corbato said:hi fdegrove, joel, 7N7
how safe or stupid is to replace a ECC82 with ECC81 or ECC83 ?
sorry..its got nothing to do with this thread but this was something that was agitating me for a while, and when I saw you gurus in one thread...
thnks
I'm completely with Frank on this; they are different devices intended for different applications.
I know that the guitarists do this, but it should not be done.
ECC82/12AU7 is designed to run a reasonable amount of current as is ECC81/12AT7; ECC83/12AX7 is not.
The one possible swap you might get away with is to replace a 12AX7 with a 12AY7 for reduced gain. These valves are designed to run at similar currents i.e. <4mA, so you will probably get away with it. 12AY7 is a good valve.
As I have implied elsewhere it is a good idea to replace ECC82 with almost anything (!) but the '81 (which is not a good valve either) is not an option.
If you want more gain, which I suspect is your reason for asking, there are no plug and play solutions realistically. Most of the higher gain alternatives have different pin-outs; many are quite expensive too. Additionally, they have different characteristics which will require an element of re-design. If I had something with an ECC82 in it and I needed more gain, I would be looking for something that had some driving ability, so for a modest increase I might try 6463 (but I would need more current) or for much more gain I would consider E88CC,. If there were only modest drive requirements, other types I would consider would be 6BQ7, 6BK7, 6BZ8, or even 5965/E180CC which has mu of 47, although this is still less than ECC81.
7N7
Hi fdegrove, 7N7. Thanks for the info.
I have an salvaged an old EL84 SE amp. It originally extracted from a Phillips Stereo radio called "Maestro" and assembled in a new chassis in the early 70's by my uncle. I don't think you would know about this radio model - it was made by Phillips in India around mid-60's.
The amp, as it reached me, has ECC82 in the driver stage. It perhaps could have had any other tube just as well.
I want to replace the ECC82 with eaither ECC81 or ECC83, simply because these are tubes I have with me at the momemt. Any mods that you might suggest?
Sorry for diverting the topic of this thread, but thanks so much for the help.
I have an salvaged an old EL84 SE amp. It originally extracted from a Phillips Stereo radio called "Maestro" and assembled in a new chassis in the early 70's by my uncle. I don't think you would know about this radio model - it was made by Phillips in India around mid-60's.
The amp, as it reached me, has ECC82 in the driver stage. It perhaps could have had any other tube just as well.
I want to replace the ECC82 with eaither ECC81 or ECC83, simply because these are tubes I have with me at the momemt. Any mods that you might suggest?
Sorry for diverting the topic of this thread, but thanks so much for the help.
Hi fdegrove..
indeed I'm the guy with those 6158's ..
In between postings, I was doing some search and came across EL84 Single-Ended - Bonavolta. It looks very similar to the thing I have at hand. Atleast, the caps are ..can this circuit work ok with a ECC81 or ECC83.
I am willing to change the radio amp circuit to the Bonavolta circuit.
thanks...and btw ECC82 is not available where I live.
Thanks for the help.
indeed I'm the guy with those 6158's ..
In between postings, I was doing some search and came across EL84 Single-Ended - Bonavolta. It looks very similar to the thing I have at hand. Atleast, the caps are ..can this circuit work ok with a ECC81 or ECC83.
I am willing to change the radio amp circuit to the Bonavolta circuit.
thanks...and btw ECC82 is not available where I live.
Thanks for the help.
This is quite a problem.
270V is not much to run a driver stage with resistive loads. Of course I have no idea what you have available to you where you are so it is not easy to make a r4ecommendation. I really do not think that the ECCs that you have are suitable
As for 6158/13D3, this is an excellent valve, but sadly again not really suitable. I am running one a s a diff pair in my experimental 13D3/D3A/6CK4 amplifier. 13D3 is low distortion but sadly has quite a high anode resistance.
The other problem is the HT you have available. You could run it with a low value of anode load and take a chance.
As I have only 300V available, I have opted for active loads; these use MJE350 PNP power transistors. The only other components are a 6.2V Zener, a few resistors and a capacitor. This arrangement gives me an anode load of about 800k which is very good for distortionm and I get to operate at the anode voltage I want (185V)
Even if you do not want the active loads, in your position I would go for the 13D3 and see how you get on. I would rather use this one than either of the other two types you mentioned.
