After a bit of musing, and an email from John Broskie, I have decided to go for the Aikido octal-tube preamp. I'll order a single stereo board and get going with the project.
John suggested that I try either 12sn7 tubes (4) or mix them with a tube such as 6DJ8. I cannot find 12sn7s available, but have been able to find 6sn7 tubes. Anyway, I do not need a huge amount of gain, so about 20db will be fine.
OK, so I need to design a power supply.
My thoughts are:
320-0320 (Hammond 276X) into
5U4GB into
a choke input filter using TWO 12H chokes (Hammond 193B)
two 50uF caps.
According to PSUDII, I given a 20mA draw (4 X 6sn7 @ 5mA each). I should see around 260V.
Anyway, does this PSU appear suitable.
Broskie's information gives resistor values for 250V. Would it be terrible to use the same values with B+ of 260V.
Otherwise, could anyone recommend a suitable tube rectified PSU that gives 250V at B+?
Thank-you,
Charlie
John suggested that I try either 12sn7 tubes (4) or mix them with a tube such as 6DJ8. I cannot find 12sn7s available, but have been able to find 6sn7 tubes. Anyway, I do not need a huge amount of gain, so about 20db will be fine.
OK, so I need to design a power supply.
My thoughts are:
320-0320 (Hammond 276X) into
5U4GB into
a choke input filter using TWO 12H chokes (Hammond 193B)
two 50uF caps.
According to PSUDII, I given a 20mA draw (4 X 6sn7 @ 5mA each). I should see around 260V.
Anyway, does this PSU appear suitable.
Broskie's information gives resistor values for 250V. Would it be terrible to use the same values with B+ of 260V.
Otherwise, could anyone recommend a suitable tube rectified PSU that gives 250V at B+?
Thank-you,
Charlie
SY said:
Max cap input for a 5U4 is 40uF. Make your first cap 40uF or less.
I have made several PS with 5U4s and have used 40uF motor run caps and 32uF electrolytics in the first position in a cap input filter without problems. (Actually I did have some arcing with one Chinese tube but all the others (Sovtek, NOS) I tried were happy with 40uF.
5U4 is a little over kill for this application - you can also try the 5V4 or 5Y3 family... I really like the old 5Z4G or 5Z4GT (GZ30) British rectifiers for preamp use.
The 12SN7 should be readily available - the best part is you can still pick up some choice '40s examples for decent prices versus the 6SN7. If I had known how much vintage 6SN7s had gone up in value, I would have invested in them instead of stocks
The 12SN7 should be readily available - the best part is you can still pick up some choice '40s examples for decent prices versus the 6SN7. If I had known how much vintage 6SN7s had gone up in value, I would have invested in them instead of stocks
Coupla things:
1) The total current draw of the 6SN7s is dependant on the resistors that you use. If you use 1000R for the input tubes and 300R for the output tubes (as Broskie suggests), then you'll draw 5mA for the input tubes and 10mA for the output tubes, for a total of 30mA. (http://tubecad.com/2006/05/blog0064.htm)
2) 6SN7s really appreciate a higher B+ than 260V. 300V is a better target.
3) I am using a 3.3uF cap before the choke to up the voltage. A preamp doesn't see the large voltage swings and current demands that a power amp does, and thus I personally don't find choke-input to be needed for a preamp.
1) The total current draw of the 6SN7s is dependant on the resistors that you use. If you use 1000R for the input tubes and 300R for the output tubes (as Broskie suggests), then you'll draw 5mA for the input tubes and 10mA for the output tubes, for a total of 30mA. (http://tubecad.com/2006/05/blog0064.htm)
2) 6SN7s really appreciate a higher B+ than 260V. 300V is a better target.
3) I am using a 3.3uF cap before the choke to up the voltage. A preamp doesn't see the large voltage swings and current demands that a power amp does, and thus I personally don't find choke-input to be needed for a preamp.
How do you calculate these?
Jayme,
I have a general question - when you have a schematic that does not show the operating point, how do you calculate it? For example, in this case we have a plate voltage of 260V on a 6SN7. The cathode resistor Rk is 1000R. How do you determine that the tube will draw 5mA (given that you have the plate curves, etc. available)?
Jayme,
I have a general question - when you have a schematic that does not show the operating point, how do you calculate it? For example, in this case we have a plate voltage of 260V on a 6SN7. The cathode resistor Rk is 1000R. How do you determine that the tube will draw 5mA (given that you have the plate curves, etc. available)?
