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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

DIY Hi-fi Stereo Tube Amplifier

Wow! Just discovered this site, what an amazing resource! You guys are like, family, man!

My question:
I would like to build a tube-powered, Hi-Fi Stereo Amp. I am going to use this to drive a set of bookshelf speakers, and possibly a subwoofer in the future. I need at least 50 watts per channel into an 8-ohm load. I will construct the speakers in the future. This setup will be run off the soundcard of my computer. I was hoping to get a schematic or circuit from something Harman Kardon, I really admire the old designs, but am not familiar with the model numbers, and do not wish to risk an E-bay purchase.

Any advice?
 
ASSASSIN!!!

It is ILLEGAL to use tube amps with PC soundcards!

Ask anyone!

You Should go for a kit, but If I were you I'll stick with a dosen of watts. 50 of them is much for valve amps (altough not impossible).

Buy a cheap CD player (but decent) (yes don't use MP3) if your low on €€€. Or a turntable, if you have one.

My valve amp is a Audio Note Kit one and it is a kit as you can imagine.

The thing in valve amps are the parts.
If you don't buy a kit you may find a little dificult(yet possible) to find the transformers, valves, chassis.

If you want I can send you some pics or schematics os this amp or goto www.audionote.co.uk and browse the kits.

This amp has 8W per channel, class A operation Single ended design, no feedback, Directly heated 300B Triode.
 
I beg to differ - I have a tube amplifier hooked to my computer (only five watts per channel though) and it sounds MUCH better than my previous sound card, which had an IC ampifier.

Fifty watts is a lot for a tube amp - 25-40 is about the limit for a single pair of output tubes (of course you can double that by using parallel pairs, but it gets expensive fast). If you use a separate subwoofer amp, you can probably get by on quite a bit less power.

The Harmon Kardon Citation II is one of the best amps ever, according to many, but it would be difficult to duplicate today. The key is the transformers - hard to find anything comparable now.

Hammond and Magnequest, to name a few, make good iron today. Select an output transformers, output tubes, driver circuit, power/filament/bias transformer(s), and get out your soldering iron... or look for a kit, if you haven't done this before. I tend toward the complete DIY approach, but I haven't built much in recent years - I am getting back into it though. Check my (temporary) website - http://www.audiophool.2y.net
 
thanks tom!
pedro, i guess i should have mentioned this is not my main listening station, merely an upgrade to the crappy stock soundcard/speaker setup. no need for alarm...i would be the first to hang my head in shame if this were otherwise....
i did look at your reccommended amp, and yes, it is sweet, but i fear, out of my budget, and, not high-powered enough. this is not to say that someday i will not want one, i have heard about the 300Bs...

tom-
checked out the hk cit2 as advised. sweet! the 4x KT88s in the output stage would give me plenty of juice. observe: us guitarists crank out about 100 watts of power from that particular setup, so ~ 40 to 50 watts of clean power into an 8 ohm load with 90+ dB efficiency JBLs should present no significant difficulties, right?

still-
i have an allied radio/knight stereo integrated hifi amp rated at ~20 watts max output, 4x 6l6s in the output stage. it was not loud enough! when i first got it, it needed a tube rectifier, it then ran BEAUTIFUL (albeit quietly) for about a month. then,
"she jes' up an' died!" this was a year ago, so bear with my memory. no filaments, no hum, no glow, no nothing. it is in my basement back home, i am in school, now. any suggestions? fix? relace? i have not been able to locate a schematic.
thanks again.
 
Find the Knight model number, and we'll see what we can do. No filaments - that sounds like the line fuse or (perish the thought) power transformer. Even then, maybe $75 for a new one - not THAT bad - assuming you can find one.

