There is no "floating ground" in this design. Ground is ground. The ideal grounding scheme calls for one (1) central grounding point to which all circuit grounds are connected, in close proximity to the power supply, with the exception of the 120VAC (or other voltage depending on your locale) ground that is bonded to the chassis as close as possible to the AC input socket.
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Hi Scott, I am going to first try the single ground with all points terminating on the chassis near the power supply as you said, and not go with star ground scheme just yet. I am going to connect the ground from the inputs, pot, tagboard, PSU caps, 6.3VCT, 375VCT, and have the buss wire terminate near the PSU.
By floating I meant to say was should I connect pin #9 to the ground that runs along the tag board near by the 6N1P? I was almost going to leave it unconnected if someone didn't say anything, because I didn't find it on any schematic.
By floating I meant to say was should I connect pin #9 to the ground that runs along the tag board near by the 6N1P? I was almost going to leave it unconnected if someone didn't say anything, because I didn't find it on any schematic.
Measurements
I have a new toy, distortion meter, so I spent some time doing some measurements with various configurations. Not that I discovered anything new, but I would appreciate your comments.
I played with driver anode load, changing 47k, 33k resistors, and CCS at 9mA.
Additionally I modified the cathode resistor for the KT88.
For the driver cathode I used two leds, with a voltage drop of 3.4 V this was useful as allowed me to keep the anode voltage stable while changing the current. Additionally I could not see any difference using a bypassed resistor.
My B+ is 415 V.
A 4 ohm resistor was used as a load, all distortion measurements were taken with 5Vrms at 1KHz. I am using Svetlana KT88 and winged C driver.
These are the results (Comma separated)
Driver load,KT88 cathode, Mode(UL or Triode), Distortion
47K,470,UL,3%
47K,470,T,4%
47K,300,UL,2%
47K,300,T,4.8%
33K,300,UL,2.5%
33K,300,T,4.2%
CCS,470,UL,4.2%
CCS,470,T,4.2%
CCS,300,UL,3.4%
CCS,300,T,4.2%
I also had a look to the harmonic distribution, and the 3rd harmonic tend to be dominant, UL mode makes things a bit better.
One thing that I noticed is that, the two tubes I have different distortion, one behave much better (the results are from the good one).
Best Regards,
Davide
I have a new toy, distortion meter, so I spent some time doing some measurements with various configurations. Not that I discovered anything new, but I would appreciate your comments.
I played with driver anode load, changing 47k, 33k resistors, and CCS at 9mA.
Additionally I modified the cathode resistor for the KT88.
For the driver cathode I used two leds, with a voltage drop of 3.4 V this was useful as allowed me to keep the anode voltage stable while changing the current. Additionally I could not see any difference using a bypassed resistor.
My B+ is 415 V.
A 4 ohm resistor was used as a load, all distortion measurements were taken with 5Vrms at 1KHz. I am using Svetlana KT88 and winged C driver.
These are the results (Comma separated)
Driver load,KT88 cathode, Mode(UL or Triode), Distortion
47K,470,UL,3%
47K,470,T,4%
47K,300,UL,2%
47K,300,T,4.8%
33K,300,UL,2.5%
33K,300,T,4.2%
CCS,470,UL,4.2%
CCS,470,T,4.2%
CCS,300,UL,3.4%
CCS,300,T,4.2%
I also had a look to the harmonic distribution, and the 3rd harmonic tend to be dominant, UL mode makes things a bit better.
One thing that I noticed is that, the two tubes I have different distortion, one behave much better (the results are from the good one).
Best Regards,
Davide
This will be my first
Wow; 49 pages, 6 hours and two glasses of Cabernet and I'm still online.
Gonna give this a go. I'll be sticking to the original schematic with the following changes; .33uF coupling cap instead of .22uF, diode bias mod and fixed 100K resister at the input instead of the 100k pot.
Time to start a layout. Guess the Academy will have to wait 😉
More to come. Thanks, to all, for all the valuable info.
Russell
Wow; 49 pages, 6 hours and two glasses of Cabernet and I'm still online.
Gonna give this a go. I'll be sticking to the original schematic with the following changes; .33uF coupling cap instead of .22uF, diode bias mod and fixed 100K resister at the input instead of the 100k pot.
Time to start a layout. Guess the Academy will have to wait 😉
More to come. Thanks, to all, for all the valuable info.
Russell
It's funny that if you check the specs of commercial amp based on SE KT88, they claim 0.1 % distortion, but it's not stated at what power and frequency. It's just a random number, even a bit unrealistic.
D.
D.
The heater is the heater and the shield is the shield - I don't see why referencing the heaters up should affect the fact that the shield should be tied to ground.
The question I'm currently asking myself is whether one should use signal ground or if it's acutaly more senseful to use main earth.
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Hi guys.
