Srpp
If you look several posts back, toward the beginning of this thread I posted an SRPP 6922/6DJ8 Tube Cad worksheet for this amp. I have never tried it, I find the current arrangement sounds perfect. You could modify the 6922 SRPP by increasing the resistors on the worksheet some for the 6N1P, or simply use a 6922/6DJ8.
Jeff
If you look several posts back, toward the beginning of this thread I posted an SRPP 6922/6DJ8 Tube Cad worksheet for this amp. I have never tried it, I find the current arrangement sounds perfect. You could modify the 6922 SRPP by increasing the resistors on the worksheet some for the 6N1P, or simply use a 6922/6DJ8.
Jeff
thank you jim
i found it , i think i will try it
did you try out some simulation with the gu50??
kind regards ko
i found it , i think i will try it
did you try out some simulation with the gu50??
kind regards ko
An SRPP is not going to give more gain than the present input stage - probably less (as I see it in LtSpice).
Going two stage is one solution, or use a higher mu triode such as 12AT7.
or something a little more exotic like the German D3A or C3M, triode coupled.
or a pentode input stage such as EL84.
Svein.
Going two stage is one solution, or use a higher mu triode such as 12AT7.
or something a little more exotic like the German D3A or C3M, triode coupled.
or a pentode input stage such as EL84.
Svein.
thank you Svein
you saved me a lot of work 🙂
can you also see in this spice program what a gu 50 will do in the output stage , instead of the kt88? i heard some really good things about this tube and its so cheap , so i was thinking about trying it
grtz ko
you saved me a lot of work 🙂
can you also see in this spice program what a gu 50 will do in the output stage , instead of the kt88? i heard some really good things about this tube and its so cheap , so i was thinking about trying it
grtz ko
GU50 should work, but will require different tube sockets, 12.6V heater supply, and of course different cathode resistor or fixed bias supply.
It requires more drive voltage, at least 120V peak-peak in triode mode, compared to about 80V for the KT88. The 6N1P should be able to drive it, but increases the need for more gain in the input.
The easiest way to get more gain is to use another 6N1P stage before the driver. The same value anode and cathode resistors, but no cathode bypass cap.This will give you about 15x (23dB) more gain.
SB.
It requires more drive voltage, at least 120V peak-peak in triode mode, compared to about 80V for the KT88. The 6N1P should be able to drive it, but increases the need for more gain in the input.
The easiest way to get more gain is to use another 6N1P stage before the driver. The same value anode and cathode resistors, but no cathode bypass cap.This will give you about 15x (23dB) more gain.
SB.
Sorry for the typo last night. What I meant to say was 6CA7 fat bottle RCA's.
Does anyone have any favorite tubes they can tell about? Or possibly favorite tweaks?
I absolutely loved my JAN Philips 6SL7's but honestly the Sovtek 6SL7's (new stuff) sounded pretty darn good too. As far as output tubes I think I'm going to have to say the fat bottles are my fav's. I've also tried EL34EH's which were very cheap and surprised me how good they sounded. I also tried the Siemens EL34's with the dimple-top bottles, my 1st in this amp actually, and sounded very nice. Not as much bottom end as with the RCA and sounded better with a 5AR4 rather than the 5U4G that I usually use.
A
Does anyone have any favorite tubes they can tell about? Or possibly favorite tweaks?
I absolutely loved my JAN Philips 6SL7's but honestly the Sovtek 6SL7's (new stuff) sounded pretty darn good too. As far as output tubes I think I'm going to have to say the fat bottles are my fav's. I've also tried EL34EH's which were very cheap and surprised me how good they sounded. I also tried the Siemens EL34's with the dimple-top bottles, my 1st in this amp actually, and sounded very nice. Not as much bottom end as with the RCA and sounded better with a 5AR4 rather than the 5U4G that I usually use.
A
Here is a quote from "Kegger" on another site that explains the UL screen grid resistor selection.
That resistor can be thought of and or used in a few ways, it can be a "grid stopper"
which is needed on some tubes for preventing oscillation (needed often on tv tubes)
and it can be used to drop voltage as well which is what it's doing here.
