hi navin,
when I build tube preamps, I always use DC for the heaters. I regulate them using the readily available LM317 and use a pnp transistor to soft-start the DC.
however, when I build tube amps, I have never used DC for the heaters, always AC. even at AC heaters, I never had problems with excessive hum or annoying noises from the speakers, I just followed the recommended way of building tube amps and grounding schemes which incidently is contained in the pages of this forum. now using AC, I don't have any sort of soft-start for my heaters and the simpliest way to do this without re-wiring an amp is the use of thermistors. this is what I did to my existing EL34 amp, simple and effective. or we can adopt the soft-start circuits used in huge ss amps to limit the inrush current.
what I am saying is that wether it's AC or DC supplies for heaters it doesn't matter much because either can ruin your amp's sound with hum if not properly implemented.
btw, the previously posted specs of your power transformer looks very good indeed.
cheers
when I build tube preamps, I always use DC for the heaters. I regulate them using the readily available LM317 and use a pnp transistor to soft-start the DC.
however, when I build tube amps, I have never used DC for the heaters, always AC. even at AC heaters, I never had problems with excessive hum or annoying noises from the speakers, I just followed the recommended way of building tube amps and grounding schemes which incidently is contained in the pages of this forum. now using AC, I don't have any sort of soft-start for my heaters and the simpliest way to do this without re-wiring an amp is the use of thermistors. this is what I did to my existing EL34 amp, simple and effective. or we can adopt the soft-start circuits used in huge ss amps to limit the inrush current.
what I am saying is that wether it's AC or DC supplies for heaters it doesn't matter much because either can ruin your amp's sound with hum if not properly implemented.
btw, the previously posted specs of your power transformer looks very good indeed.
cheers
I think you could do that.
6SL7 and 6SN7 with dc heaters and O/P stage with ac heater.
You will probably have some feedback and that should reduce the effect of any hum produced in the O/P stage.
My single stage line preamp with an ac heater has extremely low hum. The HT supply is regulated . I can hear hum ( faintly) if I put my ear next to the woofer.
So I'm not quite sure how much the dc heater will help though it certainly should reduce hum compared to an ac heater. The question is how much does it matter?
Can guys with all ac heaters give some measured values of hum in their power amps ?
Navin, make sure the heater voltage is rated at the operating current . I think down to 6 volts is probably OK but what about handling mains voltage sag . Regulated dc heaters will overcome this , but the pass transistor on the regulator will get pretty hot and need a large heatsink. Makes things complicated !
Cheers
6SL7 and 6SN7 with dc heaters and O/P stage with ac heater.
You will probably have some feedback and that should reduce the effect of any hum produced in the O/P stage.
My single stage line preamp with an ac heater has extremely low hum. The HT supply is regulated . I can hear hum ( faintly) if I put my ear next to the woofer.
So I'm not quite sure how much the dc heater will help though it certainly should reduce hum compared to an ac heater. The question is how much does it matter?
Can guys with all ac heaters give some measured values of hum in their power amps ?
Navin, make sure the heater voltage is rated at the operating current . I think down to 6 volts is probably OK but what about handling mains voltage sag . Regulated dc heaters will overcome this , but the pass transistor on the regulator will get pretty hot and need a large heatsink. Makes things complicated !
Cheers
hi
FWIW
use raw AC on the output tubes, they take more current, and the extra demands of dc power with highish currents is more bother than its worth, also, any hum is a tiny proportion of the output swing, or input swing for that matter, after all, with an earth balance pot over the heater you can null out any residual hum.
I like using current regulators, I would use one for the first stage.
as the two tubes, 6sl7 and 6sn7 have different current ratings, you cannot connect them in series, furthermore, do not connect them in parallel with a 900ma CCS. If one of the tubes is pulled it will be forced to take all 900ma, not a good look.
anyway, 317s are cheap, use one each, the sense pin needs 1.25 difference across it, therefore for the 300ma tube you will need a 4.166 ohm resistor, and for the 600ma, a 2.08, as you may guess these are not exactly thick on the ground, so use a 5 ohm resistor with a high current pot in parallel so you can adjust the current to suit.
I would use a 9volt supply to drive both ccs units., this will give you enough volts to lose over the regulator, and by the time you have the 1.4 v dc drop from the bridge rectifier, it should be sweet.
hope that this is of some help,
btw, if you want to put a switch in there as well, you can switch in other resistors so that you can put the amp on standby and reduce the heater current.
kind regards
bill
FWIW
use raw AC on the output tubes, they take more current, and the extra demands of dc power with highish currents is more bother than its worth, also, any hum is a tiny proportion of the output swing, or input swing for that matter, after all, with an earth balance pot over the heater you can null out any residual hum.
