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Old 13th April 2012, 02:46 AM   #1
Bismar is offline Bismar  Australia
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Default Looking for Tube Amp Kit Recommendations

Hi,

I was wondering if i could rack the brains of fellow Audio Enthusiasts for recommendation of complete Tube Amp Kits (minus case) for < $400. I'm after ease of purchase but if there's a particular kit thats value for money and has easily sourced better then stock components, i would definitely be interested.

I'm don't really mind if its a SE or PP design, but i would like the best sound i could get for a pair of bookshelf speakers i'm looking to buy.

These are the specs of the speakers from Firesprite Bookshelf Speakers - Adelaide Speakers - Ascension

Firesprite 502SV

Price: $595/pr (or $350 kit less cabinet)
Finish: Satin/gloss American Oak veneer (can be stained Jarrah, Maple, Walnut, Rosewood or charcoal black)
Cabinet: 300h x 200w x 215d bass reflex 7 litres
Power Handling: 60/120 wrms/wmax
Nominal Impedance: 8 ohms (or 4 ohms on request)
Frequency Response: 55 -- 35,000 hertz +/-2db
Sensitivity: 89.5db 1w/1m
Drivers: SB Acoustics 150mm high end bass/midrange and Vifa 25mm soft dome tweeter.(optional ribbon tweeter extra $100)
Description: Ultra smooth and fast response; this is a beautiful sounding little speaker that packs a lot of punch along with its "being there" clarity. Also ideal speaker as high end studio monitor, complete satelite home theatre system, or surround speaker. Ideal speaker for music shops etc. where wider dispersion is required. zribbon option recommended.

Thus far i'm thinking the 16LS kit from s5 seems to be a decent pick, but again trying to see if there's anything better that will still suit my budget.

Any help will be much appreciated.

Thanks,
Bismar
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Old 13th April 2012, 03:39 AM   #2
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Hello,
Look at pmillett.com and tubelab.com . Not kits but fine circuits and circuit boards with complete bills of materials. Also tubecad.com for complete kits
DT
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Old 13th April 2012, 03:50 AM   #3
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Those speakers require substantial power. Let's apply Paul Joppa's useful 102 dB. rule of thumb. An amp/speaker combo should be able to produce 102 dB. SPL peaks at a 1 M. distance, assuming a listening space of "average" volume. Looks like upwards of 30 WPC are in order.

BTW, you need to find out what the speakers' impedance curve looks like. 8 Ω nominal will have to be lowered, if significant dips in the impedance curve occur, especially in the power hungry deep bass region.

IF the impedance curve is reasonably flat, you might be able to do a 7591 based "El Cheapo Grande" and not blast the budget to bits. Edcor's model CXPP50-8-6.6K is suitable and costs $62.26 each. Magnetics chew a budget up, very quickly.
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Old 13th April 2012, 05:51 AM   #4
Bismar is offline Bismar  Australia
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Hi guys thanks for your replies.

I'll enquire with the manufacturer for the impedance curves.

Regarding the WPC, during my enquiry to s5, they mentioned the 8LS or 16LS will be sufficient to power it. But their WPC is no where near 30?!. Perhaps if i chose the 4 ohms nominal impedance it will be easier to drive?

DualTriode: I'm really after a kit, can you suggest which kit on tubecad is sufficient to drive those speakers?

Eli Duttman: Any idea who does a kit for the El Cheapon Grande?
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Old 13th April 2012, 12:43 PM   #5
Cassiel is offline Cassiel  Libya
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Quote:
DualTriode: I'm really after a kit, can you suggest which kit on tubecad is sufficient to drive those speakers?
TubeCad doesn't sell kits. It sells PCBs for preamps and power supplies. Not amps, at least none that I'm aware of. Tubelab.com and Pete Millet are great options. You will need a chassis and transformers though, but you will end up with a great amp.
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Old 13th April 2012, 10:06 PM   #6
Bismar is offline Bismar  Australia
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Hmm, i'm a little confused, Eli Duttman mentions that i should be looking at tube amps that do 30w per channel yet others are recommending tubelab, but their simple se amp only does 14w per channel max?
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Old 14th April 2012, 12:37 AM   #7
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"Only" is a relative turn.

It would be lot's, if your speakers were not so power hungry. (inefficient.)

Whichever way you go it will be a learning experience, hopefully not your last project.

IMO, larger, more efficient speakers sound better anyways, you may end up upgrading speakers, which would make your life in the tube world much, much easier.

Moving up just 3db will sound twice as loud, something to consider, it's more practical to use efficient speakers than building a beefier tube amp.

In reality, 30watt is not much more power then 15watt anyways, not "twice" as loud.
You could simulate the same power level increase with speakers just 3db more efficient then you have now. (92db or higher)
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Old 14th April 2012, 12:55 AM   #8
Bismar is offline Bismar  Australia
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Thanks for your reply Alvis.

I've begun to realise the speakers ive almost purchase are perhaps not that great.

So to add to the question, are there any good speaker kits - chassis but with plans for about $500?
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Old 14th April 2012, 01:10 AM   #9
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Bismar,

Other posters have correctly pointed out that more efficient speakers than those you are contemplating make life easier, if tubed power amplification is to be used. However, I have a sneaking suspicion that you have your heart set on those speakers. If the Firesprite 502SV purchase is "cast in concrete", you may be better of with quality SS power amplification and tubed preamplification. More than 1 good sounding rig has been set up that way.
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Old 14th April 2012, 01:35 AM   #10
rmyauck is offline rmyauck  Canada
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Tubelab George does have an EL84 PP amp (17W/CH) too with parts kit for $65 to populate the $35 circuit board. Those speakers look to be power hungry so you could probably run 7591 output tubes outboard of the board for 35W/CH with suitable output & PS transformers, but a bit over budget.

You could also bi-amp with one stereo EL84 PP amp per channel if the speakers have taps for separate amps to supply the woofer & tweeter , so so you would have a nice 35W/CH with great sounding EL84 tubes.

If you want more power another option in kit form is the ST-70 type Dynaco clone kit amps out there, for up to 50-60W/ CH. with KT-88 and bigger OPT's , but out of budget.

Randy

Last edited by rmyauck; 14th April 2012 at 01:40 AM.
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