First of all HI to everybody in the forum. Some background first. I have a degree as industrial designer and made some undergraduate studies in electronics engineering (never graduated), so I can do some math and can tell the difference between a resistor and a capacitor. I love tubes, I have a Cayin A-50T with EL-34 tubes and some other tube stuff. As everybody else here I want to start building some tube gear, so I can learn really how this stuff works.
I have decided I want to build a 6C33C SET amp. that can deliver around 12 watts, that way I can use the amp with 90dB sensitivity speakers. I want it to have a bandwidth of at least 20hz - 28khz. I hate hum, so it must be canceled in some way. Distortion must be below below 2% at normal power. I am not a purist so I think I will use a solid state power source, and I have no problem in using transistors of MOSFETs to regulate currents in the circuit. I don't want solid state components in the sound path.
Julian
I have decided I want to build a 6C33C SET amp. that can deliver around 12 watts, that way I can use the amp with 90dB sensitivity speakers. I want it to have a bandwidth of at least 20hz - 28khz. I hate hum, so it must be canceled in some way. Distortion must be below below 2% at normal power. I am not a purist so I think I will use a solid state power source, and I have no problem in using transistors of MOSFETs to regulate currents in the circuit. I don't want solid state components in the sound path.
- I would like to know if this requirements can be met? or am I kidding myself?
- Can someone in the forum send me drawings of 6C33C SET amps already built, so I can take a look at the designs.
- What driver tubes are recommended to be used with the 6C33C?
- I can't build the transformers. Are there any commercially available transformers I can use for this project?
Julian
Hi Julian,
I don't see any problems with your plans, I already read about getting 18W out of a single 6C33C, so 12W sounds reasonable. A lot of people asked questions about this tube here at the forum: if you search you will find a lot of information and schematics regarding this tube. If you find something with google you can always place a link here so we can comment. 'Romy the cat' (you heard about him?) uses a 6E5P triode wired to drive the 6C33C, but there should be plenty alternatives (maybe use a bifilar Hammond IT, model 126B or 126C depending on driver tube?). For an OPT you may search for INDEL on google, they have a 1k3:8R OPT that would work, and it doesn't cost a lot (even though shipping to Colombia will be expensive, but my experience - at least in BR - is that you can't get OPTs locally , so you will have to import anyway). Or maybe Edcor, in the USA is cheaper on shipment? These are budget suggestions, if money is no problem there is myriad of possible transformer out there!
Good luck, saludos!
I don't see any problems with your plans, I already read about getting 18W out of a single 6C33C, so 12W sounds reasonable. A lot of people asked questions about this tube here at the forum: if you search you will find a lot of information and schematics regarding this tube. If you find something with google you can always place a link here so we can comment. 'Romy the cat' (you heard about him?) uses a 6E5P triode wired to drive the 6C33C, but there should be plenty alternatives (maybe use a bifilar Hammond IT, model 126B or 126C depending on driver tube?). For an OPT you may search for INDEL on google, they have a 1k3:8R OPT that would work, and it doesn't cost a lot (even though shipping to Colombia will be expensive, but my experience - at least in BR - is that you can't get OPTs locally , so you will have to import anyway). Or maybe Edcor, in the USA is cheaper on shipment? These are budget suggestions, if money is no problem there is myriad of possible transformer out there!
Good luck, saludos!
HI,
Dont use PCBs, add long time reliability to your project and use hard wiring hand soldered.
Make a favor to yourself and DONT use cheap sockets like this crap:
Instead use this one(the better option for this tube):
Or at least this, that use a kind or Russian baquelite and has the pins semi-loose for not stressing the 6C33 pins/glass seals and is low priced:
Please Note the anode pin in this image above, intend that the anode output must be a very thick wire to stand the heat dissipation;
Tube rectification will offer a old fashioned sound, SS rectification will do a modern sound.
To the usual musical, warm tube sound use Input=6SL7 Drive=6SN7
Or If you want low priced Russian Triodes use Input= 6N1P or 6N2P, Drive= 6N6P
An Example: Amps
Some Tubes: ''GSTube.com''. Tubes, sockets etc. Search result for <u>6n1p</u>
IF possible use 5mm aluminium table for heat dissipation and wood sides, avoid steel chassis/table, it is magnetic and low heat dissipation.
¡Buena Suerte!
