Not ready
Hi Joe
Yes, I have fun!
Of course, I will tell you about the difference of both amps. But I am still playing/modifing this anode split version.
Yes, this is no problem with the ECC82, as you can find some very good working points with about 30V Ua in the datasheet!
I already tried many versions with the anode split amp. In fact, I began without cathode-C. This lowers the amplification factor due to local feedback but it raises the output impedance. This is an old story and I know it out of my tube bible, the 50 years old Otto Diciol, Röhren-NF Verstärker Praktikum, wich I could buy as reprint.
The impedance matching seems to be the biggest bottleneck in this configuration (and to much overall gain of course).
In fact, this version sounds very good, when I couple the chip direct to the anode, without a voltage split (in this case with an E80CC, a very fine tube, little more gain). But the amplification factor overall is to high and the zero gain version did not satisfy me, up to now.
We'll see.
Franz
Hi Joe
Yes, I have fun!
Of course, I will tell you about the difference of both amps. But I am still playing/modifing this anode split version.
Yes, this is no problem with the ECC82, as you can find some very good working points with about 30V Ua in the datasheet!
I already tried many versions with the anode split amp. In fact, I began without cathode-C. This lowers the amplification factor due to local feedback but it raises the output impedance. This is an old story and I know it out of my tube bible, the 50 years old Otto Diciol, Röhren-NF Verstärker Praktikum, wich I could buy as reprint.
The impedance matching seems to be the biggest bottleneck in this configuration (and to much overall gain of course).
In fact, this version sounds very good, when I couple the chip direct to the anode, without a voltage split (in this case with an E80CC, a very fine tube, little more gain). But the amplification factor overall is to high and the zero gain version did not satisfy me, up to now.
We'll see.
Franz
Finally, a great amp
Here it is, the results of my experiments: a so called unity gain solution.
But: in fact there is no unity gain, it is a simple voltage splitter in front of the LM3875 and it works with a gain of 10.
I am very happy with the result now.
Here the schematics, I will ad an excel sheet to play with this circuit.
Franz
Here it is, the results of my experiments: a so called unity gain solution.
But: in fact there is no unity gain, it is a simple voltage splitter in front of the LM3875 and it works with a gain of 10.
I am very happy with the result now.
Here the schematics, I will ad an excel sheet to play with this circuit.
Franz
Attachments
Excel sheet to play with this circuit
Here is the excel sheet.
You can change the values of R1, R2 and R3, the other four values are automatically calculated.
Franz
P.S.
Maybe, the calculation for the signal gain is not correct, I just remark. I will correct this later.
Here is the excel sheet.
You can change the values of R1, R2 and R3, the other four values are automatically calculated.
Franz
P.S.
Maybe, the calculation for the signal gain is not correct, I just remark. I will correct this later.
corrected now
I corrected the formulas for the gain and I hope, they are correct now.
No responsibility!
Franz
I corrected the formulas for the gain and I hope, they are correct now.
No responsibility!
Franz
Now it is a usable model, this excel sheet
I changed my mind as I was completely wrong in my last 3 postings.
Thorsten and Hans-Peter showed me, how it works. Thanks and sorry folks!
Here is the new excel sheet, allowing to change different values for other tubes or other resistance values.
Franz
I changed my mind as I was completely wrong in my last 3 postings.
Thorsten and Hans-Peter showed me, how it works. Thanks and sorry folks!
Here is the new excel sheet, allowing to change different values for other tubes or other resistance values.
Franz
I´m ready to start my amp , but I need some help: I have some tubes here ( E80CC , E88CC , E182CC ) , always seen VBGC projects with e88cc , but wich one are the best for gc , the e88cc or the e80cc ?
Thanks
Thanks
My two cents
The E88CC is very suitable for the cathode follower version, e.g. no gain in the tube buffer.
For the unity gain solution (my excel sheet) is the E80CC the better solution, because with the E88CC the Ug- (Uk) is not sufficient.
For full power with an E80CC you should add a little gain at the power stage (R2=470k).
Don't know about the E182CC. Maybe suitable for the cathode follower.