How about just a simple power supply with a Hammond 269JX > A Full Wave Rec, pair of Paralleled 47uF caps, and a 1.2k-1.5k/47uF RC filter. Draw your B+ from the RC filter which is pretty clean and with the noise rejection of the Aikido should be plenty decent for a Simple power supply... (figure a 30mA draw as above post indicates)
A simple bridge rec + 47000uF cap to get DC heaters...
Very low tech but... I don't see how it'd be a bad supply as this is not a Power amp so current demands are minimal.
A simple bridge rec + 47000uF cap to get DC heaters...
Very low tech but... I don't see how it'd be a bad supply as this is not a Power amp so current demands are minimal.
Attachments
Renegade,
OK, so I look at Vl1 to get the voltage of B+ with a 30mA load ???? In this case, the mean V is about 281V.
So, I get the PSU built. Now how do I check it without connecting it to the actual preamp ??? I mean, how can I use my multimeter to check the B+ voltage without a 30mA draw from the multimeter ?? Maybe, this is rather a dumb question, in which case....duh!
Regards,
Charlie
OK, so I look at Vl1 to get the voltage of B+ with a 30mA load ???? In this case, the mean V is about 281V.
So, I get the PSU built. Now how do I check it without connecting it to the actual preamp ??? I mean, how can I use my multimeter to check the B+ voltage without a 30mA draw from the multimeter ?? Maybe, this is rather a dumb question, in which case....duh!
Regards,
Charlie
This article by Broskie shed some light in the calculations of operating points. http://www.tubecad.com/articles_2003/Grounded_Cathode_Amplifier/index.html
Good luck
Erik
Calculating operating point on existing schematic
Erik,
The question is not how to establish an operating point when designing a new topology, but rather how to infer/determine the operating point of an existing schematic (that you did not author). In this example, we have the Aikido topology with 6SN7. The 6SN7 has a plate voltage of 260V, and a cathod resistor of 1000R. How does one determine the bias point here?
Do you merely pick an example bias voltage - e.g., -3V, then run the numbers (V=IR on the cathode resistor), obtain a current, look at the plate curves to see if it works (i.e., the operating point falls on the correct curve in the plate characteristics chart)? If not, pick another bias voltage and recalculate.
Erik,
The question is not how to establish an operating point when designing a new topology, but rather how to infer/determine the operating point of an existing schematic (that you did not author). In this example, we have the Aikido topology with 6SN7. The 6SN7 has a plate voltage of 260V, and a cathod resistor of 1000R. How does one determine the bias point here?
Do you merely pick an example bias voltage - e.g., -3V, then run the numbers (V=IR on the cathode resistor), obtain a current, look at the plate curves to see if it works (i.e., the operating point falls on the correct curve in the plate characteristics chart)? If not, pick another bias voltage and recalculate.
So will this work????
Well, I finally seem to have things figured:
Hammond 270BX 275-0-275 50mA for the power transformer
Hammond 167L12 12.6VAC 2A heater transformer
Hammond 193C 20H 181 ohm choke
16uF for Cap1
50uF for Cap2
5Y3GT rectifier
12SN7 preamp tubes (I may swap the outputs to 6DJ8)
I'll use secondary filament (5V) from the 270BX for the 5Y3GT
The 12SN7's require 12V, so I'll give them 12.6V AC from the Hammond 167L12
What size fuse should I use for the IEC socket????
The schematic from PSUDII is attached.
Please, please send me comments.
Thanks,
Charlie
Well, I finally seem to have things figured:
Hammond 270BX 275-0-275 50mA for the power transformer
Hammond 167L12 12.6VAC 2A heater transformer
Hammond 193C 20H 181 ohm choke
16uF for Cap1
50uF for Cap2
5Y3GT rectifier
12SN7 preamp tubes (I may swap the outputs to 6DJ8)
I'll use secondary filament (5V) from the 270BX for the 5Y3GT
The 12SN7's require 12V, so I'll give them 12.6V AC from the Hammond 167L12
What size fuse should I use for the IEC socket????
The schematic from PSUDII is attached.
Please, please send me comments.
Thanks,
Charlie
Attachments
Awesome project. Having designed a number of PSU's from scratch,
I think I can save you money...
I'd go for the Triode Electronics ST35 replacement power transformer. This is 330-0-330 180mA plus two windings that each do 6.3V / 2.2A.
I'd use 1 6.3 winding to power a 6V rectifier of your choice... I like
the 6X5, EZ81/6CA4, 6BY5. You can pick up the 6V full wave rectifiers far cheaper than vintage 5V rectifiers. Plus, you can use the small 9-pinner (6CA4) to keep the overall size of your PSU managed.
