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Old 4th October 2009, 04:19 PM   #141
housing is offline housing  Hong Kong
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Quote:
Originally Posted by Nelson Pass View Post
Yes, there will some sort of project based on them, although
I expect a limited DIY participation due to the scarcity of
the parts.

I bought 10 pair from

Acronman Electronics <acronmanelectronics@gmail.com>

and the service was quite good.

They appear to be genuine, however I have only tested
one of each so far, and I haven't had time to build a proper
output stage to see what the performance is likely to be.

Maybe tomorrow...

I had no problem with this Singaporian's sale of the Sony's.
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Old 4th October 2009, 04:44 PM   #142
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... but the circlotron output stage on passdiy has no gain. Do I understand it correct:

If you use fets, use the circlotron as follower. If you could use semisouth devices, go for voltage amplification in the circlotron...

Regs, Dirk

P.S.: Is there any special reason, that the circlotron was historically only used for current amplification???
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Old 4th October 2009, 05:01 PM   #143
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The Circlotron on the right has a gain of ~µ. You can use transistors with the appropriate bias arrangements:
http://www.tubecad.com/august99/page2.html
If you reconnect the secondaries to the opposite sides of the load, the gain will be ~1.
The first circlotron here (output stage) has a gain of ~2:
http://www.tubecad.com/august99/page3.html
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Old 4th October 2009, 06:13 PM   #144
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Ok, if I understand it properly: The transformer coupled circlotron has a mu amplification. In case of symmetrical ground reference, it would be 1. But this is the only feasible design, otherwise - how could we drive it???
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Old 4th October 2009, 08:43 PM   #145
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The transformer (secondaries) here is a concept (and a very good design idea).
It is used to model how to apply the input voltage to each FET (I will speak of FETs now). So, if we connect each secondary:

Between gate and source - gain=Gm×Rl
Between gate and the other side of the load (connected to the OTHER source) - gain=1
Between gate and ground - gain=2. In this last case you can feed circlotron from
differential/balanced stage without signal visual connection to ground. The circlotron stage will be referenced to the ground by two resistors divider in parallel with load. And these two resistors can be connected to any voltage to provide the required bias for the output transistors.

The secondary windings can be replaced by resistors fed by current to produce
voltage drop, like in this example:
http://www.ne.jp/asahi/evo/amp/CSPP/2SJ18.htm

There are plenty of possibilities in designing circlotron amplifiers.
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Old 4th October 2009, 09:43 PM   #146
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Can you post a schematic without transformer and without ground reference problem that gives a mu amplification?

Sorry for beeing quite unexperienced...
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Old 4th October 2009, 11:07 PM   #147
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HV, You might look at The Amazing Circlotron on the Passdiy web page. That amp is
an example where the output is taken from the drains of the mosfets so it has voltage
gain. There is no reason tubes couldn't be used like this but rember the output impedience will be a lot higher.
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Old 4th October 2009, 11:10 PM   #148
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Hi woody, the pass ciclotron gets the voltage gain from the input fets, not from the output devices.

@stephenoh: could you explain the japanese circuit to me???

Regs, Dirk
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Old 4th October 2009, 11:45 PM   #149
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It gets gain from both. All the FETs are operated common-
source mode, in which there is both voltage and current
gain.

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Old 5th October 2009, 01:53 AM   #150
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Well, Dirk, you are not the only one, who is trying to learn the circlotron specifics.

Since you are asking about µ-level gain, the example in post 145 is exactly what
we are talking here:
Signal current from 2SK215 going through 10K produces voltage drop on this resistor,
which is applied (via bias battery V1, V4) between the gate and source of each SIT -
this is COMMON SOURCE connection and the gain is the highest possible (for 2SJ18 µ~5).

Another example is SEPP stage:
http://www.amplimos.it/images/VFET_2...020908A3_2.gif
Voltage, developed on 3.3K, is applied via the source followers Tr16, Tr17
between the gate and source of each 2SK82 - again COMMON SOURCE connection and the gain is highest possible (for 2SK82 µ~4).

In each case the signal current into corresponding resistor is coming from the stage
with a reasonably high output impedance.

Do not take this as an endorsement/approval of each design. Each of them may require
some "polishing". But they are good examples of how to read or design circlotron
stage.
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