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DISCLAIMER: Vacuum tube circuits work with dangerously high voltages. Do not attempt to build circuits presented on this site if you do not have the required experience and skills to work with such voltages. I assume no responsibility whatsoever for any damage caused by the usage of my circuits.

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Wednesday, April 10, 2013

Low Cost Single Ended 6CB5A Amplifier - Part 6

Hi!

Many people asked me already how these little monos sound. If you read my article series 'How Does It Sound' you know that I am reluctant to give sound descriptions since they can only be very subjective.




But I understand that there is a lot of interest and that it is difficult to have an idea about the sound from the previous posts. So I will try my best.




The amps have been playing in my small system for over a week now. They have the sound character I am looking for. No harsh sound or annoyance. Neutral frequency response as could be expected from the measurements. Resolution is good.




How do they compare to the transformer coupled version? Of course the bigger version gives more of everything, especially in the resolution department and also richer tone colours. These amps are a stripped down version, so some compromises had to be done.

For the cost of the parts (just below 1000 Euros for all the electronic parts for both monos, without chassis, or about 800,- for a stereo version) I think it gives a more than excellent sound. If you have a good stock of parts yourself and if you are a bit creative with salvaging power transformers or output transformers from old radios, these can even be built for a lot less. The cost mentioned above includes the high quality Lundahl transformer and choke and the excellent quality power transformers.




These amps do not sound 'tubey' at all. They are neutral and have a solid bass given the size of the amps and their power. Of course suitable speakers need to be used with them. Yet they retain the ability of good single ended designs which excel in musical flow.

How do they compare to amps with directly heated triodes? Of course a well implemented DHT amp will give even more of the single ended magic and will be better able to reproduce the atmosphere of  a recording. But to achieve that requires much higher expenses. A poorly designed DHT amp or one with poor quality parts will not be able to compete with these 6CB5As. The system needs to be of very high quality before these amps would become the limiting factor.

As mentioned I have been using these amps for over a week now and I can happily listen to music with them. Even though I have some behemoth amps in the basement, there was no urge to pull one of them over. My last record review was done with these small monos.




Let me share a big secret about how to get good sound with you: Be happy with what you have or rather what you can afford. No matter how much you spent or how much effort you put into an amp, there will always be something better out there somewhere. There are always possibilities to do details better. Stop worrying about sound and enjoy the music! Sounds ridiculous? Especially since I offer much more elaborate and expensive designs myself? I don't think so. I know many audiophiles who are always worrying about the sound quality and are never happy. This is supposed to be fun! Don't do the mistake to listen for the faults in an amp or a system. You will always find faults. Once you concentrate on the weaknesses, that's what you hear. Rather concentrate on the strengths of an amp. And these little buggers have many strengths to offer.

Enough ranting. Here some cool photos which I shot at night:








I hope you enjoyed this series of posts about these amps. If you want to build these or a stereo version of the circuit and need parts, don't hesitate to contact me.

Best regards

Thomas



18 comments:

  1. I really like your comments on being happy and enjoying what you have. I have a friend who is a musician that is happy listening to music on a portable boombox. It doesn't occur to him to get a better stereo. There is much many audio nuts could learn from people like this.


    Great posts and beautiful amp.

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  2. Hi Iain,

    Musicians very often have crappy systems. They have the ability to listen to the music and not to the sound. Something many audiophiles are lacking.

    Best regards

    Thomas

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  3. Oh ... and thanks for the compliment :-)

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  4. Love the wood chassis on this particular amp Thomas... what wood is this if I may know?

    Excellent finish as always!

    Regards
    Dixon

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  5. Hi Dixon,

    that is birch wood

    Best regards

    Thomas

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  6. Hello Thomas,
    I've been building tube amp/preamp circuits for a while now but am not yet able to design. I Wanted to say how much I appreciate the approach to your designs. Can you provide some fodder for learning your transformer and design approach? I would love to learn how inductors fit into these circuits.
    I have collected most of the parts and Teak wood for your latest "low cost 6CB5A amplifier" and can't wait to finish.
    Best regards,
    Dave from California

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  7. Hi Dave!

    Thanks!

    I am not quite sure what you mean by fodder about my design approach? When I publish schematics I usually do share those details.

