Thanks Alex and Glenn. I'll try to stay within the limit of the 5U4-G. The power trans is my last purchase, if all is well, this is the CLC PSU that I'll use:
Hammond 274BX 375V @ 175ma
Sovtek 5U4-G
10uF to 40uF for C1 (ASC motor run)
10H 200ma choke (Hammond 193J)
(2) 50uF parellel = 100uF total for C2 (ASC motor run)
PSUD2 simulations:
- Assuming "off-load current" is 375V (rated voltage), then a 40uF C1 yields 392V B+.
- Assuming "off-load current" is 392V (1.05X rated voltage), then a 10uF C1 yields 410V B+.
Close enough...
Questions:
1. How do you calculate ripple on PSUD2 for the above circuit?...
2. Alex and Glenn, what are your PSUD2/measured B+ voltages on your PSU?...
3. To calculate the resistor value for a LM317 regulator for an 8ma 6N1P cathode bias, is this right: 1.25/0.008A = 156ohm resistor?...
(resistor placed between the Adj & Out pins with the Inp pin to cathode and Out pin to Gnd)?...
Thanks again, guys!
Hammond 274BX 375V @ 175ma
Sovtek 5U4-G
10uF to 40uF for C1 (ASC motor run)
10H 200ma choke (Hammond 193J)
(2) 50uF parellel = 100uF total for C2 (ASC motor run)
PSUD2 simulations:
- Assuming "off-load current" is 375V (rated voltage), then a 40uF C1 yields 392V B+.
- Assuming "off-load current" is 392V (1.05X rated voltage), then a 10uF C1 yields 410V B+.
Close enough...
Questions:
1. How do you calculate ripple on PSUD2 for the above circuit?...
2. Alex and Glenn, what are your PSUD2/measured B+ voltages on your PSU?...
3. To calculate the resistor value for a LM317 regulator for an 8ma 6N1P cathode bias, is this right: 1.25/0.008A = 156ohm resistor?...
(resistor placed between the Adj & Out pins with the Inp pin to cathode and Out pin to Gnd)?...
Thanks again, guys!
My measured B+ voltages are listed on my web page for various tubes:
http://webpages.charter.net/porkchop/tubeamp/tube_dissipation.jpg
I used 175mA for my load:
http://webpages.charter.net/porkchop/tubeamp/SET-power_supply.jpg
http://webpages.charter.net/porkchop/tubeamp/tube_dissipation.jpg
I used 175mA for my load:
http://webpages.charter.net/porkchop/tubeamp/SET-power_supply.jpg
Last edited:
Has anyone built this design using the 5H choke/10uF capacitor for the plate source of the 6N1P?
Is this additional filtering pointless?
Could this be possible?: If you calculate the LC filter formed by the 5H choke & 10uF cap, and based on 10mA current for the 6N1P plate current, this should provide 29dB of filtering for the 120Hz AC component of the B+. It should also drop the B+ by 2.7V
I have also read that the use of a plate choke will increase the dynamic range of the preamp tube.
I'm not an expert by any means, so someone please chime in.
Hello,
I noticed that you added a 1K resistor feeding the control grid of the KT88. Can you tell me about this?
Zekk,
I wanted to have a more symetrical layout on my chassis with some flexibility on the preamp/gain stage so I actually have built this with x2 6N1P tubes and plan to try it 2 different ways. One will be the original circuit using 1/2 of 2 seperate 6N1P or 6JD8 tubes. Then I will try the SRPP circuit above in place of the orginal gainstage. The SRPP requires a whole 6N1P (twin triode) for each channel.
The PSUD2 is a power supply modeling software available free at Duncanamps.
Jeff
Actually my plan was to parallel a 1K with the original 1k to get 500R (470R). So in essence, yes.
Jeff
That's a grid stopper resistor. I'm just used of putting them in my guitar amps for oscillation prevention. I'm not sure it's needed in this amp, as I haven't scoped it to see if this is happening.
Here's my post on the need for this part:
http://www.diyaudio.com/forums/tubes-valves/118420-grid-stopper-resistor-required-kt66.html
30H in preamp filter stage
I have a 30H 40mA Hammond choke I found in a box of stuff I forgot about today. I was wondering what disadvantage there would be in trying to use this insted of the 5H described earlier on the power supply to the preamp stage of the amp. Any thoughts of concerns with trying this here. I have used this filter in many of my preamp designs in a CLC cofiguration for a dead silent supply. I have used it on several SRPP designs with the 5670 and 5687 tubes as well as a cathode follower preamp with a 5687. I adapted it from the simple 5687 preamp at diyparadise.com to all of my other preamps I have done lately. What is the difference in trying to use it here? Seems to me it would work just fine but I have been grossly incorrect in the past.....
