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6AS7GA as push pull output?
6AS7GA as push pull output?
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Old 6th December 2017, 06:28 AM   #161
ChrisABC is offline ChrisABC  Canada
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here's a 2-PP-6AS7G on this site

Amplificateur ? tubes Ren? Cariou
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Old 6th December 2017, 08:36 AM   #162
artosalo is offline artosalo  Finland
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And a lot of good basic circuits.
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Old 7th December 2017, 03:19 AM   #163
mr2racer is offline mr2racer  United States
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6AS7GA as push pull output?
I've taken another stab at a schematic. I can see why the 100 volt/90ma route would make sense. Less voltage swing and from what I know of load lines less distortion. But I already have the power transformer and I want to extract as much power from the amp as I may. This amp is an experiment as much as anything else.

As for the schematic. I added grid stoppers and cathode resistors instead of sinks. In one way the cathode resistors work out well because with the B+ I have the voltage dropped across the cathode resistors will mean 250 volts across each tube. At 1400 ohms it seems like the cathode resistors should be bypassed? I still have to figure those out.

The interstage design is lifted from the original Magnavox schematic.

As for the front end I thought using a CCS set to 20ma and letting the cathode resistors for 6N6P/ECC99 divide the current between them might work. I might be wrong on this. Also, it would be nice to DC couple the two voltage amps if it will work. The .1uf coupling cap acts as a parafeed for the interstage to keep the DC out of its primary.

The glaring errors will be easy for everyone to spot so constructive criticism is welcome.
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File Type: jpg 6N13S schematic.jpg (89.4 KB, 135 views)
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Old 7th December 2017, 03:27 AM   #164
Shef is offline Shef
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I do not get it how you are gonna have zero volts DC across the primary with those IXCPs. .. they are CCSs, right?
Or, you suppose a gapped SE OPT? .. then why not just go SE. ..
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Old 7th December 2017, 09:24 AM   #165
Shoog is offline Shoog
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Quote:
Originally Posted by mr2racer View Post
I've taken another stab at a schematic. <snip>
Running the outputs with CCS loads brings almost nothing good to the party in this application. Since the Output transformer has a fraction of the impedance of the CCS it will dominate the distortion generating components. It will also limit your output swing - and I suspect will probably fry the CCS when the OT tries to swing higher than the B+ and reverse the drain and source voltages.
If you are going to use CCS's anywhere in this circuit it would be in the front end and in the cathodes of the 6080's. Running the 6080's with CCS in the cathodes has specific benefits which have to be understood as they come at the cost of limiting the circuit to low power class A operation (good for low distortion and DC intolerant transformers but little else). Putting CCS in the cathodes of circuits has become somewhat trendy but rarely do the people doing it understand the consequences.

I would get familiar with the joys of SPICE and model all of these ideas to see what is possible. I have taken raw ideas and refined them to workable circuits this way and learnt a huge amount along the way.

Shoog

Last edited by Shoog; 7th December 2017 at 09:32 AM.
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Old 9th December 2017, 03:12 AM   #166
mr2racer is offline mr2racer  United States
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6AS7GA as push pull output?
Hey anyone, I'm back to TL783 as a constant current sink at the cathode of the outputs. The reference voltage across the parallel resistor is 70 volts. The same as it would be using a 1400 ohm cathode resistor. But the actual current would be through the regulator. The drop across the regulator is 1.3 volts maximum. If I understand this correctly the actual drop through the CCS will be something less than 1.3 volts. So 251.3 across the tube and the CCS would leave about 77 volts unaccounted for. That means I could use a 1.54k plate resistor or larger if I wanted to drop 250 or more across the tube? Also without the huge cathode resistor I wouldn't have to bypass it would I?
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Last edited by mr2racer; 9th December 2017 at 03:17 AM.
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Old 9th December 2017, 03:18 AM   #167
mr2racer is offline mr2racer  United States
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6AS7GA as push pull output?
Thanks ChrisABC for the link to the 2pp 6as7 schematic!
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Old 9th December 2017, 06:35 AM   #168
Shef is offline Shef
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Quote:
Originally Posted by mr2racer View Post
Hey anyone, I'm back to TL783 as a constant current sink at the cathode of the outputs. The reference voltage across the parallel resistor is 70 volts. The same as it would be using a 1400 ohm cathode resistor. But the actual current would be through the regulator. The drop across the regulator is 1.3 volts maximum. ..
Some mess detected.
I just can't get what the circuit you intend (( If that is a CCS - what "cathode resistor" are you talking about?? If CCS - then the drop across the TL is 70V - 1.3V. If you "load" TL with a resistor to make TL less heating (as you say the 1.3V drop across it) in this case the TL provides no (nil, null, zero) CCS performance. Aka "useless".
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Old 9th December 2017, 11:53 AM   #169
mr2racer is offline mr2racer  United States
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6AS7GA as push pull output?
70 - 1.3 is all the answer I needed.
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Old 9th December 2017, 05:23 PM   #170
ChrisABC is offline ChrisABC  Canada
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see page 5 for a pp6as7

http://www.fva.is/~flemming/hsakram/...spmagasine.pdf
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