kt77 so has 4 grids? When reading the description you expect that replacing it in a el34 circuit UL cause a boost in power, etc.
However it is not the case, I tested it thoroughly in two circuits, I can confirm everything which is said about the sound... which I attribute to a raise of 3rd harmonics and more.
Maybe it is only attributable to this particular manufacturer JJ...
However it is not the case, I tested it thoroughly in two circuits, I can confirm everything which is said about the sound... which I attribute to a raise of 3rd harmonics and more.
Maybe it is only attributable to this particular manufacturer JJ...
I dropped in the EL34 amp some Kt88 and it performed the worst, I attributed this to the 0.1 Amp required per tube = 400mA which potentially caused a problem in the power transformer, enough to tax the B+ available power. the heaters are AC and the B+ is solid state.
In an amplifier with 600+ volts B+ the EL34 and Kt77 performed worst, in the amplifier designed for KT88
In an amplifier with 600+ volts B+ the EL34 and Kt77 performed worst, in the amplifier designed for KT88
I have a B+ of 600 Volt (with and without load) and run KT150’s with 90 mA per tube (UL / Triode). So far - still developing - this works very well and sounds good.
Regards, Gerrit
Regards, Gerrit
I am currently rummaging if I can improve the schematic of the 6sl7 paraphrase and 6sn7 cathode follower...
Ideally I would love to have the 6sn7 at input in parallel common anode, followed by another 6sn7 and transformer/splitter driver
Ideally I would love to have the 6sn7 at input in parallel common anode, followed by another 6sn7 and transformer/splitter driver
I also think about using ferrites on critical connections, potentially reducing the input grid resistors to both coupling stages.
the equivalent inductance attenuation is not something I can easily calculate. On the internet the ieLogical modifications uses 2.8uH on a 47R
Also the potential impact of using a steel perforated cage over the components, the max height of hammond is 5.2 inches and my output transfo is almost 6 inches tall, ill have to cut a square to let it protrude 🙁
the equivalent inductance attenuation is not something I can easily calculate. On the internet the ieLogical modifications uses 2.8uH on a 47R
Also the potential impact of using a steel perforated cage over the components, the max height of hammond is 5.2 inches and my output transfo is almost 6 inches tall, ill have to cut a square to let it protrude 🙁
I am running into some problems already...
I have here 2 edcor xpr 720V 230ma, and 3 unknown hammonds I know they are size x20, ill have to measure this but I don't have the dummy load necessary I'll have to improvise something like loading it with 1.2 K I have for around 100W + of these, I can test at 60Vac and see what it does in the output, I estimate the values would double with 120Vac...
this is an assumption !
I think I might have to purchase another set of power transformers.
If anyone interested I have 2 5k 100Watts hammond output transformers, one 270hx in the box
Meanwhile I think I have enough parts to build a prototype, I dismantled one amplifier but the other I will keep to roughly test the circuit.
I have here 2 edcor xpr 720V 230ma, and 3 unknown hammonds I know they are size x20, ill have to measure this but I don't have the dummy load necessary I'll have to improvise something like loading it with 1.2 K I have for around 100W + of these, I can test at 60Vac and see what it does in the output, I estimate the values would double with 120Vac...
this is an assumption !
I think I might have to purchase another set of power transformers.
If anyone interested I have 2 5k 100Watts hammond output transformers, one 270hx in the box
Meanwhile I think I have enough parts to build a prototype, I dismantled one amplifier but the other I will keep to roughly test the circuit.
I tested my edcor xpr002 and in full wave it gives me 471V at 147mA, )115Vac Line
On bridge rectifier it gives me around 600V at 145mA , this is with a 65Vac Line
70uf Input caps, this is also going through the choke.
My house line is around 122 Vac... so I am too high on bridge rectifier and I would only get 500Vac in full wave rectifier
On bridge rectifier it gives me around 600V at 145mA , this is with a 65Vac Line
70uf Input caps, this is also going through the choke.
My house line is around 122 Vac... so I am too high on bridge rectifier and I would only get 500Vac in full wave rectifier
I don't see other choices than buying two Hammond 372 FX , 600vac 173ma 5A. To bring the bridge rectifier B+ to acceptable levels. Otherwise I still use the 300BX with 450V at 85ma bias per tube.
This would make the amp a class A 40watt or so amp, with the 372FX I get around 600VDC at 65ma bias per tube.
I encourage anyone to build it with the 300BX or PRW002 from Edcor in class A, but I want for the ultimate amplifier to go over in class AB.