Franz
The E88CC is very suitable for the cathode follower version, e.g. no gain in the tube buffer.
For the unity gain solution (my excel sheet) is the E80CC the better solution, because with the E88CC the Ug- (Uk) is not sufficient.
For full power with an E80CC you should add a little gain at the power stage (R2=470k).
Don't know about the E182CC. Maybe suitable for the cathode follower.
Franz
Turn on Noise
Hi,
I used to have a Conrad Johnson PV3 tube preamp that I used with a Hafler DH220 mosfet amp. I enjoyed the combo but it had one issue. If I did not wait to turn on the amp until the preamp had warmed for about 30 seconds it would fry my woofers ...literally.
How are you guys getting around the DC that seems to get by the output cap when the tube stage warms up. I would expect to see a delay relay on the outputs...
Best,
Paul
Hi,
I used to have a Conrad Johnson PV3 tube preamp that I used with a Hafler DH220 mosfet amp. I enjoyed the combo but it had one issue. If I did not wait to turn on the amp until the preamp had warmed for about 30 seconds it would fry my woofers ...literally.
How are you guys getting around the DC that seems to get by the output cap when the tube stage warms up. I would expect to see a delay relay on the outputs...
Best,
Paul
Hi,
It is quite normal practice to leave the mute in on position during warm up.
There should also be a bleeder resistor behind the output coupling cap to prevent DC build-up on the output of the preamp.
If this is the case and the problem persists it is not unthinkable that the cap is faulty and passes DC to the amp...
This in turn could explain the DC on the woofers as well.
Cheers,😉
It is quite normal practice to leave the mute in on position during warm up.
There should also be a bleeder resistor behind the output coupling cap to prevent DC build-up on the output of the preamp.
If this is the case and the problem persists it is not unthinkable that the cap is faulty and passes DC to the amp...
This in turn could explain the DC on the woofers as well.
Cheers,😉
Solution one. Timer circuit to power up power amp section after tube buffer is warmed up.
Solution two. Something like a Velleman 4700 to disconnect speakers until after buffer has warmed up.
We like our woofers! 😉
Nuuk said:
Thanks Nuuk. Since I am just finishing my GC in a very tight case I will need to look at muting for the preamp or tubed DAC... not sure which I favor yet. Perhaps the Velleman circuit will work with the line level outputs of the Scott Nixon DAC I am looking at. Time to break out all of those old issues of Audio Amateur...
So many circuits, so little time🙂
The Velleman unit is connected so that the output from the power amp goes to the module. The speakers are also connected to the module which then connects the two via a relay which is open until the valve buffer has warmed up and DC offset has settled down.
You can mount the Velleman module inside the amp or outside in it's own case. It's mains connections must be connected to the supply for your amp so that it is powered up at the same time.
The module also needs modifying as I have described here . 😉
Hi, I'm resurrecting this thread simply because it seems the most obvious place to convey news about the Sovtek 6922 valve that Joe recommends. (Sorry if it belongs on the Tube forum, but I'm building Joe's VBIGC...)
I have just heard that Sovtek has discontinued the 6922, replacing it with 6DJ8W, supposedly with identical specs. (Question: if it has the same specs, why change the part number??) The replacement is only about 10% higher in cost to the 6922.
However, my supplier recommends the EI Elite Gold 6DJ8EG instead, claiming that it is sonically superior to the 6922. Any comments on this?? I have to make a choice now. I've been waiting for a month or more for delivery on the 6922, only to hear that they are obsolete...
🙁
I have just heard that Sovtek has discontinued the 6922, replacing it with 6DJ8W, supposedly with identical specs. (Question: if it has the same specs, why change the part number??) The replacement is only about 10% higher in cost to the 6922.
However, my supplier recommends the EI Elite Gold 6DJ8EG instead, claiming that it is sonically superior to the 6922. Any comments on this?? I have to make a choice now. I've been waiting for a month or more for delivery on the 6922, only to hear that they are obsolete...