I been following this thread cause im building the same amp finish it last night, but im runing in a little problem. my first turn on i use a variac and everything seem fine. but when i didnt use the variac my fuse keeep blowing. i use 1amp fuse is this too low?
I been following this thread cause im building the same amp finish it last night, but im runing in a little problem. my first turn on i use a variac and everything seem fine. but when i didnt use the variac my fuse keeep blowing. i use 1amp fuse is this too low?
I'm starting to order parts for this build. I am going with the Edcor transformers. The output trannies are load specific and I'm going to go with the 4 ohm version. I am currently running on 8 ohm speakers but may go to 4 ohm in the future. The only issue I can see is a decrease in power at 8 ohms. Is my thinking correct, are there any other issues with doing this?
A 1 amp fuse is too low. My build draws 1.17A after everything gets warmed up. I am using a 2 amp standard fuse. I did not have any slow-blow fuses, but I think that would probably be best.
Thanks for the replies guys.
Got some 1.6amp fuse and everything is going good so far, hopes there's no suprises in the next few day.
Got some 1.6amp fuse and everything is going good so far, hopes there's no suprises in the next few day.
I hope you folks don't mind if I jump in here. I, actually, have never belonged to a forum. Of any kind, in fact this is even my first attempt at a post. I have built an amplifier very similar to this one and have a couple questions. My amp is basically a combination of yours, and Angela's single-ended EL34, plus a few changes and/or personel interjections I guess. If anyone's interested I can be more specific about it later.
What I need opinions on are, I've built mine as a power amp. No volume pot, so now I'm thinking; should I add a grid leak resistor? Any Idea on a value to start with? Also, has anyone tried this amplifier with NFB? Results? And what about values there.
I'm sure I have more questions, but I can't think of 'em now so I guess that'll do! And thank you in advanve for your patience and for anyone taking the time to respond.
What I need opinions on are, I've built mine as a power amp. No volume pot, so now I'm thinking; should I add a grid leak resistor? Any Idea on a value to start with? Also, has anyone tried this amplifier with NFB? Results? And what about values there.
I'm sure I have more questions, but I can't think of 'em now so I guess that'll do! And thank you in advanve for your patience and for anyone taking the time to respond.
Welcome to the forum.
I built my amp almost exactly as described at: KT88 Single Ended (SE) Tube Amplifier
The changes I made were:
1) I changed the 470K grid leak resistor for the KT88 to 220K to fall in line with the KT88 specs.
2) I did not use a volume pot and substituted a 100K resistor.
3) I used a 1.2K for the UL mode and stayed with the 100R for the triode mode. I made these two modes switchable.
4) I tried a 330K for NFB between the KT88 and 6N1P plates. I found it to take away from the sonics of the amp.
5) The triode mode seems to offer better dynamics, but the UL mode offers more gain and sounds nice also.
I built my amp almost exactly as described at: KT88 Single Ended (SE) Tube Amplifier
The changes I made were:
1) I changed the 470K grid leak resistor for the KT88 to 220K to fall in line with the KT88 specs.
2) I did not use a volume pot and substituted a 100K resistor.
3) I used a 1.2K for the UL mode and stayed with the 100R for the triode mode. I made these two modes switchable.
4) I tried a 330K for NFB between the KT88 and 6N1P plates. I found it to take away from the sonics of the amp.
5) The triode mode seems to offer better dynamics, but the UL mode offers more gain and sounds nice also.
Thank you, scitizen, for your response. I was thinking exactly as you did as far as replacing the pot with a 100k resistor. So I think I'll add that to my to-do list. I also made mine switchable between triode and u-l but I did not increase the resistance to the screen in u-l. What benefit would that offer? Although I admit, I listen to mostly jazz, classic rock and classical, I'm running NOS jan philips 6sl7's into NOS RCA EL34/6csa7 fat bottles so I rarely see (hear) ultra linear! Beautiful sound in triode!
Anyone else that can weigh in, please do!
Anyone else that can weigh in, please do!
srpp 6n1p in this kt88 amp ?
i find the pre amplification of the 6n1p a bit low ,i am thinking to try a srpp
with 1 6n1p a chanel , i tryed srpp a long time ago with a se el 34 in triode
with 2 times 150 ohm kathode resistors a tube but this gave a much to strong
deforming pre when i turned it a litle loud , any body tryed sucsesfull a srpp 6n1p in this project?
or knows the right value for the both resistors in the srpp like this ?
kind regards ko 🙂
i find the pre amplification of the 6n1p a bit low ,i am thinking to try a srpp
with 1 6n1p a chanel , i tryed srpp a long time ago with a se el 34 in triode
with 2 times 150 ohm kathode resistors a tube but this gave a much to strong
deforming pre when i turned it a litle loud , any body tryed sucsesfull a srpp 6n1p in this project?
or knows the right value for the both resistors in the srpp like this ?
kind regards ko 🙂
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