Hi everyone,
I have an idea of using IT coupling in cathode to get very low output impedance. This is important thing in design of Class A2 amplifier.
6C45P and some penthode tubes like E810F, 6E5P, EL84, EL34... (these tube in triode mode) ... maybe replace 6BX7.
B+ of 811A can reach 415V, so Vak get 400V.
Does it have any problem in my plan ?
Regards,
QA.
I have an idea of using IT coupling in cathode to get very low output impedance. This is important thing in design of Class A2 amplifier.
6C45P and some penthode tubes like E810F, 6E5P, EL84, EL34... (these tube in triode mode) ... maybe replace 6BX7.
B+ of 811A can reach 415V, so Vak get 400V.
Does it have any problem in my plan ?
Regards,
QA.
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some people call it cathode feedback. Sorry, I foget 1 resistor in 811A kathode.
feedback here play role of lowering gain of 811 (mu 160) and lowering output impedance, so get more damping factor. But this FB can get disadvantage. It need one FB coil in secondary. My OPT has no this coil.
I never try this NFB before. So I don't know how to design correctly. Could anyone help me ?
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Most of the time feedback is injected back into the first stage. http://sarris.info/main/files/811acircuit.jpg
I've built an 811A amp before but didn't use an interstage transformer. It worked pretty well. The only tricky part is the 811A filament supply has to be very well filtered.
I've built an 811A amp before but didn't use an interstage transformer. It worked pretty well. The only tricky part is the 811A filament supply has to be very well filtered.
I did build an ampli SE with SV811-10, first and driver stage is 6FD7. IT couple is used for driver stage to SV811-10 and power tube is biased by negative volatage. No NFB is used, sound is very good.
Now, I will try class A2 with cathode FB to 811A.
the global FB like your schema you post is easy and very good when you have RC couple. But It become complicated in case of IT coupling. From Sarris, IT is the best couple for this case.
First I will do my schema with non NFB.
I'm wondering if the IT in cathode will work OK ? How do you think ?
Now, I will try class A2 with cathode FB to 811A.
the global FB like your schema you post is easy and very good when you have RC couple. But It become complicated in case of IT coupling. From Sarris, IT is the best couple for this case.
First I will do my schema with non NFB.
I'm wondering if the IT in cathode will work OK ? How do you think ?
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The 10 ohm cathode resistor will absorb half of your output power. This will reduce efficiency even further.
The 6.45k resistor below the transformer will need to be bypassed, otherwise it will raise the CF effective output impedance which is not what you want when driving an A2 stage.
My gut feeling is that you may be trying to run before you have learnt to walk?
The 6.45k resistor below the transformer will need to be bypassed, otherwise it will raise the CF effective output impedance which is not what you want when driving an A2 stage.
My gut feeling is that you may be trying to run before you have learnt to walk?
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