When you look at the output tranny that has UL taps, follow the voltage coming into
the tranny and where the voltage goes to the plates, you see the UL tap is between
those two, well there is a certain resistance in those windings the farther the voltage
travels the more voltage will be lost/dropped, so the UL tap will have more voltage on
it then the Plate tap does.
The UL tap is connected to Screen/G2, "technically" you never want screens to have
more voltage on them then what the plate does so we use a resistor to drop some of
that voltage on the screen, the screens typically draw very little current so a decent
sized resistor is used to actually get some voltage to drop there.
I used the 1.2K for the UL tap connection and the voltages I measured were 397V on the KT88 plate and 396V on the UL screen grid of the KT88.
Hope this helps,
Scott
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Makes sense. Thanks again for your input scitizen, I always appreciate it. I will give it a try!
David,
If you are watching this forum now....I didn't call you back b/c I lost the number in my phone....accidentally erased it when I was going through some messages. I have been extremely busy at the hospital but that is coming to a close....please call me back in the next couple of days.
Jeff
If you are watching this forum now....I didn't call you back b/c I lost the number in my phone....accidentally erased it when I was going through some messages. I have been extremely busy at the hospital but that is coming to a close....please call me back in the next couple of days.
Jeff
D3a driver
Seel34,
I also did some planning for using a D3a. Not for this but for a SE 2A3 build. What I came up with was using a K&K Audio Basic CCS ($8 ea) set at 20mA for the plate load, a cathode resistor of between 75 and 82 ohms, a 1K grid stopper, and a 220uF bypass cap. I think this might just work on the GU50.
BTW, I recently added a CCS plate load to this KT88 for the 6N1P. It worked very well, a bit more gain and brightness. I ended up pulling them and returning it all to original b/c I needed the CCS for my 2A3 (I bought several at once but 1/2 of them I had to send back b/c the board was shorted, they have the problem fixed now though and I got the replacements recently). Now that I have enough to put a pair back into this build I may just do it again.....feeling lazy with tinkering on this one right now though, my new 300B JEL dx has all of my attention now.
Seel34,
I also did some planning for using a D3a. Not for this but for a SE 2A3 build. What I came up with was using a K&K Audio Basic CCS ($8 ea) set at 20mA for the plate load, a cathode resistor of between 75 and 82 ohms, a 1K grid stopper, and a 220uF bypass cap. I think this might just work on the GU50.
BTW, I recently added a CCS plate load to this KT88 for the 6N1P. It worked very well, a bit more gain and brightness. I ended up pulling them and returning it all to original b/c I needed the CCS for my 2A3 (I bought several at once but 1/2 of them I had to send back b/c the board was shorted, they have the problem fixed now though and I got the replacements recently). Now that I have enough to put a pair back into this build I may just do it again.....feeling lazy with tinkering on this one right now though, my new 300B JEL dx has all of my attention now.
thanks everybody for all the answers and good advice
made some changes yesterday
replaced the el34,s with sovtek kt88
i like the sound ,it handels my speakers with more ease
replaced the 5u4gb with a sovtek 5ar4
the b + went up with 43 volts to 415
the whole amp seems to be more powerfull ,better bass response
i think i leave it a few weeks like this ,to simply enjoy the music
instead of lissening for a better bass or crispyer high etc etc
i am queit satifyed with the sound at the moment
and the weather is getting better, so my old vintage vw baywindow bus [1976] is asking for maintaince [a lot of it] 🙂
greetings from a sunny amsterdam
ko
made some changes yesterday
replaced the el34,s with sovtek kt88
i like the sound ,it handels my speakers with more ease
replaced the 5u4gb with a sovtek 5ar4
the b + went up with 43 volts to 415
the whole amp seems to be more powerfull ,better bass response
i think i leave it a few weeks like this ,to simply enjoy the music
instead of lissening for a better bass or crispyer high etc etc
i am queit satifyed with the sound at the moment
and the weather is getting better, so my old vintage vw baywindow bus [1976] is asking for maintaince [a lot of it] 🙂
greetings from a sunny amsterdam
ko
thanks everybody for all the answers and good advice
made some changes yesterday
replaced the el34,s with sovtek kt88
i like the sound ,it handels my speakers with more ease
replaced the 5u4gb with a sovtek 5ar4
the b + went up with 43 volts to 415
the whole amp seems to be more powerfull ,better bass response
i think i leave it a few weeks like this ,to simply enjoy the music
instead of lissening for a better bass or crispyer high etc etc
i am queit satifyed with the sound at the moment
and the weather is getting better, so my old vintage vw baywindow bus [1976] is asking for maintaince [a lot of it] 🙂
greetings from a sunny amsterdam
ko
Yeah, getting that B+ up a little above 400V makes a big difference doesn't it? I too really like the KT88 tubes. Glad it's sounding great for you.
