Hi everyone,
For the last few months I've been looking around for a nice monobloc project to do over the summer holidays. I've had a little experience with valve amps, built and tweeked a KT88 PP integrated and presently building a triode SE headphone amplifier. I'm not quite ready to play around with those rather high voltage transmission tubes (as much as I would like to though) so I’ve started looking for a lower voltage triode project. I originally considered a PP 300b amplifier (my speakers are rather insensitive
) but 4 good quality 300bs would be rather costly, also I wanted to use a less commonly used tube. Then I stumbled across the 6C33C indirectly heated triode. The thing that appealed to me most was the rather low plate voltages just over 200V and also the fact you can use a very low primary resistance on the OPT giving good bandwidth.
At the moment I have 4 well matched 6C33C tubes and a set of good quality teflon sockets.
After searching for a while I found this quite nicely laid out schematic IMO.
http://www.jogis-roehrenbude.de/Leserbriefe/Roessler-6C33C-PP/6C33C_PP_Schematic-1.gif
http://www.jogis-roehrenbude.de/Leserbriefe/Roessler-6C33C-PP/6C33C_PP_Schematic-2.gif
I've emailed the chap that created this circuit to ask for permission to use it but I have had no reply. As it’s from a German web site I think my translated English was clearly rubbish.
Just wondered what you guys thought of it.
Thanks!
Hesky
For the last few months I've been looking around for a nice monobloc project to do over the summer holidays. I've had a little experience with valve amps, built and tweeked a KT88 PP integrated and presently building a triode SE headphone amplifier. I'm not quite ready to play around with those rather high voltage transmission tubes (as much as I would like to though) so I’ve started looking for a lower voltage triode project. I originally considered a PP 300b amplifier (my speakers are rather insensitive
) but 4 good quality 300bs would be rather costly, also I wanted to use a less commonly used tube. Then I stumbled across the 6C33C indirectly heated triode. The thing that appealed to me most was the rather low plate voltages just over 200V and also the fact you can use a very low primary resistance on the OPT giving good bandwidth.At the moment I have 4 well matched 6C33C tubes and a set of good quality teflon sockets.
After searching for a while I found this quite nicely laid out schematic IMO.
http://www.jogis-roehrenbude.de/Leserbriefe/Roessler-6C33C-PP/6C33C_PP_Schematic-1.gif
http://www.jogis-roehrenbude.de/Leserbriefe/Roessler-6C33C-PP/6C33C_PP_Schematic-2.gif
I've emailed the chap that created this circuit to ask for permission to use it but I have had no reply. As it’s from a German web site I think my translated English was clearly rubbish.
Just wondered what you guys thought of it.
Thanks!
Hesky
Hi,
If it were me, I wouldn't worry about that aspect too much.
As long as it's for private use that is.
As for the amp itself, it seems straightforward enough, with a little change you can even drive it from a balanced source and the 6C33-C are great sounding monsters.
Just be aware of the high heater current which tends to carbonize the pins on the sockets. I was advised by (316A I think) to wrap the wire around the pin(s) a few times to increase surface area and provide some cooling surface area.
Cheers,
If it were me, I wouldn't worry about that aspect too much.
As long as it's for private use that is.
As for the amp itself, it seems straightforward enough, with a little change you can even drive it from a balanced source and the 6C33-C are great sounding monsters.
Just be aware of the high heater current which tends to carbonize the pins on the sockets. I was advised by (316A I think) to wrap the wire around the pin(s) a few times to increase surface area and provide some cooling surface area.
Cheers,
Hi Frank, yes this project will just be for my own musical pleasure
This was my thinking also, as there monoblocs a balanced connection would help a lot to reduce the chance of ground loops as I may have to use nasty 1-2m interconnections. Also with the removal of the interstage/phase splitter transformers a little more money can be spent on better decoupling capacitors and good quality resistors.
The transformer attenuator I'm building will have balanced connection which is convenient.
That’s a good tip for increasing the heat transfer on the filament connections, Im also glad this circuit has manual biasing for both output tubes.
Hesky
This was my thinking also, as there monoblocs a balanced connection would help a lot to reduce the chance of ground loops as I may have to use nasty 1-2m interconnections. Also with the removal of the interstage/phase splitter transformers a little more money can be spent on better decoupling capacitors and good quality resistors.
The transformer attenuator I'm building will have balanced connection which is convenient.
That’s a good tip for increasing the heat transfer on the filament connections, Im also glad this circuit has manual biasing for both output tubes.