This would make the amp a class A 40watt or so amp, with the 372FX I get around 600VDC at 65ma bias per tube.
I encourage anyone to build it with the 300BX or PRW002 from Edcor in class A, but I want for the ultimate amplifier to go over in class AB.
Anyone reading this please don't despair, I found a solution , I have a brand new 270hx and another one in a el34 amp. I will just switch the 270hx for the edcorpwr002 to feed my el34 amp and upgrade the capacitor ratings inside, and it will give me two 270hx with approximately 600V of fun for playing with the kt120 amplifier, in BRIDGE rectifier mode, with the regulated supply on the input stage and screens, it should not be any problem versus using the more current stable full wave.
There is some development,
I switched main transformers, and modified the bias,
In the original circuit I have 2 diodes going from the HV AC , one each side , through 120k then some caps and bias.
In the new circuit I connected the dedicated 60Vac from the power transformer, it is not a split from the HV, so one wire is to ground the other to the single diode.
I observed many strange phenomenon's,
One tube started acting out in the bias, and later I powered it up with speakers and this tube is making horrible sounds when gently tapped. I think it is dead. (that tube was problematic just the week before when I listened to music I heard it, then the bias was getting out of control).
I did not connect the ground for the tests with the variac, and this caused a lot of problems, the bias readings were all over the place depending where I placed the ground test lead.
There was also a 45VAC potential with the earth that I could measure, no clue why??????
I noticed after connected the earth ground that the bias was reading lower now and was more stable.
0.35V was now reading 0.2V on the 10R resistors in average
This makes me question a lot the designs, a grounded device could be dangerous if it is not grounded especially if the case is metal and now has 45VAC potential.
There could be a lot of issues with properly biasing an amplifier , according to bias location on the case or circuit board and if it is grounded or not.
For now I will replace the EL34 with Kt77, I am sad one EL34 died at only 1300 hours of use... I don't like the KT77
I will monitor that bias issue and probably replace the coupling capacitor with ones with increased voltage, can't take a chance they only see 200V from the cathodes followers, but you never know, ill do this and report if i find anything suspicious.
I switched main transformers, and modified the bias,
In the original circuit I have 2 diodes going from the HV AC , one each side , through 120k then some caps and bias.
In the new circuit I connected the dedicated 60Vac from the power transformer, it is not a split from the HV, so one wire is to ground the other to the single diode.
I observed many strange phenomenon's,
One tube started acting out in the bias, and later I powered it up with speakers and this tube is making horrible sounds when gently tapped. I think it is dead. (that tube was problematic just the week before when I listened to music I heard it, then the bias was getting out of control).
I did not connect the ground for the tests with the variac, and this caused a lot of problems, the bias readings were all over the place depending where I placed the ground test lead.
There was also a 45VAC potential with the earth that I could measure, no clue why??????
I noticed after connected the earth ground that the bias was reading lower now and was more stable.
0.35V was now reading 0.2V on the 10R resistors in average
This makes me question a lot the designs, a grounded device could be dangerous if it is not grounded especially if the case is metal and now has 45VAC potential.
There could be a lot of issues with properly biasing an amplifier , according to bias location on the case or circuit board and if it is grounded or not.
For now I will replace the EL34 with Kt77, I am sad one EL34 died at only 1300 hours of use... I don't like the KT77
I will monitor that bias issue and probably replace the coupling capacitor with ones with increased voltage, can't take a chance they only see 200V from the cathodes followers, but you never know, ill do this and report if i find anything suspicious.
There is no problem, just a dead tube, just remember to ground the amplifier, because the magnetic and potential in the ground can falsify the delicate bias readings.
I read many possible usage of bias and screen bias which follows with fix grid bias etc.
In the final amplifier I will use a choke in the bias circuit, and I will probably use a choke in the screen too...
Right now I will use LR8 , with heatsinks, for the driver stage not sure about placing them in parallel.
I read many possible usage of bias and screen bias which follows with fix grid bias etc.
In the final amplifier I will use a choke in the bias circuit, and I will probably use a choke in the screen too...
Right now I will use LR8 , with heatsinks, for the driver stage not sure about placing them in parallel.
Finally the tube was fine, it was the 10ohm 3Watt bias resistor which had become broken with intermittent connection.
I am in the process to now convert the prototype kt88 amp to the new transformer.
I was wondering the effect of the 10R resistor on the cathode feedback winding, Audio Research uses 0.5R in the anode or 1R only in the cathode in series with the CF winding, I just don't really know how to calculate the effect or how this will make a difference in the feedback formula.
I might as well use only a 475V PS in the final kt120 amplifier and not go to 650V or so.
