Hey Chris, I have the 3.0, and have started modding it.
I noticed the extensive filtering. I checked voltages, as I am pondering placement of 4 (30uf, 400v) film caps in the unit, for PS bypass.
The B+, right at the tubes, is measuring an average of 50V? That's a bit freaky. Preamp sounds a little constricted, but otherwise..fine. I'm curious what those voltages are supposed to be. I'm getting like 250VDC on average on one side of the resistor..and between 50 and 32V on the other, right at the tube.
That don't seem right. I'm not that much of an engineer, and only a middling tech, and don't profess to know much abut tube circuits. Parts, molecular science, vibration, and issues surrounding parts positioning, use, placement, magnetics, etc, materials.etc, I do know that -like the back of my hand. What I'm saying is, I don't know if those voltages are supposed to be that low. The resistors, from the caps to the tubes is like..22k ohm, which seems a bit high, like someone replaced them and it should have been 2.2k instead. Someone read the value wrong or something. The voltage drop seems to be (to my tube circuit illiterate self) to be far too great.
I mean, there are some rails (at the orange caps) at 415V. And the preamp seems to not be using them. Very strange.
Anyway, a schematic would work quite well here. One with voltages.
Edit: Just read the 5.1 circuit at ys audio. The numbers are correct. Which just confuses the heck out of me. Why have such rails if you never use them.
I noticed the extensive filtering. I checked voltages, as I am pondering placement of 4 (30uf, 400v) film caps in the unit, for PS bypass.
The B+, right at the tubes, is measuring an average of 50V? That's a bit freaky. Preamp sounds a little constricted, but otherwise..fine. I'm curious what those voltages are supposed to be. I'm getting like 250VDC on average on one side of the resistor..and between 50 and 32V on the other, right at the tube.
That don't seem right. I'm not that much of an engineer, and only a middling tech, and don't profess to know much abut tube circuits. Parts, molecular science, vibration, and issues surrounding parts positioning, use, placement, magnetics, etc, materials.etc, I do know that -like the back of my hand. What I'm saying is, I don't know if those voltages are supposed to be that low. The resistors, from the caps to the tubes is like..22k ohm, which seems a bit high, like someone replaced them and it should have been 2.2k instead. Someone read the value wrong or something. The voltage drop seems to be (to my tube circuit illiterate self) to be far too great.
I mean, there are some rails (at the orange caps) at 415V. And the preamp seems to not be using them. Very strange.
Anyway, a schematic would work quite well here. One with voltages.
Edit: Just read the 5.1 circuit at ys audio. The numbers are correct. Which just confuses the heck out of me. Why have such rails if you never use them.
Leading Counterpoint Preamps astray
No problem Chris. As in: I'm being stupid and the preamp is fine. Once I figured out what was going on in the circuit, the light went on.
Now, what I'm looking to do, is to change the circuit so it can effectively use the 6CG7, instead of the 6DJ8. I dropped the 6CG7 into the circuit, like mikey's website says I can (counterpoint 3.0), and upped the capacitance on either end to 7.5uf, (I'm using the 5.1 schematic link at YS audio as a reference) but that was apparently a mistake. Too much rumble coming through, and overdriving the tube at the subsonic end of things, and also, the distortion characteristic is coming up too fast. Something is either starved, or overdriven.
I suspect the circuit is very similar to this 5.1 here, and casual looking seems to confirm this. There are obvious value changes that are minor but the general layout seems to be near identical, without the adjustability for the negative voltages that the 5.1 has. I very much suspect that the cure is largely in the way of being some minor adjsutments in capacitance and resistance, but I'm not sure what directions to move in and what to change. I can only suspect. Suggestions would be appreciated. I can hack my way to somethign that works, but will end up taking the preamp apart about 20 times, to get there. Best to start with some assistance that leads in the right direction, from the get go.
I very VERY much like what the 6CG7 does (sonically), in comparison to the wimpy assed and thin 6DJ8. (at least for the line out) In my estimation, the 6CG7 is far more dynamically 'natural', which sounds far more like 'music', comapred to the 6DJ8. I won't give that particular aspect up, as it is the one that makes music move you.
Any ideas?
No problem Chris. As in: I'm being stupid and the preamp is fine. Once I figured out what was going on in the circuit, the light went on.
Now, what I'm looking to do, is to change the circuit so it can effectively use the 6CG7, instead of the 6DJ8. I dropped the 6CG7 into the circuit, like mikey's website says I can (counterpoint 3.0), and upped the capacitance on either end to 7.5uf, (I'm using the 5.1 schematic link at YS audio as a reference) but that was apparently a mistake. Too much rumble coming through, and overdriving the tube at the subsonic end of things, and also, the distortion characteristic is coming up too fast. Something is either starved, or overdriven.