A Citation 2 goes for about $1000 in original shape - and they're not that easy to find. But most modern amps with KT88s or 6550s will be as much or more.
 
thanks, dude!
i go home in about 4 wks, so i can get the model number then. you know, i may end up replacing the transformers with some higher-rated Hammonds anyways, as i will then be able to tweak some values and get more output, correct?
40 or 50 watts is still my main goal. this should be no problem from 4 6l6s.
i also have an rca tube manual that has schematics in it. one for a 50 watt stereo int. amp, with very impressive specs. it even has a parts list!
as far as the citation goes, that is way too much money for me to spend, maybe i could build a citation clone with the knight?
 

Brett

Member
2002-01-07 6:02 pm
el capitan83 said:
i may end up replacing the transformers with some higher-rated Hammonds anyways, as i will then be able to tweak some values and get more output, correct?
40 or 50 watts is still my main goal. this should be no problem from 4 6l6s.
The Hammonds are good iron for the money, and picking up a pair of these in the right size and impedance will put you in the best position to get your 50W

I agree with Tom below that a pair of 6L6's might not be the best for trying a 50W power level. KT 88's or 6550's are a much better bet, especially for long term reliability. The 6L6's would be running a bit hot for my taste.

i also have an rca tube manual that has schematics in it. one for a 50 watt stereo int. amp, with very impressive specs. it even has a parts list!
Might be OK, but it would depend on the circuit design. Resaerch around on the net, and see how the design is regarded, to get some idea as to how good it will sound. Low feedback designs, or using exactly the OPT specified are the best ones for you too be looking into.
as far as the citation goes, that is way too much money for me to spend, maybe i could build a citation clone with the knight?
I reckon a well restored or mint Citation is probably excellent value for money, especially compared to some of the high-end dross that's being sold for big money today. There are reasons why designs like this and the Marantz 8 are still highly sought after and fetch good money. They were very well thought out, designed and optimised for the purpose by people who <i>really</i> knew what they were doing.

As for making a Citation 'clone', sorry, you won't. The Citation uses nested feedback loops and is dependant on the exact OPT as specified or it probably won't be dynamically stable. Stu Hegeman (original designer) might make it work with a Hammond, but you or I won't.

So the big question: do you really <b>need</b> 50W or is it a number you have in mind? If you can deal with 35W, then the Dyna Stereo 70 is a possibility, and there are tons of them out there, lots of mods and spares and knowledge. It's a great design that uses EL34's in ultralinear. There are lots of nice sounding, cheap new EL34s, and Magenquest even make an exact replica of the A470 OPT with better materials, if you can't find a pair cheap on ebay. BTW the difference between 35W and 50W is only 1.5dB, hardly a huge amount. If your speakers are at least 85dB, 35 W is plenty. Remember tube amps don't clip hard like SS amps do, and seem to give lots more level than their rated power would suggest. Take a look at this <a href="http://www.stereophile.com/fullarchives.cgi?357">article</a> on the subject.

I disagree with Pedro at the top of the thread about parts availability for things like tube, transformers and chassis. They are easy to get online at lots of sources in the US, Europe and Asia. Let me know what you want and I probably have a URL or two for it.

In the meantime, look at
http://www.worldtubeaudio.com/directory/directory.htm
www.tnt-audio.com/ampli/dynaco1e.html
www.tnt-audio.com/ampli/dynaco2e.html
http://www.audioasylum.com/forums/tubediy/bbs.html

HTH some
Cheers
Brett


np: Alison Krauss and Union Station: so long so wrong
 
Where to start...
First of all, thanks for the carefully thought out answer! I have had nothing but good experiences using Hammonds in several of my tube guitar amplifiers, so yes, I would have no problems working with them. As I am in the US, parts have not proved to be too difficult to obtain.

Here's the deal. I know I have posed many questions. I know that I may seem unfocused. ( I am!) The enitre goals of my DIY tube amp project, all things considered, are the following:

1. I much prefer (through my 6+ years of playing guitar) the sound of a tube amplifier as opposed to solid-state. In fact, I don't even own a SS amplifier. The last one I owned, a $100 Fender practice amp, blew up under playing conditions that a tube amp would laugh at...(forever closing the argument in the tube vs. ss argument in my mind...)