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Socket:
http://www.diyaudio.com/forums/swap-meet/228266-tube-socket-6c33c-plk7-collect-eu-locate-new.html
I still have them
http://www.diyaudio.com/forums/swap-meet/228266-tube-socket-6c33c-plk7-collect-eu-locate-new.html
I still have them
6S33S is quite a beast for a first project. Heaters require lots of current with the risk of getting hum due to a non-perfect heater wiring...
With a properly planned power supply, it shouldn't be possible to tell from the sound if its tube or solid state rectification. If you hear a difference, the power supply is poorly planned. Rectification is a part of the power supply. It provides a DC rail with the properties needed by the amplifier, it does *not* do any sound. If it adds anything to the 'sound', build a better power supply.
Rundmaus
With a properly planned power supply, it shouldn't be possible to tell from the sound if its tube or solid state rectification. If you hear a difference, the power supply is poorly planned. Rectification is a part of the power supply. It provides a DC rail with the properties needed by the amplifier, it does *not* do any sound. If it adds anything to the 'sound', build a better power supply.
Rundmaus
i use 12volt heater arrangement, filaments are ac, yet amp is quiet, no hum....http://www.diyaudio.com/forums/tubes-valves/216206-my-russian-set.html
Thanks for your input. I mention it why it was stated by this builder:
Tube or Solid State Rectification?
Tube vs. SS in amplifiers: Tube rectifiers can be thought of as cushions while SS diodes can be thought of as a concrete pad. The cushioning effect has the ability to make an amp sound more organic and smooth. Sometimes this is desirable.
I would prefer SS rectification for one less valve to retube.
Thanks for all the enthusiast answers. Here in Colombia is easy and relatively cheap to import things for USA or CANADA. So buying the power and output transformers in the US is my best option, but if there are better transformers available in Europe (lets say something like Lundhal) I would give it a try. I want to use the best components I can afford, ceramic sockets are on the list. I would like to use tubes that are still in production no rare exotic stuff for this project.
I have in stock 6N1P and NOS 6DJ8 tubes, I like the 6N1P because it's low noise.
What about the 6C45PI as drivers, it would be great to use just to tubes per channel to keep the things simple as Dmitry Nizhegorodov's design.
I know this is a dangerous task for a newbie, but I have the expert help of an engineer with lots of experience. What fun do we have if we don't take risks?
I have been looking at all the designs you've post, and all of them seem amazing.
Please, need more advice on transformer selection. I have looked at EDCOR in USA but don't really know what to look for, I send them a message. But it would be great if some one can point me to the right OPT and PT.
I would like to include the option to use zero feedback or some feedback (-3dB, -6dB) with a toggle switch.
I have in stock 6N1P and NOS 6DJ8 tubes, I like the 6N1P because it's low noise.
What about the 6C45PI as drivers, it would be great to use just to tubes per channel to keep the things simple as Dmitry Nizhegorodov's design.
I know this is a dangerous task for a newbie, but I have the expert help of an engineer with lots of experience. What fun do we have if we don't take risks?
I have been looking at all the designs you've post, and all of them seem amazing.
Please, need more advice on transformer selection. I have looked at EDCOR in USA but don't really know what to look for, I send them a message. But it would be great if some one can point me to the right OPT and PT.
I would like to include the option to use zero feedback or some feedback (-3dB, -6dB) with a toggle switch.
Sowter can made a great sound OPT for 600 or 1K Ohms primary, but it is more expensive than EDCOR.
Brian Sowter is very friendly on custom orders.
SOWTER AUDIO TRANSFORMERS
EDCOR is inexpensive, but not C core, seems E I laminated, 25W only, Primary are 300, 600 ohms or more:
EDCOR - CXSE25-8-600
Also there is Ogonovski, price is good, 600 ohms, 50W, C core:
Ogonowski.eu - profesjonalne transformatry do wzmacniaczy lampowych
Brian Sowter is very friendly on custom orders.
SOWTER AUDIO TRANSFORMERS
EDCOR is inexpensive, but not C core, seems E I laminated, 25W only, Primary are 300, 600 ohms or more:
EDCOR - CXSE25-8-600
Also there is Ogonovski, price is good, 600 ohms, 50W, C core:
Ogonowski.eu - profesjonalne transformatry do wzmacniaczy lampowych
Hi Fullrangeman, I looked at the specs of SOWTER, EDCOR and OGONOWSKI OPTs, I want an extended bandwidth ( 20hz to 28khz +-1 dB), SOWTER SE5 seems OK. If I have plans for a 12 watt amp how much safety margin should I have? should I buy a 20 watt OPT? or look the closest thing to my spec? I am also looking at Hammond, INDEL as Erik suggested. I found a design that uses LUNDHAL (AudioMirror-6C33). What about toroidal transformers like PLINTRON?
