Hi,
I did plenty of searching prior to posting. Has anyone combined the 6H30 cascode front end driving an interstage transformer like the Amity/Karna?
1:1+1 - 6H30 Cascode - 1+1:1+1 - 300b PP - OPT
I'm not sure what the implications are with driving an IT with a high gain cascode.
Thank you very much! I really appreciate it.
I did plenty of searching prior to posting. Has anyone combined the 6H30 cascode front end driving an interstage transformer like the Amity/Karna?
1:1+1 - 6H30 Cascode - 1+1:1+1 - 300b PP - OPT
I'm not sure what the implications are with driving an IT with a high gain cascode.
Thank you very much! I really appreciate it.
it ia doable, that is what the DPA-300B is (with additional CSS loaded 300B tails). My partenr heard the 1st ever and said it was one of the best amps he had ever heard.
dave
Right! I've been looking at Gary Pimm schematics of CCS cathode loaded finals to try to wrap by head around it.
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Just put a cathode follower (DC coupled to the 300B) between the 0.47 uF capacitor and the 300B grid and you will be almost free to optimize the cascode as you want. With a dual supply for the cathode follower you can retain fixed bias for the 300B. Have a look at Audio Note older amplifiers.
IMHO, RC coupling to the 300B is simply a waste of money and resources. Never able to get the best out of it.
CCS in power stage is another waste. CCS's everywhere too bad......it can work fine ONLY if it will work in pure class A in any condition which is not the case of the PP ouput stage in general. It will depend very much on the actual real load. 😀
IMHO, RC coupling to the 300B is simply a waste of money and resources. Never able to get the best out of it.
CCS in power stage is another waste. CCS's everywhere too bad......it can work fine ONLY if it will work in pure class A in any condition which is not the case of the PP ouput stage in general. It will depend very much on the actual real load. 😀
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I'm pretty sure the intention of CCS on the Cathode in Allen's DPA-300b was to force class A operation as well as force symmetry under load. I'm not an EE but here's a quote: (VSAC 2003)
"Allen has now applied the same principles to a power amplifier; this picture shows the first disclosure of Allen's circuit. The addition of a current source to the power tube's cathode converts a conventional PP amplifier to an all-differential, all-Class A amplifier. In fact, the current source actually prevents the circuit from entering into Class AB. If excessive current is demanded, the amp clips, just like a SE amplifier. As a result, the current drawn from the power supply is almost constant, and the high degree of balance rejects nearly all power-supply noise.
In addition, just as in a low-level circuit, the current source compensates for variations in gain-matching between the pair of tubes, so the overall circuit gain is always precisely the gain of A+B/2. Although the current source looks like a minor addition, it actually converts a parallel amplifier (conventional PP) into a series amplifier - the output tubes are effectively connected in series with each other, like a string of Christmas-tree lights."
I've been using a differential output stage for a number of years. It's true that it limits the power to class A but I really like the way it sounds within its range. OTOH, I also have a more traditional PP 6B4G class A amp output stage driven by IT's and it sounds glorious.
John
John
Is that the one on the big piece of plywood? It is a lovely amplifier for sure.
dave
You know, I like that style of construction. It's no good for my wife, my 10 year old, her friends, or the cat. But, for the bachelor or man cave it has a lot of appeal.
The all differential amp is a different one. The plywood amp in that picture from a couple years ago is a traditional class A PP output stage with an RC couple LTP. This amp now has interstage transformers and different driver tubes which handle the transformer load better but retains the nice unfinished plywood look. I've been asked to bring it again this year and I'm planning to bring the all differential amp too.
John
Why? A normal (properly deisgned) cathode follower would do just fine.
You can do that of course.
I am no fan. Only go for the best option time by time.
Then first you have to be sure about what it is going drive. Otherwise it might not be as intended.
I don't believe it. I have used cathode followers for years. I cano only think about unproperly designed cathode followers.
In this case it is not even required to go into positive grid that would likely also turn the amp into AB mode....
In this case it is not even required to go into positive grid that would likely also turn the amp into AB mode....
What's the point in discussing cathode followers here...
Allen optimized them his way by applying active loads, calling them Super Linear Cathode Followers.
By now it should be well known how to design them properly, using active loads or not.
The topic here is about cascodes driving an output stage through an interstage transformer.
Not a good idea IMO.
Allen optimized them his way by applying active loads, calling them Super Linear Cathode Followers.
By now it should be well known how to design them properly, using active loads or not.
The topic here is about cascodes driving an output stage through an interstage transformer.
Not a good idea IMO.
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