2. I then recalled that I had that Knight amp sitting in my basement, and yes, when it was running, it had sounded excellent, but not loud enough for my musical tastes. The Knight is rated at 20 wpc into 4,8, or 16 ohms, and my 'best' speakers are a pair of JBL S38II bookshelf speakers. (I know, they are not Martin Logans, but at 89dB efficiency, they are decent, and hey, I'm a poor college kid. I love their sound, and that's what counts, right?)
I listen to MANY types of music, but for simplicities sake, the majority of it is rock. Classic rock. Zeppelin, Who, Floyd, SRV, etc... this is music that was PRODUCED on tube amplifiers. So yes, in some warped part of my mind, it became IMPERATIVE that I must therefore reproduce the program material on a system that was tube powered.
As I was always told one must double the output watts to get a "perceivable" notice in volume, (before the Stereophile article, thanks, Brett!) I believed that in order to produce satisfiable results, I must have a TUBE setup pushing at least 40, if not 50 watts (+10 watts for cleaner headroom couldn't hurt any, right?) into the 8 ohm JBLs resulting in massive levels of volume and much joy for myself.

3. So, how to do this? I have the following already:
i. Dead Knight Amp. Died approx. last year, causes unknown. Powered by 4 6l6s in the output, produces 20 watts max.
ii. One schematic for an RCA Stereo Hifi Int. Amp, 50 [email protected] 8 ohms, decent specs (don't recall them off the top of my head, RCA manual is located in Harrisburg PA, I am currently in Pittsburgh, so please forgive me!)
iii. A soldering iron and balls of steel.
iv. The help of the good folks like you guys at DIY Audio!

So I guess my options are as follows:

1. Fix the Knight amp, leave it stock
2. Fix the Knight amp, boost the power output to 50 wpc, converting to KT88s, 6550s, upgrading the transformers and power supply, etc...
3. Build the schematic in the RCA manual.
4. Spend my college funds on a MINT H/K Citation II !
5. Research the Dyna Stereo 70 as posted by Brett.
6. Give up on audio, cry like a little girl, and take up croquet as a hobby.

Opinions! Let's hear 'em!

BTW, Option 6 is not an option!

Oh, and my current setup is a Denon DCM-460 5 disc-changer running into a nondescript [email protected] ohm Onkyo receiver which powers either a pair of JBL bookshelves (see above) or a (shitty) pair of Onkyo Towers (3 way, 12 in, 4 in, tweeter, modded by ME with sand-filled base, etc.). Sometimes I run the output from my soundcard on my computer, (watching DVDs, the occaisional sin of an MP3) into the AUX input on the Onkyo. I have an Onkyo turntable (fully auto) with an AudioTechnica cartridge (installed by myself) that sounds good for when I have the time to put on an LP.

Let the fun begin!
 
Cap,
1st thing you might want to think about is instead of the $$ and time involved in completely rebuilding an amp for a bit more power is to get some more efficiant speakers. Much easier way for those extra dbs. Also when you think about those watts the caps that supply them can be more important than the number of them. That is why a 300Bs 8 watts can really flap the carpets with the right speakers. Oh ... back to the speakers. Not every speaker will like tubes, or SS for that matter. Another thought on going the vintage route is that you might want to think integrated so you don't have to spring for a preamp too. An Eico ST70 might be a better way to go than the Dyna now that you can get real replacement 7591s. I think the iron is a bit better too. My opinion.
Thatch
 
Cap,

I read thru your posting and replies. No one seems to have mentioned the Consonance "Ella" kit. Check out this URL: http://www.diyhifisupply.com/diy_kits/the_ella.html

and also, the Stateside source: http://www.diycable.com/home.htm

You mentioned a shortage of funds, but this seems a good solution for in the neighborhood of $600. I recently acquired a Consonance M99 integrated amp; not the same amp, it uses 4X6L6 output tubes, and not a kit. However, it is the sweetest sounding electronics I have owned in the last 25 years. It has reawakened my interest in recorded music that has laid dormant for several years.

