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It is currently 14 Nov 2018, 17:43

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PostPosted: 10 Feb 2018, 23:30 
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Joined: 15 Nov 2013, 10:16
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Location: MB, Canada
I've got a friend interested in tube amps. He doesn't have any experience owning or operating tube amps, but he loves the idea of owning something that's somewhat unique, sounds good, and is a bit of a show piece. He's asked if I would build something for him, and I'm having trouble figuring out what would be the best route to go.
I still need to gather some information from him regarding what speakers he would be using, but I suspect based on the equipment he currently has that something with a moderate amount of power would be the way to go - as in I don't think a 3 - 5W SET amp is going to cut it.
My initial thought was to go for something like the Dynaco ST 70, but I'm curious to see what suggestions people might have for me.. I'm thinking something in that 15 - 30W power range, so I think this will likely mean a push-pull class AB design. I need the amp to be simple though, and to be somewhat a set and forget type thing.

I know this is pretty vague, but I haven't really been paying very close attention to the world of tube amps for a little while now, and I'm wondering what suggestions you all might have.
I've built a number of amps, but they've all been low power SET designs. The only high power amp I've built is a rather finicky 845 SET amp, which is definitely not the route I want to go for him.
The only push-pull AB amps I've built have been guitar amps, which are obviously similar, but I'm looking for a rock solid, bread and butter classic design that will just sound good and be easy in general.


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PostPosted: 10 Feb 2018, 23:49 
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Joined: 06 Apr 2009, 10:08
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Location: US Pacific Northwest
Oddwatt - EL34?

Sounds good. Simple to build and operate. More power than a SET but still nice clean class-A.

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PostPosted: 10 Feb 2018, 23:57 
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1) How big is his sound room?
2) What speakers does he have?
3) What genre of music does he mainly listen to?

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PostPosted: 11 Feb 2018, 18:33 
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Oddwatt is definitely something I was thinking about.
I gathered some more specifics. He's using a pair of Polk Audio RTIA9 speakers https://www.polkaudio.com/products/rtia9
90dB sensitivity.. Are these speakers that would respond okay to a design like the Oddblocks?

His room is 14'x20'.

He listens to a lot of heavier rock type stuff..


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PostPosted: 11 Feb 2018, 19:25 
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After having a bit more discussion with him, I'm kind of wondering now if this might not actually be a solution to what he's trying to accomplish. His thought initially was to integrate tube amplification into his home theater system.. I guess his home theater receiver has preamp outputs, so he had thought that possibly running the preamp outs for his two mains into a 2 channel tube power amp, or mono blocks, and leaving the rest of his system to be amplified by the amplification built into his receiver. I'm not really sure what to think of that, and I don't really know if that would mesh overly well or not.

Has anyone ever played around with this concept before?.. I guess that means that he's thinking the tube power amps would handle home theater type audio reproduction as well.. I'm kind of wondering (if this even is a viable) if I wouldn't want to go for a fairly high powered design, maybe more like somewhere in that 50 - 100W power range.


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PostPosted: 11 Feb 2018, 20:59 
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90dB is ok with a Push-pull tube amp as that will play >100dB at <20W. Looking at the speakers, they look like they will have at least a 3-way crossover and it may even be a 3.5 way, both of which may not be friendly with tubes. Before investing in a tube kit for those speakers, you will either want to sweep the impedance response of the speakers to see how difficult a load they will be to drive with tubes. Another option is to try them out with a tube amp to hear how they preform.

Those speakers can be bi-amped. If he wants to try tubes, the most reasonable approach may be to use solid state to drive the bass drivers, and tubes to drive the mid and tweeters. I use this sort of setup with an open baffle. Solid state drives the 15" bass drivers and I use a pair of kt88 oddblocks to drive fullrange drivers covering the high frequency, but with an active crossover.

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PostPosted: 12 Feb 2018, 16:59 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, A pair of the KT88 Oddwatts would be my recommendation. They will use EL34s, KT77s and 6550, as well. All Oddwatts are not bothered by weird speaker crossovers or impedance dips and bumps. They were designed to be stable from the get go. Using the specified transformers the bass response (important for rock music) will go below 15HZ at full power. If you really want killer power the KT120 version will do it. Where else can you get 40-45 watts of class A tube sound that you can build inexpensively. That of course is relative.....transformers are always the big expense in tube amps. It is one reason why solid state gear is so popular...cost.

Good listening
Bruce

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PostPosted: 14 Feb 2018, 00:36 
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Joined: 29 Oct 2014, 12:32
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Location: Russia Komi republic
Agree with Bruce. I am owner of pair of kt120. Best amp for rock, heavy rock and metal. With kt88 sounds more warm, with kt120 articulate sound.
So kt88 version IMHO best choice for sound/money.

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Last edited by zyu on 14 Feb 2018, 02:27, edited 1 time in total.

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PostPosted: 14 Feb 2018, 00:54 
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Joined: 08 Aug 2009, 03:11
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Location: Chilliwack, BC
Thirded.

We've had Polk and rock lovers in the store want tubes.... they ended up with some bigarse KT88 or 120 Rogue's to be happy.

Cheers!

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* Ratings are for transistors - tubes have guidelines*
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PostPosted: 14 Feb 2018, 17:39 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
I'd go oddwatt PPs Should be plenty of power.

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