IMO: Security margin for a OPT is at least 100%(or 25W in your case) if you want run the amp 5 hours, but as your country is a hot area you must use OPTs with 40 or 50W.
You will need this extra power capacity to run the amp 8 or more hours continuously with no over heat.
Of course the PS must be according this task too.
Please Note: the 6C33 run well over 200ºC when in use:
Thermografie / Thermography Heat Russian Tube Röhre 6C18C 6S18S 6C33C 6S33C - YouTube
This amp use Toroidal home made, and the sound was reported as great for a local magazine, if it worth anything:
HOME Schmaedecke
I read about laminated OPTs works as natural filters due the laminations, what dont happen with the Toroidal cores.
Otherwise I unaware what kind of sound Toroidal and 6C33 could offer; but I also could prefer a big Toroidal core.
Seems to me the Toroidal and Laminated cores has different sounds, it would be nice to discover it in detail.
I would rate Lundahl, Sowter, ElectraPrint and Tribute as first rate quality but pricey.
And EDCOR as a simple and affordable option.
The Ogonovski core seems small for 50W on the site photo, but if it is a true 50W core it is my personal choice as 115 dolars are a great price.
I could dismiss Hammond as it is suited to guitars only, same for chinese brands.
Others brands mentioned I unknow.
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Just to add an observation about toroidals (PP only) and their sound. Depending on the make they can easily achieve bandwidths out to 50khz before serious tail off. They do not tolerate DC which imposes design constraints, but the upside is that they do not exhibit substantial hysterics which equates to a lack of the micro detail smudging reported for many EI PP transformers. Their inductance tends to be substantially better than most EI's which gives them the capability of producing very deep powerful bass response.
Because the output impedance of a 6c33 is so low a toroidal power transformer can exhibit all of these desirable properties at minimal cost.
Unfortunately SET toroidals are a highly specialized beast of which there is only one manufacturer (Piltron) and they are EXTREMELY expensive.
Shoog
Because the output impedance of a 6c33 is so low a toroidal power transformer can exhibit all of these desirable properties at minimal cost.
Unfortunately SET toroidals are a highly specialized beast of which there is only one manufacturer (Piltron) and they are EXTREMELY expensive.
Shoog
I found that SAC form Thailand has several OPTs for the SET 6C33C ( SACThailand ). Models: S-1000A 40 watts, S-6-6C33F and S-1-6C33F 20 watts, bandwidth is excellent. Price is OK (not cheap at all), have to see if shipping from Thailand is not ultra expensive. PLINTRON has nice OPTs toroidals ( Tube Output - Single Ended )for the 300B, I suppose there is no problem using them with the 6C33C, but they are very expensive, 492 USD each.
I live in Bogota, temperature is not really high, average 16 - 20 Celsius, nights can be freezing, usually around 10 Celsius can drop to 0. Colombia is in the tropics, but Bogotá is at 2600 meters above sea level.
I live in Bogota, temperature is not really high, average 16 - 20 Celsius, nights can be freezing, usually around 10 Celsius can drop to 0. Colombia is in the tropics, but Bogotá is at 2600 meters above sea level.
Some years ago I quoted a GM70 OPT from SAC and the price was around us$450 each, but the Fedex ship was us$600 for the pair.
But the sound quality is the finest avaliable.
These Plitron OPTs are intended to run 300B tubes/max 7w at 2.5K, 3K and 5K ohms primary,
For 6C33 you will need 600 or 1K primary.
On Plitron you would use one of these specialist range models, if they accept a 600 ohms custom order for you:
Tube Output - Specialist Range
Price are expensive but not too much.
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Hi FullRangeMan, thanks for all the information. I will wait for the SAC quotation.
I now have some questions about the driver tubes. I was reading in Morgan Jones excellent "Valve Amplifiers" book that the signal swing must for any class A is "always twice the grid to cathode bias". I have the 6C33C datasheet, but I didn't find this information (or I couldn't figure out). I want to keep the circuit simple and use just one driver tube, I've read elsewhere that the very common 6SN7 is not really the ideal tube to drive the 6C33C. I would like to know what tubes are ideal for this quest and in what configuration, common cathode, mu-follower, SRPP? I have 61NP and 6DJ8 tubes in stock, but I have also read rave information about the 6C45PI, what would you suggest? Anyone in the forum has ideas to share about the ideal driver for the 6C33C?
Should I use a coupling transformer between the driver stage and the power stage?
