TUBE ROLLERS
When designing amps, I always try to make it simple in all ways... including the choice of tubes. For instance, the ECC81 is a tube that I somehow believe everyone has at hand, or could find for petty cash.
On the other hand, whenever DIYers see a schematics, sometimes even without trying it first, they consider whether they could change the tube for another.
While the amps are simple, and this one is the simplest to date
the choice of tubes should be respected. While KT88 and 6550 are basically the same and for the purpose of this amp it does not really matter which one you use (or KT90 for that matter) - the ECC81 is the driver tube which is closely connected with the functioning of the circuit itself. Not only will you have less gain deploying some other type of tube, but you will also have less or more of some other products.
In the first generation there were very few tubes that could work in a circuit replacing the driver, and this second generation adds more possibility.
The ECC81 in my designs can generally be replaced with E180CC (5963, if I am not misspelling it) and very few other tubes (the EF86 in triode mode is a "lucky shot" which basically has the adequate characteristics for the job).
When it comes to the RH88, the ECC81 can be replaced with various mu 20 tubes like the ECC82 (which I have done and found very nice, since the amp gets a laid back character), also applicable should be a 6SN7 with similar results but octal socket and larger size. On the other hand, the 6SL7 (12SL7) is not that suitable, since the transconductance of this tube is very low. It might work, but the results are poor (have not simulated that for a long time, so I cannot say how poor).
For those "eager" just to add that I did a design employing the ECC88 (in any form, of course) for those who like this a little extreme tube.
Regards,
Alex
PS
Still not finding the time, sorry... will revert to all emailers
When designing amps, I always try to make it simple in all ways... including the choice of tubes. For instance, the ECC81 is a tube that I somehow believe everyone has at hand, or could find for petty cash.
On the other hand, whenever DIYers see a schematics, sometimes even without trying it first, they consider whether they could change the tube for another.
While the amps are simple, and this one is the simplest to date
the choice of tubes should be respected. While KT88 and 6550 are basically the same and for the purpose of this amp it does not really matter which one you use (or KT90 for that matter) - the ECC81 is the driver tube which is closely connected with the functioning of the circuit itself. Not only will you have less gain deploying some other type of tube, but you will also have less or more of some other products.In the first generation there were very few tubes that could work in a circuit replacing the driver, and this second generation adds more possibility.
The ECC81 in my designs can generally be replaced with E180CC (5963, if I am not misspelling it) and very few other tubes (the EF86 in triode mode is a "lucky shot" which basically has the adequate characteristics for the job).
When it comes to the RH88, the ECC81 can be replaced with various mu 20 tubes like the ECC82 (which I have done and found very nice, since the amp gets a laid back character), also applicable should be a 6SN7 with similar results but octal socket and larger size. On the other hand, the 6SL7 (12SL7) is not that suitable, since the transconductance of this tube is very low. It might work, but the results are poor (have not simulated that for a long time, so I cannot say how poor).
For those "eager" just to add that I did a design employing the ECC88 (in any form, of course) for those who like this a little extreme tube.
Regards,
Alex
PS
Still not finding the time, sorry... will revert to all emailers
ANY NEWS FROM DIYERS?
Well, in the meantime I have found the time to send the RH88 schematics to most interested (sorry if I have ommitted someone).
But I do not see many comments, and for a long time. Is it possible that everyone is waiting for the RH300B?
The RH300B is there as a concept, but the general idea was to avoid expensive tubes
Come on, I would like to hear your comments if anyone has made the amp so far!
Regards,
Alex
Well, in the meantime I have found the time to send the RH88 schematics to most interested (sorry if I have ommitted someone).
But I do not see many comments, and for a long time. Is it possible that everyone is waiting for the RH300B?
The RH300B is there as a concept, but the general idea was to avoid expensive tubes
Come on, I would like to hear your comments if anyone has made the amp so far!
Regards,
Alex
Re: ANY NEWS FROM DIYERS?
See my previous post - I plan on using these Grundig transformers to build the RH84.
The RH300B is next - would appreciate a schematic so I can start buying parts. To avoid expensive tubes, could it be used with 2A3s as well?
Thank you for ypur designs and all your hard work.
Alex Kitic said:Well, in the meantime I have found the time to send the RH88 schematics to most interested (sorry if I have ommitted someone).
But I do not see many comments, and for a long time. Is it possible that everyone is waiting for the RH300B?
The RH300B is there as a concept, but the general idea was to avoid expensive tubes
Come on, I would like to hear your comments if anyone has made the amp so far!
Regards,
Alex
See my previous post - I plan on using these Grundig transformers to build the RH84.
The RH300B is next - would appreciate a schematic so I can start buying parts. To avoid expensive tubes, could it be used with 2A3s as well?
