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EL84 no0b SPPUD?
EL84 no0b SPPUD?
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Old 11th September 2019, 01:34 PM   #11
kodabmx is offline kodabmx  Canada
Spreading triode love.
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EL84 no0b SPPUD?
If you use 6BM8 or ECL82 (or similar), you can get the extra gain needed for gNFB, but still only two tubes.

Here's an example: ECL82 PP2
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Old 11th September 2019, 04:38 PM   #12
baudouin0 is offline baudouin0
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Maybe this (designing tube preamps for guitar and bass).
If one of those EL84's goes short your LED array will be toast.
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Old 12th September 2019, 03:32 AM   #13
markusA is offline markusA  Sweden
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After careful consideration, I think going with Tubelab's SPP is the best option. So, I'll be sending George an email...

I couldn't find where/how to edit my previous post? Anyway, where do you go for parts these days? Is there any Asian one-stop-shop where you can get most of what you need in one go and at a great price?
Living in Europe makes buying anything from the US horribly expensive. I'm not joking, the last items I looked up would cost me twice as much as the list price due to shipping, VAT, customs duties, etc.

I'm thinking James transformers might be a good option if ordered directly from the source. But the rest of the parts???
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Old 12th September 2019, 04:27 AM   #14
vinylkid58 is offline vinylkid58  Canada
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EL84 no0b SPPUD?
Quote:
Originally Posted by markusA View Post
I'm thinking James transformers might be a good option if ordered directly from the source. But the rest of the parts???
Pretty sure James transformers have been OOP for some time. What about Lundahl? Lundahl Transformers • Audio Transformers • Home

jeff
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Old 12th September 2019, 04:36 AM   #15
markusA is offline markusA  Sweden
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Have they? I just checked their web page out the other day... :/ Ah well, life goes on. Lundahl are awesome, and they are located almost next door. The only negative part is that they don't offer "pretty" transformers that you mount on top. Everything is industrial look for built-in purposes. If I could get Lundahls in a nice looking packaging, that would be my go to choice without a doubt. I was hoping to mount all the Iron on the outside of the chassis...

Edit. My bad, it appear they now sell "covers" for their tube amp transformers, I'll have to look into that.
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Old 12th September 2019, 09:17 PM   #16
PRR is offline PRR  United States
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Quote:
Originally Posted by markusA View Post
I couldn't find where/how to edit my previous post?...
You have a limited time (15 minutes??) to edit your words here.

Apparently in the past some folks mis-used the Edit function and made trouble.
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Old 12th September 2019, 10:24 PM   #17
smoking-amp is offline smoking-amp  United States
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A pair of low cost 6LU8 tubes can make for a low cost but high quality amplifier.

Vertical deflection tubes for audio output?

tony's 6LU8 push-pull power amp build
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Old 13th September 2019, 06:20 AM   #18
planet10 is offline planet10  Canada
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EL84 no0b SPPUD?
Quote:
Originally Posted by Eli Duttman View Post
Without loop NFB of some kind, UL mode O/P tubes will frequently exhibit an inadequate damping factor.
And with a pentode connection it becomes a current amp.

While Eli’s use of the word “inadequate” applies to 99.9% of loudspeakers but not universally. Some speakers work better with highish output impedance amplifiers (like a UL connection), and a few are happy with current amps.

Flat frequency response requires a quite flat impedance curve on your loudspeakers (or a rise at the extremes where normally the response would start to slump).

What does the impedance of your speakers look like?

I wouldn’t hesitate to connect the EL84s in triode, should be enuff for your speakers. And that would make the amp simplier… is the OPT from your stash?

dave
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Old 13th September 2019, 08:56 AM   #19
markusA is offline markusA  Sweden
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How to describe my speakers... ehm... There was a fairly well known speaker project some years back, but I can't for the life of me remember any names.

It's basically a 15" mid/bass + PA tweeter in a wave guide with a passive x-over in the 1200-1300 Hz area (AE TD15M, SEOS15). The impedance is surprisingly flat (stays pretty well between 5-6 ohm), nothing is perfect but really nice for such a simple concept.

What sets them apart from other siblings and the original project, is the box and using a DSP to extend the low frequency response (Linkwitz 10db). The boxes are sealed and as small as you can make them and still fit the 15" driver. Think slightly larger than a 15" cube...

Heavily braced internally, but with thin plywood walls in a sandwich construct. Works like a charm, no problems what so ever with resonances or anything. And I can easily move them around if needed.

Googling the TD15M, I see now the 1WSPL is 97.8dB.

The only reason I've been so focused on getting the wattage up, is because of the frequency compensation. With compensation, they stay flat down to 35'ish Hz, without I think they start rolling off at 70-100 something Hz. Maybe one could look at it like them needing close to the same power as a pair of speakers with 88dB 1WSPL, due to the compensation (since most on the power is used by the low end).

So, how much power do I really need? I dunno? I've been using Hypex nCore monoblocks and for this particular application, that can be equated to unlimited power more or less. I quit long before speakers or amps quit...

If I could get away with a smaller amp, that would suit me perfectly. ;D
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Old 13th September 2019, 09:34 AM   #20
markusA is offline markusA  Sweden
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Quote:
Originally Posted by smoking-amp View Post
A pair of low cost 6LU8 tubes can make for a low cost but high quality amplifier.

Vertical deflection tubes for audio output?

tony's 6LU8 push-pull power amp build
Nice find, that does look interesting. I would have to take some time to study the schematics, but it definitely looks interesting. It would make the tube total 2 tubes per channel, manageable heater current, and super simple PSU. If anyone has heard this build and can vouch for the sound quality, it would certainly be a contender. It must be the simplest schematics I've seen while still packing a respectable punch.
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