yes. i meant on the B+, does the pass circuit have any load on the HT winding of the transformer? the model i have in mind has 3a filament windings.
Hi,
Sorry, I misread you. I thought you meant the heaters.
The heaters of the ECL85 as said require roughly 1A per channel, 3A is ample.
Naturally the regulator loads the B+ (HT) winding as well or it wouldn't work at all. Assuming you're going to build the regulator as per the drawing choosing a xformer with a secondary of 250V/1A (not 285va as per the drawing)should more than suffice.
I often leave a nice margin so the xformer runs cool and doesn't buzz like a yellow jacket in the wind. I also prefer EI xformers over toroids in this application. If you can source one with an electrostatic shield then that's nice to have too.
Furthermore, for best sound the caps behind the regulator can be polypropylene filmcaps or else electrolytics of low esr bypassed with MKP caps of good quality.
Back in the days when this was designed, large filmcaps at say above 300VDC weren't available. Nowadays these are quite common.
For ultimate performance a tubed rectification should be used IMHO but this was designed with a budget in mind.
Cheers, 😉
Sorry, I misread you. I thought you meant the heaters.
The heaters of the ECL85 as said require roughly 1A per channel, 3A is ample.
Naturally the regulator loads the B+ (HT) winding as well or it wouldn't work at all. Assuming you're going to build the regulator as per the drawing choosing a xformer with a secondary of 250V/1A (not 285va as per the drawing)should more than suffice.
I often leave a nice margin so the xformer runs cool and doesn't buzz like a yellow jacket in the wind. I also prefer EI xformers over toroids in this application. If you can source one with an electrostatic shield then that's nice to have too.
Furthermore, for best sound the caps behind the regulator can be polypropylene filmcaps or else electrolytics of low esr bypassed with MKP caps of good quality.
Back in the days when this was designed, large filmcaps at say above 300VDC weren't available. Nowadays these are quite common.
For ultimate performance a tubed rectification should be used IMHO but this was designed with a budget in mind.
Cheers, 😉
Frank looking the data sheet I guess I set up the tubes bias to 13mA with -3V grid & 180V anode, is ok?
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Hi,
Why run so much current? The valve won't last very long. Have you run this through a sim? Also, for preamp use with a 2VRMS source I'd rather bias it more negative.
Cheers, 😉
Why run so much current? The valve won't last very long. Have you run this through a sim? Also, for preamp use with a 2VRMS source I'd rather bias it more negative.
Cheers, 😉
Wich is the optimum bias current?
Lowering the anode resistor to 10K can lower the bias current?
I'm sorry I don't know how to use the simulation soft.
TIA
Felipe
Lowering the anode resistor to 10K can lower the bias current?
I'm sorry I don't know how to use the simulation soft.
TIA
Felipe
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Hi,
That depends on what you want to do but for this I'd say no more than half of what you're suggesting.
Surely you can use this loadline sim:
Triode Loadline Simulator v.2.5 (20141229 www.trioda.com)
Furthermore I don't quite understand why you want all these changes.
Cheers, 😉
That depends on what you want to do but for this I'd say no more than half of what you're suggesting.
Surely you can use this loadline sim:
Triode Loadline Simulator v.2.5 (20141229 www.trioda.com)
Furthermore I don't quite understand why you want all these changes.
Cheers, 😉
I'm sorry Frank, I only want to use the optimum bias for the schematic you designed, that's the reason of questions someone wrong like to reduce the anode resistor in place to increase the negative grid voltage to reduce to 6.5mA the bias point.
Since Frank designed the thing and did all the work to determine a suitable operating point (range) why not just build it as he intended? Either that or start from scratch with entirely your own design? 😀
I have had a number of instances where someone took one of my designs assuming that they knew things I apparently didn't and changed it. When it didn't work as expected of course they then came to me to understand why???
I have had a number of instances where someone took one of my designs assuming that they knew things I apparently didn't and changed it. When it didn't work as expected of course they then came to me to understand why???
