So this is just musing, questioning and would like to hear your guy's take on an idea that I had.
SETs are still very popular and most builders still seem to use the usual DHTs. However, the 6C33C seems like it has some things going for it that are a bit unusual together with a reputation for not being the most linear tube.
In its favor are 1) potential for higher power, 2) low B+ requirement (for that higher power), 3) low Rp (better dampening factor?). Cons are 1) not super linear, 2) high heater current (hot!), 3) some care needed to make sure they last like a burn in period.
It seems like this tube could be a very good project for a relative newbie looking to build their next amp (likely not first) that could be used with more speakers than a 1 watt flea amp.
So why not drive it with a pentode and use plate to grid feedback on the 6C33 to linearize it. The tradeoff is higher gain needed by the driver, but there are some good pentodes with reasonably high gm that seem like they could fit the bill. 6E5P maybe? D3A, etc?
Thoughts? I was wondering how much the Schade style feedback would make up for the downsides of this tube and let you realize the benefits.
SETs are still very popular and most builders still seem to use the usual DHTs. However, the 6C33C seems like it has some things going for it that are a bit unusual together with a reputation for not being the most linear tube.
In its favor are 1) potential for higher power, 2) low B+ requirement (for that higher power), 3) low Rp (better dampening factor?). Cons are 1) not super linear, 2) high heater current (hot!), 3) some care needed to make sure they last like a burn in period.
It seems like this tube could be a very good project for a relative newbie looking to build their next amp (likely not first) that could be used with more speakers than a 1 watt flea amp.
So why not drive it with a pentode and use plate to grid feedback on the 6C33 to linearize it. The tradeoff is higher gain needed by the driver, but there are some good pentodes with reasonably high gm that seem like they could fit the bill. 6E5P maybe? D3A, etc?
Thoughts? I was wondering how much the Schade style feedback would make up for the downsides of this tube and let you realize the benefits.
I see no reason not to try it, and if it doesn't work well a triode connected D3A driver stage is a few hours of work away. Nothing to loose. 😀
The D3A is a great choice, consider also the 7788 (E810F IIRC) as a driver.
The D3A is a great choice, consider also the 7788 (E810F IIRC) as a driver.
Kevin Carter had put up a schematic for using 6C33 in SE form.
http://www.kandkaudio.com/images/Monoblock SE 6C33CB Amplifier.pdf
We are discussing the same elements. I am just wondering if it would not be better to forgo the interstage or CCS, regulate the screen on the D3A and use P2G FB around the 6C33. I am wondering what would work better.
I don't plan to build this anytime soon, I am using this as an example to try to understand how well does the Schade help.
http://www.kandkaudio.com/images/Monoblock SE 6C33CB Amplifier.pdf
We are discussing the same elements. I am just wondering if it would not be better to forgo the interstage or CCS, regulate the screen on the D3A and use P2G FB around the 6C33. I am wondering what would work better.
I don't plan to build this anytime soon, I am using this as an example to try to understand how well does the Schade help.
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JoshK,
Can you please check the link in the post above - might be my machine but it doesn't seem to work for me.
Thanks,
Ian
Can you please check the link in the post above - might be my machine but it doesn't seem to work for me.
Thanks,
Ian
I guess I need to set up my lab, breadboard it and test it myself. That requires me getting up the learning curve on some of my equipment. (I have no training in electronics, only self-taught on forums and books)
Link now works for me.
Build it as per Kevin's schematic first - once it is going then if unhappy look at doing a Schade mod.
The Schade feedback will impose extra demands on the front end / driver stage.
Look up "Partial Feedback" (same thing) in the John Broskie blogs for a description of how it works if you want more info.
Cheers,
Ian
Build it as per Kevin's schematic first - once it is going then if unhappy look at doing a Schade mod.
The Schade feedback will impose extra demands on the front end / driver stage.
Look up "Partial Feedback" (same thing) in the John Broskie blogs for a description of how it works if you want more info.