I suspect the circuit is very similar to this 5.1 here, and casual looking seems to confirm this. There are obvious value changes that are minor but the general layout seems to be near identical, without the adjustability for the negative voltages that the 5.1 has. I very much suspect that the cure is largely in the way of being some minor adjsutments in capacitance and resistance, but I'm not sure what directions to move in and what to change. I can only suspect. Suggestions would be appreciated. I can hack my way to somethign that works, but will end up taking the preamp apart about 20 times, to get there. Best to start with some assistance that leads in the right direction, from the get go.
I very VERY much like what the 6CG7 does (sonically), in comparison to the wimpy assed and thin 6DJ8. (at least for the line out) In my estimation, the 6CG7 is far more dynamically 'natural', which sounds far more like 'music', comapred to the 6DJ8. I won't give that particular aspect up, as it is the one that makes music move you.
Any ideas?
Hi KBK,
That's another one I'd have to sit down and look over. Normally with Counterpoint, as you start looking the design unravels and you end up fixing a whole host of problems. My work on the SA-100 certainly proved that. What started as a simple circuit change ended up being a revamp. There are still some things I'd like to do with it.
The 3.0 / 3.1 is another project I was interested in doing once I was happy with the SA-100. The SA-1000 is another. The SA-5000 may have gone to far to be corrected, the SA-9 has gone too far down the wrong road for an easy fix.
We'll have a peek if you want Ken. I do have a couple ideas floating around. It is possible there isn't enough B+ voltage, but we'll look at that too.
-Chris
That's another one I'd have to sit down and look over. Normally with Counterpoint, as you start looking the design unravels and you end up fixing a whole host of problems. My work on the SA-100 certainly proved that. What started as a simple circuit change ended up being a revamp. There are still some things I'd like to do with it.
The 3.0 / 3.1 is another project I was interested in doing once I was happy with the SA-100. The SA-1000 is another. The SA-5000 may have gone to far to be corrected, the SA-9 has gone too far down the wrong road for an easy fix.
We'll have a peek if you want Ken. I do have a couple ideas floating around. It is possible there isn't enough B+ voltage, but we'll look at that too.
-Chris
Found this, so far, concerning a swap on a Audible illusions preamp:
Since it's a one-tube circuit, using both halves of a 6922 according to your description, and since 6CG7s are relatively cheap as you say, why not just stick a 6CG7 into the circuit and take the same set of measurements? (Plus be sure to check the grid bias voltage, which you did not mention.) If I remember correctly, the 6CG7 has a higher plate resistance than does the 6922, so current and maybe also plate dissipation will go down, not up, meaning the 6CG7 is unlikely to be stressed. Then use those measurements in conjunction with a copy of the current vs plate voltage curves for a 6CG7 to finagle the 6CG7 into an acceptable operating point. You may have to change the plate and cathode resistor values, but that's no big deal, and if the cathode resistor value goes down significantly you may want to increase the value of the cathode bypass capacitor (to maintain adequate bass response). If the bias on the 6CG7 is found to be between -2V and -5V, you may need to do nothing at all.
This seems to be true, as the voltage went from about 45-50V with the 6DJ8 in there, to about 85-87V with the 6CG7. As you say, voltage issues? The voltage before that resistor, is a regulated 250 or so, IIRC.
Since it's a one-tube circuit, using both halves of a 6922 according to your description, and since 6CG7s are relatively cheap as you say, why not just stick a 6CG7 into the circuit and take the same set of measurements? (Plus be sure to check the grid bias voltage, which you did not mention.) If I remember correctly, the 6CG7 has a higher plate resistance than does the 6922, so current and maybe also plate dissipation will go down, not up, meaning the 6CG7 is unlikely to be stressed. Then use those measurements in conjunction with a copy of the current vs plate voltage curves for a 6CG7 to finagle the 6CG7 into an acceptable operating point. You may have to change the plate and cathode resistor values, but that's no big deal, and if the cathode resistor value goes down significantly you may want to increase the value of the cathode bypass capacitor (to maintain adequate bass response). If the bias on the 6CG7 is found to be between -2V and -5V, you may need to do nothing at all.
This seems to be true, as the voltage went from about 45-50V with the 6DJ8 in there, to about 85-87V with the 6CG7. As you say, voltage issues? The voltage before that resistor, is a regulated 250 or so, IIRC.
Hi Ken,
There is a little more to it.
You want to measure distortion and noise. It would be nice to find the proper operating point and gain some benefits to using a different tube rather than end up with something else with it's own problems.
That's one of the dangers to "tube rolling" and listening.
-Chris
There is a little more to it.
You want to measure distortion and noise. It would be nice to find the proper operating point and gain some benefits to using a different tube rather than end up with something else with it's own problems.
