First tube project. Need advice.

[-=Zepplock=-]

Hello All,

I have fullrange 91db speakers.
And I decided to build my first DIY Tube Amp.

I'm looking at K12 tube amp kit which fits my starting budget $150-200. I may invest more later if I like the way it goes.

So are there any other kits/PCBs/designs that will fit into my budget?

p.s. I'm familiar with soldering/electronics.

Thank you!

[poobah]

Wait for Eli Duttman to respond...

[SHiFTY]

Remember watts are not hugely important. 5-10 Watt will be easily enough to fill a room with music.

The best way to start out is to restore an old piece of gear. Look around for something in a thrift store / ebay etc.

Push-Pull EL84 is a good choice for a beginner, great sounding tube and about 12W. Or even Single Ended EL84 for about 5W.

[-=Zepplock=-]

Originally posted by SHiFTY
Remember watts are not hugely important. 5-10 Watt will be easily enough to fill a room with music.

The best way to start out is to restore an old piece of gear. Look around for something in a thrift store / ebay etc.

Push-Pull EL84 is a good choice for a beginner, great sounding tube and about 12W. Or even Single Ended EL84 for about 5W.

Well, i'd rather build something new from scratch than restore old.
I think I have more chances in building new than troubleshooting old.

What's the price of PushPull EL84 or SingleEnded EL84.
Is it sold as a kit?

Thank you.

[Eli Duttman]

It's a good idea to be able to play 102 dB. peaks. If 1 W. = 91 dB., 2 W. = 94 dB., 4 W. = 97 dB., 8 W. = 100 dB., and 16 W. = 103 dB. So, a 15+ WPC amp is indicated for 91 dB. efficient speakers. Also, a thing to watch out for is the efficiency claimed for 4 Ohm nominal speakers. Some manufacturers give the SPL for 2.83 V. of drive. 2.83 V. into 4 Ohms is 2 W., not 1 W. In such a case, a claim of 91 dB. has to be reduced to 88 dB. A 30+ WPC amp is indicated for use with 88 dB. efficient speakers.

Check the spec's for your speakers out carefully. You could EASILY be miserable using an 8 WPC amp, if their true efficiency is 88 dB. There's no point in throwing your money away.

Please post again with more details about your speakers. IMO, it's hard to give good advice with insufficient data.

FWIW, a DECENT 15 WPC amp is doable with about $150 in "iron".

[-=Zepplock=-]

The drivers are these:
http://www.partsexpress.com/pe/showd...number=290-045

correction: 90db

[poobah]

Eli,

Please tell us your background. You know so much... and you are calm, humble (as you can be), and wise.

[-=Zepplock=-]

Originally posted by poobah
Eli,

Please tell us your background. You know so much... and you are calm, humble (as you can be), and wise.

And he's a programmer too. (like me) ;-)))

[wa2ise]

Originally posted by -=Zepplock=-



Well, i'd rather build something new from scratch than restore old.
I think I have more chances in building new than troubleshooting old.

There's always upsides to old gear restoration, and downsides as compared to new design and construction.

Pro restoration: An old commercially built amp was a design that was refined and proven in an engineering lab to work well (or at least decently). A homemade custom design and layout may have unforseen flaws that might cause hum (ground loops) and may have errors that the engineers at the lab above would have caught.

Usually replacing all the old caps with some good modern ones will make that old amp work better than new.

Con restoration: An expensive part (power or output transformer) may be defective. However, what might cause that is usually bad capacitors, so if the orginal fuse is blown, the transformers likely survived, and just replace all caps and you will likely have a working amp.

Be sure to have a fuse on the primary side of the power transformer be it a restoration or your own design and construction. You don't want to burn out a transformer because of a wiring mistake...

[Eli Duttman]

OK, 90 dB./8 Ohm nominal single driver speakers, with poor response in the 1st octave. 15 or so WPC WILL do the job, especially if the really deep bass is rolled off at the I/P.

Take a look at "El Cheapo". That 8 WPC triode wired circuit can easily be turned into "15" ultralinear W., if better O/P "iron" is used. "El Cheapo" Project

DynaClone O/P trafos are $60 each (that's an increased price ). Use them and 6BQ5/EL84 tubes instead of the guitar amp trafos and 12AQ5s. I'll talk to Jim McShane about revising the bias networks. Frankly, I foul that computation up regularly.

As shown with 10 KOhm log pots. at its I/Ps, "El Cheapo" will work well with most CDPs and FM tuners. 100 KOhm stepped attenuators can be used as 'T7 grid leak resistors to eliminate the low I/P impedance, but there is a significant cost penalty. High precision is required for the 'T7 grid leak resistors to ensure the I/P high pass filters have "identical" turnover freqs.

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About me: Joined the Geezer's Brigade last May (turned 60). Educated as a Chemist. Earn living as a CICS System Programmer. Built 1st crystal radio at age 8. Electronics in 1 form or another have been a life long hobby. Primarily a classical music listener, with a secondary interest in Jazz.