Hi guys, is it possible to get 60W of power output from a pair of 6C33C? I see some designs getting 40W out from pushpull Class A. How about Class AB 6C33C with more of power output? Can anyone recommend bias point?
I'm also looking at EL509 triode mode which has Rp of 200 ohm. It may be a good alternative to 6C33C class AB because of its high peak current?
Thanks in advance for your suggestion.
I'm also looking at EL509 triode mode which has Rp of 200 ohm. It may be a good alternative to 6C33C class AB because of its high peak current?
Thanks in advance for your suggestion.
I 6 planning to post a thread for 6c33c PP on how to maximize the power it can give and here you are starting this. Thanks..
For JazBo...thanks for the link....on those people here who have tested 6CC33C PP....can this tube really make more than 60w and how about using 400ohm OPT which I have..can we got more wattage or just more distortion?
For JazBo...thanks for the link....on those people here who have tested 6CC33C PP....can this tube really make more than 60w and how about using 400ohm OPT which I have..can we got more wattage or just more distortion?
400 is tougher, does it have multiple output taps, if so, you can try putting 8R on the 4R tap for example to get the primary up to 800.
It's closer to class B operation to get the high power output, if you want more linearity, you can increase the bias a bit and use a higher Ra load (e.g., 1.2k~1.6k).250V 110mA bias point for 6C33 doesn't look very linear to me I may need to add some NFB to lower distortion. Overall, I now have idea where to start.
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Looking at simulations, 250V +B, Idle at 200mA, 1000 ohms p-p, driving the grids from a low impedance source positive by about 26V will yield 71W RMS with about 4% 3H at full power in the o/p stage. For the first 15 Watts or so, it will remain in class A mode.
pk cathode-current is around 750mA, so thats not a huge issue for these valves, they'll do OTL at 2.5A on pk....
Input drive voltage needs to be around the 117V pk and I recommend MOSFET followers direct to grids.
--These big ugly Russians can start to sink grid-current while still a little negative so needs a low drive impedance....
Simulating the quoted design, you're looking at 5 -6% H3, and only 52W RMS. but this doesn't include the distortion/non-linearity you'll get as the grids near 0v and start to draw currents, and blocking-distortion as the coupling-caps charge...
Also, you'll only be in Class-A territory for 4.5W of output.
Whatever you do, make sure you burn the 6C33C's in for a few Days First--Minimum 6 hours burn in! They'll just Love to arc over if you don't, and once thats happened, the valve is stuffed--even though it may still work--it WILL arc again, and cause who-knows what damage.
pk cathode-current is around 750mA, so thats not a huge issue for these valves, they'll do OTL at 2.5A on pk....
Input drive voltage needs to be around the 117V pk and I recommend MOSFET followers direct to grids.
--These big ugly Russians can start to sink grid-current while still a little negative so needs a low drive impedance....
Simulating the quoted design, you're looking at 5 -6% H3, and only 52W RMS. but this doesn't include the distortion/non-linearity you'll get as the grids near 0v and start to draw currents, and blocking-distortion as the coupling-caps charge...
Also, you'll only be in Class-A territory for 4.5W of output.
Whatever you do, make sure you burn the 6C33C's in for a few Days First--Minimum 6 hours burn in! They'll just Love to arc over if you don't, and once thats happened, the valve is stuffed--even though it may still work--it WILL arc again, and cause who-knows what damage.
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Isn't it too hot?
Pda idle for the above condition is 250 x 0.2 = 50W, isn't it above the 30W Pdiss limit per the datasheet (at least the one I have)? Also for class AB2 operation, shouldn't the "70% rule" be applied? i.e., Pda < 21W.
An externally hosted image should be here but it was not working when we last tested it.
Its possibly a little high--But reducing the current and therefore the dissipation, and the H3 rises....
--If possible, its best to keep this low before any FB is applied.....
6C33 is tough as old boots--it'll take it--IF You can stand the heat! Main issues can be the tube Sockets--not the tube.....
Need to use Very heavy copper multi-strand, pref silicone covered, and well soldered to socket--to act as heatsinks!
--During its military service it was found (allegedly) that the 6C33 didnt usually ever give trouble--The Sockets on the other hand.......
--If possible, its best to keep this low before any FB is applied.....
6C33 is tough as old boots--it'll take it--IF You can stand the heat! Main issues can be the tube Sockets--not the tube.....
Need to use Very heavy copper multi-strand, pref silicone covered, and well soldered to socket--to act as heatsinks!
--During its military service it was found (allegedly) that the 6C33 didnt usually ever give trouble--The Sockets on the other hand.......
Quite literally the tube was made for a socket design that simply does not support the filament current. As a result in the original Russian spec sheets it was recommended that the socket be replaced with the tube- every 750 hours
Of course the military could afford that. In the old days (we were the first to use the tube in the US) the socket was supplied with the tube. To get the best life:
1) make sure that the hole in the chassis is larger than the base of the tube to allow air flow
2) install Teflon washers between the chassis and the socket (assuming the socket is placed below the sheet metal) to allow air flow. Teflon will allow you to tighten the retaining nuts without fracturing the ceramic as easily. Use self-locking nuts but not NyLocs!
3) surround the socket location with holes in the sheet metal (or slots), also the bottom cover should have similar perforations.
4)Use silver solder (800 F) for the filament connections. Its a good idea to install Teflon tubing over the filament wiring to prevent it melting and shorting (Silicon insulation as Alastair pointed out is a good idea)
5) if you can fabricate a tin-plated heatsink for each filament pin on the socket they will last longer.
6) a fan is not a bad idea...
Of course the military could afford that. In the old days (we were the first to use the tube in the US) the socket was supplied with the tube. To get the best life:
1) make sure that the hole in the chassis is larger than the base of the tube to allow air flow
2) install Teflon washers between the chassis and the socket (assuming the socket is placed below the sheet metal) to allow air flow. Teflon will allow you to tighten the retaining nuts without fracturing the ceramic as easily. Use self-locking nuts but not NyLocs!
3) surround the socket location with holes in the sheet metal (or slots), also the bottom cover should have similar perforations.
4)Use silver solder (800 F) for the filament connections. Its a good idea to install Teflon tubing over the filament wiring to prevent it melting and shorting (Silicon insulation as Alastair pointed out is a good idea)
5) if you can fabricate a tin-plated heatsink for each filament pin on the socket they will last longer.
6) a fan is not a bad idea...
When you buy 6c33c socket esp larger qty, you should ask or buy a sample to check. The vital component matters is the clamping U spring for tube receptor. Make sure they are genuine steel or better (very strong and tight). Run a 24V DC fan with 8V or so is very quiet and effective, must have ventilation gap or holes on top surround the tubes.
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Sockets
I still have some sockets for sell:
http://www.diyaudio.com/forums/swap-meet/264820-tube-socket-6c33c-plk7-collect-eu-locate-new.html
I still have some sockets for sell:
http://www.diyaudio.com/forums/swap-meet/264820-tube-socket-6c33c-plk7-collect-eu-locate-new.html