Hesky
6C33
Hello ,
The Russian military used to replace the sockets more often than the valves from what I have heard ! The wrapping is a good idea if Russian / Chinese ceramic or British teflon B7A sockets are used , just strip away about 40mm of insulation then wrap the wire around the socket pins a few times before soldering , this only needs to be done with the filament pin contacts . I found this out the hard way and ended up with some sockets with crusty , burnt contacts , my fault really for running the 6C33 at 55W . US Johnson sockets are apparently immune to this problem but are rather expensive . Some advice : Running at 55 watts I also had a 6C33 outgas and split on me , quite a spectacular little firework display inside the thing but also a complete P.I.T.A . Run the things at around 40-45 watts and they'll last and last and don't run any hotter than this with fixed bias .
ps Just one last thing : make sure the 6C33 pins are cleaned before usage , Brasso wadding follwed by a rinse with isoprop and cottonbud does the trick
cheers
316a
fdegrove said:I was advised by (316A I think) to wrap the wire around the pin(s) a few times to increase surface area and provide some cooling surface area.
Cheers,
Hello ,
The Russian military used to replace the sockets more often than the valves from what I have heard ! The wrapping is a good idea if Russian / Chinese ceramic or British teflon B7A sockets are used , just strip away about 40mm of insulation then wrap the wire around the socket pins a few times before soldering , this only needs to be done with the filament pin contacts . I found this out the hard way and ended up with some sockets with crusty , burnt contacts , my fault really for running the 6C33 at 55W . US Johnson sockets are apparently immune to this problem but are rather expensive . Some advice : Running at 55 watts I also had a 6C33 outgas and split on me , quite a spectacular little firework display inside the thing but also a complete P.I.T.A . Run the things at around 40-45 watts and they'll last and last and don't run any hotter than this with fixed bias .
ps Just one last thing : make sure the 6C33 pins are cleaned before usage , Brasso wadding follwed by a rinse with isoprop and cottonbud does the trick
cheers
316a
Thanks 316a, I think using that technique and rather thick gauge wire the sockets will live as long as the tube.
55W is a heck of a lot of anode dissipation Kt88 extreme maximum is some where in the region of 42W I think.
I know this maybe a little hard to answer as there are many circuit topologies, but what sort of sound characteristics do these indirectly heated triodes have? I've heard the BAT PSE tube amp which uses the same tubes but only for a very short time
Hesky
55W is a heck of a lot of anode dissipation
Kt88 extreme maximum is some where in the region of 42W I think.I know this maybe a little hard to answer as there are many circuit topologies, but what sort of sound characteristics do these indirectly heated triodes have? I've heard the BAT PSE tube amp which uses the same tubes but only for a very short time
Hesky
6C33 ctnd...
Hello ,
Yes , the 6C33 is a hot ****** with a greedy filament , make sure the chassis is large enough , remember that the filaments take 36 watts alone . I can't really compare what I built to a standard SE amp as I used stacked 6C33 in SRPP topology . This had a standalone 380V 250mA PSU per channel , and was big , ugly and very innefficient . It would heat my workshop better than an electric heater in the winter Mains toroids were used as output transformers which surprisingly work particularly well with low Ra valves I did notice that at low volumes , probably a few watts , the sound was remarkably clean which would suggest that if sensitive speakers are used these would be an ideal match . Bass was also clean and not peaky like many SE amps , probably as a result of improved speaker damping . The only thing I did find was that medium mu valves such as 6SN7 don't really have the legs to drive these things adequately . After first trying E182CC and 6SN7 then trying 6BX7 , 6BL7 I eventually plumped with 2C50 which is a 12.6V filament double triode with mu of 10 .
cheers
316a
Hesky said:Thanks 316a, I think using that technique and rather thick gauge wire the sockets will live as long as the tube.
55W is a heck of a lot of anode dissipation
I know this maybe a little hard to answer as there are many circuit topologies, but what sort of sound characteristics do these indirectly heated triodes have? I've heard the BAT PSE tube amp which uses the same tubes but only for a very short time
Hesky
Hello ,
Yes , the 6C33 is a hot ****** with a greedy filament , make sure the chassis is large enough , remember that the filaments take 36 watts alone . I can't really compare what I built to a standard SE amp as I used stacked 6C33 in SRPP topology . This had a standalone 380V 250mA PSU per channel , and was big , ugly and very innefficient . It would heat my workshop better than an electric heater in the winter
Mains toroids were used as output transformers which surprisingly work particularly well with low Ra valves I did notice that at low volumes , probably a few watts , the sound was remarkably clean which would suggest that if sensitive speakers are used these would be an ideal match . Bass was also clean and not peaky like many SE amps , probably as a result of improved speaker damping . The only thing I did find was that medium mu valves such as 6SN7 don't really have the legs to drive these things adequately . After first trying E182CC and 6SN7 then trying 6BX7 , 6BL7 I eventually plumped with 2C50 which is a 12.6V filament double triode with mu of 10 . cheers
316a
Brasso
Hello ,
Brasso is a brand of British metal polish . Wadding is mildly abrasive spongy stuff impregnated with the polish . Seems to do the trick . Maybe this is a British thing like Bovril that doesn't appear anywhere else I haven't measured the temperature at the pins but running at 55 watts the solder at the tags starts to go crispy within a few months with the Russian sockets
cheers
316a
grataku said:
Hello ,
Brasso is a brand of British metal polish . Wadding is mildly abrasive spongy stuff impregnated with the polish . Seems to do the trick . Maybe this is a British thing like Bovril that doesn't appear anywhere else
I haven't measured the temperature at the pins but running at 55 watts the solder at the tags starts to go crispy within a few months with the Russian sockets cheers
316a
I used my 6C33C based SE amp a couple of years, for a SE amp I think the sound is very good and comparable to amps using 300B and 845, I myself believe a lot of the sound quality comes from the topology and component quality rather than the output tubes used. One advantage of the 6C33C is that it has low Ri which make it easier to make a good output transformer, my amp has a Tango XE-20-600S transformer which is very good which contributes to the good sound.