Thank you for ypur designs and all your hard work.
rh88
Alex, I was one of those who requested the '88 schematic. I haven't built it yet, I have built two 84's, one with lundahl outputs, the other with one-electron output. Both are good sounding amps. I have been kicking about the idea of using 7591 outputs instead of kt88, as I have a few, and the drive requirements are basically the same as the el84, so the driver stage could probably be used with minor modifications. It will probably be sometime this summer before I build, but I will post the results.
Alex, I was one of those who requested the '88 schematic. I haven't built it yet, I have built two 84's, one with lundahl outputs, the other with one-electron output. Both are good sounding amps. I have been kicking about the idea of using 7591 outputs instead of kt88, as I have a few, and the drive requirements are basically the same as the el84, so the driver stage could probably be used with minor modifications. It will probably be sometime this summer before I build, but I will post the results.
QUICK REPLY, OTHER TUBES
Just a quick reply while I'm online, about other tubes and other alternatives.
1) It might work with a 2A3, but in some completely different form. Maybe a "third generation" in the future: the reason I did not do that one although I actually use a 6B4G amp of very classic design (driver 6SN7 + output, no feedback whatsoever, excellent choke loaded PSU) is the fact that the power is so little that it does not make a lot of sense improving. The second generation idea was mainly to achieve more power and compete with the 15W league, i.e. 211 and 845 -- and of course win in comparison with the various 300B designs (the tube that everyone loves so much... but why, except for the 8-9W promise of golden sound?).
2) Other tubes in the RH88 -- 6550 and KT90 are almost identical, so it is just a matter of choice and availability. As previously mentioned, I built mine actually with nicely shaped RCA 6550s and do not own any KT88s (but since the sub is the same and the name is shorter, I prefer to call it RH88). An alternative is to use the 8417 with a little care given to the slightly different current handling (and other) characteristics, but quite easilty feasible without important modifications (basically, to take care of the max anode dissipation). The 7519 has a much lower max anode dissipation and quite a different sub i.e. model, therefore that might be a new amp completely... you can try with that one based on the RH88 principle schematics, but be careful and aware that without simulation or calculus it will be a trial and error affair.
Regards to all... the RH300B official schematics coming soon for all those who want to rewire their amps and those who want to spend big bucks on tubes
Just a quick reply while I'm online, about other tubes and other alternatives.
1) It might work with a 2A3, but in some completely different form. Maybe a "third generation" in the future: the reason I did not do that one although I actually use a 6B4G amp of very classic design (driver 6SN7 + output, no feedback whatsoever, excellent choke loaded PSU) is the fact that the power is so little that it does not make a lot of sense improving. The second generation idea was mainly to achieve more power and compete with the 15W league, i.e. 211 and 845 -- and of course win in comparison with the various 300B designs (the tube that everyone loves so much... but why, except for the 8-9W promise of golden sound?).
2) Other tubes in the RH88 -- 6550 and KT90 are almost identical, so it is just a matter of choice and availability. As previously mentioned, I built mine actually with nicely shaped RCA 6550s and do not own any KT88s (but since the sub is the same and the name is shorter, I prefer to call it RH88). An alternative is to use the 8417 with a little care given to the slightly different current handling (and other) characteristics, but quite easilty feasible without important modifications (basically, to take care of the max anode dissipation). The 7519 has a much lower max anode dissipation and quite a different sub i.e. model, therefore that might be a new amp completely... you can try with that one based on the RH88 principle schematics, but be careful and aware that without simulation or calculus it will be a trial and error affair.
Regards to all... the RH300B official schematics coming soon for all those who want to rewire their amps and those who want to spend big bucks on tubes
next generation ?
In another thread mr. Kitic sounded somewhat frustrated
about the lack of recognition he got for the RH84 design that also could be used in a PP setup (but people did not try that).
I built a SE 6N1P/el84 version (will try 6N2p later) with 0A2 regulator tube (150V) on the screens of the el84. I will clearly state here that it sounds outstanding (on a small 50 year old OPT) and it is obvious that it would be tough to find a better alternative soundwize for the same money. That said I think I will experiment further to stretch the concept. I have a old Philips tube radio (b5x14a, from the sixties or seventies) that uses the El84 and 800 ohm speakers. They use a device that is either a choke or a OPT to transform to 800 ohm. I wonder if that device can be used as a interstage coupler to a powertube like 300B or similar. Nice to try in the future.
By the way, is EI still making el84 tubes ?