I like using current regulators, I would use one for the first stage.
as the two tubes, 6sl7 and 6sn7 have different current ratings, you cannot connect them in series, furthermore, do not connect them in parallel with a 900ma CCS. If one of the tubes is pulled it will be forced to take all 900ma, not a good look.
anyway, 317s are cheap, use one each, the sense pin needs 1.25 difference across it, therefore for the 300ma tube you will need a 4.166 ohm resistor, and for the 600ma, a 2.08, as you may guess these are not exactly thick on the ground, so use a 5 ohm resistor with a high current pot in parallel so you can adjust the current to suit.
I would use a 9volt supply to drive both ccs units., this will give you enough volts to lose over the regulator, and by the time you have the 1.4 v dc drop from the bridge rectifier, it should be sweet.
hope that this is of some help,
btw, if you want to put a switch in there as well, you can switch in other resistors so that you can put the amp on standby and reduce the heater current.
kind regards
bill
JojoD818 said:
What I was trying to sy is that if I dont need DC for heaters then I dont need the 9-0-9V winding either right? And also if all 7 tubes are going to have AC heaters then the 3.15-0-31.5 winding should be 10A and not 8A. right? so having DC or not having DC does change the power tranny specs a bit.
ashok said:
I was verifying the need for a DC heater to confirm the spec of the power tranny as given below.
370V AC, 1Amp, additional taps at 340V and 355V
3.15-0-3.15 AC 8A CT (for EL34 heaters)
9-0-9V AC 2A CT (for 6SL7 and 6SN heaters) to be rectified to DC
70V AC (no need for CT) 0.2A for bias...
12V AC 0.5A for delay ckt and relays
just a suggestion, why not increase the 3.15-0-3.15 to 10A and still have the 9-0-9 2A? that way, you can both try AC or DC for the 6SN7 and 6SL7?
i understand that the presence of another winding can cost more money but this way you can test both AC and DC for your heaters.
i understand that the presence of another winding can cost more money but this way you can test both AC and DC for your heaters.
JojoD818 said:
Slow and Steady. I cross verify everything before doing it. Once I have the parts I will lay them down ans see if they all fit and it my hopes for hainvg a short signal path is possible.
Just so that I can be sure of this I am building 2 boxe ( 12" square and 14" square) in case the 12" square chassis gets too congested.
This friend of mine has a Prima Luna Prologue 1 and Prologue 2 and built tube amps 20+ years ago.
billr said:
Thanks AC for EL34, DC for 6SL7 and 6SN7 it is! Any contrary opinoins?
Do I need 2 317 based CCS or 3. There are 3 tubes 2 6SN7 and 1 6SL7? confused.
at least you have the options to have a new tranny with custom spec voltages... me I'm just using what I already have.
here's my tranny... needs hi-yemp painting though.
http://img.photobucket.com/albums/v70/jojod818/JD Labs Tube Amp/HFTranny.jpg
oh btw, here's my other pp el34 amp with all tube and all AC heater supply.
http://img.photobucket.com/albums/v70/jojod818/JD Labs Tube Amp/JDL03.jpg
here's my tranny... needs hi-yemp painting though.
http://img.photobucket.com/albums/v70/jojod818/JD Labs Tube Amp/HFTranny.jpg
oh btw, here's my other pp el34 amp with all tube and all AC heater supply.
http://img.photobucket.com/albums/v70/jojod818/JD Labs Tube Amp/JDL03.jpg
JojoD818 said:
I thought of that! and I could report if the DC heaters made any difference. My power tranny guy is gonna kill me. this is the 5th time I have changed the specs! 🙂 Thank god they are 1000 miles away.
navin said:
That's the spirit of this forum I guess, we share our experiences wether they're good or bad. 😀
I think your power tranny guy will understand. 😉
JojoD818 said:
Thanks. That was great.
I would love to see more pics of this the tubes look quite close together. A pic of the underside would help too.
The 3 transformers look different. I would have guessed atleast 2 would look the same.
Q: whay does everyone have holes around the tubes drilled in the chassis? I would like to avoid this to reduce dust going in.
JojoD818 said:
Mine might well be downright ugly!
Also is there some recomended topologies for tube amps? Any do and donts like running power cable near the RCA cable? How does one run the HT and heater current to all the tubes without coming close to the singal wires? etc...any ideas on this.
