In my two stages amp 211, , I have changed the driver tube by a 6j51p ( ef184) as triode, with a gain of 60 I have more head room, go up faster that with the 6e5p, the 6e5p is a little more clear than 6j51p, but good enough.
Is funny but the cheap 6j51p sound better than expensive NOS Philips or Siemens EF184. 🙂
I have changed parts to try to increase the quality sometimes yes sometimes not.
Grid stopper are mandatory to avoid the oscillation.
Led as cathode bias, same of them are good other not, in my case I have changed to traditional resistor-capacitor. I am not sure what is better.
The filaments of he 211 in my case like more with DC I use
two switched-mode power supply with good results.
About the load by CCS I have a question:
When I change the load of the 6j51 by resistor load 20k, I listen very clear that have more bass present. Using both cathode bias ( resistor-capacitor) and resistor load.
I like more the CCS ( dn2540 cascade), have more details and air, but what is about the bass, why resistor load give more. Any idea about what?
Is funny but the cheap 6j51p sound better than expensive NOS Philips or Siemens EF184. 🙂
I have changed parts to try to increase the quality sometimes yes sometimes not.
Grid stopper are mandatory to avoid the oscillation.
Led as cathode bias, same of them are good other not, in my case I have changed to traditional resistor-capacitor. I am not sure what is better.
The filaments of he 211 in my case like more with DC I use
two switched-mode power supply with good results.
About the load by CCS I have a question:
When I change the load of the 6j51 by resistor load 20k, I listen very clear that have more bass present. Using both cathode bias ( resistor-capacitor) and resistor load.
I like more the CCS ( dn2540 cascade), have more details and air, but what is about the bass, why resistor load give more. Any idea about what?
A schematic would be helpful.
Try this plate load out!
Use R26 & R27 to set the plate voltage; select R22 so that it drops about 10V. MOSFET can be for example IRF820. Take the output from the MOSFET source.
Use a LED on the cathode. Make sure the LED has a healthy current thru it, or else bass will suffer. 15mA should do, 20mA at least.
This gyrator plate load with LED bias will give very clear and powerful bass performance.
Try this plate load out!
Use R26 & R27 to set the plate voltage; select R22 so that it drops about 10V. MOSFET can be for example IRF820. Take the output from the MOSFET source.
Use a LED on the cathode. Make sure the LED has a healthy current thru it, or else bass will suffer. 15mA should do, 20mA at least.
This gyrator plate load with LED bias will give very clear and powerful bass performance.
Attachments
Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum =)
Schematic
Led have been changed by resitor 220R and capacitor 220uf, the 6e5p have been changed by 6j51p., the 4k7 before CCS have been removed.
The 6j51p as triode ( G2 + G3 ) + 200R to anode. at 10mA
About the led, I have always used the LED but now I want to try same weeks with tradicional resitor. At the moment I dont listen a clear different.
About Gyrator what's opinion do you have, CCS or Gyrator, I had problems with CCS because the DN2540 need to replace two or three times.
An externally hosted image should be here but it was not working when we last tested it.
Led have been changed by resitor 220R and capacitor 220uf, the 6e5p have been changed by 6j51p., the 4k7 before CCS have been removed.
The 6j51p as triode ( G2 + G3 ) + 200R to anode. at 10mA
About the led, I have always used the LED but now I want to try same weeks with tradicional resitor. At the moment I dont listen a clear different.
About Gyrator what's opinion do you have, CCS or Gyrator, I had problems with CCS because the DN2540 need to replace two or three times.
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At 10mA the LED was probably not completely properly biased. Try 12mA at the least, 15mA better.
I prefer the gyrator. For one, it doesn't drift, and it allows to adjust the plate voltage very easily. As per sound quality; you'll have to try for yourself. I prefer the gyrator.
Do you have adequate heat sinks on the MOSFETs?
I prefer the gyrator. For one, it doesn't drift, and it allows to adjust the plate voltage very easily. As per sound quality; you'll have to try for yourself. I prefer the gyrator.