In another thread mr. Kitic sounded somewhat frustrated
about the lack of recognition he got for the RH84 design that also could be used in a PP setup (but people did not try that).I built a SE 6N1P/el84 version (will try 6N2p later) with 0A2 regulator tube (150V) on the screens of the el84. I will clearly state here that it sounds outstanding (on a small 50 year old OPT) and it is obvious that it would be tough to find a better alternative soundwize for the same money. That said I think I will experiment further to stretch the concept. I have a old Philips tube radio (b5x14a, from the sixties or seventies) that uses the El84 and 800 ohm speakers. They use a device that is either a choke or a OPT to transform to 800 ohm. I wonder if that device can be used as a interstage coupler to a powertube like 300B or similar. Nice to try in the future.
By the way, is EI still making el84 tubes ?
Attachments
Here is the post by DHTrob on the 5k to 800R output transformers used as interstages.
http://www.dhtrob.com/blog/index.php?pg=3
he comments that the units are flat from 20Hz to 20kHz, but one should note that he probably tested this at 2VRMS out, while a 300B will need much more swing (and therefore bandwith may become smaller/worse).
http://www.dhtrob.com/blog/index.php?pg=3
he comments that the units are flat from 20Hz to 20kHz, but one should note that he probably tested this at 2VRMS out, while a 300B will need much more swing (and therefore bandwith may become smaller/worse).
Rh And Pp And Frustration
If I sounded frustrated, it was about the fact that no one seems to be listening (reading) or thinking about what they are writing (speaking) about. And, quite a bunch of armchair diyers with propensity towards endless shooting of new ideas without rethinking the old ones. Just writing for the sake of writing.
The most common mistake is that people start with inexpensive tubes and compelement them with inexpensive parts and then whine about the fact that expensive tubes with expensive parts might actually sound better. Well, while you can always use transformers from old radio receivers, it would obviously sound better with Lundahl, or Tango, or Tamura... and the same inexpensive tubes. It depends on how much do you want to spend.
Regards,
Alex
If I sounded frustrated, it was about the fact that no one seems to be listening (reading) or thinking about what they are writing (speaking) about. And, quite a bunch of armchair diyers with propensity towards endless shooting of new ideas without rethinking the old ones. Just writing for the sake of writing.
The most common mistake is that people start with inexpensive tubes and compelement them with inexpensive parts and then whine about the fact that expensive tubes with expensive parts might actually sound better. Well, while you can always use transformers from old radio receivers, it would obviously sound better with Lundahl, or Tango, or Tamura... and the same inexpensive tubes. It depends on how much do you want to spend.
Regards,
Alex
Re: Rh And Pp And Frustration
hi Alex
i agreed completely whith you on using better components. i have built your rh84 with great suscess using edcor output transformer but when i change out the edcor for a pair of transdecar "much beefier" and wow! what a different i would not built another amp untill i get quality iron. its worth the efford.
Alex Kitic said:
hi Alex
i agreed completely whith you on using better components. i have built your rh84 with great suscess using edcor output transformer but when i change out the edcor for a pair of transdecar "much beefier" and wow! what a different i would not built another amp untill i get quality iron. its worth the efford.
I have just tried the 6N2P (sort of 12ax7) on the rh84 without a capacitor under the cathode. I recommend this, sounds very good (and loud, mu is 100 or so). If you can afford the gainloss, take this capacitor out !
I now changed 6N2P for a ecc40 (=e80cc), has lower mu so it sounds weaker but quality of sound is great. Next experiment is to put the capacitor back on the cathode. See what happens.
By the way, last experiment with single LN150 ccs on top of driver tube
Question. I like to try try 6au6 (or ef86) in pentode mode as driver. Any opinions beforehand ?
I now changed 6N2P for a ecc40 (=e80cc), has lower mu so it sounds weaker but quality of sound is great. Next experiment is to put the capacitor back on the cathode. See what happens.
By the way, last experiment with single LN150 ccs on top of driver tube
Question. I like to try try 6au6 (or ef86) in pentode mode as driver. Any opinions beforehand ?
DRIVER CATHODE CAPACITOR
As previously commented, the ECC83 can be used instead of the ECC81, due to its high gain. But, the transconductance is very low and this offsets the high gain, and you actually get less gain than with the ECC81 -- but you are still able to reach full power.
On the other hand, the low anode voltage and relatively high current put the ECC83 in a rarely used (in general designs) very linear part of the anode curves -- with obviously interesting results. While I like the sound of the RH84 with ECC83 driver, it is a little bit on the hot side.
Finally, you need to exclude the capacitor over the Rk of the driver: if you include the cap, everything changes completely and the amp is not RH84, but something else. Almost all what it standed for is lost. I think I already was explaining this a long time ago.
As previously commented, the ECC83 can be used instead of the ECC81, due to its high gain. But, the transconductance is very low and this offsets the high gain, and you actually get less gain than with the ECC81 -- but you are still able to reach full power.
