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Push pull output transformer, no phase splitter?
Push pull output transformer, no phase splitter?
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Old 15th February 2020, 01:53 AM   #11
nigelwright7557 is offline nigelwright7557  United Kingdom
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Not quite sure why you are skipping phase inverters.
You can do it two ways with valves either with one triode with same resistor in anode and cathode (cathodyne) or using LTP technique.
Both are on the internet.
See:
The Valve Wizard
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Old 15th February 2020, 03:07 AM   #12
brightcity is offline brightcity  United States
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Do you think I need any output transformer negative feedback regardless of using 6SG7 vs 6SN7?
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Old 15th February 2020, 03:29 AM   #13
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by brightcity View Post
Do you think I need any output transformer negative feedback regardless of using 6SG7 vs 6SN7?
Depends how much warmth you want in the sound.

Guitar amps tend not to use feedback to get some colour in the sound.
Hi fi amps usually have negative feedback.
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Old 15th February 2020, 04:05 AM   #14
audiowize is offline audiowize  United States
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#1. What purpose do the 3uF caps serve?

#2. The 6SG7 has a 3W plate dissipation rating. I don't see any triode curves, did you find any? Without the phase inverter this is a 1W amp at best, with the phase inverter 2W would be an achievement.

This would be as silly as doing something like putting a resistor in parallel with the coupling cap at the output of a headphone amp.
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Old 15th February 2020, 09:11 AM   #15
jhstewart9 is offline jhstewart9  Canada
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Quote:
Originally Posted by planet10 View Post
Here is an example of a self-splitting (no phase splitter) amp that works. Not the actual example i was looking for but much the same. You can achieve about half the power (so i understand) from if you put a phase splitter in front of itů

Click the image to open in full size.

dave

I did an exhaustive look at the self inverting output stage 2-3 yrs ago. Some of the results were shewn in this forum. And you are correct, the available output is about half what is otherwise possible. The cct must be operated Class A only. Saving a single triode in a driver is not a good return for a result that does not deliver.
I tried cathode tails of resisters, NFETS & chokes. Choke tails delivered the best results. Examples of self inverting stages go back to WW2. I would put this cct in the category of 'don't waste your time'.
Attached Images
File Type: jpg 117L7GT X2 PP Hifi.JPG (89.9 KB, 106 views)
Attached Files
File Type: pdf Self Inverting Power Stage Distortion Results.pdf (104.3 KB, 13 views)
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Old 15th February 2020, 01:57 PM   #16
analog_sa is offline analog_sa  Europe
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Push pull output transformer, no phase splitter?
Quote:
Originally Posted by audiowize View Post
#1. What purpose do the 3uF caps serve?
None whatsoever. Is it surprising?
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Old 15th February 2020, 02:22 PM   #17
brightcity is offline brightcity  United States
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Huh, coupling caps? They can help to protect from overloading the previous stage. The four 6SG7's I have currently are quite "hot". And the planned 12AU7 will stay in.

On another note, a very important question, does anyone think a mic transformer will survive in the 600 CT : 600 CT position?

Last edited by brightcity; 15th February 2020 at 02:28 PM.
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Old 15th February 2020, 05:49 PM   #18
jhstewart9 is offline jhstewart9  Canada
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Default Self Inverting Output Stage Some Test Results

For the curious & others here are some of the D% measurements taken on various versions of the PP 6V6 tail on the test cct. The test cct is essentially the same as the PP 6V6 amp in Popular Electronics Magazine with the exception the driver is a triode connected 6AU6 instead of the pentode connected 6SJ7 on the schematic.
The Self Inverting stage requires 2X the drive of an ordinary PP stage.
One example of many Scope & D% shows lots of distortion even at low power.

There is a photo of the 'mule' test chassis.
The Sparton 8549 is an ordinary receiver we would find on sale in a 40s electronics store.
Attached Images
File Type: jpg Self Inverting PP 6V6 Stage Distortion.jpg (113.8 KB, 78 views)
File Type: jpg Sparton 8549 Output Stage 7H.jpg (79.6 KB, 75 views)
File Type: jpg PP 6V6 Self Inverting Amplifier.jpg (59.8 KB, 75 views)
File Type: jpg IMG_2081 Self Inverting Amp 14H E.jpg (288.7 KB, 33 views)
File Type: jpg NFET Tail Result at 3.75 Watts.jpg (265.3 KB, 33 views)
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Old 15th February 2020, 07:21 PM   #19
planet10 is offline planet10  Canada
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Push pull output transformer, no phase splitter?
Quote:
Originally Posted by jhstewart9 View Post
I did an exhaustive look at the self inverting output stage 2-3 yrs ago. Some of the results were shewn in this forum.
There is an even earlier thread somewhere on the same circuit.

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Old 15th February 2020, 07:25 PM   #20
jhstewart9 is offline jhstewart9  Canada
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Would be interesting to see that thread. The thread I did was in 2017.
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