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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 29 Sep 2016, 20:31 

Joined: 17 Feb 2014, 21:32
Posts: 1
Location: Washington DC area
My name is Tom and this is my first post on the forum. I am 55 years old and besides photography music is my big hobby. Electronics used to be long time ago and life forced me to take different path ( I am a geophysicists), but I always thought about coming back to it. I do have a limited knowledge on the subject and this is why I am here asking for the help. My plans are to build few low wattage amplifiers, SE, for baroque music which I am fond of. I am not "bass hungry" and mid range is the frequency band I am the most interested in. I heard a lot of good about single drive and open baffle speakers and the latter ones are in the scope. Problem is with my financial situation based on health issues and I cannot spend to much money on components. I would like to try to use drivers I have: RadioSchack 40-1354 and 40-1197, 1" paper tweeters from Onkyo system, and bass drivers from old Fisher XP-320 2-way speakers. Few days ago I started to search for information about OB system design, but got lost. First issue is with Fisher drivers... they are 8" rated 8W at 8 ohms. It looks like they are not the best candidates for the project, but I have them for 6 years and do not want them to get damaged in continues process of moving them around (please see attached images). Still, I would like to use them to see what OB systems sound like. I would like to build them similar way like ones from the following website: ... -speakers/
Like I mentioned above they would be used for chamber music with low power amps like tube Darling, GainClone, and one from this site; Class-A 2SK1058 MOSFET Amplifier.
I am still not sure to use 2 or 3-way system and which RadioSchack drivers to use; the 1345 or 1197. I do not know anything about the bass unit parameters. The drivers were given to me and came from time when Fisher went down with low cost designs. The XP-320 are so insignificant I could not find anything on the net in reference to parameters. My friend said the crossover had only capacitor for tweeters. In this case I am puzzled with inductor for the bass units. Is there any suggested value I can start with? As I said I do not expect much base from them, but a little bit would be nice. My listening space is rather small and I do not need to have a very loud system. Also, I do not understand the crossover designs for amplifier to see the single impedance with multiple drivers. The all mentioned drivers are rated at 8 ohms. May I ask anyone for suggestions/help?

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PostPosted: 30 Sep 2016, 13:43 
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Joined: 05 Aug 2016, 14:35
Posts: 227
A few things:

a) Those fisher drivers are very nearly certainly not designed to be installed in an open-baffle system. It is very likely that they are designed for an acoustic-suspension or properly baffled ported design to prevent the voice-coils from bottoming while in service. This may not be the actual case, but from the era, and visual design of the speaker, this looks likely.
b) SE amp (fly-weight) driven speakers are a special case and require a great deal of attention to produce in any way that makes good sonic sense.
c) Baroque music has a broad range from Bach to Vivaldi, and from trumpets and kettle drums to very subtle woodwinds. It also can have a broad dynamic range such that you do not want your amp to be gasping even before reaching a loud passage. This has nothing to do with bass vs. treble, but with peak-to-average range and basic physics.
d) SE amps are also a "special case". The iron (transformers) and other design elements are unique to the species, such that you would not be able to re-purpose output transformers should you not be happy with the result.

This is not to suggest that what you wish cannot be done. This is only to suggest that you think long and hard, and "build on paper" before you invest in materials to execute your design. And be prepared either to be very patient, or spend more than you expect. Time = money = good results. Having no idea of your budget (other than 'challenged') that, too will be a controlling factor.

Now, one more thing. Again, having no idea why you are going down this particular path, I will blatantly speculate:

a) You already have a high-quality conventional 2-channel audio system and you are looking into SE out of curiosity. With this in mind, have at it! You will learn something, and you will achieve something - whether per, better, worse or somewhere else - they will probably be greater than your expectations.

b) You do not have a conventional 2-channel audio system, and/or it is of poor quality, and you want to step up a bit, but at a moderate budget, and by your own efforts. With this in mind, there are many conventional designs, speaker and electronic, that are of moderate cost without the pretty important limitations of SE devices. Put another way, the cost-per-watt for an SE design of excellent quality is much greater than the cost-per-watt for a conventional PP design.

Now, comes in the question of legacy equipment (AKA "Used". The bang-for-the-buck with care, a bit of luck and some patience for this option is a tiny fraction of new moderate-to-high-end equipment. And, there are many legacy designs out there that are extremely well supported and could give you the satisfaction of a strong DIY component but at a much lower risk of disappointment.

Lastly, and writing only for myself, speakers are about the last thing I would build myself. I am more a wood-butcher than a carpenter than a cabinet maker, so that is one factor. The other is that there are many, many, many pairs of very excellent speakers out there for sparrow-feed prices if one is patient and has some few repair skills.

You pays you money, you takes you chances... You have an admirable goal that will give you very pleasing results if you pursue it thoughtfully. I am NOT trying to rain on your parade, even a little bit. But do the research so that you have the information and knowledge to be successful. Best of luck with it!

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