard back from him. Has this been the experience af anybody who has built it? Has anybody here actually built this amp yet? I think it looks like a fabulous design and from what I have modeled there is very little ripple in the power supply. Comments wanted...
Jeff
 
#20
I am not sure if this is really allowed but I figure it souldn't be too much of a big deal.....I recently bought a batch of 0.1uF and 0.33uF Russian PIO caps. I have 6 of each that I doubt I will ever use. Should anybody need any of these I will sell them at my cost which should be a fairly good discount seeing how the shipping from USSR is what drives the cost up on these things. That means if you are here in the USA these would be very cheap. The 0.33's are the K40's and the 0.1's are the other K (can't remember) green ones. Both sound great in the amps and preamps I have used them. So if anybody here wants a cheap trial of these send me a PM.
Jeff
 
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