That's one of the dangers to "tube rolling" and listening.
-Chris
The thing I'm having a hard time finding, is a preamp cicuit of similar character and layout, that utilizes a 6CG7 tube. And, I don't know how closely the 5.1 circuit at YS Audio correleates to the 3.1 circuit. Dang. I'll have to break down and trace it out. One step at a time. Like, throwing the 6DJ8 back in the circuit and see how it behaves with the extra capacitance for signal pass. That should neatly cut the issue in half....SOP tech work. (I committed the sin conducting multiple experiments at one time, as I always seem to do 
)
My methods may be different, but the outcome will be the same. it WILL work. I do know how to use a scope (and there is one no further away from me than 5 feet, as I type - it hasn't been used in over 10 years), and measure things, but I find it to be more of an interesting challenge to do it my way. It's not that I prefer things to be more difficult than they need to be, but to be difficult enough to bother with attempting, and to enter and exit my skull in a way that works for me.
PS: I do also own the final version of the Black Sylvania Tube Tech Manual-complete with additions, RCA RC-30, and the "Tube Lore" book. (mint B&K Dyna-Jet 707, etc)
)My methods may be different, but the outcome will be the same. it WILL work. I do know how to use a scope (and there is one no further away from me than 5 feet, as I type - it hasn't been used in over 10 years), and measure things, but I find it to be more of an interesting challenge to do it my way. It's not that I prefer things to be more difficult than they need to be, but to be difficult enough to bother with attempting, and to enter and exit my skull in a way that works for me.
PS: I do also own the final version of the Black Sylvania Tube Tech Manual-complete with additions, RCA RC-30, and the "Tube Lore" book. (mint B&K Dyna-Jet 707, etc)
Chris,
Thank you very much for the offer. Repairing and restoration of old equipment, such as this Couterpoint, is my livelihood. Buying the manual from Michael E doesn't seem to be worth it for the reparing of one Counterpoint. I usually don't even attempt to repair anything without having the schematics first. In this case, one channel doesn't work so I can compare the signal to working channel, but this will be a long and painful process. That is why I was wondering if anyone had the schematics. Chris, will you be able to provide the schematics of the one component (when I find out which step-up cacade is not working) or is there a block diagram with the voltages?
Thank you,
Ra
Thank you very much for the offer. Repairing and restoration of old equipment, such as this Couterpoint, is my livelihood. Buying the manual from Michael E doesn't seem to be worth it for the reparing of one Counterpoint. I usually don't even attempt to repair anything without having the schematics first. In this case, one channel doesn't work so I can compare the signal to working channel, but this will be a long and painful process. That is why I was wondering if anyone had the schematics. Chris, will you be able to provide the schematics of the one component (when I find out which step-up cacade is not working) or is there a block diagram with the voltages?
Thank you,
Ra
Hi mr_ra,
You won't believe this, but the voltages are provided in a list on another page entirely from the diagrams. This was a pain under warranty, let me assure you!
This is a non-feedback tube amp. Just chase the signal. This kind of repair is dead easy. Also, may I suggest Electroharmonix 6922's if you need to replace a valve. If you're lucky you have Sovtek 6922's in there. They are reliable. If you see other tube numbers, check the heater current. If it's higher than a stock 6DJ8 / 6922, they have to go. No kidding.
There may be adjustments for gain and distortion trim, as well as DC offset. I haven't looked yet because I'm just starting to choose valves and do a total setup on an SA-5000. You think yours is hard to trace! I had an oscillating HV supply on this, input B+ was fine. The oscillation was like a squarewave on - off - on - off .... Got it solved but now it's retube and setup time. 3 hours easy on this, possibly longer if it get's silly.
Counterpoints are no fun, but I've serviced many. Therefore I still do them.
-Chris
You won't believe this, but the voltages are provided in a list on another page entirely from the diagrams.
This was a pain under warranty, let me assure you!This is a non-feedback tube amp. Just chase the signal. This kind of repair is dead easy. Also, may I suggest Electroharmonix 6922's if you need to replace a valve. If you're lucky you have Sovtek 6922's in there. They are reliable. If you see other tube numbers, check the heater current. If it's higher than a stock 6DJ8 / 6922, they have to go. No kidding.
There may be adjustments for gain and distortion trim, as well as DC offset. I haven't looked yet because I'm just starting to choose valves and do a total setup on an SA-5000. You think yours is hard to trace! I had an oscillating HV supply on this, input B+ was fine. The oscillation was like a squarewave on - off - on - off .... Got it solved but now it's retube and setup time. 3 hours easy on this, possibly longer if it get's silly.
Counterpoints are no fun, but I've serviced many. Therefore I still do them.
-Chris
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