I use 6C33C in my OTL amp also which I think is a good choice, I have only heard the 6C33C in transformer coupled push-pull for a shorter time so I can't judge the sound from that really.
Regards Hans
And there was me thinking brasso was universally known. To be fair I’m not a real fan of Bovril, to beefy for me apparently the Scotts love it though
Sorry digressing a little there.
I plan to use good grade CPIO capacitors and tantalum resistors in the audio circuit in an effort to add a bit more transparency. I'm sure it will end up in a bit of trial and error though. We will see,
still much to be learnt.
Just a question what do you guys use for volume attenuation?
Thanks
Hesky
would scotchbrite do a similar thing? would be a rougher finish no doubt...maybe it would be a good thing to have polished pins to combat 'corrosion' or random carbonization
never liked bovril, bit too rich for me i think. oxo though!that did strike me as something good to do as theyre relatively low voltage and high current
is that a typo? guess you meant Ra
Wouldnt toroids be ok with pp topologies anyway? I guess the only advantages would be size but i dont know.
Steve
Hi,
I think most people use ALPS or PANASONIC plastic film pots.
Personally I either use stepped attenuators (phono preamp) or NOBLE carbon track pots (Amplifier).
Some claim xformer volumecontrols are excellent, I haven't tried one yet.
I think you'll find as many opinions as there are different pots out there anyway.
To me, Ra or Rp mean anode/plate resistor, Ri means internal resistance.
Cheers,
I think most people use ALPS or PANASONIC plastic film pots.
Personally I either use stepped attenuators (phono preamp) or NOBLE carbon track pots (Amplifier).
Some claim xformer volumecontrols are excellent, I haven't tried one yet.
I think you'll find as many opinions as there are different pots out there anyway.
To me, Ra or Rp mean anode/plate resistor, Ri means internal resistance.
Cheers,
No I meant Ri, internal resistance of the tube, low internal resistance means that also the load impedance Rp should be low which is an advantage especially in a SE amp as the output transformer can be made with higher bandwidth.
It doesn't matter if it is toroids or not, lower Ri and subsequently Rp is always better from a bandwidth point of view.
Have you compared toroids with C-core transformers in a real amp? the DC sensitivity of toroids demand better matching both static and dynamic of the output tubes but they can still drift apart when they are aging so toroids maybe not is the perfect solution they can seem to be.
I use a stepped attenuator based on a rotary switch from ELMA, I prefer stepped attenuators before pots due to better channel balance and better life expectancy, (pots can easily get bad when old).
Regards Hans
At the Highend 2004 in Munich I have had a look at the Graaf GM 20. They use specially made tube sockets for the 6c33 which look quite interesting. Unfortunately I have not taken a photo. In principle they are a plate of a black material and pins stick out, so that the tube is about 1.5 cm above the plate, a bit similar to what was proposed here:
http://www.diyaudio.com/forums/show...=15&highlight="diy+tube+sockets"&pagenumber=3
If anybody has access to this amp a photo of the sockets will be appreciated. Does anybody know if Graaf is willing to sell these sockets separately, or to display info on the manufacturer?
http://www.diyaudio.com/forums/show...=15&highlight="diy+tube+sockets"&pagenumber=3
If anybody has access to this amp a photo of the sockets will be appreciated. Does anybody know if Graaf is willing to sell these sockets separately, or to display info on the manufacturer?
There are some photographs here where you can get an idea of the Graaf 6C33 sockets:
http://www.connoisseuraudio.co.uk/AmpsGraaf.htm
http://www.connoisseuraudio.co.uk/AmpsGraaf.htm
Does anyone know what anode voltage and current that the Graaf amp is using? the reason I ask is that it seems that the problems with the sockets seem to be critical when using the tube at max specifications but the problem seems quite less severe when using lower dissipation.
I am myself using ~160V anode voltage and ~220mA or totally ~35W dissipation per tube in my OTL and I have not experienced any problems with the sockets so far, (more then 4 years use).
316A used up to 55W dissipation and experienced problems and I have heard about others with similar experiences. BTW Viktor Khomenko of BAT recommends to run the 6C33 at max 40W dissipation for long life, similar recommendation as by 316A.
Regards Hans
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