Thoughts, comments, rebukes welcomed.
Jeff
I have a 30H 40mA Hammond choke I found in a box of stuff I forgot about today. I was wondering what disadvantage there would be in trying to use this insted of the 5H described earlier on the power supply to the preamp stage of the amp. Any thoughts of concerns with trying this here. I have used this filter in many of my preamp designs in a CLC cofiguration for a dead silent supply. I have used it on several SRPP designs with the 5670 and 5687 tubes as well as a cathode follower preamp with a 5687. I adapted it from the simple 5687 preamp at diyparadise.com to all of my other preamps I have done lately. What is the difference in trying to use it here? Seems to me it would work just fine but I have been grossly incorrect in the past.....
Thoughts, comments, rebukes welcomed.
Jeff
There is additional discussion concerning this topic in this thread:
KT88 SE Abdellah (modified by Alex Gendrano) - AudioKarma.org Home Audio Stereo Discussion Forums
KT88 SE Abdellah (modified by Alex Gendrano) - AudioKarma.org Home Audio Stereo Discussion Forums
Help needed with non-center tapped filament supply
Hello,
I just realized that my Edcor power transformer 6.3v secondaries are not center tapped. The schematic at the beginning of this thread uses a center tapped 6.3v secondary with the CT connected to float the voltage closer to the HT. The circuit at the DIYaudioprojects does not show a CT 6.3v secondary and is just connected to the filaments without attention to this. Is there any issues I might have without a CT 6.3v as above? I built x2 rectifier/filter modules with a bridge rectifier and x2 4700uF caps on either side of a 1.2R resistor (what I calculated to get the voltage back down to 6.3v after rectification assuming about a 2.1a draw on 1 KT88 and 1 6N1P). I have x2 6.3v secondaries rated at 3 amps each so I was going to use one for each side (L/R) having each run a KT88 and a 6N1P. Also, if I rectify and filter the filament supply, how would it be possible to float the DC higher to the HT?
Thanks for your help with this.
Jeff
Hello,
I just realized that my Edcor power transformer 6.3v secondaries are not center tapped. The schematic at the beginning of this thread uses a center tapped 6.3v secondary with the CT connected to float the voltage closer to the HT. The circuit at the DIYaudioprojects does not show a CT 6.3v secondary and is just connected to the filaments without attention to this. Is there any issues I might have without a CT 6.3v as above? I built x2 rectifier/filter modules with a bridge rectifier and x2 4700uF caps on either side of a 1.2R resistor (what I calculated to get the voltage back down to 6.3v after rectification assuming about a 2.1a draw on 1 KT88 and 1 6N1P). I have x2 6.3v secondaries rated at 3 amps each so I was going to use one for each side (L/R) having each run a KT88 and a 6N1P. Also, if I rectify and filter the filament supply, how would it be possible to float the DC higher to the HT?
Thanks for your help with this.
Jeff
Can somebody tell me if a ripple of 0.020v Peak to trough is very much or likely to be audible? This is what I get with my PSUD2 simulation with a CLC of 47u-10h-102u. If I add about 100uF more I can drop it to about 1/3 of this value. Problem is it pulls the MAX on the current on the 5u4gb and about 0.2a over max on the 5u4g.
Also, how huch would it hurt my 5u4g to run it over that much? Will it immediately explode on me or will it just wear out alot faster?
I like the looks of the 5u4g better than the gb!
Jeff
Also, how huch would it hurt my 5u4g to run it over that much? Will it immediately explode on me or will it just wear out alot faster?
I like the looks of the 5u4g better than the gb!
Jeff
You caught me while doing the final design on own version of this amplifier in monoblock with DC filaments and a fully regulated supply. I havn't chimed in here yet, but have thought this through a bit.
