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Old 15th May 2012, 10:11 PM   #1
Stee is offline Stee  Italy
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Default 6550 PUSH-PULL

6550 PUSH-PULL WITH CURRENT FEEDBACK
http://www.esafono.it/DOCMONO.pdf

is mine Yaqin MC-100B modified
that it's ideal for two monoblocks

the secondary 4 ohm and 8 ohm are in parallel
to increase current
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Old 15th May 2012, 11:41 PM   #2
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Hey Stee:

Dude you need to look for another supplier or stop going to pick and save for your drugs!

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Quote:
Originally Posted by Stee View Post
6550 PUSH-PULL WITH CURRENT FEEDBACK
http://www.esafono.it/DOCMONO.pdf

is mine Yaqin MC-100B modified
that it's ideal for two monoblocks

the secondary 4 ohm and 8 ohm are in parallel
to increase current
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Old 16th May 2012, 07:27 AM   #3
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Paralleling up the 4R and 8R outputs will not increase current, the primary will see shorted turns so you'll end up with rather less current.
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Old 16th May 2012, 10:59 AM   #4
oshifis is offline oshifis  Hungary
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Stee,

Could you explain how the current feedback works, and why is it better than the conventional voltage feedback? I suppose the source impedance of the preamplifier should be low.
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Old 16th May 2012, 11:50 AM   #5
DF96 is offline DF96  England
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I can't see any current feedback, just a resistor added in series with the output. I can see shunt feedback, which will give you an unusually low input impedance - almost certainly unhelpful and it may raise distortion in the source. You could try doing shunt feedback properly, with higher resistance values. There is a small advantage to shunt feedback: it removes common-mode distortion from the input stage, but this is usually so small that it can be ignored.

Paralleling 4 and 8 ohms secondaries is daft - you just use up power heating your copper windings.
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Old 16th May 2012, 01:18 PM   #6
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Almost 8K8 input impedance ! too low , you will need a preamp with very low output impedance to drive it .
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Old 16th May 2012, 09:07 PM   #7
Stee is offline Stee  Italy
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Default thanks for your contributions

Meanwhile precise that it is not of a proposed
is a change that is playing very well

the feedback current functions as a real-time equalizer
(shunt power resistor 50W)
corrects the defect of natural bass tones
However, the input impedance becomes 2K2
the pilot with a V-DAC

the parallel between the secondaries is effective for the current delivered
really have to reconnect 8 windings (16 wires)
I highly recommend it
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Old 16th May 2012, 10:40 PM   #8
DF96 is offline DF96  England
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Sorry, I don't understand. You mention a shunt power resistor but your circuit shows a series resistor. This has nothing to do with shunt feedback.

If your OPT secondary wiring works then it is not as you have described. Paralleling 4 and 8 ohm outputs will fail. However, some OPT (e.g. Sowter) have four identical secondaries which can be wired in different ways to get 1, 4, 9 or 16 ohms.
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Old 16th May 2012, 10:47 PM   #9
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Taking the feedback from a current-sampling resistor will cause a boost in the voltage response at the bass resonant frequency of most speakers. Since that would be more agreeable with some speakers than others, it might be worth having a pot to vary between current mode and the usual voltage mode (variable damping).

I'd move the coupling caps and bias adjust components to the driver follower grids, then direct drive the output grid stoppers from the follower cathodes which would have the cathode resistors returning to the negative supply. Supporting grid current, that variation would increase the available output power without adding any parts or giving up performance at lower power. A switch on the screens to allow pentode mode would be handy if one ever had the need for the full 75 Watts or so output (100 if plate supply is bumped up to 600V).

I like the performance of inverting mode. Then the feedback takes care of hum and noise in the input stage and there are no common-mode issues. I would scale the input/FB values up a bit even though my current gear can drive 2.2K. (the grid is a virtual ground)
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Old 17th May 2012, 05:19 AM   #10
Stee is offline Stee  Italy
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Default easy to try

Like all tube amp owners complain
pressure is always low enough
with this arrangement equalizes the system directly on the load current
compensating for the response of the whole amp / speaker in real time
must give up some power, however,
This is why I turned to minimum bias
22mA is a class AB

However DF96, some OPT (e.g.this Yaqin) have four identical secondaries in each output 4, 8 ohms which can be wired in parallel

I repeat also
that the lifting-up of the cathode as internal feedback
(with positive signal)
should never be used
because it introduces emphasis
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Last edited by Stee; 17th May 2012 at 05:23 AM.
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