On the other hand, the low anode voltage and relatively high current put the ECC83 in a rarely used (in general designs) very linear part of the anode curves -- with obviously interesting results. While I like the sound of the RH84 with ECC83 driver, it is a little bit on the hot side.
Finally, you need to exclude the capacitor over the Rk of the driver: if you include the cap, everything changes completely and the amp is not RH84, but something else. Almost all what it standed for is lost. I think I already was explaining this a long time ago.
Re: DRIVER CATHODE CAPACITOR
I used the 6N2P with about 160V on anode and 1,1 mA; ECC40 with 130V on anode and 1,4 mA. Rk=2200 ohm.
I regulated the screen of el84 with 0A2 regulator tube on 150Volt, because I had one in the box. Any thoughts about the best voltage on the EL84 screen ? My B+ is 250/260 volt.
Alex Kitic said:
I used the 6N2P with about 160V on anode and 1,1 mA; ECC40 with 130V on anode and 1,4 mA. Rk=2200 ohm.
I regulated the screen of el84 with 0A2 regulator tube on 150Volt, because I had one in the box. Any thoughts about the best voltage on the EL84 screen ? My B+ is 250/260 volt.
G2 VOLTAGE
I actually just connect the g2 via a resistor, like 2.2k or similar, to achieve Vg2 to be as similar as possible to Va.
This, of course, mainly to keep it simple and to let it all "float" with the other voltages in function of the B+ voltage chosen/available to the DIYer.
A second solution would be to "fix" it via voltage splitter, i.e. one Rg2 resistor to B+ and another proportional to ground, determining the fraction of B+ voltage that becomes Vg2. Of course, this second resistor to ground needs to be bypassed by cap thus creating a separate flow of AC and DC, etc.
Applying one OA2 means regulating the g2 voltage at 150V, causing the tube to conduct more current than it would if Vg2 was 150 or 300 VDC. While there has been lots of praise for the sound of pentodes with regulated Vg2, I am not that conviced, and think that it is more a matter of taste. You could try excluding the 02A from the circuit and leaving just a, for instance, 2.2k resistor from g2 to B+. Than eventually you could express your opinion of the sound in respect to the RH circuit application.
Personally, I omitted any regulation from the circuit to make it as cheap to make and as simple to build (and get everything correct even for first time builders). If I were to regulate, I would prefer 300V, like two 02A one above the other.
Of course, that would be for a B+ supply of 300V, a necessity to obtain as much output power as possible from relatively high anode load impedance transformers (6.8k, for instance). In your case, that translates to 250V.
I actually just connect the g2 via a resistor, like 2.2k or similar, to achieve Vg2 to be as similar as possible to Va.
This, of course, mainly to keep it simple and to let it all "float" with the other voltages in function of the B+ voltage chosen/available to the DIYer.
A second solution would be to "fix" it via voltage splitter, i.e. one Rg2 resistor to B+ and another proportional to ground, determining the fraction of B+ voltage that becomes Vg2. Of course, this second resistor to ground needs to be bypassed by cap thus creating a separate flow of AC and DC, etc.
Applying one OA2 means regulating the g2 voltage at 150V, causing the tube to conduct more current than it would if Vg2 was 150 or 300 VDC. While there has been lots of praise for the sound of pentodes with regulated Vg2, I am not that conviced, and think that it is more a matter of taste. You could try excluding the 02A from the circuit and leaving just a, for instance, 2.2k resistor from g2 to B+. Than eventually you could express your opinion of the sound in respect to the RH circuit application.
Personally, I omitted any regulation from the circuit to make it as cheap to make and as simple to build (and get everything correct even for first time builders). If I were to regulate, I would prefer 300V, like two 02A one above the other.
Of course, that would be for a B+ supply of 300V, a necessity to obtain as much output power as possible from relatively high anode load impedance transformers (6.8k, for instance). In your case, that translates to 250V.
Desperately Seeking RH84SE Schematic.
Guys ... where can I get hold of Alex's RH84SE schematics?
Wish to build my very first amp to drive Altec 604E of 101dB!
Can't understand the science behind all the discussions going on.
I beleives that with all the advices provided by this great community of intelect, and with a passion for this interest, I'll make it.
Presently using McIntosh MC-30 monobloc to drive a 101dB and it's indeed overkill! Volumn control is a hairline different.
I'm desperate
Thanks all in advance.
Guys ... where can I get hold of Alex's RH84SE schematics?
Wish to build my very first amp to drive Altec 604E of 101dB!
Can't understand the science behind all the discussions going on.
I beleives that with all the advices provided by this great community of intelect, and with a passion for this interest, I'll make it.
Presently using McIntosh MC-30 monobloc to drive a 101dB and it's indeed overkill! Volumn control is a hairline different.
I'm desperate
Thanks all in advance.
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