The drawing at the beginning of this post shows the filament center tap grounded, thus keeping the filament voltages close to ground. This helps keep the internal filament (heater technically) in the proximity of it's cathode voltage which shouldn't exceed 50V or so above ground. I'm not sure if this has any real advantages, as in the event of a filament-cathode short, unpleasant things will happen either way. It's only really 3.15V different than grounding one side of the 6.3V winding. Either may slightly reduce any switching noise from the rectifer tube which could be coupled to the 6.3V secondary winding from the 5V one.
What I'm doing on the filament supply is using a $12 computer Switch Mode Power Supply - 12V 5A, then regulating to 6.3V using a LM7805 3 terminal regulator with a couple of diodes in the reference circuit (~.7v per) which gives 6.3 - 6.4 VDC regardless of load. I'm using a separate regulator for each tube. I know some hate using any silicon devices, but in power supplies they shine.
Which brings us to ripple. Shunt supplies, as you are finding are power hungry, and rapidly reach the point of diminishing returns. Fortunately, that is usually sufficent, especially for output stages (I doubt you'll hear 20mv unless you terminate the inputs and put your ear to the speaker). What I have done with my setup is add a separate RC from the main B+ to supply the driver stage. This could work for you, dropping the ripple level to the driver plate where it really counts, and adding virtually no additional load to the main supply.
The drawing at the beginning of this post shows the filament center tap grounded, thus keeping the filament voltages close to ground. This helps keep the internal filament (heater technically) in the proximity of it's cathode voltage which shouldn't exceed 50V or so above ground. I'm not sure if this has any real advantages, as in the event of a filament-cathode short, unpleasant things will happen either way. It's only really 3.15V different than grounding one side of the 6.3V winding. Either may slightly reduce any switching noise from the rectifer tube which could be coupled to the 6.3V secondary winding from the 5V one.
What I'm doing on the filament supply is using a $12 computer Switch Mode Power Supply - 12V 5A, then regulating to 6.3V using a LM7805 3 terminal regulator with a couple of diodes in the reference circuit (~.7v per) which gives 6.3 - 6.4 VDC regardless of load. I'm using a separate regulator for each tube. I know some hate using any silicon devices, but in power supplies they shine.
Which brings us to ripple. Shunt supplies, as you are finding are power hungry, and rapidly reach the point of diminishing returns. Fortunately, that is usually sufficent, especially for output stages (I doubt you'll hear 20mv unless you terminate the inputs and put your ear to the speaker). What I have done with my setup is add a separate RC from the main B+ to supply the driver stage. This could work for you, dropping the ripple level to the driver plate where it really counts, and adding virtually no additional load to the main supply.
Standby Switch
In case anyone is interested, I did some research on the best type of switch to use for the standby switch. The folks at NKK Switch recommended this switch for breaking the B+ line. They indicated that "the biggest issue is that when the switch is actuated there is a significant change in voltage causing a big arc even with the small current." This switch has internal magnets that extinguish the arc. It may be overkill, but I bet it lasts a long, long time.
S822D-RO NKK Switches Toggle Switches
In case anyone is interested, I did some research on the best type of switch to use for the standby switch. The folks at NKK Switch recommended this switch for breaking the B+ line. They indicated that "the biggest issue is that when the switch is actuated there is a significant change in voltage causing a big arc even with the small current." This switch has internal magnets that extinguish the arc. It may be overkill, but I bet it lasts a long, long time.
S822D-RO NKK Switches Toggle Switches
When I run PSUD2 with:
Hammond 374BX, 5U4GB, 10uF-10H-200uF, 180mA load, I am showing 217mA draw on the rectifier. Changing C1 to 47uF, I show 221mA.
The 5U4GB datasheet shows the typical DC output current as 275-300mA.
Hammond 374BX, 5U4GB, 10uF-10H-200uF, 180mA load, I am showing 217mA draw on the rectifier. Changing C1 to 47uF, I show 221mA.
The 5U4GB datasheet shows the typical DC output current as 275-300mA.
Actually, if you use 5ar4 for the rectifier, you don't need a standby switch, The B+ will ramp up slowly and will give your tubes to warm up before the full B+ is applied.
You can also make some soft start devices for slow ramp up of B+.
HTH.
Just put one 100R resistor on each leg of the 6.3V secondaries, and ground the other end of the resistor. This will reference the 6.3V secondaries to ground, much like having a center tap. I usually match my resistors if I need to do this, less hum.
I this SE KT88 circuit, referencing the 6.3V secondaries a few volts above ground is not necessary.
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