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Old 28th March 2013, 05:11 PM   #3031
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You want to tell me use the scope with real power amps?
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Old 28th March 2013, 05:45 PM   #3032
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No, use a resistor the value of the input impedance of your power amp as dummy load.
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Old 28th March 2013, 05:50 PM   #3033
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OK, thanks George. How to know the input impedance of the power amps: measuring with a ohm-meter?
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Old 28th March 2013, 05:57 PM   #3034
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Don' t you have their specs? Usually you can tell by looking at the schematic. Be careful with an ohm meter or lcr, it may overload the input. These things sometime have up to 9V out.
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Old 28th March 2013, 06:14 PM   #3035
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I ask Erno Borbely.
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Old 28th March 2013, 07:18 PM   #3036
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Quote:
Originally Posted by merlin el mago View Post
Attached schematic how I wired the Lundhals LL1660, help will welcome?
Quote:
Originally Posted by andyjevans View Post
I don't know if it matters, but I think you have the outputs the wrong way round on the LL1660. Plus should go to plus.
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Originally Posted by andyjevans View Post
Have you got a 150v glow tube e.g. 0D3 from B+ to ground? As in my schematic? If you do and you have the DN2540 set for 32.5 to 35mA, then the 0D3 should light up pink and you can only have 150v on the top of the LL1660 and 145v on the plate. Follow the schematic and the voltages should be correct!

Your wiring diagram for the LL1660 is fine - doesn't really matter that the output is reversed or not. If you have wired the LL1660 as in your schematic it will be correct.
I asked Thomas Mayer aka Vinylsavor about Lundhals wiring, attached the correct wiring for next diyers.

So all measurements were taken with swapped the polarity at the output
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File Type: jpg Lundahl LL1660 for #26.jpg (254.3 KB, 197 views)
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Old 28th March 2013, 07:33 PM   #3037
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It doesnt matter. The thing is that your 26 preamp is an anode follower, and anode followers inverts the signal. That means that what is going out from your anode is an inverted signal from that of your source. As long as you do the same on both channels, there is no difference for the measures or the following amplifier.

If your scope has two channels you can put a sine on the input and measure input and output signals simultaneus. If the two sines has their tops on the same vertical line, your output is the same polarity as your signal. But, as I said, it really doesnt matter.

Last edited by stajo; 28th March 2013 at 07:52 PM.
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Old 28th March 2013, 07:34 PM   #3038
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Thanks, so now I have a non inverting stage.
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Old 28th March 2013, 07:43 PM   #3039
stajo is online now stajo  Sweden
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I dont know. Depends on how Per Lundahl chosed to draw his spec. But you dont have to care fortunately
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Old 28th March 2013, 07:44 PM   #3040
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Hi Felipe,

as I wrote you can connect the secondary either way depending if you want the stage to be inverting or non inverting. Some transformers have different high frequency performance depending on the polarity. Not the Lundahls. So you can choose.

Best regards

Thomas
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