🙁
I cannot comment on that particular valve, but if it helps, I'm using Electro Harmonics 6922. I've compared them to Telefunken6922 and must say are sonically identical in the VBIGC 😉
regards,
will.
regards,
will.
falcott said:
The Sovtek 6922 was/is a relabeld 6H23pi ... alternative tubes to look at are the 6H30pi and i've been told the hot ticket is now the ECC99 (these aren't just drop in replacements thou -- they probably need different boas and perhaps more B+ (a good idea anyway).
dave
falcott said:
It should work just fine. The tube buffer that I conceived is extremely tube tolerant - something very intentional from the outset as I wanted it to be very attractive project for non-tube DIY'ourselfers. The 10K resistor sets the current almost irrespective of tube choice and the split rail +/- supplies means DC coupling of the input (no input caps). This makes the tube self-biasing.
So a variety of tubes can be used provided they are of the 6DJ8/ECC88 family. These are frame grid types (resulting in high transconductance) and useable at much lower voltages than usual triodes. There are re-numbered Soviet tubes that fits this bill as well, some of them so close to 6922 (also of the 6DJ8 family) that they are labelled as such.
One final thing to keep in mind: They don't all sound the same. I have used some Old Stock Mullard PCC88 in the JLTi and prefer them quite markedly to the Sovtek 6922 variants. But alas, they are not available new, but I wish somebody would resurrect them and renew manufacturing
Joe R.
Hi,
Yep...Unfortunately the ECC88/PCC88 are so often used that NOS prices have shot through the roof.
Yet, the Ei ECC88 series are as close to the NOS quality as you can get provided Ei has done the QC which isn't always the case.
For info, Ei is a Philips licensee manufacturing their tubes using the old Telefunken machines. On paper that gives them a substantial headstart over the competition, they only need some convincing on putting in the effort....
Other excellent current production is being made by the folks at JJ/TESLA:
JJ/TESLA
For the CF you want a high transconductance tube and that's exactly what the ECC88 and family are, making them an excellent choice for this particular application among a raft of others.
As for Sovtek, well I don't see any reason for them to change the nomenclature of the already renamed 6H23-Pi...
With the current demand on that type of tube I feel this would be a rather bad move on their part . More so as there are other plants besides Reflector in the former USSR that are perfectly capable of producing the 6H23-Pi should Sovtek throw in the towel on that tube.
Also beware that there are countless 6H1-Ps floating around that are rebranded as ECC88/6DJ8; they're not true equivalents even if these "work" in numerous applications as such.
Fortunately these are very easy to recognise as these have wing-type plates (looks like a V) contrary to the folded type the ECC88s and most other RF tubes for cascode service have.
For an overview of ECC88s and peoples expeirence with them you can wade through this listing:
ECC88 AND MUTANTS....
Cheers,😉
Yep...Unfortunately the ECC88/PCC88 are so often used that NOS prices have shot through the roof.
Yet, the Ei ECC88 series are as close to the NOS quality as you can get provided Ei has done the QC which isn't always the case.
For info, Ei is a Philips licensee manufacturing their tubes using the old Telefunken machines. On paper that gives them a substantial headstart over the competition, they only need some convincing on putting in the effort....
Other excellent current production is being made by the folks at JJ/TESLA:
JJ/TESLA
For the CF you want a high transconductance tube and that's exactly what the ECC88 and family are, making them an excellent choice for this particular application among a raft of others.
As for Sovtek, well I don't see any reason for them to change the nomenclature of the already renamed 6H23-Pi...
With the current demand on that type of tube I feel this would be a rather bad move on their part . More so as there are other plants besides Reflector in the former USSR that are perfectly capable of producing the 6H23-Pi should Sovtek throw in the towel on that tube.
Also beware that there are countless 6H1-Ps floating around that are rebranded as ECC88/6DJ8; they're not true equivalents even if these "work" in numerous applications as such.
Fortunately these are very easy to recognise as these have wing-type plates (looks like a V) contrary to the folded type the ECC88s and most other RF tubes for cascode service have.
For an overview of ECC88s and peoples expeirence with them you can wade through this listing:
ECC88 AND MUTANTS....
Cheers,😉
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