Cheers,
Ian
I guess my question was not "what is better" but a thought experiment on what is a better approach, and maybe how would the "not so linear" regulator type tubes compare to other popular SET designs if it used a bit of ingenuity.
My two cents are:
Its know that the best sound to frive the 6C33 are the 6SN7 or 6SL7.
Why reinvent the wheel.
Because I don't believe that one bit. There is no absolute best, things can always be bettered and I am an inquisitive person who wishes to learn rather than accept some dogmatic blessing that x & y are the best.
The D3A is quite linear and in some applications will allow a single stage when the 6SN7 requires two, which IMO is always a win. I graduated from the 6SN7 to the D3A (there are other choices) some years ago, but like both. I also like a lot of other types. No question the 6SN7 is a great tube, but there are plenty of others properly employed that will give it a good run for the money.
I'm also a fan of IT or choke coupling in applications where large voltage swings are required on reasonable supply voltages.
I'm also a fan of IT or choke coupling in applications where large voltage swings are required on reasonable supply voltages.
I think there are many interesting possibilities with the D3A > 6C33, two shown in K&K's schematics. There is also direct coupling. I am trying to grasp the comparison with Schade. Guess I am going to have to breadboard and see.
I think the Schade connection would be quite effective at reducing distortion and a significant amount of feedback is possible in pentode mode..
The D3A is also very linear in triode connection and has a fairly low rp (<2K) particularly considering a mu of 77+.
The D3A is also very linear in triode connection and has a fairly low rp (<2K) particularly considering a mu of 77+.
i built an all Russian set using the 6P15p pentode driving the 6C33 here...http://www.diyaudio.com/forums/tubes-valves/216206-my-russian-set.html
Direct coupled Schades is quite demanding and makes the final result either very inefficient and/or places huge demands on the driver and its load resistor. I have built a few in my time and they all needed -B supplies and they all have very low overall gain - which for most people means adding another gain stage which in turn adds further complexity.
Best avoided is my advice.
Shoog
stupid question, the 6C33 with its low plate resistance, how can Schade help...?
and being a triode, isn't it that negative feedback is already built in?
and being a triode, isn't it that negative feedback is already built in?
Schade converts mu to gm and so can be applied to triodes with the effect of lowering rp. However with these low mu finals the benefits are fairly marginal.
Shoog
Shoog
I think that is part of the answer I was looking for. I guess it would make more sense with a 10Y.
Kevin's circuit is said to sound really good as it is, as are a number of other amps using the 6C33C, and the 10Y is also a tube known for it's use in good sounding amps.
If your interest is in exploring the audible usefulness of Schading per se, it would make more sense to tack together a circuit with a tube farther away from sonic perfection without the feedback, listen to it, then add the schade.
Listening to gross examples first and refining as you go gives a much better picture.You don't even need two channels. No more than parts, clip leads and a piece of plywood to lay them out on is needed.
You can never have too many clip leads! 8^)
If your interest is in exploring the audible usefulness of Schading per se, it would make more sense to tack together a circuit with a tube farther away from sonic perfection without the feedback, listen to it, then add the schade.
Listening to gross examples first and refining as you go gives a much better picture.You don't even need two channels. No more than parts, clip leads and a piece of plywood to lay them out on is needed.
You can never have too many clip leads! 8^)
yes, and in the case of the 6C33 gm is already very high at about 39mA/V, rp is like 120 ohms...http://www.radiovilag.hu/images/6C33C.pdf
http://www.jogis-roehrenbude.de/Russian/6C33C/6C33C-B-6S33S-VExtendedDatasheetMB.pdf
compared to the 6L6GC, http://frank.pocnet.net/sheets/164/6/6L6GC.pdf
pentode rp is like 33k, gm is 5.2mA/v, trioded, rp is still much higher at 1700 ohms and gm at 4.7mA/V.....
further reading...http://altor1.narod.ru/DIY_Hobby/Friend_s_Projects/va022002simplexredux.pdf
http://www.polisois-audio.com/documenti/Simplex and Simplex Redux .pdf
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