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grungeman91 17th May 2011 05:47 AM

phase splitter issue
 
Has anyone ever built a concertina phase splitter and have the signal be perfectly split but they differed in amplitude?

ChrisA 17th May 2011 06:14 AM

Quote:

Originally Posted by grungeman91 (Post 2574435)
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

kenpeter 17th May 2011 06:38 AM

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.

artosalo 17th May 2011 08:38 AM

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 ?

DF96 17th May 2011 09:57 AM

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.

richwalters 17th May 2011 10:17 AM

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.

SY 17th May 2011 10:19 AM

Quote:

Originally Posted by artosalo (Post 2574511)
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.

richwalters 17th May 2011 10:47 AM

1 Attachment(s)
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

M Gregg 17th May 2011 12:13 PM

Quote:

Originally Posted by richwalters (Post 2574582)
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

richwalters 17th May 2011 02:44 PM

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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