Do you have adequate heat sinks on the MOSFETs?
Green led running at 11mA seem ok and sound is good
about the DN2540 use :
I dont see any heat problem, but I am going to make a gyrator with them.
About the bass I am going to test again because maybe the bass is only in one CD
In my test CD as Tutty fron RR all is the correct place and extension.
thanks
about the DN2540 use :
An externally hosted image should be here but it was not working when we last tested it.
I dont see any heat problem, but I am going to make a gyrator with them.
About the bass I am going to test again because maybe the bass is only in one CD
In my test CD as Tutty fron RR all is the correct place and extension.
thanks
do you have any form of electrical isolation between the DN2540s and the heatsink? to me it looks there is none there, this would connect all drains together, not a good thing...
Good vision, this picture is without but now have silicone isolation..
Yesterday I put again the resistor load 20k to ef184 and put again the led to biasing, my opinion is that I like more with led. About CCS I am going to try with the gyrator with one dn2540. Try is the best way to find your sound. 🙂
If you have a resistor plate load, make absolutely sure that the load line never goes under 10mA.
If the LED doesn't have AT LEAST 10mA of current thru it, it will not have a constant voltage. This will affect sound, esp. bass.
If the LED doesn't have AT LEAST 10mA of current thru it, it will not have a constant voltage. This will affect sound, esp. bass.
Well,. I measure 11.5mA across the load resistor, and the led 2.1 V ,the sound is great, I need to test more, but I can affirm that the resistor load give more dynamic and maybe silent are better, is possible that the dn2540 dont work correctly with 10mA.
About the gyrator, which FET will be better that dn2540?
I drew up your loadline (6j51p curves from Klausmobile, great site).
If you have a non-horizontal load line, it doesn't matter if at the quiescent point you have 10mA or more current, it matters that the whole of the load line is above 10mA, or at least most, or the useable portion.
As you can see, your load line has pretty much the entirety of the right side from the quiescent point very much below 10mA.
If a LED has insufficient bias current, it will not have a constant voltage across it.
Either
1) operate the tube with a (near) horizontal load line, using a gyrator or a CCS,
2) supply the LED bias current via a separate resistor from B+, so that the LED is biased at all points of the load line independently from the tube
I would suggest using a gyrator, and setting the plate voltage such that the tube operates at around 12, maybe 15 mA current.
As per MOSFET choise; I use IRF820 or IRF840. Because they're cheap and easy to get.
If you have a non-horizontal load line, it doesn't matter if at the quiescent point you have 10mA or more current, it matters that the whole of the load line is above 10mA, or at least most, or the useable portion.
As you can see, your load line has pretty much the entirety of the right side from the quiescent point very much below 10mA.
If a LED has insufficient bias current, it will not have a constant voltage across it.
Either
1) operate the tube with a (near) horizontal load line, using a gyrator or a CCS,
2) supply the LED bias current via a separate resistor from B+, so that the LED is biased at all points of the load line independently from the tube
I would suggest using a gyrator, and setting the plate voltage such that the tube operates at around 12, maybe 15 mA current.
As per MOSFET choise; I use IRF820 or IRF840. Because they're cheap and easy to get.
Attachments
In post 9 the OP says he's running 20k plate load resistor at the moment. That's what I used to draw the load line.
If you have a battery, maybe go fixed grid bias rather than cathode?
(By the way, the DN2540 are completely fine and good to use for any plate load. No need to look for replacements.)
(By the way, the DN2540 are completely fine and good to use for any plate load. No need to look for replacements.)
If you use the battery as fixed bias I am not sure that the life time of the battery be enough and when I tried as cathode give me the best sound of all cathode bias. I am going to try next weekend with the battery to be sure
If you use the battery as grid bias voltage reference, it pretty much doesn't supply any current, so it'll have a very long life. Much longer than at the cathode, where it does in fact supply current.
Have a look at some russian tubes! They're cheap and plentiful, and many have great curves and performance.
Have a look at some russian tubes! They're cheap and plentiful, and many have great curves and performance.
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