JNLiu
 
el capitan83 said:
1. Fix the Knight amp, leave it stock
2. Fix the Knight amp, boost the power output to 50 wpc, converting to KT88s, 6550s, upgrading the transformers and power supply, etc...

1a/ Fix the Knight amp, tweaking and removing all unnecessary bits

2/ probably not an option because your power output is limited by the Output transformers.

dave
 

Brett

Member
2002-01-07 6:02 pm
el capitan83 said:
Here's the deal. I know I have posed many questions. I know that I may seem unfocused. ( I am!)
Questions are good. Design it lots, and then build it and tweak from there. IME you almost always end up closer to the desired result

1. I much prefer ... the sound of a tube amplifier as opposed to solid-state. ...(forever closing the argument in the tube vs. ss argument in my mind...)
I never knew there was an argument. Tubes rule.
When I get some decent heatsinks though, I might just build an AlephX and see.

2. ... my 'best' speakers are a pair of JBL S38II bookshelf speakers. (I know, they are not Martin Logans, but at 89dB efficiency, they are decent, and hey, I'm a poor college kid. I love their sound, and that's what counts, right?)
I listen to MANY types of music, but for simplicities sake, the majority of it is rock. Classic rock. ...... and much joy for myself.
Sorry for the big snip, I don't want to exceed the character limit for the post.
Speakers make the biggest difference in sound, and you like the JBLs, so good. Listen to some MLs at a store sometime. I've never found them to rock. I agree most of that great music you listen to (great taste BTW) was made on tube gear, but it's not neccessary for you to use tubes for playback, but IME, they help with the joy. Great word. It's what it's all about.

3. So, how to do this? I have the following already:...
iii. A soldering iron and balls of steel.
iv. The help of the good folks like you guys at DIY Audio!
This is all you'll need. Probably :D

So I guess my options are as follows:

1. Fix the Knight amp, leave it stock
2. Fix the Knight amp, boost the power output to 50 wpc, converting to KT88s, 6550s, upgrading the transformers and power supply, etc...
3. Build the schematic in the RCA manual.
4. Spend my college funds on a MINT H/K Citation II !
5. Research the Dyna Stereo 70 as posted by Brett.
6. Give up on audio, cry like a little girl, and take up croquet as a hobby.

OK.
1:Yes. It'll make a nice back up amp.
2:No. It'll take far more work trying to modify it for such a large power increase than leaving it stock, and modifying or even scratch building a whole new amp. Personally, I don't see extreme mods as being worth the time.
3:Without seeing the schematic, it's hard to know what to say about it. Can you scan and post, or email it to me?
4:They're not <i>that</i> expensive. But spend the money on education, partying and trying to get laid. Stereos you can get later but you won't ever have this time again.
5:I still think this is the best option, as well as several alternative 'vintage' peices like Fisher 500C, 800B/C receivers, X101 integrated amps, as well as similar Scott 299's, Eico (like the one David suggested) etc. I'm not an expert on these units, as we tended to get the British equivalents in Oz, but most are point to point wired, and won't need all that much done to them if you find a nice one. Caps, tubes and a good clean is often all thats required. If you get a receiver, you also get a good FM receiver, but the downside is receivers take a lot of setup and specialised knowledge and gear (ie $$) to align the radio sections if they're not good. An integrated means you have a tube pre section as well, with a phono section that might surprise you with how much better your vinyl can sound. IME, the pre is often a bigger determinant on sound quality then the power stage.

Of cource you can build a poweramp now, and a matching pre later as funds allow. With the vintage items I suggested, try and find out when the ham radio swaps are on in your area, and / or see if there is an older repair tech nearby who works on tube gear. Sometimes you can pick up a good deal and can test it before it goes home with you. Ebay is definitely a risk unless you know exactly whay you're looking for. Garage and estate sales are another option, but I don't know how much time you have to spend on this. Summer break is coming up though, yes?

