Future plan for 300B XLS amp
- andrew Ivimey
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#182
who hasn't ! and some 6N6Ps I have some where that were advertised as being special for some reason ... then there are ECC99s. I could dig out some of those too
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
- Paul Barker
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#183
I don't have any
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
- IslandPink
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#184
I might buy a few old-ish 6N6P's for the phono , yes. Currently I'm not using any, anywhere in my amp or phono, but the LCR phono will use some.
ECC99's I used in the Aurora and didn't like - moved to 5687, then 6N6P .
On the 4P1L's, just tried another one in the left channel . It started ringing at roughly the same frequency as the other one, after about 10 minutes !
Then I got out another one, put that in, and it has been fine over about an hour of playing . Fingers crossed !
With this one in, it's sounding really nice, should be good at the meeting. I have a couple of demo records in mind to bring, now .
I have a load of Dave Elson's valves I should bag-up and bring to Owston . I have been secretly getting a few for myself , Nick , Len etc, but there are lots left .
ECC99's I used in the Aurora and didn't like - moved to 5687, then 6N6P .
On the 4P1L's, just tried another one in the left channel . It started ringing at roughly the same frequency as the other one, after about 10 minutes !
Then I got out another one, put that in, and it has been fine over about an hour of playing . Fingers crossed !
With this one in, it's sounding really nice, should be good at the meeting. I have a couple of demo records in mind to bring, now .
I have a load of Dave Elson's valves I should bag-up and bring to Owston . I have been secretly getting a few for myself , Nick , Len etc, but there are lots left .
"Once you find out ... the Circumstances ; then you can go out"
- andrew Ivimey
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#185
sfunny, I didn't like ECC99s (-> Amity) and concluded that perhaps I wasn't doing them right. When Max waltzed along with his own version of a balanced push pull amp (300b) being driven by 5687s I went out and bought some!
Relatively imho 6N6Ps sound er, 'dark' but I am halfway through a build to use them to drive GM70SE.
Relatively imho 6N6Ps sound er, 'dark' but I am halfway through a build to use them to drive GM70SE.
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
- IslandPink
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#186
I tend to think that the 'good' 6N6P's are 'not bright' , ie. correct !
I'll bring a roll of mu-metal, and build a wall around my amp, just in case .Paul Barker wrote:Bet you're glad you didn't use these Cisco power supplies. Bad enough having an oscilator in the amp....
We'd better not have our amps too close together, yours will detect all the RF in my power supply!
"Once you find out ... the Circumstances ; then you can go out"
- IslandPink
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#187
Still messing about with filament supplies here.
Gone back to the V-reg supplies for the 4P1L's after using the Rod Coleman ones for a while.
The 'floaty' spacious feel, realism, and great upper midrange are there again , which none of the current-reg supplies could quite give. I think it's a lot to do with the elusive 'low-level detail' .
I also tried ( along the way ) and reported to the guys ( on e-mail ) that if I swapped out the Guido Tent current-reg supply for the 300B in favour of a Thorsten Loesch ( design) passive supply, as per the 'WE91B' amp and 'Ladyday' mods ; basically Rect>R>C>L>C>CMC ; then I got more 'space' and realism, at the expense of less focus and extension in the bass. Similar to the V-reg vs. I-reg supplies applied to the 4P1L really .
So, there are more options to try, which we have been discussing . The key one is to try the V-reg supply and take the cathode connection off a virtual centre-tap , NOT one end of the filament supply . I will do that one tomorrow or Wednesday .
This seems to be really crucial, the difference between getting it right and not right is really significant , and not always apparent immediately .
Gone back to the V-reg supplies for the 4P1L's after using the Rod Coleman ones for a while.
The 'floaty' spacious feel, realism, and great upper midrange are there again , which none of the current-reg supplies could quite give. I think it's a lot to do with the elusive 'low-level detail' .