    Best regards

    Thomas

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  8. Hello Thomas,
    sorry for the lack of clarity. By fodder I mean learning tools-books, websites, and anything else I can use for learning/implementing the various transformers (other than power and output)in your curcuits. If I missed anything you've already published please point them out.
    Thanks again!
    Dave

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  9. Hi Dave,

    check the website which I presented in my last 'cool links' post:
    http://vinylsavor.blogspot.de/2013/04/cool-links-wwwtubebooksorg.html
    There you will find tons of books for download. The Radiotron Designers Handbook is a classic. The 4th edition is huge, ,may be better to start with the 3rd edition which is also more focused on AF amplifiers. Man other useful books there. Just browse through the content.

    Best regards

    Thomas

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  10. Hi Thomas. Let me first say what a pleasure it is to discover your blog. After a long hiatus from DIYing due to business and family, I've found myself with more leisure time and your blog has rekindled my interest in very positive ways. I've been living happily with a pair of 300B monoblocks for a while now--just a simple direct-coupled 6SN7 cascade driver, direct-input design that Joe Esmilla put out there many years ago. It suited my needs. I used James transformers, Angela universal power trans and quaility internal parts. Last night I got busy and substituted some 6CB5s for the 300Bs, and I have to say I'm startled. I've never been much of a fan of triode-wired beam tubes as a substitute for DHTs, but this one sounds very different to me. I'm impressed with the mid-range presence and depth of staging, combined with very fine articulation of details and clean, tight bass. My voltage options were either too high or below your 400 VDC, so I opted for 380 with about 70 volts bias. I'm getting a little red on the plates but I figure that won't hurt. The speakers are my trusty ProAc Response 2s in a smallish listening space, and with--what?--probably 5-6 watts at most it's pretty enjoyable. I'm wondering if I'll really go back to the 300Bs! I can honestly say that a builder on a budget could save $300-500 on output tubes, spring for a decent pair of output transformers and some nice internal caps, and have a mighty sweet SE amp for not much money--and with more going for it than a lot of other "budget" projects I've tried. So thanks for this idea, it's a really pleasant surprise. My next project was to revisit PP 2A3s, but I'm wondering if PP 6CB5s might not be more fun to try!

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  11. Hi Grover,

    thanks a lot for your comment and for sharing your experience with the 6CB5A!

    Thomas

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  12. Dear Thomas,

    I´m very impressed by your tube amplifier designs and I´m now collecting parts to build a 6CB4A amplifier.
    I found out that you were using OPTs with different primary resistance. Do you recommend a transformer with 5K or can I use a 3,5K transformer as well.

    Best regards
    Peter

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  13. Hi Peter,

    this depends mainly on the speaker you use. If the speaker has a rather difficult impedance curve, use a 5k transformer. Contact me if you have difficulties to find a suitable OPT. I can provide all the parts I use.

    Best regards

    Thomas

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  14. Dear Thomas,

    many thanks for your quick reply!

    The speakers that I currently use are easy to drive, but one is a open baffle (nom. 4 Ohm) the other a TQWT with nom. 8 Ohm. :-)

    I have two SE transformers to hand with a big M102b core and an impedance of 2K5/4R, this would be fine with the TQWT but may be not suitable for my open baffle.

    Best regards
    Peter

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  15. Hi!

    Nominal impedance values are quite meaningless. More important is the impedance variation over frequency. The primary impedance is not a hard spec but can vary over a wide range. 2k5:4r will work but give a lousy damping factor. Depends on your speaker if it still sounds ok

    Best regards

    Thomas

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  16. Hi Thomas,

    Thank you for the explanation.

    If I get you right, does that mean, that I better use the 2K5 OPTs for a different project and go for two new ones with a 5k primary and maybe two secondary windings (4/8 Ohm), if I want to be on the safe side?

    Best regards
    Peter

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  17. Hi!

    Without knowing your OPT it is difficult to say. There is no standard way which defines what 2k5:4 actually means in terms of turns ratio and primary inductance. The turns ratio most likely is the square root of the impedance ratio, but not every winder is strict about this.
    Also as I wrote above nominal 4 Ohm leaves a lot of room for variance. If your speaker is over most of the frequency range above 4 Ohm, it is probably quite ok. If it dips even a lot below 4 Ohm, probably not.

    I generally prefer higher primary impedances (and thus higher turns ratios). So if you are not sure, get a OPT which fits better.

    But on the other side you can first try it and see how it sounds. Might work nicely. If not you can still get another OPT

    Best regards

    Thomas

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  18. Hi,
    300B Monoblock Amplifier

    Hey friend. I think your site is very interesting for me, your site give me some important information, thanks a lot!

    ReplyDelete