Kevin I built as intended, I only want to experiment with battery bias because I used RC & LEDs, I only want to follow Frank design and I want to use the same bias point: 6.5mA so now is time to calculate how many negative volts have I to use, I added other 1.5V cell so now I have -4.5V connected at the grid and I guess I reduced the bias point to 8mA.
Frank, do you know what's the red trace using the simulator?
Frank, do you know what's the red trace using the simulator?
Frank, build the two pres, one tube & two tube CF, I will keep the CF, sounds easy listening without fatigue, the songs seems shorter, congrats very very nice pre.
Hi,
I am in the process of building the pre-amp and was wondering... has any one tried loading the output with 32ohm headphones? How would that sound?
The preamp will serve my gu46 amp but was just wondering (before building) how it would pair up with headphones.
Thanks!
I am in the process of building the pre-amp and was wondering... has any one tried loading the output with 32ohm headphones? How would that sound?
The preamp will serve my gu46 amp but was just wondering (before building) how it would pair up with headphones.
Thanks!
Frank, after completing your 6sn7 active stage and testing it extensively with your ecl85 regulated supply I breadboarded I was wondering if there was any advantage to the el86/12ax7 version you also posted. just a quick question before I start drilling holes in this chassis. I have parts for both designs since I was planning on building both versions of your preamp. 😉
David
David
Hi,
The other series regulator was designed for a phono stage running off a 300 vdc B+.
It uses a cascaded 12ax7 as an error amp which allows for tighter voltage regulation.
I've not looked into what to adjust to make it put out 250vdc though.If at all possible.
Cheers, 😉
The other series regulator was designed for a phono stage running off a 300 vdc B+.
It uses a cascaded 12ax7 as an error amp which allows for tighter voltage regulation.
I've not looked into what to adjust to make it put out 250vdc though.If at all possible.
Cheers, 😉
No problem Frank. Do you know how much current capability in mA this regulator has?
I am interested in building Frank's Ultimate Tube Preamp, but I see that this thread has not been active for two years.
Could someone point me to the latest / last versions of the schematics for the preamp and power supply.
Thanks.
Could someone point me to the latest / last versions of the schematics for the preamp and power supply.
Thanks.
Hi,
Thank you for your interest in the preamp.
You can find circuit drawings from page 8 and onwards in this thread.
From a gainless line pre to a MM or MC phono preamp.
Should you like the PSU to be truly regulated then higher voltage xformers and caps are needed so the delta between the filtered output and the regulated output is at least 100 VDC.
There are quite a few things I could change using components available today but the basic circuit still stands.
Hope this helps, 😉
Thank you for your interest in the preamp.
You can find circuit drawings from page 8 and onwards in this thread.
From a gainless line pre to a MM or MC phono preamp.
Should you like the PSU to be truly regulated then higher voltage xformers and caps are needed so the delta between the filtered output and the regulated output is at least 100 VDC.
There are quite a few things I could change using components available today but the basic circuit still stands.
Hope this helps, 😉
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Thanks for your reply Frank, and for offering the design in the first place.
I will certainly try to build your Ultimate Tube Preamp.
If you were to design the circuit today what would you change ?; Sorry I had to ask.
Hi,
Given the available of HV polypropylene caps these days, I'd consider replacing the electrolytic caps behind the regulators with these.
Or at least listen to that and see if that sounds OK.
Same for the cathode resistors' decoupling caps.
If you like you can also expirement with a totally passive RIAA correction circuit that does away with the cathode decoupling caps altogther. I never had the chance to see how that would sound in comparison.
Up to you really.
All the best, 😉
Given the available of HV polypropylene caps these days, I'd consider replacing the electrolytic caps behind the regulators with these.
Or at least listen to that and see if that sounds OK.
Same for the cathode resistors' decoupling caps.
If you like you can also expirement with a totally passive RIAA correction circuit that does away with the cathode decoupling caps altogther. I never had the chance to see how that would sound in comparison.
Up to you really.
All the best, 😉
OK, thanks again Frank.
One last question, in the power supply diagram it says a transformer of 300VA, but in the part list on page 4 you mention 300mA. I am thinking of using a Hammond 369KX which is 450V @ 300mA (quoted as 188VA) - do you think this will be up to the job ?.