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Old 30th November 2005, 08:25 AM   #1
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Default Wondering if Upcoming DIY design will work with Tubes? Cheap DIY Kits?

I'm planning a Seas CA18RNX + LPG 26nafm DIY combination very soon, and i wanted to eventually build a stereo tube amp, as it looks from www.Diytube.com, but i wanted to make sure that these speakers would actually work well with them.

I'm not sure what the overall sens of the combo will be yet, as my passives havn't been designed, but the LPG's are 92db, and Seas are 88db. But i am looking for a cheap DIY tube kit that would power these adaquately for pure SQ. I don't listen at that loud of volumes, but when i do occasionally watch a movie i do bump the volume up more.

Any DIY tube kits out there, for say $150, that would give me say 50-100w @4ohms?

I'm pretty new to thinking about building my own amps, granted tubes shouldn't be my first choice, i've never even heard a tube amp before, but people rave about them, so i wanted to hear one, as well as build one. Possible to find what i'm looking for for the price i'm aiming, or even less, or would solid state be better for my pocket? Would really like to try some Tubes....But not sure if my speaker choices would work well.
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Old 30th November 2005, 09:02 AM   #2
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50 WPC takes a pair of KT88s. The O/P trafos needed cost MORE than $150. Significant power O/P from tubes combined with a low price is simply out of the question.

There are kits available using 11MS8 tubes that deliver about 8 WPC at the $150 price level.

Tube amps mate poorly with speakers that have significant dips in their impedance curve. I'm concerned that your design will have the dips.

A practical way to get some of THE sound is to pair a nice tubed preamp with a quality SS power amp. A preamp is a GOOD 1st project. With careful shopping, you should be able to do something pretty good for < $200.
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Old 30th November 2005, 04:36 PM   #3
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I'm somewhat confused how a Tube preamp would work well with a SS amp.....Could you explain please, i'm very new to the inner workings of amps and such.

What would be a good preamp+SS amp to look into for what i'm wanting?
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Old 30th November 2005, 06:37 PM   #4
Wodgy is offline Wodgy  United States
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A tube preamp gives you a taste of the tube sound/flavor without the expense of building a full power amp. Solid state watts are cheaper. If you use 4.5dB baffle step compensation when building your speakers, you'll end up with 83.5dB/watt speakers, which are going to require a lot of power.
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Old 30th November 2005, 06:52 PM   #5
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I was plannin on no using baffle step on the midbass, but rather just level matching them, and using any EQing that needed to be done through the passive, as i'm currently talking with madisound on the passive design.

Was looking at around .7cf~38hz, f3 looks like 51hz with a steep roll off below there. My aim is for a Hifi SQ setup.....hopefully this size and tuning will do what i'd like. Bassbox 6 recommends .6cf ~ 39hz, f3 is 53hz.

Would that change the overall sensativity any for the better?

Would i even need baffle step comp for the best sound?

I'm planning on 8.5-9"wide cabinets.
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Old 30th November 2005, 08:08 PM   #6
Wodgy is offline Wodgy  United States
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It depends on your room and placement, but you probably won't be happy with less than 3dB baffle step compensation. Whether you do this in the crossover or externally through some kind of equalizer, the effect on the speaker's sensitivity is the same.

Your low end tuning won't have any effect on the baffle step. It's a separate issue. The need for baffle step compensation starts at about 500Hz.

I don't want to discourage you from building a tube amp; you might be satisfied with just 30 watts per channel. But with a budget of $150, you can't even buy the iron for a 30 watt tube amp for that price. You could always build the K501 8 watt kit that has been mentioned. It's a nice sound, and it won't sound awful with your speakers, but it also won't go loud or have a great level of control over speakers that are as inefficient as yours. On the other hand, with that budget, you can build a nice tube preamp.
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Old 30th November 2005, 09:20 PM   #7
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I don't really want to have too much midbass, but just right, and i guess thats the hard thing to find out, how much is right. The baffle step if used will be implemented into the passive. I am waiting for madisound to re-email me on this issue, because i'm not really sure how much would be needed to have the best response possible, i'm sure they might be able to let me know.

My room isint really that big, lets say 13x20 at the most.....soundstage is across the 13' wall, tv sits in the center, bookshelfs currently sit about 1' from each side wall. Stage is quite wide. I don't really know how much midbass i want though, i mean i'd like it to just sound very full, pretty equalized without any peaks or troughs, and just have a very high level of detail, and reproduce everything i throw at it with ease, dynamics, and fullness.
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Old 30th November 2005, 09:48 PM   #8
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You should be thinking about picking up a Dynaco ST-70 and upgrading it. A ST-70 should be available for less than 100.00. The remaining 50.00 you can put into upgrades. Upgrading an amp is much simpler for someone with little experiance. Doing an upgrade is excellent place to start your DIY journey. There are many upgrade kits available for the ST-70. The ST-70 won't be 50w but it will get you a nice 35w. If your speaker impedence swinge isn't to low then you should be in good shape.
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Old 1st December 2005, 10:12 PM   #9
kevinkr is offline kevinkr  United States
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I second Andy's notion that an ST-70 would be a good starting point.
In my neck of the woods (boston) good working ST-70's start at about $250 and go up from there, but occasionally they do show up in yard sales ridiculously cheap - I found one for $75 a couple of years back. (It wasn't working.) Many upgrades are available for these amplifiers.
See my website for some ideas if you are of a more diy bent: www.kta-hifi.net, schematics and a lot of information is there about modifying this amplifier.

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Old 2nd December 2005, 01:05 PM   #10
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Default How about an OTL?

With something like 6C33C's (Cheap off fleabay) and something like Andria Cuiffoi schematic, its fairly easy to stay away from the expensive iron of the O/P Tx, which can be very overpriced for some types, BUT maybe the PSU needs a bit more attention and expense, especially as in the case of a Circlotron.............

I personally dont have the sort of money to spend on iron so I either end up winding my own or doing without as in the case of an OTL............
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