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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6as7/6080 Se Otl

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#21
revintage said:
To make this cicuit work you have to take out max currents through the 6080s which means their workingpoint should be Ia 125mA, Ua 100V.

You should also use a choke or a CCS from the cathodes to ground. A B+ of 130-170V will do.

Every triode has an theoretical (simplified 1/Gm)Rout of ca 140ohms, so adding a separate 10 ohm to each one will not make you loose so much. Without NFB Zout will be high anyway.

If going for a 8ohm load I would suggest using at least 5 but preferably 10 6080s/channel.
Click to expand...


I suggested using a CCS some time ago.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=91200

However, there was concern that oscillation would (had) occured.
Maybe a CCS per cathode?


Andy
 
#22
Have anyone really tried a CCS as I know you suggested? Must be the most costeffective way to go as chokes cost a lot. Just using a resistor will make you lose to much power and worsen THD.

Think a CCS robbed from Pass would be fine......
 
#23
To be honest, I could not see why a CCS would cause oscillation and instability as it is well used, as you say in Pass designs.

And as you say, cost is minimal !!!

So far, I have not had chance to try anything due to work. ( I am now 200km off the east coast of India ! )


Andy
 
#24
If you can find transformer cores, bobbins and magnet wire there´s no need to pay 60 bucks each for cathode chokes. I made my own for my SE OTL with 4x PL504 (per channel):

600 turns 0,45mm wire on EI78 cores with ~0,5mm airgap.
 
#26
Hey Fuling,
As I know you are keen to try new solutions, have you tried CCSs?

My (theoretical) idea is that one could lower B+ to consist of 100V over the 6080s, the negative swing at decided load and the voltage drop over the CCS.

So a std 115V secondary transformer should be sufficient.
 
#27
This is a theoretical model of what I mean. Simmed it works well. Stole the CCS from Pass Zen and turned it upside down and changed P to N😉 !

Almost like it is too simple as the grids are at ground level. 12,5W through each 6080. At 5% THD output is 12W/16ohm and 6W/8ohm. At 1% THD output is 2,5W/16ohm and 0,5W/8ohm
 

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#30
As I said earlier 100V/125mA through the tubes. No need to bias the tubes otherwise than with the CCS. If you check UaIa-curves, Ug is in the ballpark of -30V. So there is enough room for negative swing even if we should loose 10V over the CCS.
 
#31
Lars: Good idea but you´re not the first one to think about using an Aleph-type CCS in an SE OTL amp, I wrote something about that on this forum at least two years ago. Never got any replies though...😉

The whole thing would be sort of a White follower.
 
#34
Fuling,
Anyway, did you ever try it? Maybe we should give it a try? I have a ICA-plasticbag with at least 50pcs 6080s somewhere in my warehouse.

Gain is -7dB with 16ohm and -10dB with 8ohm so the driver must have good voltageswing capability.
 
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