Anyway you convinced me. Mr. Toroidal please understand.
see http://www.toroidal.com/
holes around the power tubes helps a lot in cooling through natural air convection. I read about this somewhere in the net, even fellow members here advised such practice.
dust here in my amp is no problem since I have an air compressor and just one swooosh and all dust are gone! 😀
i think I have posted an old underside pic of this amp, it has undergone several reworks as well as some adjustments in the parts. the small tranny on the left is the choke, the big one is the power tranny, the 2 trannies behind the el34 are the opt.
here it is again navin (old one): http://img.photobucket.com/albums/v70/jojod818/JD Labs Tube Amp/JDL02.jpg
cheers
dust here in my amp is no problem since I have an air compressor and just one swooosh and all dust are gone! 😀
i think I have posted an old underside pic of this amp, it has undergone several reworks as well as some adjustments in the parts. the small tranny on the left is the choke, the big one is the power tranny, the 2 trannies behind the el34 are the opt.
here it is again navin (old one): http://img.photobucket.com/albums/v70/jojod818/JD Labs Tube Amp/JDL02.jpg
cheers
navin said:
some of these tips are all in the old pages of this forum, a search would be very useful and helpful in your project's constructions.
tips like... cross signal wires with power carrying wires in a 90 degree angle. when using AC for heaters, use the appropriate wire size and twist the wires together with a minimum of 8 twist per inch and unwind it only as close to the tube as possible.
construction tips like these can all be found in this wonderful forum my friend. 😉
JojoD818 said:
Hey super thanks. Now I feel ok. I was trying to work on a layout that kept the power and signal cables far apart. It is hard work.
JojoD818 said:
I dont know what to seach for! I hope when I start building it and run into problems guys like wayne, SY and yourself will still be around to help
SY and Wayne have passion for electronics, I guess they'll always be here to fuel that passion and help us in the process.
It will surely make you feel more ok to know that I will also build this amp... with just slight variations to accomodate parts from my stockpile.
It will surely make you feel more ok to know that I will also build this amp... with just slight variations to accomodate parts from my stockpile.
Got this data.
EL34
AB1 P/P UL 43%
Va 430V
Ia 125 - 130mA
Ig2 10.0 - 15mA
Rk 470
Zout 6,600
Shared Rg2 = 1000 ohms
-----------------------
A P/P (triode)
Va 400
Ia 130 - 142mA
Rk 220
Zout 5,000
-------------------
Heater Voltage 6.3 V
Heater Current 1.5 A
6Sl7GT
Heater Voltage 6.3 V
Heater Current 0.3 A
------------------------
Va 250V
Ia 2.3 mA
6SN7
Heater Voltage 6.3 V
Heater Current 0.6 A
--------------------------
Va 250V / 90V
Ia 10mA
Q: will 70V / 200mA do for biasing all these tubes?
EL34
AB1 P/P UL 43%
Va 430V
Ia 125 - 130mA
Ig2 10.0 - 15mA
Rk 470
Zout 6,600
Shared Rg2 = 1000 ohms
-----------------------
A P/P (triode)
Va 400
Ia 130 - 142mA
Rk 220
Zout 5,000
-------------------
Heater Voltage 6.3 V
Heater Current 1.5 A
6Sl7GT
Heater Voltage 6.3 V
Heater Current 0.3 A
------------------------
Va 250V
Ia 2.3 mA
6SN7
Heater Voltage 6.3 V
Heater Current 0.6 A
--------------------------
Va 250V / 90V
Ia 10mA
Q: will 70V / 200mA do for biasing all these tubes?
I'm an administrator, so I have to be around!😉
DC on the input stage heaters won't hurt, but really, if wiring and grounding are done properly, you will get no hum from using AC on all the heaters.
DC on the input stage heaters won't hurt, but really, if wiring and grounding are done properly, you will get no hum from using AC on all the heaters.
My experience with amp building is from guitar amps. They have a very high sensibility (around 2 mV for full output) and no feedback at all.
I have mesured the hum with AC and DC for the heater, and even for the output stage, it was an improvment with DC. So I use DC for the whole amps.
With AC, the noise was like hum; with DC, I get a white noise.
The main problem was heat dissipation, I put a big radiator on the outside of the case.
Another source of hum I get in my first guitar amp was the g1 alimentation of the output stage. It was really a diificult problem to solve. But I want not talk more about it here, because a class B pp have nothing to do with an hifi amplifier.
I have mesured the hum with AC and DC for the heater, and even for the output stage, it was an improvment with DC. So I use DC for the whole amps.
With AC, the noise was like hum; with DC, I get a white noise.
The main problem was heat dissipation, I put a big radiator on the outside of the case.
Another source of hum I get in my first guitar amp was the g1 alimentation of the output stage. It was really a diificult problem to solve. But I want not talk more about it here, because a class B pp have nothing to do with an hifi amplifier.
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