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Old 13th February 2010, 09:42 PM   #1
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Default entry level int-amp?

looking for an entry level tube amp kit or design for stereo, 20-25 watts would be great.
Would it be better to do separate pre+ pwr amp?

Thx,
Rob
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Old 13th February 2010, 10:44 PM   #2
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Rob,

You can extrapolate the "El Cheapo" design I've uploaded onto 7591 O/P tubes. 7591 "finals" operating in ultra-linear (UL) mode will yield an honest 30 WPC. Check the 7591 data sheet out. FWIW, I'd build with triode/UL mode switches. Many recordings will do just fine with the 15 or so WPC triode mode yields. Triode mode is "sweeter".

Power supply requirements for the 7591 are a bit tougher meet than those needed for 'AQ5s. The folks on this "board" will help you pull things together.

An important part of the "El Cheapo" concept is that an inexperienced builder need own no more instrumentation than a multi-meter in order to successfully complete the project. Decent hand tools and respectable soldering equipment are an obvious necessity.
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Old 13th February 2010, 10:44 PM   #3
Glowbug is offline Glowbug  United States
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TriodeElectronics Dynaco ST-70 Tube Amp Kit

That comes to mind...or maybe a pair of the OddWatt monos.

Quote:
Would it be better to do separate pre+ pwr amp?
That depends. I like the separate pre-power amp route for right now, but having it all-in-one might make more sense for you. Takes up less space, less to fiddle with, etc. Comes down to how much you see yourself tweaking with things in the future
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Old 14th February 2010, 12:55 PM   #4
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Eli .. neat. How is the sound?

Rob
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Old 14th February 2010, 02:02 PM   #5
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Originally Posted by albireo13 View Post
Eli .. neat. How is the sound?

Rob

Reports from the field indicate that we achieved our objective. The cheapy guitar amp trafos shown in the graphic yield an OK amp. Moving up in quality to Dynaclone Z565 "iron" yields a good amp. The topology is valid and O/P trafo quality seems to be the limiting factor.

You can find the lengthy saga of "El Cheapo" here.
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Old 14th February 2010, 06:26 PM   #6
munorc is offline munorc  United States
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Eli, is there a schematic that shows expected voltages at test points? I have been reading through the 67 pages over at audiophiletalk.com but still have a few to look at. ;-)

-Ray
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Old 14th February 2010, 08:23 PM   #7
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Originally Posted by munorc View Post
Eli, is there a schematic that shows expected voltages at test points? I have been reading through the 67 pages over at audiophiletalk.com but still have a few to look at. ;-)

-Ray

The key to the situation is to get a 200 to 220 V. 12AT7 section plate to cathode differential. By itself, a Triad N-77U doesn't quite get there. So, the currently recommended set of power "iron" (all from Allied Electronics) is a Triad N-77U as primary B+, a Triad VPS24-1800 as B+ boost and "12" V. heater power, an Allied 6K27VF as B- and 'T7 heater power, and a Triad C-24X as B+ filter.

The decoupling network drops less than 2 V. 150 V. get dropped in each of the 50 KOhm 'T7 load resistors. Therefore, a B+ rail voltage of 355 to 365 V. is "ideal". Somewhat "taller" is OK, but caution indicates that the 'AQ5 bias resistor value be increased to 390 Ω.
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Old 14th February 2010, 11:44 PM   #8
munorc is offline munorc  United States
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Thanks. I was looking at trying this out with a bench supply on a prototype board (ala Tubelab). I was looking for a low cost amp to build for the shop. I have a bunch of NOS 6AQ5's, 6AL5's and some 12AT7's. Seems like a good match ;-)

-Ray M.
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Old 15th February 2010, 09:26 PM   #9
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Default 10 watts/ch !

Hmmm .. my latest thinking is to go for a more modest amp. This will be my 1st tube project. My goal is an amp for my bedroom system ... Energy RC-minis and a sub. I had a Shanling MC-30 driving them and that sounded nice. The MC-30 is only 3w/ch output so I think my output requirements are modest.

I'm thinking that 10w/ch stereo output, input is audio in from my Apple iMAC ... streaming iTunes and online radio.

Should I now maybe consider other designs?
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