• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

First tube project. Need advice.

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-=Zepplock=-

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vova.org
#1
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!
 
#3
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.
 
#4
SHiFTY said:
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.
Click to expand...


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.
 
#5
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".
 
#9
-=Zepplock=- said:



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


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...
 
#10
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.
 
#12
-=Zepplock=- said:
So what's the total cost of el Cheapo?

p.s. PA774 Dyna ST35/SCA35 Power Transformer is $45 on sale.
Click to expand...


Jim McShane has to finish up the parts kit. I'm not sure about the parts kit cost. For the 8 WPC triode wired amp, "iron" costs are under $100. Add $80 for the DynaClone O/P trafos instead of the guitar amp O/P trafos.

While the Dyna ST35 power trafo would save the expense of the R/S filament trafo, an additional trafo would still be needed for the B- supply. The Triad isolation trafo and the R/S filament trafo together are about $10 less than the PA774 sale price. Also, I think the doubler supply has more "muscle" than the ST35 PSU does.

FWIW, an 8 WPC "El Cheapo" would definitely be listenable with your speakers. However, you would lack realism when playing the ffff marked portions in the scores of List and Tchaikovsky "potboilers" (100+ players). Smaller ensembles should be OK.
 
#14
-=Zepplock=- said:
Thank you for the information Eli Duttman.

Classical music is not on top of the list for me anyway.
Maybe only played by Jaque Loussier ;-)

Do you have any ideas how the sound would be compared to K12 kit?
Click to expand...


A system that can play classical music well plays ALL music well.

For several reasons, I think an "El Cheapo" will sound better than a K12. The B+ PSU in "El Cheapo" is a robust 200 mA. "El Cheapo" uses triode wired "finals", while the K12 uses pentode mode. Pentode mode can sound good, but steps that increase costs, like regulated screen grid B+, have to be taken. "El Cheapo" is configured to operate in Class "A" most of the time, crossing into Class "B" only when peak power O/P is called for.

Rock lovers like to crank things up, at least occasionally. With 90 dB. speakers, a 15 WPC amp is indicated for loud listening.
 
#16
I've built (and tweaked) a K12. It's not a bad little amp, but I really think that I'll be more satisfied when I finally finish up a tube amp from scratch.The only reason I did wind up building/modifying the K12 is because I got it for about $60 on head-fi 😀

These designs look interesting, and I'll definitely have to keep 'em in mind. Gotta watch the ol' wallet so I don't go dropping a bunch of money on iron right now!
 
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