I also tried ( along the way ) and reported to the guys ( on e-mail ) that if I swapped out the Guido Tent current-reg supply for the 300B in favour of a Thorsten Loesch ( design) passive supply, as per the 'WE91B' amp and 'Ladyday' mods ; basically Rect>R>C>L>C>CMC ; then I got more 'space' and realism, at the expense of less focus and extension in the bass. Similar to the V-reg vs. I-reg supplies applied to the 4P1L really .
So, there are more options to try, which we have been discussing . The key one is to try the V-reg supply and take the cathode connection off a virtual centre-tap , NOT one end of the filament supply . I will do that one tomorrow or Wednesday .
This seems to be really crucial, the difference between getting it right and not right is really significant , and not always apparent immediately .
"Once you find out ... the Circumstances ; then you can go out"
- IslandPink
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#188
Just done a modification ( voltage divider off B+ ) to provide a small adjustable voltage to the suppressors ( G3 ) on the 4P1L valves, to evaluate the sound of moving G3 up slightly :
http://www.audio-talk.co.uk/phpBB2/view ... 3&start=45
Unfortunately after laboriously connecting up everything and switching on , I have no glow on the right-channel VR tube. Something must have gone wrong in the rat's nest once I put the driver board right side up and connected all the wires.
I will say the good (left) channel sounded a bit sweeter on the one track I played , but it's early days, and I've got to go under the hood again later this afternoon . Damn !
http://www.audio-talk.co.uk/phpBB2/view ... 3&start=45
Unfortunately after laboriously connecting up everything and switching on , I have no glow on the right-channel VR tube. Something must have gone wrong in the rat's nest once I put the driver board right side up and connected all the wires.
I will say the good (left) channel sounded a bit sweeter on the one track I played , but it's early days, and I've got to go under the hood again later this afternoon . Damn !
"Once you find out ... the Circumstances ; then you can go out"
- IslandPink
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#190
Ah, I saved myself some work by swapping another OA2 into that socket - bingo, it lit Whether it's a failing OA2 or a difference in how thing 'strikes' caused somehow by the G3 being altered, I'm not sure.
Anyway , have done some listening . I would say there's a small but useful improvement in tone on vocals and some instruments. There might be a slight loss of detail too - maybe that is also a result of taking out a little 3rd-harmonic . On the other hand , there was a slight loss of detail when I did the virtual centre-tap mod on the filament supply for the left channel , so maybe I'm still hearing that .
I need to do more listening obviously . Things are becoming a bit confusing at times, and it hasn't helped that there's an earthing problem ( probably crappy RCA sockets on the input ) from the phono causing intermittent hum .
Currently I should have about G3 at +10 or +11V above cathode.
I will check this, then try +15V too .
Anyway , have done some listening . I would say there's a small but useful improvement in tone on vocals and some instruments. There might be a slight loss of detail too - maybe that is also a result of taking out a little 3rd-harmonic . On the other hand , there was a slight loss of detail when I did the virtual centre-tap mod on the filament supply for the left channel , so maybe I'm still hearing that .
I need to do more listening obviously . Things are becoming a bit confusing at times, and it hasn't helped that there's an earthing problem ( probably crappy RCA sockets on the input ) from the phono causing intermittent hum .
Currently I should have about G3 at +10 or +11V above cathode.
I will check this, then try +15V too .
"Once you find out ... the Circumstances ; then you can go out"
- Paul Barker
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#191
You are of course playing with the Timbre in the driver by changing the distortion profile which means best looking curves may not sound best.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
- IslandPink
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#192
Well yes, but from the LTSpice sims, I think the main thing you get from the soft bend is a bit of third harmonic. From the basic pentode curves ( straight, but bunching-up towards the bottom ) you get 2nd-harmonic, which I'm less bothered about, and in fact I believe you need some of that in an amp .
What the G3 mod should do is allow me to more or less tune out the H3 without much affecting the H2 .
All I'm doing effectively is straightening-out the pentode curves of the 4P1L a bit, so it looks more like a C3m, or a 2E24 ( which I haven't tried ) . I felt I'd lost a bit tonally in going from the C3m to the 4P1L, which I didn't initially expect . I think this may be the explanation now.