Best of luck
7N7
270V is not much to run a driver stage with resistive loads. Of course I have no idea what you have available to you where you are so it is not easy to make a r4ecommendation. I really do not think that the ECCs that you have are suitable
As for 6158/13D3, this is an excellent valve, but sadly again not really suitable. I am running one a s a diff pair in my experimental 13D3/D3A/6CK4 amplifier. 13D3 is low distortion but sadly has quite a high anode resistance.
The other problem is the HT you have available. You could run it with a low value of anode load and take a chance.
As I have only 300V available, I have opted for active loads; these use MJE350 PNP power transistors. The only other components are a 6.2V Zener, a few resistors and a capacitor. This arrangement gives me an anode load of about 800k which is very good for distortionm and I get to operate at the anode voltage I want (185V)
Even if you do not want the active loads, in your position I would go for the 13D3 and see how you get on. I would rather use this one than either of the other two types you mentioned.
Best of luck
7N7
Re: EL84
Well the drawing shows 300-0-300 going into an EZ81; with cap input at 50mA this would give about 350V.
With 350V available, then he could use 33k as an anode load and run the valve at about 5mA and 200V. Bias would be about 3.5V and I would expect gain of around perhaps 24 or so.
R out of the stage I would guess to be in the order of 12k; a little high but not too disastrous and he could probably get away with a large value of grid leak on the EL84.
Perhaps it's a goer?
7N7
fdegrove said:Hi,
That 270 VDC B+ was just my wild guess really since this a common anode voltage for the the output valve.
Let's wait and see,
Well the drawing shows 300-0-300 going into an EZ81; with cap input at 50mA this would give about 350V.
With 350V available, then he could use 33k as an anode load and run the valve at about 5mA and 200V. Bias would be about 3.5V and I would expect gain of around perhaps 24 or so.
R out of the stage I would guess to be in the order of 12k; a little high but not too disastrous and he could probably get away with a large value of grid leak on the EL84.
Perhaps it's a goer?
7N7
JUST MY IMPRESSION.
Hi,
You're referring to the Bonavolta circuit I presume?
I was under the impression that Corbato wanted to get rid of the ECC82 input/driver stage and replace it with something he has in his box.
I suggested the 13D3 since he has some and I know you're around anyway.
Now I haven't got the foggiest idea what exactly he's got available for B+.
I mentioned the 270 VDC since that seems a likely minimum voltage.
Cheers,
Hi,
You're referring to the Bonavolta circuit I presume?
I was under the impression that Corbato wanted to get rid of the ECC82 input/driver stage and replace it with something he has in his box.
I suggested the 13D3 since he has some and I know you're around anyway.
Now I haven't got the foggiest idea what exactly he's got available for B+.
I mentioned the 270 VDC since that seems a likely minimum voltage.
Cheers,
Re: JUST MY IMPRESSION.
Oh dear! I've got the wrong end of the stick again.
Yes we are really in the dark then.
I'll shut up
7N7
fdegrove said:Hi,
You're referring to the Bonavolta circuit I presume?
I was under the impression that Corbato wanted to get rid of the ECC82 input/driver stage and replace it with something he has in his box.
I suggested the 13D3 since he has some and I know you're around anyway.
Now I haven't got the foggiest idea what exactly he's got available for B+.
I mentioned the 270 VDC since that seems a likely minimum voltage.
Cheers,
Oh dear! I've got the wrong end of the stick again.
Yes we are really in the dark then.
I'll shut up
7N7
Attachments
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Ok…
I finally bought the ECC82 and built one channel of the http://Bonavolta EL84 SE
After some initial hiccups ( I managed to plug in ECC82 in the EL84 socket and vice versa, and wired up the Plate line from OPT to Pin 6) the Amp started functioning.
But wait a minute…where is the wonderful “valve warmth” that is supposed to “engulf” me? Where is that mushy feel good thingy? I built the amp exactly as per plan using premium grade components.
The out power is really low. The schema claims 4.5 watts but it seems much lower than that. Used with JPW 202 Bookshelf. The sound quality is much worse than the ordinary Micro system that my wife listens to.
What could have possibly gone wrong? Some observation:
+B is 273 Volts after the tubes are plugged in.
Grid 1 is –10.3 Volts
Valve gives a faint orange glow, but running terribly hot.
Can’t be touched after 15 min of operation.
The Output Transformers are 4.9k primary with 4, 18 ohm sec. Labeled 60 cps to 14,000cps. Physical dimensions are quite modest 2” x 1.5” core. There is a pair of tap in the primary (other than for the plate) and one knowledge person informed that it is built in Choke for power supply. Cost cutting measure perhaps – sharing the same core.