I now have some questions about the driver tubes. I was reading in Morgan Jones excellent "Valve Amplifiers" book that the signal swing must for any class A is "always twice the grid to cathode bias". I have the 6C33C datasheet, but I didn't find this information (or I couldn't figure out). I want to keep the circuit simple and use just one driver tube, I've read elsewhere that the very common 6SN7 is not really the ideal tube to drive the 6C33C. I would like to know what tubes are ideal for this quest and in what configuration, common cathode, mu-follower, SRPP? I have 61NP and 6DJ8 tubes in stock, but I have also read rave information about the 6C45PI, what would you suggest? Anyone in the forum has ideas to share about the ideal driver for the 6C33C?
Should I use a coupling transformer between the driver stage and the power stage?
Hi,
the signal swing must for any class A is "always twice the grid to cathode bias".
Iam not a tech like you so I can not help in this issue.
the very common 6SN7 is not really the ideal tube to drive the 6C33C.
I feel 6SN7 is a great drive tube for the 6C33 if you want a musical and warm sound.
I would like to know what tubes are ideal for this quest and in what configuration, common cathode, mu-follower, SRPP?
I prefer SRPP and Mu-Follower for low DHT.
I have 61NP and 6DJ8 tubes in stock, but I have also read rave information about the 6C45PI, what would you suggest?
Lampizator site rave about the 6N1p and 6N6P, this both inexpensive tubes are used in Russia to drive 6C33 with good sound. I suggest you read the ARG amps section of Lampizator site.
In a brief seach I could not find reports of a 6C45 driving a 6C33, but AR now is using 6N1P in its equips, which is a good sing.
Anyone in the forum has ideas to share about the ideal driver for the 6C33C?
The subject of ideal driver for the 6C33 would spend a entire book with no certain result as it is a personal taste, like music.
Should I use a coupling transformer between the driver stage and the power stage?
Not necessary, 12W is a easy task for two tubes. If you will use no preamp(CD player direct) maybe need a hi gain input tube as 12AX7 or 6N2P.
In the past De Haviland used a 12SN7 to drive a big GM70, so a 6SN7 or 6N6P must do the job for a 6C33.
As you mention dont want any hum noise, you may want read this revelatory article from Electraprint:
Electra-Print.com Tech Blog
the signal swing must for any class A is "always twice the grid to cathode bias".
Iam not a tech like you so I can not help in this issue.
the very common 6SN7 is not really the ideal tube to drive the 6C33C.
I feel 6SN7 is a great drive tube for the 6C33 if you want a musical and warm sound.
I would like to know what tubes are ideal for this quest and in what configuration, common cathode, mu-follower, SRPP?
I prefer SRPP and Mu-Follower for low DHT.
I have 61NP and 6DJ8 tubes in stock, but I have also read rave information about the 6C45PI, what would you suggest?
Lampizator site rave about the 6N1p and 6N6P, this both inexpensive tubes are used in Russia to drive 6C33 with good sound. I suggest you read the ARG amps section of Lampizator site.
In a brief seach I could not find reports of a 6C45 driving a 6C33, but AR now is using 6N1P in its equips, which is a good sing.
Anyone in the forum has ideas to share about the ideal driver for the 6C33C?
The subject of ideal driver for the 6C33 would spend a entire book with no certain result as it is a personal taste, like music.
Should I use a coupling transformer between the driver stage and the power stage?
Not necessary, 12W is a easy task for two tubes. If you will use no preamp(CD player direct) maybe need a hi gain input tube as 12AX7 or 6N2P.
In the past De Haviland used a 12SN7 to drive a big GM70, so a 6SN7 or 6N6P must do the job for a 6C33.
As you mention dont want any hum noise, you may want read this revelatory article from Electraprint:
Electra-Print.com Tech Blog
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Hi Julian,
In class 1 signal swing must indeed be twice the grid cathode bias. If you have more swing then you will drive the grid positive in relation to cathode, and the grid will start pulling current (this is class 2). Power will be higher, but driver circuit to maintain low distortion will be more complex. I don't think there is a 'better' here.
First thing to determine is how you will 'bias' the 6C33C. Will you use auto bias, with a big resistor in the cathode, or fixed bias: ground the cathode and bias the grid from a negative source. Note that generally these high gm tubes are auto biased, but there are people who do fixed bias, but limit the plate dissipation to about 40W (of the 60W max). With fixed bias you have a higher risk of thermal runaway: the tube consumes more and more current and auto destroys itself, possibly taking the OPT with it. For a first time project I would therefore recommend to use auto-bias. A nice operating point could be at 160V plate cathode, 250mA, which requires 50V bias. Total B+ is therefore 210V, cathode resistor 200R dissipating 12,5W!! Required swing is 100V peak to peak.