Anyway, just been measuring the G3, and despite my simple-minded voltage divider calc ( to give about 20V on G3 ) I'm actually testing about 11V , with 9V on the cathode . No wonder the effect was subtle !
So, I'm guessing there must be appreciable current out of the G3 which is affecting the DC bias point .
I just twiddled the carbon pot on there a fair bit, to get me a higher voltage, but I've only got to about 12V now, ie. +3V rel to cathode.
It does sound very nice though - worth pursuing .
What I need to do next is increase the flow through this divider a bit . I've only got ~1mA through it ( & supplying 2x G3's ) so I probably need to get some lower resistors ( power ones , for the voltage ) . I currently have 2x 200K , then a 50K pot set to ~20K . Need a pair of 100K's or lower . Another rummage in the box then .
What the G3 mod should do is allow me to more or less tune out the H3 without much affecting the H2 .
All I'm doing effectively is straightening-out the pentode curves of the 4P1L a bit, so it looks more like a C3m, or a 2E24 ( which I haven't tried ) . I felt I'd lost a bit tonally in going from the C3m to the 4P1L, which I didn't initially expect . I think this may be the explanation now.
Anyway, just been measuring the G3, and despite my simple-minded voltage divider calc ( to give about 20V on G3 ) I'm actually testing about 11V , with 9V on the cathode . No wonder the effect was subtle !
So, I'm guessing there must be appreciable current out of the G3 which is affecting the DC bias point .
I just twiddled the carbon pot on there a fair bit, to get me a higher voltage, but I've only got to about 12V now, ie. +3V rel to cathode.
It does sound very nice though - worth pursuing .
What I need to do next is increase the flow through this divider a bit . I've only got ~1mA through it ( & supplying 2x G3's ) so I probably need to get some lower resistors ( power ones , for the voltage ) . I currently have 2x 200K , then a 50K pot set to ~20K . Need a pair of 100K's or lower . Another rummage in the box then .
"Once you find out ... the Circumstances ; then you can go out"
- IslandPink
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#193
Actually, thinking about this more ; it's an ideal application for a small 9V battery to supply G3 relative to cathode. No current drawn when it's off.
The voltage divider at present is non-ideal in several ways -
1. Not the right voltage ( yet )
2. Not 'stiff' enough
3. Referenced to ground, not cathode.
In fact at present with G3 3V over the cathode at nominal, the cathode may go above G3 at times . Certainly the potential between k and G3 is very variable. I think this explains some loss of dynamics and bass focus I can hear as well .
However, it's worth the effort as the tone is very nice.
I will have a look on RS for small 9V batteries, need a few odds and ends currently .... or Rapid .
The voltage divider at present is non-ideal in several ways -
1. Not the right voltage ( yet )
2. Not 'stiff' enough
3. Referenced to ground, not cathode.
In fact at present with G3 3V over the cathode at nominal, the cathode may go above G3 at times . Certainly the potential between k and G3 is very variable. I think this explains some loss of dynamics and bass focus I can hear as well .
However, it's worth the effort as the tone is very nice.
I will have a look on RS for small 9V batteries, need a few odds and ends currently .... or Rapid .
"Once you find out ... the Circumstances ; then you can go out"
#194
Agree that G3 needs to be referenced to the cathode - I've been looking for typical G3 currents when held positive to the cathode but I haven't found anything yet. Certainly some current must flow but it would be nice to know if its 1mA or 10mA or more!!!
J
J
#195
Okay,G3 will draw little current at these sorts of voltage - typically less than 1mA.
Besides straightening the anode curves it also ups the valves transconductance but typically by 10-15%..
And it reduces g2 current draw - not sure by how much but significantly enough if using a resistor divider on g2 to move the op point - should be OK with the VR setup on g2...
Its also been used on the SV83 and by Decware on the EL34...
J
Besides straightening the anode curves it also ups the valves transconductance but typically by 10-15%..
And it reduces g2 current draw - not sure by how much but significantly enough if using a resistor divider on g2 to move the op point - should be OK with the VR setup on g2...
Its also been used on the SV83 and by Decware on the EL34...
J