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pforeman 23rd April 2009 01:08 PM

best tube (not amp)
 
I wanted to build a SE tube amp to go with open baffle speakers I'm building should be about 92-94dB efficient. Will have a plate amplifier feeding a 18 inch open baffle woofer, so the full range speaker will only produce down to about 200 Hz.
300B? real expensive! EL34? (E34L??) EL84 and others(?) . I've read pro's and con's on several.
Deep bass probably not too much of a concern
More concerned about upper bass on up, but especially that
"tube magic" that you get from a triode (connected) SE tube
If your going to suggest the virtues of a somewhat esoteric tube please discuss availability and cost as well.
Thanks
Paul

Zen Mod 23rd April 2009 01:29 PM

307A triode wired

but - please , don't tell anyone .....

:clown:

el`Ol 23rd April 2009 01:41 PM

The amp with the most tube "magic" I have heard so far is the 833 amp from Wavac for 300,000 $ or so, followed by the Melody 845 amp. But I think my experiences with valve amps are not sufficient to generalize that broadcasting tubes have more magic than audio tubes.

andyjevans 23rd April 2009 05:00 PM

I just keep on liking the 300b - almost any 300b. I find it more musical and magical than the 2a3, which for me is correct but a bit bland. Others disagree of course.

The thing with the 300b is to use a really good driver - that makes or breaks the sound. I'd use a 71A - easy for DC filaments and I'd use a 01A for input tube.

All these are easy to get on ebay or from dealers, and well worth it. They're a level up from EL84 and EL34.

If you find the 71A expensive, use a 31. That's good and cheap

I just built a SET with 01A>71A>300b and it's magical. One of the nicest sounds I've heard.

andy

Miles Prower 23rd April 2009 07:04 PM

Re: best tube (not amp)
 
Quote:

Originally posted by pforeman
I wanted to build a SE tube amp to go with open baffle speakers I'm building should be about 92-94dB efficient. Will have a plate amplifier feeding a 18 inch open baffle woofer, so the full range speaker will only produce down to about 200 Hz.
Your choices are really rather limited here. There just aren't that many power triodes out there since the beam power revolution occurred early, and killed off the commercial demand for power triodes suitable for audio use. About the only ones commonly available are the 45, 2A3, 300B, and 845. The various power triodes for vertical deflection duty are all in the same power class as the 2A3, and the remaining power triodes were RF finals with high u-factors, high r(p) (i.e. the "zero bias" tubes) that will need to operate in Class A2. Low-u, low r(p) RF finals are quite rare since what you want in an RF final is good power sensitivity. The 806 just might make a really decent power triode for audio, but just try to find one.

Other possibilities would include pseudotriodes made from pentodes.

Your best bet would probably be a 300B. Just make sure that you have a decent grid driver for this type, since complaints about sonic inadequacy with the 300B seem to almost always be due to a lack of grid drive. For that, I would use a power MOSFET source follower.

bigwill 23rd April 2009 07:49 PM

There is no 'best tube', the sound of the amp depends on the implementation of whatever tubes are used.


Even amps made entirely with pentodes (and operated as so) can sound good.

Eli Duttman 24th April 2009 01:09 AM

Paul,

The 8 or so W. a 300B yield is about right. Unfortunately, you indicated that the type is too costly. You might make out well using triode wired EH KT88s: the power yield is correct, the expense comparatively modest, and Class A2 operation is possible.

rtsang 24th April 2009 03:30 AM

Triode connected IDH pentodes
 
I also agree with Eli's choice.

While they may be a bit worse than a DHT like 300B, a triode connected IDHT like KT88 would give around 8Ws, not too diffcult to drive and you can even choose bewteen pentode, UL and tridoe mode.

I would say, the sound is quite respectable.

Of course, a KT88 will not break the bank.

rjhanauer 24th April 2009 09:01 AM

Hi All
I wold agree with Andyjevans i build PSE 300B- PSE 2A3
and Triple SE KT88 i find 300B is more Musical and Finesse
I design and wind my Transformers use semi automatic
Winder. My 300B is as follows D3A-as Triode Inter stage
TX -Fixed Bias-300Bs. Use separate TX for HV-Bias-Heathers
all Film Caps. IMHO 300B is a very Good TUBE
Regards Rudi:hot: :hot: :hot:

gorgon53 24th April 2009 07:01 PM

Best tube?
In what respect "best"?
Best suitable for a certain application?
You have to be very specific about the application first, then you can look for the best suitable candidate...


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