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Old 8th February 2013, 09:35 PM   #21
midmoe is offline midmoe  United States
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I will keep the ac for the 6550s and series the 3 driver tubes, so as to filter it down for dc, keeping load to fil xfmr to a minimum...Russel came down and took pic with his phone, but came out badly...so at this point, any one who wants a paper copy please email me at finite47@gmail.com and I will be happy to mail you one. Sorry about the delay. Russel also said he had trouble with triad tansformers running hot. Didn't know why, but I think it's because theyre not tuned to 60 hz. Will look for better xfmr. for companion monoblock. Of course the series string is coming off 120 ac input, not xfmr, so no problems with that....midmoe
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Old 9th February 2013, 02:59 AM   #22
cnpope is offline cnpope  United States
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Quote:
Originally Posted by midmoe View Post
Of course the series string is coming off 120 ac input, not xfmr, so no problems with that....midmoe
Understood...that's what I'm doing too. It works very well.

Chris
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Old 10th February 2013, 03:06 AM   #23
midmoe is offline midmoe  United States
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I haven't bothered with seriesing up the small tubes yet as I'm busy building companion model...but the formulae of 1/sqrt 2 is to multiply the 120v by .707 as I understand it. But isn't that the formulae for full wave rectification, not half-wave? Seems if you chopped the sinewave in half, you'd get less than the .707 figure....we will see. I will be needing 34 more 8 ohm bose 901 type drivers to build 2 columns of 26 series wired, each side 208 ohms. will have to check to see if theyre avail. from bose still. Last time I looked, only 1 ohms were avail. Anybody out there got extra 4" drivers from 901s lying around? Probably not too many people parting them out. The 16 ohm subs haven't shown to be a problem....got them on a 120 ohm resistor. Still can't believe how much energy shows up with such large resistance in the way. midmoe
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Old 10th February 2013, 11:53 AM   #24
cnpope is offline cnpope  United States
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Quote:
Originally Posted by midmoe View Post
I haven't bothered with seriesing up the small tubes yet as I'm busy building companion model...but the formulae of 1/sqrt 2 is to multiply the 120v by .707 as I understand it. But isn't that the formulae for full wave rectification, not half-wave? Seems if you chopped the sinewave in half, you'd get less than the .707 figure....we will see. midmoe
Chopping off the lower half of the sinewave means that the heaters in the chain will get exactly half the power they would otherwise have received, and thus the heating effect will be exactly the same as would be achieved by instead reducing the rms voltage of a pure sinewave by a factor 1/sqrt2.

In other words, the true rms voltage of the chopped-off sinewave will be exactly 1/sqrt2 of the rms voltage of the original sinewave. And it is this true rms voltage that should be, for example, 6.3V for the 6550 tube, since the power dissipation, and hence heating effect, is always, more or less by definition, V^2/R where V is the true rms voltage.

An ordinary ac voltmeter may very likely give an incorrect reading of the true rms voltage in the "chopped-off" case, since it is typically designed under the assumption that it is measuring a sinewave. A true rms meter, which is much more sophisticated and effectively carries out the process of squaring the instantaneous voltage, then time-averaging, and then square-rooting the result, would read correctly, and would give the correct 1/sqrt2 answer.

However, in this case where one is simply chopping off the lower half of the sinewave, it is elementary to see that the result of the squaring, time-averaging, and then square-rooting will be to give a value that is 1/sqrt2 of the answer for the full sinewave.

(Of course there should, strictly speaking, be a tiny correction to the above discussion becasue of the 0.7V forward voltage drop across the diode, but that is pretty insignificant when considering a 120V rms sinewave.)