I am in the process to now convert the prototype kt88 amp to the new transformer.
I was wondering the effect of the 10R resistor on the cathode feedback winding, Audio Research uses 0.5R in the anode or 1R only in the cathode in series with the CF winding, I just don't really know how to calculate the effect or how this will make a difference in the feedback formula.
I might as well use only a 475V PS in the final kt120 amplifier and not go to 650V or so.
I guess I used 10 ohm since it was in all schematics of diy ,
I just installed new 10 ohms to replace the one that was faulty, but not a big problem, I prefer not change them if they don't affect the 16 ohm cathode feedback windings because I have no idea of the phase of the feedback generated along the 10ohm cathode in relation to the feedback the dedicated cathode windings provide,
If Audio research reduced them to 1 ohm it could be important.
I just installed new 10 ohms to replace the one that was faulty, but not a big problem, I prefer not change them if they don't affect the 16 ohm cathode feedback windings because I have no idea of the phase of the feedback generated along the 10ohm cathode in relation to the feedback the dedicated cathode windings provide,
If Audio research reduced them to 1 ohm it could be important.
Just to tell you, I went from kt77, el34, and now kt88 and the kt88 is in another league, everything is clear, just not the bass of the kt120 and refinement.
one big difference was to change the coupling capacitors from film generic square ones, to round ones, in one channel I have the mundorf silver 1000V in the other I have a generic film round caps, I though the mundorf were leaking but then I found out it was the 10 ohm
I only have now to determine the gain in pentode, estimate how much voltage i need for screen, everything else is working 100% to my liking.
I only have now to determine the gain in pentode, estimate how much voltage i need for screen, everything else is working 100% to my liking.
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I just right now play it with 360V with a 390uf cap, no regulator supply, straight from the main input PS cap through a 7.5k resistor, the grid bias is stable.
In pentode the gain in higher than ultralinear and I might adjust the feedback, right now i am trying in the same amplifier UL and cathode feedback with kt88, before using the kt120.
In pentode it sounds like distortion, like the opposite of triode, doesn't seem to have any details to the sound.
I am replacing all the mundorf silver in oil 1000V (50$) after one is found to be leaking. I am placing a smallish 1839HQ 220nf 850V Vishay (3$) , might not sound as good, but at least it wont blow up my tubes.
Since it is a ultimate amplifier, the durability of the vishay is more important of the so called sound of the supreme.
The best caps in my opinion were the ampohm tin cans, and I don't have the 0.22uf and they are too big anyways.
In pentode the gain in higher than ultralinear and I might adjust the feedback, right now i am trying in the same amplifier UL and cathode feedback with kt88, before using the kt120.
In pentode it sounds like distortion, like the opposite of triode, doesn't seem to have any details to the sound.
I am replacing all the mundorf silver in oil 1000V (50$) after one is found to be leaking. I am placing a smallish 1839HQ 220nf 850V Vishay (3$) , might not sound as good, but at least it wont blow up my tubes.
Since it is a ultimate amplifier, the durability of the vishay is more important of the so called sound of the supreme.
The best caps in my opinion were the ampohm tin cans, and I don't have the 0.22uf and they are too big anyways.
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It will be paramount that the capacitor is isolated with thermal sink during soldering and that the leads are kept at maximum length and folded to prevent any damage to the polypropylene foil.
I found out that the buzz problem was not caused by failed 10ohm resistor nor by the Mundorf..
My problem was a defective 12sng7 driver tube for the cathode follower, and any vibration was sending it into buzzing.
Maybe I damaged it while moving the amplifier still warm?
Now I have a serious problem....
I tested the amplifier on the bench with a variac and everything seems fine.
When I install the amplifier in my system I switch the first power button which has the power line going through 40ohm to reduce and then I press the second power button which removes the 40ohm from the line for full power.
When I press the second button the amp immediately emits through speakers a very loud high pitch tone so I turn it off immediately.
I have no idea what causes this only on the new modified cathode feedback channel with pentode.
My problem was a defective 12sng7 driver tube for the cathode follower, and any vibration was sending it into buzzing.
Maybe I damaged it while moving the amplifier still warm?
Now I have a serious problem....
I tested the amplifier on the bench with a variac and everything seems fine.
When I install the amplifier in my system I switch the first power button which has the power line going through 40ohm to reduce and then I press the second power button which removes the 40ohm from the line for full power.
When I press the second button the amp immediately emits through speakers a very loud high pitch tone so I turn it off immediately.
I have no idea what causes this only on the new modified cathode feedback channel with pentode.