And indeed, as fullrangeman said, to drive this is a very personal taste. Not that the 6SN7 is not up to it, but gain of this tube is relatively low and you would probably need to cascade two stages, while nowadays it is more common to see the use of high transconductance, high gain tubes (like the 6C45PI, or triode wired pentodes as D3a, 6J9P, E280F, etc etc). Still, these tubes require good care to avoid oscillation, so maybe a 6SN7 into triode wired 6W6 into 6C33C... As said, enough possibilities.
In my first post I wrote you could possibly use the Hammond Interstages. There is no real need for them here, I agree with fullrangeman, but they do allow some nice things. First: low mu tubes as the 6C33C generally require low B+. I showed an example where you will need 210V B+ for the output stage and at least 100VPP to drive it. You may end up with other operating point, but you will see that you will always need big swing and have little B+ for it. An option is to use a separate B+ of maybe 300V or more for the driver stage, which has it own merits but adds complexity. Or use an interstage fed from the same B+ of the output stage (with proper decoupling between stages) as the interstage (just as an OPT) allows the output to swing above B+. Second: interstage driven from a powerfull tube allows to drive the output stage into class 2. You may not need it on a continuous base, but it gives a nice headroom. You could use a tube as the D3a with these interstages as the driver, or maybe a 6N6P (resistor loaded) into a 6W6 loaded with interstage.
You mentioned you have MJ's valve amplifiers. Have a look at the chapter for the 'scrapbox challenge', as it is an excellent walkthrough into designing a SE amplifier. It uses a power tube which shares lots of characteristics with the 6C33C, as both were designed for series regulation services.
good luck with the project! Erik
In class 1 signal swing must indeed be twice the grid cathode bias. If you have more swing then you will drive the grid positive in relation to cathode, and the grid will start pulling current (this is class 2). Power will be higher, but driver circuit to maintain low distortion will be more complex. I don't think there is a 'better' here.
First thing to determine is how you will 'bias' the 6C33C. Will you use auto bias, with a big resistor in the cathode, or fixed bias: ground the cathode and bias the grid from a negative source. Note that generally these high gm tubes are auto biased, but there are people who do fixed bias, but limit the plate dissipation to about 40W (of the 60W max). With fixed bias you have a higher risk of thermal runaway: the tube consumes more and more current and auto destroys itself, possibly taking the OPT with it. For a first time project I would therefore recommend to use auto-bias. A nice operating point could be at 160V plate cathode, 250mA, which requires 50V bias. Total B+ is therefore 210V, cathode resistor 200R dissipating 12,5W!! Required swing is 100V peak to peak.
And indeed, as fullrangeman said, to drive this is a very personal taste. Not that the 6SN7 is not up to it, but gain of this tube is relatively low and you would probably need to cascade two stages, while nowadays it is more common to see the use of high transconductance, high gain tubes (like the 6C45PI, or triode wired pentodes as D3a, 6J9P, E280F, etc etc). Still, these tubes require good care to avoid oscillation, so maybe a 6SN7 into triode wired 6W6 into 6C33C... As said, enough possibilities.
In my first post I wrote you could possibly use the Hammond Interstages. There is no real need for them here, I agree with fullrangeman, but they do allow some nice things. First: low mu tubes as the 6C33C generally require low B+. I showed an example where you will need 210V B+ for the output stage and at least 100VPP to drive it. You may end up with other operating point, but you will see that you will always need big swing and have little B+ for it. An option is to use a separate B+ of maybe 300V or more for the driver stage, which has it own merits but adds complexity. Or use an interstage fed from the same B+ of the output stage (with proper decoupling between stages) as the interstage (just as an OPT) allows the output to swing above B+. Second: interstage driven from a powerfull tube allows to drive the output stage into class 2. You may not need it on a continuous base, but it gives a nice headroom. You could use a tube as the D3a with these interstages as the driver, or maybe a 6N6P (resistor loaded) into a 6W6 loaded with interstage.
You mentioned you have MJ's valve amplifiers. Have a look at the chapter for the 'scrapbox challenge', as it is an excellent walkthrough into designing a SE amplifier. It uses a power tube which shares lots of characteristics with the 6C33C, as both were designed for series regulation services.
good luck with the project! Erik
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