I have done some more experiments using CCS. The conclusion is that the original design is very optimized.
With a CCS and led I can bring the distortion of the driver from 1.3 % to 3 % at 10V swing, but the overall distortion of the amp increases slightly, compared to 47K resistor. Probably there is the distortion cancellation effect between the first and second stage that plays a role, as someone adviced.
To reduce overall distortion the only way I found is to decrease the cathode resistor of the KT88. From my calculations you can go down to 330-350 ohm and still be on the safe side. like this you will drain around 90 mA and still be inside the max plate dissipation.
I have to do some listening, tired of 1 KHz tone 🙂
Any comment ?
Davide
With a CCS and led I can bring the distortion of the driver from 1.3 % to 3 % at 10V swing, but the overall distortion of the amp increases slightly, compared to 47K resistor. Probably there is the distortion cancellation effect between the first and second stage that plays a role, as someone adviced.
To reduce overall distortion the only way I found is to decrease the cathode resistor of the KT88. From my calculations you can go down to 330-350 ohm and still be on the safe side. like this you will drain around 90 mA and still be inside the max plate dissipation.
I have to do some listening, tired of 1 KHz tone 🙂
Any comment ?
Davide
Edcor OPT
Hi all,
I am in process of building this amp but I got stuck in OPT.
Would it be sufficient to use GXPP15-8-5K from Edcor, considering it's a 15w transformer or I must go with CXSE25-8-5K ?
Thanks,
alex
Hi all,
I am in process of building this amp but I got stuck in OPT.
Would it be sufficient to use GXPP15-8-5K from Edcor, considering it's a 15w transformer or I must go with CXSE25-8-5K ?
Thanks,
alex
Thanks Tim.
Awesome amplifier you built here.
Just waiting for an answer, I browse 5u4-gb datasheet. What they say here is that you MUST NOT connect the tube directly to the transformer but to use a resistor so that the transformer resistive value +the additional resistor should be in the range of 170Ohms. I didn't buy the transformer yet as I was looking at Edcor XPWR033 or XPWR002 , tube 5u4-GB 33uF - 10H (Hammond 193J) 220uF. Could you please share your working schematic?
Thanks,
alex
Awesome amplifier you built here.
Just waiting for an answer, I browse 5u4-gb datasheet. What they say here is that you MUST NOT connect the tube directly to the transformer but to use a resistor so that the transformer resistive value +the additional resistor should be in the range of 170Ohms. I didn't buy the transformer yet as I was looking at Edcor XPWR033 or XPWR002 , tube 5u4-GB 33uF - 10H (Hammond 193J) 220uF. Could you please share your working schematic?
Thanks,
alex
Davide
I am building a SE with 6L6GC-STR in the finals (RH807 / Kegger used as base). What I am doing is putting a variable resistor in the cathodes of the output tubes. There are some very nice and small 12.5 Watt, 500 Ohm rheostat from Ohmite on eBay at this moment at a very reasonable price. After I got the first pair in I ordered this week a second pair just to have them for some future project.
At this moment there are over 10 available and shipping to New Zealand is USD 6.00.
( OHMITE 500 OHM 12.5 WATT RHEOSTAT - eBay (item 400092245495 end time May-15-10 18:07:40 PDT) )
This allows me to easily adjust the anode current for the "sweet spot".
AM
Alex
depending on voltage different transformer resistance values are required but also be carefull of not using a capacitor larger than specified. These values are required to prevent too large peak currents through the recitifier tube. Model the PSU in PSUD II (duncanamps.com), it takes only a short time to get familiar with the software and prevents a lot of troubles later on.
AM
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