Another thing that is nagging me the filter caps at power supply used by Bonavolta. Is more than 50u ok for the EZ81?
I remember back in early ’70 my uncle used to build similar amps, but they used to sound real loud. Sufficient for dances at his home.
However, I’m really pleased with the overall tolerance of the valve. There is absolutely no Hum or Hiss or any kind or noise even at full output before clipping. Only sad about that low power and that missing octave at both side of the bandwidth. While I believe the output tranny is the culprit here, what could be done to enhance the power so that listening is possible while remaining 10 feet away from the speakers. Any suggestion to improve matters?
Meanwhile, I will console myself that this “flat” sound is the real stuff, uncolored and pristine. That things will improve once the Amp has “burned-in”.....and so on....
I finally bought the ECC82 and built one channel of the http://Bonavolta EL84 SE
After some initial hiccups ( I managed to plug in ECC82 in the EL84 socket and vice versa, and wired up the Plate line from OPT to Pin 6) the Amp started functioning.
But wait a minute…where is the wonderful “valve warmth” that is supposed to “engulf” me? Where is that mushy feel good thingy? I built the amp exactly as per plan using premium grade components.
The out power is really low. The schema claims 4.5 watts but it seems much lower than that. Used with JPW 202 Bookshelf. The sound quality is much worse than the ordinary Micro system that my wife listens to.
What could have possibly gone wrong? Some observation:
+B is 273 Volts after the tubes are plugged in.
Grid 1 is –10.3 Volts
Valve gives a faint orange glow, but running terribly hot.
Can’t be touched after 15 min of operation.
The Output Transformers are 4.9k primary with 4, 18 ohm sec. Labeled 60 cps to 14,000cps. Physical dimensions are quite modest 2” x 1.5” core. There is a pair of tap in the primary (other than for the plate) and one knowledge person informed that it is built in Choke for power supply. Cost cutting measure perhaps – sharing the same core.
Another thing that is nagging me the filter caps at power supply used by Bonavolta. Is more than 50u ok for the EZ81?
I remember back in early ’70 my uncle used to build similar amps, but they used to sound real loud. Sufficient for dances at his home.
However, I’m really pleased with the overall tolerance of the valve. There is absolutely no Hum or Hiss or any kind or noise even at full output before clipping. Only sad about that low power and that missing octave at both side of the bandwidth. While I believe the output tranny is the culprit here, what could be done to enhance the power so that listening is possible while remaining 10 feet away from the speakers. Any suggestion to improve matters?
Meanwhile, I will console myself that this “flat” sound is the real stuff, uncolored and pristine. That things will improve once the Amp has “burned-in”.....and so on....
The bonavolta design uses feedback...feedback is evil in my book...try adding a switch to the feedback line so you can hear the difference between feedback and non feedback.
The extra taps are probably for running it in Ultra linear mode. And not some kind of built in choke.
Your output transformer is arguably the most important part of the amp. If it only goes up to 14000Hz and starts of at 60Hz..than that may very well be one of the prroblems..if not the biggest problem.
The extra taps are probably for running it in Ultra linear mode. And not some kind of built in choke.
Your output transformer is arguably the most important part of the amp. If it only goes up to 14000Hz and starts of at 60Hz..than that may very well be one of the prroblems..if not the biggest problem.
Pentodes
Hi Bas,
I'm no pentode lover or expert. But I do know that they have high ra values, and so it is not feasable to load them with a transformer of 3*ra, which is what we generally do with triodes to keep the distortion down. If we were to try, the power output would be miserably low.
Additionally, the transfer characteristic gives rise to odd order harmonic distortion, which many, though not all*, find unpleasant.
*I was reminded last night that both brass instruments and violin sounds include significant amounts of 3H. This is what makes them seem "bright".
Thank you 7N7
Cheers,
Hi Bas,
I'm no pentode lover or expert. But I do know that they have high ra values, and so it is not feasable to load them with a transformer of 3*ra, which is what we generally do with triodes to keep the distortion down. If we were to try, the power output would be miserably low.
Additionally, the transfer characteristic gives rise to odd order harmonic distortion, which many, though not all*, find unpleasant.
*I was reminded last night that both brass instruments and violin sounds include significant amounts of 3H. This is what makes them seem "bright".
Thank you 7N7
Cheers,
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