6:I don't find crying like a little girl satisfying. A good old fashioned tantrum is much more fun.:D
Croquet might surprise you with how tough and bitchy it can be. Remember people have big wooden mallets in their hands.

Oh, and my current setup is a Denon DCM-460 5 disc-changer running into a nondescript [email protected] ohm Onkyo receiver which powers either a pair of JBL bookshelves (see above) or a (shitty) pair of Onkyo Towers (3 way, 12 in, 4 in, tweeter, modded by ME with sand-filled base, etc.). Sometimes I run the output from my soundcard on my computer, (watching DVDs, the occaisional sin of an MP3) into the AUX input on the Onkyo. I have an Onkyo turntable (fully auto) with an AudioTechnica cartridge (installed by myself) that sounds good for when I have the time to put on an LP.

Let the fun begin!
Here's my opinion.
<b>Speakers</b>
-Keep the JBLs. I like JBLs; they have a lot of life and make good rock speakers. Good review <a href="http://www.stereophile.com/showarchives.cgi?365">here</a> BTW. In the future, look into some higher efficiency speaks, especially horns like some Klipsch, Altec and JBLs. Tweaked properly, they can be amazing, irrespective of what a lot of audiophile snobs say. Keep the Onkyo towers as party speakers. Not such a loss if they get trashed.

<b>Amps.</b>
-Look into what i suggested above. I still think they could be the best value for you. I'll do some digging around and see what I can find in the way of good schamatics for higher power amps for you to scratch build. You said you didn't want to do the ebay thing in your first post, but maybe a set of Dyna iron would be a small risk. Email the seller and check them out well and you should be OK for iron. <a href="http://store.yahoo.com/triodeel/index.html">Triode Electronics</a> have a huge schematic and tube data index, as well as some replacement boards for the Stereo 70, so you don't need to fix one up, you can build from scratch if you like. A scratch build won't have the same resale value though. Triode are also great for tubes and parts. <a href="http://www.curcioaudio.com/">Curcio Audio</a> have a number of Dyna mods and upgrades as well as the full service manual available for free download. <a href="http://www.quadesl.com/schematics.shtml">SDS Labs</a> also have Dyna and other amp mods and info.

<b>Preamps</b>
-If you don't get a receiver or integrated, once you've finished the power amp, look into a tube pre. Cheaper to build in many ways, due to less iron. The best single ended pre schematic I know is <a href="http://www.vacuumstate.com/images/FVP5_Rev_1.GIF">this one</a> with a review <a href="http://www.tnt-audio.com/ampli/vse_fvp5a_e.html">here</a>. I can provide a PSU diagram. Better than any PAS out there by a loooooong way. This pre, and a good Dyna etc, will probebly keep you happy in amps for years.

If your Onkyo doesn't have a pre-out, simply come off the volume pot and run some leads from there to your power amp input. If you dont drill holes in the Onkyo, and run thin wores out of it, you van sell it for more money whaen you have a whole tube system.

<b>Sources</b>
Enjoy them and upgrade when / if you find it neccessary and funds allow. Better amps will show up the limitations in the source though. You've been warned. :D

Buy more music.

The floor is still open for more questions.
HTH
Brett

PS. I thought you might like this.
<img src=http://www.geekculture.com/geekculturestore/webstore/webstoreimages/tubesrock/cath.gif>
 

mbeards

Member
2012-03-18 10:54 pm
Im in the middle of a KT88 mono-block Williamson build based on Acrosound.

My goal is about 70 Watts each channel. There are not too many circuit components (resistors and caps). I spent most of my money on very high quality output iron from Electra print. Conservatively rated at 100W with a 3.8K primary. 15HZ to 36KHZ at-1db. They weigh 15lbs each! The filter caps were a bit expensive too because I am at a weird voltage where I needed to put caps in series with dropping resistors to make sure they are not over taxed. This led to alot of caps.

Its not the most modern design by any means but I have heard of people building these with middle of the road components with great results so I figured with great components, it sound sound spectacular.