The important design parameter to manage when modelling is PSUDII
is the Peak Current through the choke.... Select I(L1) and look at the current pulses.... Do any of the pulses exceed the mA rating of the choke? If so you choke is not going to cut it. You choke needs to be rated much higher than the idle draw of the load. That's because of charging pulses of current that are drawn by the capacitor when the rectifier switches on.
The Triode Electronics transformer is really nice, and its small, and it will provide way more B+ than you need.... With a second LC filter stage, you will also be able to power a nice phono preamp too!
-- Jim
I think I can save you money...
I'd go for the Triode Electronics ST35 replacement power transformer. This is 330-0-330 180mA plus two windings that each do 6.3V / 2.2A.
I'd use 1 6.3 winding to power a 6V rectifier of your choice... I like
the 6X5, EZ81/6CA4, 6BY5. You can pick up the 6V full wave rectifiers far cheaper than vintage 5V rectifiers. Plus, you can use the small 9-pinner (6CA4) to keep the overall size of your PSU managed.
The important design parameter to manage when modelling is PSUDII
is the Peak Current through the choke.... Select I(L1) and look at the current pulses.... Do any of the pulses exceed the mA rating of the choke? If so you choke is not going to cut it. You choke needs to be rated much higher than the idle draw of the load. That's because of charging pulses of current that are drawn by the capacitor when the rectifier switches on.
The Triode Electronics transformer is really nice, and its small, and it will provide way more B+ than you need.... With a second LC filter stage, you will also be able to power a nice phono preamp too!
-- Jim
I think I can beat your design proposal in cost, performance and parts.
Try this; its a choke input supply (use an LC filter)
Triode Electronics ST35. T1 = 346V 91 ohms (for 330V / 180mA)
Pick a 6V rectifier: 6X5GT, or EZ91 (6CA4)
Hammond 195L Choke: 10H 155 ohms 125 mA
50uF cap (just parallel up the 25uF section of the JJ Electrolytic)
You'll get 1V ripple on 299 VDC. I(L1) < 125mA which is great.
It will be much quieter than a CLC supply...
Use 1 6V winding to fire the rectifer, the other 6V winding you can use at your leisure.
This supply will let you draw more current than 30mA (!). With
an additional LC stage, you can also power a phono preamp which you can put in the same box as the Aikido preamp.
-- Jim
Try this; its a choke input supply (use an LC filter)
Triode Electronics ST35. T1 = 346V 91 ohms (for 330V / 180mA)
Pick a 6V rectifier: 6X5GT, or EZ91 (6CA4)
Hammond 195L Choke: 10H 155 ohms 125 mA
50uF cap (just parallel up the 25uF section of the JJ Electrolytic)
You'll get 1V ripple on 299 VDC. I(L1) < 125mA which is great.
It will be much quieter than a CLC supply...
Use 1 6V winding to fire the rectifer, the other 6V winding you can use at your leisure.
This supply will let you draw more current than 30mA (!). With
an additional LC stage, you can also power a phono preamp which you can put in the same box as the Aikido preamp.
-- Jim
Here's another example
As it turns out, I am building an Aikido-based phono preamp right now. Here is the power supply (300V, 50mA):
Hammond 270DX (275-0-275, 90mA)
5U4 rectifier
20uF ASC oil polyprop
Hammond 193C choke (20H, 100mA)
50uF ASC oil polyprop
Hammond 158M choke (10H, 100mA)
50uF ASC oil polyprop
300R resistor
50uF ASC oil polyprop
Ripple is 6.5uV according to PSUDII - not sure how much I believe it, but it will be considerably lower than 1V.
On another note - if Charlie is going to use a dedicated heater transformer, why not consider a delay tube like the Amperite 115N060 for a soft start.
As it turns out, I am building an Aikido-based phono preamp right now. Here is the power supply (300V, 50mA):
Hammond 270DX (275-0-275, 90mA)
5U4 rectifier
20uF ASC oil polyprop
Hammond 193C choke (20H, 100mA)
50uF ASC oil polyprop
Hammond 158M choke (10H, 100mA)
50uF ASC oil polyprop
300R resistor
50uF ASC oil polyprop
Ripple is 6.5uV according to PSUDII - not sure how much I believe it, but it will be considerably lower than 1V.
On another note - if Charlie is going to use a dedicated heater transformer, why not consider a delay tube like the Amperite 115N060 for a soft start.
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