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Old 17th May 2011, 05:47 AM   #1
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Default phase splitter issue

Has anyone ever built a concertina phase splitter and have the signal be perfectly split but they differed in amplitude?
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Old 17th May 2011, 06:14 AM   #2
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by grungeman91 View Post
Has anyone ever built a concertina phase splitter and have the signal be perfectly split but they differed in amplitude?
If the outputs are not balanced then my guess is at least one of the following:
  1. The loads being driven are not the same or,
  2. You are over driving the phase splitter to clipping
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Old 17th May 2011, 06:38 AM   #3
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Ideal cathode bias would be at 1/4 B+, for maximum headroom on both ends...
1/3 is often preferred, I'm not sure why... (same idle voltage drop across both
triodes of a twin?).

If input ever exceeds B+/2, the concertina becomes forward biased diodes to
both the plate and the grid. Both ends locked together travel in same phase...
Whatever's driving a concertina usually can't supply DC current, so both ends
will not travel together far beyond that collision...

Bias at B+/2 or higher would be a huge mistake. I still see it often drawn that way.

Last edited by kenpeter; 17th May 2011 at 06:40 AM.
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Old 17th May 2011, 08:38 AM   #4
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Quote:
Has anyone ever built a concertina phase splitter and have the signal be perfectly split but they differed in amplitude?

The output impedance from cathode is much lower than from anode.
Then, if the load impedance is too low - but equal at both outputs - the output voltages can be different.

What is the load impedance of both outputs ?
And what are the value of anode/cathode resistors ?
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Old 17th May 2011, 09:57 AM   #5
DF96 is offline DF96  England
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No, the same current flows through both impedances so equal impedance means equal voltage however low that impedance is. The complication is that the impedance includes everything attached, so what looks to be equal may not be. For example, if the anode supply is decoupled and the decoupling cap goes open circuit then the anode load has increased so the voltage will too.
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Old 17th May 2011, 10:17 AM   #6
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What impedance probe are you using relative to anode load ?

Ideal concertina requirements: Use Lo mu tube, ECC82,6SN7, ECF80 t sect ,7199 t sect and so on. Bias for 0.33 HT volts across tube and equal resistor anode/cathode resistors.
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Old 17th May 2011, 10:19 AM   #7
SY is offline SY  United States
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Quote:
Originally Posted by artosalo View Post
The output impedance from cathode is much lower than from anode.
Not so. Please see my article in Linear Audio which examines this theoretically and experimentally.

If signals are different at cathode and anode, the loads are different. As DF96 points out, the load isn't just the load resistors... One common error is changing the load from one side inadvertently through measurement. To maintain the equal loading, the measurement has to either not perturb the circuit whatsoever (i.e., the measurement device has infinite impedance) or two identical measurement devices be used simultaneously.
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Old 17th May 2011, 10:47 AM   #8
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The circuit enclosed using an ECF80 performs the function brilliantly with near equal swing symmetry. Expect 25V+25V rms swing and no excuse for signal voltage discrepancies.

richy
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File Type: jpg concertina example.jpg (16.9 KB, 1453 views)
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Old 17th May 2011, 12:13 PM   #9
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by richwalters View Post
The circuit enclosed using an ECF80 performs the function brilliantly with near equal swing symmetry. Expect 25V+25V rms swing and no excuse for signal voltage discrepancies.

richy
Richy,

Please excuse my ignorance, SOT?


Regards
M. Gregg
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Old 17th May 2011, 02:44 PM   #10
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Sorry... 33Kto 56K......I've got several thous of these tubes from differing manu's, Aero, Mullard, you name it all with varying current requirements... this supply resistor adjusted to get roughly 95-110V on the anode. The concertina should easily drive an o/p pair to obtain 10-15W class A. A Zobel snubber would be probably required across the 100K 1st stage anode res, je noch design..o/p tranny etc.

Good luck

richy
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