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Kofi Annan in: "Tube Amp for Multi-Way Speakers"
Kofi Annan in: "Tube Amp for Multi-Way Speakers"
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Old 6th August 2019, 05:36 PM   #1
Kofi Annan is online now Kofi Annan  United States
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Default Kofi Annan in: "Tube Amp for Multi-Way Speakers"

Hey! It's been a while since I've posted on the forums, but I'm looking to get back into the DIYAudio world now that my kid is 12 and has adopted a policy of aggressive indifference toward me! Hooray for vindictive apathy!

Anyway, a friend of mine wants to build a tube power amp that can push some reasonably efficient (maybe 93dB?) speakers. He's still working on the speaker selections (he's interested in some classic Altec Lansing designs-- think Voice of the Theater, but updated) and wants me to put the amp together.

Given that he'll probably need to push some wattage to achieve the desired SPL , I was thinking about either a push-pull EL34 or KT88 design, but it's been a while and wanted to get some feedback from the community.

I have looked through the EL84 Baby Huey thread and guessing that this design would work well, but wanted to see if anyone could recommend something that they built or feel would be a good fit for some multi-way speakers.

I'd be glad to go outside the EL84 / KT88 topologies as well. NO GREAT IDEA WILL BE REFUSED!

Thanks in advance for any advice you can offer.

As always,
Kofi
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Old 6th August 2019, 10:51 PM   #2
Eli Duttman is offline Eli Duttman  United States
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Apply Paul Joppa's 102 dB. rule to a 93 dB. sensitivity and you get 8 WPC. The 30 or so WPC you get from PP 5881 equivalent Russian 6Π3C-E (6p3s-e) tubes will be plenty, even with losses in the crossover.

Depending on O/P "iron" quality, either Mullard or Williamson style small signal circuitry will be just fine.
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Old 7th August 2019, 01:34 AM   #3
Tjj226 is offline Tjj226
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I mean if he is interested in altec/western electric stuff, why not build a western electric amplifier? A 124 or a 142 would be fine. Heck if you want to shoot for the moon, you could build a 143.

If you aren't stuck on building a PP amplifier, a single ended 300b amplifier pairs very nicely with vintage horn speakers.
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Old 7th August 2019, 02:19 AM   #4
kevinkr is offline kevinkr  United States
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Kofi Annan in: "Tube Amp for Multi-Way Speakers"
Hey welcome back!
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Old 7th August 2019, 02:13 PM   #5
Kofi Annan is online now Kofi Annan  United States
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Hey! Thanks for all the replies!

Quote:
Originally Posted by Eli Duttman View Post
Apply Paul Joppa's 102 dB. rule to a 93 dB. sensitivity and you get 8 WPC. The 30 or so WPC you get from PP 5881 equivalent Russian 6Π3C-E (6p3s-e) tubes will be plenty, even with losses in the crossover.
Aha! Thanks for the insight, Eli. Looks like the 5881 is a 6L6 / 6L6G only more rugged (increased dissipation ratings). I'm assuming that either these, EL84s of KT88s will push about the same power out, so I should be able consider any designs using these output tubes?

Quote:
Depending on O/P "iron" quality, either Mullard or Williamson style small signal circuitry will be just fine.
I am guessing you mean I should use something like an EF86 for the first-stage voltage gain and the ECC88 as the splitter, correct?

Quote:
I mean if he is interested in altec/western electric stuff, why not build a western electric amplifier? A 124 or a 142 would be fine. Heck if you want to shoot for the moon, you could build a 143.

If you aren't stuck on building a PP amplifier, a single ended 300b amplifier pairs very nicely with vintage horn speakers.
Actually, he has no idea what an Altec Lansing / WE amp / speaker is. He just thought the looked cool. Also, I would like to see if I can find something with some depth of documentation online as he wants it done in about 4 - 6 weeks, which will limit my build -> blow it up -> wallow in self pity -> find the strength to go on -> rebuild amp cycle.

Quote:
Hey welcome back!
Great to be back! Thanks, man!

I'm currently leaning toward the Claus Byrith EL84 Push Pull Amp. I remember reading this paper years ago and thinking it would be a fun build, but there may be better designs out there. It's basically a modified Mullard 5-20.

Any comments on this design?

And thanks again!

Kofi!
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Old 7th August 2019, 04:48 PM   #6
Eli Duttman is offline Eli Duttman  United States
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EL84s are good for approx. 15 WPC. KT88s are good for 60+ WPC.

The best "vintage" version of Mullard style circuitry I'm aware of is the Harman/Kardon Citation V. Notice the high gm theme in the small signal types. 12BY7s are becoming scarce. So, a 6922 cascode is provided as a substitute high gm/low CMiller voltage amplifier.

Possible enhancements to the Cit. 5 are a CCS in the LTP tail, instead of a resistor, and employing the ECC99 (yet higher gm) as the LTP.
Attached Images
File Type: gif Citation-V-full-final.gif (273.3 KB, 789 views)
File Type: jpeg Cascode 6922 Mullard Front End.jpeg (636.5 KB, 783 views)
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Old 7th August 2019, 05:21 PM   #7
Kofi Annan is online now Kofi Annan  United States
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Thanks, Eli!

I actually misstated the Claus Byrith amp-- it's actually an EL34 push pull, not an EL84. That should be 35W output according to the design docs (I think there's a good amount of NFB in the amp driving down the power). 35W should be fine, right?

I'll review the amp design you posted and will likely post some questions about it soon.

Thanks!
Kofi
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Old 7th August 2019, 07:35 PM   #8
aardvarkash10 is offline aardvarkash10  New Zealand
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this is a thread screaming for Pete Millett's Engineer Amp. Link to Pete's page, or search for the many threads here.

Fast build time, scalable up to around 200W if George and other extremeists are to be believed, proven board and circuit, and Pete's usual documentation and happy free consulting if your questions are halfway intellegent or better.
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Old 7th August 2019, 09:29 PM   #9
Parafeed813 is offline Parafeed813  Netherlands
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Quote:
Originally Posted by Kofi Annan View Post
.... now that my kid is 12 and has adopted a policy of aggressive indifference toward me!
It looks like I'm not the only one with a 12yo at home, lol

@Eli
How about another high gm pentode like the EF184 as replacement for the 12BY7?
I don't need the gain as my version is too sensitive as it is with trioded EF86. I'm not keen on heavy gNFB but might give it a try.
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Old 7th August 2019, 11:07 PM   #10
Eli Duttman is offline Eli Duttman  United States
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The EF184/6EJ7 looks interesting as a voltage amp. The 6922 cascode has (IMO) the big advantage of using an in production type.
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