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Old 6th December 2010, 01:32 AM   #1
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Default Cheap and easy tube amp.

I have been away from this for a while just enjoying life, kids, listening to music and then bam... My SS amp died.

Money is not my strong suit right now but I dread Christmas without the music.

Are there any good cheap kits or plans with decent sound quality that I could put together? Something PP 20-30W. An ST-70 would be great but the $ of that is too high.

Thoughts?
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Old 6th December 2010, 01:43 AM   #2
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define "cheap"
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Old 6th December 2010, 01:56 AM   #3
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Yes that is important. I guess a few hundred dollars tops.
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Old 6th December 2010, 02:20 AM   #4
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Short-form kits:
Tubelabs Simple SE - won't get you to 20W without a bit of heroics, but solid and well supported.

The Engineer Amp (otherwise known as the Red Board)- will get you to 20W stock or, if you follow George's path, any point north of that.

Plans
El-Cheapo or Baby Huey - just south of 20w but still willing contenders with thousands of posts of support information

Either way:
OddWatt series - pick a size to suit your budget and listening level. From plans or as a kit. Seems well supported by Bruce and others here and on their own www

Just quietly...
An LM1875 amp - heresy I know, but when on a budget... Would mean you can spend more on fruity bits for it and not spend a fortune on iron.
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Old 6th December 2010, 02:26 AM   #5
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Thank you very much. I will look into each one of these suggestions in the next couple of days. Again, thank you.
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Old 6th December 2010, 02:39 AM   #6
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Quote:
Originally Posted by portlandlay View Post
Yes that is important. I guess a few hundred dollars tops.
Without a well-stocked junk box, I don't see any way you will build a 20-30W tube amp for a 'few' (2,3?) hundred dollars.
If you just want something for the holidays, my advice is to grab a cheap used SS receiver/amp and plan the tube amp project for the future.
BTW, unless you have inefficient speakers, a large room, or like deafeningly-loud music, you will probably not need 20W+ of tube amplifier as a 'first, IMO.
Another SS possibility would be something like a Behringer 500 - I'm assuming here you just need a power amp.

John
EDIT: Aardvark's suggestion about the chip amp is a good one. Get a couple of assembled boards from eBay, buy a toroid and slap em in a case. They can sound surprisingly good.

Last edited by VictoriaGuy; 6th December 2010 at 02:43 AM.
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Old 6th December 2010, 02:52 AM   #7
20to20 is offline 20to20  United States
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Quote:
Originally Posted by portlandlay View Post
Yes that is important. I guess a few hundred dollars tops.
Power tranny: $65-$75 delivered
2 OPT $ $75 -$100 delivered
4 output tubes, 2 driver tubes, 1 Rectifier tube $75 delivered

That leaves a chassis, sockets, resistors, pots, caps, choke, jacks, speaker terminals, screws & nuts, wire, solder....
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Old 6th December 2010, 05:14 AM   #8
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Let's see what a UL mode, 12 WPC, "El Cheapo" is going to cost.

Edcor's CXPP25-8-7.6K O/P trafo costs 47.13 each. A full set of power "iron" can be had from Allied Electronics. $25.82 buys a Triad N-77U (stock # 967-2343), which is main B+. $17.31 buys a Triad VPS24-1800 (stock # 967-8019), which is "12" V. heater power and B+ boost. $7.74 buys a Triad C-24X (stock # 967-1004), which is the B+ filter choke. $13.41 buys Allied's own 6K27VF (stock # 227-0034), which is B- and 12AT7 heater power. 158.54 plus shipping for the "iron" in a competent design is (IMO) a very good deal.

Jim McShane carries parts and tubes for the design that are good performers, while being reasonably priced. A large Aluminum baking pan intended for service in a commercial kitchen makes for a cost effective, sturdy, chassis.
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Old 6th December 2010, 07:44 AM   #9
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Quote:
Originally Posted by Eli Duttman View Post
Let's see what a UL mode, 12 WPC, "El Cheapo" is going to cost.

Edcor's CXPP25-8-7.6K O/P trafo costs 47.13 each.
Doubtful one could have those in hand in 3 weeks, much less have an amp built around them.

I think I'd do the chip amp. LM3875's are $7.90 at Digikey, and an Antek power transformer is under $30, which leaves a few caps, a handful of resistors, and a box. Whole thing can be done for under $100.
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Old 6th December 2010, 08:07 AM   #10
rmyauck is offline rmyauck  Canada
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Tubelab Simple PP EL84 amp should be mentioned. George has boards and kits for it. At least 15-17 watts per/CH. I think you could drive 7591 tubes off the board for 35 W/CH + as they have the same drive requirements as EL84's. . Lots of info in Tubelab form on this site.

Sometimes you can find a great deal on a vintage PP EL84 amp or bigger. May even work, but usually just needs recapping and maybe output tubes. Check for Scott, Eico, Fisher, Heathkit, Dynaco, Harman Kardon and others. Check estate, garage, internet sales and auctions. I think you can find a Heathkit AA-151 for $100-180 depending on condition. I mention this one as I think there are lots out there and it is spread out chassis wise so is easy to work on. Has decent iron and could be modded to sound very good. If you want one you don't have to mod try Eico mono integrated HF-12's which can be found for a bit more in nice working condition and sound very nice. They are mono versions of HF-81 Stereo which is higher priced on Auction sites because of demand. I think these all go for much less at garage and estate sales. Another popular one is Magnavox stereo console amps which can be found in the big wood consoles for very low $. They are supposed to sound nice. Probably need a subwoofer as output tansformers are quite small. Anyway vintage amps when fixed up are quite sellable if it is a popular amp, say you want something bigger or different.

On short notice with todays economy I think you can find a decent working or even fixed up integrated amp or two mono's integrated for under $300. A friend near Boston, NY just sold a working 35-40 W/CH Fisher 400 Receiver for about $260. It should be recapped, but worked nicely.

Good luck!

Randy

Last edited by rmyauck; 6th December 2010 at 08:31 AM.
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