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Old 29th December 2012, 07:37 PM   #91
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Default Faking wrenchone's L'Fake amp ...maybe

Hello wrenchone. L'Fake's Fake was put together with only bjts, operates in Class A and is low power; but has the key elements you taught in post #14, and more as bonus. The attached jpg shows its design components:
  • The simplified schematic of the chip amp LM386 by Texas Instruments.
  • The Fake's simplified schematic based on LM386, a power NPN, and incandescent bulbs using the heaters of the vacuum tube type 12AX7.
  • Three 12AX7 heaters [3H] connected in series as collector load to the power NPN.
  • One 12AX7 heater [1H] connected as emitter resistor
  • Idle current through the power NPN is 0.3 Amperes; because the tube heaters are connected for 6.3 V service.
  • Pass Feedback from the power output port [Vo] to the non-inverting input of LM386 which is a summing junction of two out of phase signals.
I'll attach a detailed schematic, a build picture of L'Fake's Fake, and its salient measurements in following posts. Noteworthy of mention is to connect LM386 exactly as recommended [its application by TI], and not to exceed its Absolute Maximum V+ rail Voltage of 15 VDC.

Best regards.
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Old 29th December 2012, 08:08 PM   #92
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Default Faking wrenchone's L'Fake Amp..maybe

Here is a more detailed schematic of the subject in the attached jpg. Please note the following:
  • A +/- 15 VDC dual power supply was used.
  • The negative rail is signal ground; because the inputs of LM386 are referenced to it and not to the center tap [0 VDC; see its schematic by TI].
  • The center tap of the power supply is 0VDC. It is the V+ power rail to LM386. I subtracted ~1.8 VDC from ~15 VDC by using the series connected LED as insurance so as not to exceed its rail rating of +15 VDC.
  • LM386 is configured as recommended by TI [10 uF bypass cap, Zobel].
  • Note the sense resistor [1 Ohm ] in series with the +15 VDC rail. The voltage drop across it is ~0.3 VDC or the idle current flowing through the output circuit is 0.3 A.
  • Note the blocking electrolytic capacitors for the path of Pass Feedback, and power output
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Old 29th December 2012, 08:17 PM   #93
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Antoinel

that Pass Feedback path is nothing else than overall feedback , common arrangement for inverting gain stage
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Old 29th December 2012, 09:20 PM   #94
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Default Interesting digressions

.....we have here, similar but not in sync with Wrenchone's design....perhaps Antoinel, it is appropriate to start another thread with your design. Yours and my circuits are different creatures than the OP's. Just a thought. If you open another thread I would be glad to chime in.

Cheers,
Terry
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Old 29th December 2012, 09:56 PM   #95
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Quote:
Originally Posted by Zen Mod View Post
Antoinel

that Pass Feedback path is nothing else than overall feedback , common arrangement for inverting gain stage
I gave the nomenclature "Pass Feedback" to a specific type of overall feedback which emanates from a high impedance port [collector] to a summing junction which in this case is phase non-inverting. It is clearly different from that used in an inverting Op Amp; or a non-inverting power amp whereby the origin of the feedback [Black] is a voltage source or low impedance port. In semiconductor circuits, Pass Feedback [ also in L'Fake amp by wrenchone] is like that of Schade Feedback in vacuum tubes. Schade Feedback is not called Black Feedback!

Last edited by Antoinel; 29th December 2012 at 10:07 PM.
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Old 29th December 2012, 10:11 PM   #96
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Quote:
Originally Posted by Parasonic View Post
.....we have here, similar but not in sync with Wrenchone's design....perhaps Antoinel, it is appropriate to start another thread with your design. Yours and my circuits are different creatures than the OP's. Just a thought. If you open another thread I would be glad to chime in.

Cheers,
Terry
Terry, thank you for your recommendation. I'll start a fresh thread.
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Old 29th December 2012, 10:14 PM   #97
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whatever

for fact that I'm not following you can blame only me
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Old 30th December 2012, 04:03 PM   #98
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Default Other Applications of Vacuum Tubes

Quote:
Originally Posted by Parasonic View Post
.....we have here, similar but not in sync with Wrenchone's design....perhaps Antoinel, it is appropriate to start another thread with your design. Yours and my circuits are different creatures than the OP's. Just a thought. If you open another thread I would be glad to chime in.

Cheers,
Terry
The new Topic or Thread is in the Everything Else Forum. It is entitled "Other Applications of Vacuum Tubes".
Kind regards.
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Old 17th February 2013, 03:18 AM   #99
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I was up at the hardware store getting a replacement flood light, and picked up a couple of pairs of 300W linear quartz-iodine lamps (Feit Electric again, cheap and cheerful) to try out as possible loads for L'fake Lite. The 300W linear bulbs bias up much the same as the 300W bulbs that started this thread, such that a pair in parallel will be needed, just as with the 300W standard bulbs. They glow brighter than the old bulbs for the same current, for those who care. Next time I'm shopping, I'll pick up some higher wattage bulbs, as I'd like to make do with just one bulb per channel. The hard part will be picking up the contacts for properly mounting the linear bulbs. A China source on Ebay sells them, but I'd like to find someone local.
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Old 17th February 2013, 01:03 PM   #100
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Quote:
Originally Posted by wrenchone View Post
I was up at the hardware store getting a replacement flood light, and picked up a couple of pairs of 300W linear quartz-iodine lamps (Feit Electric again, cheap and cheerful) to try out as possible loads for L'fake Lite. The 300W linear bulbs bias up much the same as the 300W bulbs that started this thread, such that a pair in parallel will be needed, just as with the 300W standard bulbs. They glow brighter than the old bulbs for the same current, for those who care. Next time I'm shopping, I'll pick up some higher wattage bulbs, as I'd like to make do with just one bulb per channel. The hard part will be picking up the contacts for properly mounting the linear bulbs. A China source on Ebay sells them, but I'd like to find someone local.
This is an interesting application which generates electrically neutral Iodine free radicals [unpaired electrons]. There is a probability to detect a sonic difference between your standard incandescent [baseline] and this halogen lightbulb [a radical change!]?
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