Chris
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Old 10th February 2013, 12:05 PM   #25
midmoe is offline midmoe  United States
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as the circlotron nears final design completeness, I have used small variations from what is common knowledge available in literature, and seems trivial compared to the way I have the amp's output stage coupled to the driver stage. It seems the method of ground referencing the cathodes rails back to the driver's cathodes instead of to chassis ground through 1K resistors, may be unique and allows a real advancement in circlotron utility, with the only problem remaining, of having a a non-standard output impedance. If, indeed the coupling is unique and I am the first to come up with it, do I not have the right to name it? If I should be, then I call it the "inverted cathodic floating return drive". ICFRD or I see fred, or "freddie" for short. midmoe
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Old 12th February 2013, 03:23 PM   #26
midmoe is offline midmoe  United States
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chris, isn't what your'e saying is, with a single diode, power is .5 and voltage is .707 ? Since the tube fils. are dealing with power, should the math be oriented in a power requirement instead of voltage requirement? Also, I thought the foward voltage drop across a standard diode junction was .6v, not .7 I'm waiting for xfmrs. and tubes to come in. I'm running out of organ chassis' to scavenge for octal and 9 pin miniature sockets ( the old ones are so nice). Other than that, I should have another monoblock ready in no time. Are you building one too? I'm trying to "class-up" the next one's appearance, using aluminum tread plate on top for tube mountings. It's too thick and hard to punch, so I got special metal cutting hole saw blades that works great. The box is 8"X14" and 4" deep and hinged in a cigar box style. All power supply components are on the bottom of the inside, amp components under the top, only the tubes and input/output posts on the exposed alum. tread surface. This has worked out well for the prototype, giving easy access for alterations, so I think I'll continue to use this motif on any production units. These are the smallest dimensions for a reasonably uncramped assembly. I will get real camera today to phograph both the schematic and the amp itself. since the camera phone thing did't work out. My friend Ben is coming over later and perhaps we can figure out how to post. I did add a small muffin fan too cool the fil. xfmr, now I can keep the top closed when using for extended periods. midmoe
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Old 12th February 2013, 04:42 PM   #27
cnpope is offline cnpope  United States
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Quote:
Originally Posted by midmoe View Post
chris, isn't what your'e saying is, with a single diode, power is .5 and voltage is .707 ? Since the tube fils. are dealing with power, should the math be oriented in a power requirement instead of voltage requirement? Also, I thought the foward voltage drop across a standard diode junction was .6v, not .7 midmoe
Precisely. Suppose, for example, the filament string was operating at its correct voltage with the full wave supply. If a diode is now inserting in the chain, the power to the tube heaters drops to half of what it was. This means that the "effective" voltage to the heaters (i.e. the true rms voltage) must have dropped to 1/sqrt2 of what it was.

In other words, if a 120V rms sinewave is connected in series with a diode, the resulting output, with the bottom half chopped of, has a true rms voltage of 120/sqrt2 ~ 84.9V.

So a heater string connected to such a half-wave rectified sinewave would need the to be composed of tubes whose standard rms heater requirements
added up to 84.9V. (And, of course, all the same current draw.)

I think that whether the forward voltage drop is 0.7V or 0.6V is a fairly fine detail here.

Chris

Last edited by cnpope; 12th February 2013 at 04:45 PM.
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Old 13th February 2013, 04:58 AM   #28
midmoe is offline midmoe  United States
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I got tired of trying to find my misplaced camera, so I bought a new one today. I succeeded in getting the schematics for power supply and amp loaded onto my computer, and they are reasonably legible, but will need to call in help to get them to upload to this site. Please bear with me a little longer...if anyone could give me a consise tutorial on how to do this, it might speed things up....midmoe
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Old 13th February 2013, 02:05 PM   #29
midmoe is offline midmoe  United States
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BIAS SUPPLY MOD since each side's bias supply is referenced to it's respective cathodes, doesn't this introduce a small positive feedback in the bias supply system? I was thinking it might, and as an early concept was to squeeze in as much local neg feedback in as many places as possible, especially the output stages, so as to lessen parasitic tendencies and lower impedance...so I thought that swapping each bias supply's reference point to the opposite cathode rails might do the trick on addl. NF. It seems to have done so, as the volume seems just a little lower than before. Will have to dig up a double-pole double-throw non-shorting toggle to flip the references on the fly. Will go to radio shack to acquire the switch and visit my computer guy and try to get him out here to upload schematics, which are already in documents, and are fairly legible. I am also presuming at least several of you have already built my design as per my discriptions, and don't need the schematics, and have even come up with improvements of your own. Of course,I am especially intrested in output impedance estimations.....good luck. midmoe
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Old 13th February 2013, 05:52 PM   #30
midmoe is offline midmoe  United States
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went to town, got dpdt switch, hooked it up... no difference.....couldn't hear even a slight "click" during switchover, which is puzzling....I left the bias references in inverted mode as perhaps under full load and with a scope, some small improvement would be detected, or a miniscule drop in output impedance......with a repeated A/B comparison......midmoe
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