• 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.

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?
 
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.
 
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.
 
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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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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.
 
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
 
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What great forum. It has been some time since I have been around but many many thanks.

Every good plan has to have a good back up plan and the Chip amp sound like mine :D

I started this with the idea of Tube since I have worked them (no pro here but can one step above a monkey) and have the tools etc to build one up.

Not knowing much about chip amps (I know they have been around a very long time) I did not mention them.

Changing gears. Point me to the way of easy fun decent sound with a min of 20 watts or so (LS3/5a speakers). I have run less power but 20 is a about as low as reasonable.

Thank you everyone. I hope that next year brings some good fortune around here so I can build up a tube amp also. At one time I had several and I really miss them.
 
LM1875. National Semi datasheet has the schematic, but there are literally thousands of documented builds out there.

If you want to go diy, Rod Elliott does the LM1875 or the big brother LM3886 as bare boards at very attractive prices. Good thing about Rod is he has a range of other useful stuff that you can add on to make a more user friendly or high end experience.

ESP are not alone - there are many other providers of these ideas.

Take a look...
 
What great forum. It has been some time since I have been around but many many thanks.

Every good plan has to have a good back up plan and the Chip amp sound like mine :D

I started this with the idea of Tube since I have worked them (no pro here but can one step above a monkey) and have the tools etc to build one up.

Not knowing much about chip amps (I know they have been around a very long time) I did not mention them.

Changing gears. Point me to the way of easy fun decent sound with a min of 20 watts or so (LS3/5a speakers). I have run less power but 20 is a about as low as reasonable.

Thank you everyone. I hope that next year brings some good fortune around here so I can build up a tube amp also. At one time I had several and I really miss them.

I've got a pair of Brian GT's original boards with LM3876T. I think the chips are OK (long time, so I don't remember exactly). Also rectifier boards. Yours if you want em. Send me a PM with address.

Sheldon
 
This sounds cool and fun. I am not sure the power requirements I have for now are a perfect match for this.

I do like your point to point gainclone idea too. Since I am in Spokane I will have to see these in person one day.

Actually, I think my 6LU8 Spud could be built for a few hundred bucks. As could many other Spud amps probably.

6LU8: $10
5AR4: $17
Sockets: $6
OPTs: $40
Power transformer: $30
Solen capacitors: $12
Connectors, misc: $25
Shipping: $25
-------------------
TOTAL: $165

~Tom
 
I second Randy's recommendation to look for something used. It is getting tough to find anything really nice for cheap (vintage true hi-fi), but there are occasionally bargains on craigslist. Sometimes consoles can be had free. At your power level, you obviously want push pull, but I think there are 6V6 PP units out there (thinking Magnavox). Maybe not 20W, but close. Old organ/tone cabinet amplifiers are good choices, but tougher to find ultra cheap (Baldwins are popular). Beware amps with separate high and low frequency output transformers, as you want something fullrange! Basically you are looking for a donor for transformers at least, and hopefully a chassis. Plan on replacing everything else. If you are looking for actual hi-fi components, search the lesser known brands: Pilot, Sherwood, etc.

I started with chip amps. They sound alright, and are easy first projects. But to my ears, they don't compete with decent tube circuits, even using budget parts. Also think about getting some more efficient speakers. Your big problem is the 20W requirement. New little tube amps can be had in your price range (chinese, on ebay) and could be fun to mod. And of course, DIY options with new parts abound. If you can get by with 5-15W. You might consider just trying a smaller amp. Even with inefficient speakers, a handful of tube watts might surprise you.

Paul
Wild Burro Audio Labs - DIY Full Range Speakers
 
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
I give my vote to the Simple PP from George. I have one of these and I really have enjoyed it along with my Simple SE. I personally have the 6cw5 version of the amp. No complaints here.
 

quikie22

Member
2009-09-24 1:53 pm
a simple SE EL84 amp using Schade feedback might just do. Surprisingly loud for a 4-5W amp and extremely simple to put together and most importantly, pocket friendly. BTW, dun let the 4W rating fool you, it drives my dad's inefficient 85dB/W Kef to quite satisfactory volumes.