Something I forgot to ask, did you modify the heater connection when you swapped the ECC81/82 for 6N2P? Sorry, it may be a stupid question.
Hi, I did indeed. There's no such thing as a stupid question! I appreciate your help 👍
I have these values written down. I will update the sketch to show all the resistor values tonight and repost. I think I will go over all of them again and just check the values I've got on the sketch for any errors as well.
I have these values written down. I will update the sketch to show all the resistor values tonight and repost. I think I will go over all of them again and just check the values I've got on the sketch for any errors as well.
At this stage I'm considering just completely rewiring it following a schematic for a known circuit which uses the same line up of valves (if we count the 6N2P's as 12ax7's).
I posted another thread on here looking for suggestions about what to do with this amp, which is actually a PA. My intention is to use it for a guitar amp. I thought I'd try to get it working 'as is' for the experience and then look at rebuilding the circuit afterwards.
I think it might be easier to just follow a known guitar amp schematic with known expected voltages etc. There's a lot of potential for further modification as well given the redundant mic stages and their valve sockets and volume pots etc.
I posted another thread on here looking for suggestions about what to do with this amp, which is actually a PA. My intention is to use it for a guitar amp. I thought I'd try to get it working 'as is' for the experience and then look at rebuilding the circuit afterwards.
I think it might be easier to just follow a known guitar amp schematic with known expected voltages etc. There's a lot of potential for further modification as well given the redundant mic stages and their valve sockets and volume pots etc.
Those red circled 0.15uF coupling caps are not Electrolytic.
If they were electrolytic, there would be far too many + volts on the grids.
You can find lots of 600V or 630V non electrolytic caps.
It is hard to find 600V or 630V electrolytic caps, but even if you could . . . do not use them for coupling cap duty.
If they were electrolytic, there would be far too many + volts on the grids.
You can find lots of 600V or 630V non electrolytic caps.
It is hard to find 600V or 630V electrolytic caps, but even if you could . . . do not use them for coupling cap duty.
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What specs?
I might have missed it, but what is the actual performance problem with the amp?
What is the measured output power before clipping?
When redrawing your sketch, don't forget to correct the connection of the upper (0.15µ) PI output coupling cap.
It should connect to the cathodyne plate (pin 1).
Whenever there's a need to change the plate resistor of a cathodyne (which I don't see here), remember that a cathodyne needs to have equal value plate and cathode resistors.
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Correct, the plate load resistor and the cathode load resistor need to be equal for a concertina phase invertor.
The amplifier circuit of this thread has a self bias resistor. That requires a little more thought.
That resistance does not count for the total cathode signal load resistance, since the output of the concertina is not taken from the cathode, instead it is taken from the junction of the self bias resistor with the cathode's signal load resistor.
If the lower resistance is not equal to the plate load resistance, then there will be less volts across the junction of the self bias resistor and the concertina cathode resistor.
By the way, the marked Ohms values are not equal on the schematic 21.2k for the plate, and 22.7k for the cathode (again, not including the 0.76k self bias resistor).
Use matched 22k resistors, and match the Rg resistors of the output stage grids too)..
The amplifier circuit of this thread has a self bias resistor. That requires a little more thought.
That resistance does not count for the total cathode signal load resistance, since the output of the concertina is not taken from the cathode, instead it is taken from the junction of the self bias resistor with the cathode's signal load resistor.
If the lower resistance is not equal to the plate load resistance, then there will be less volts across the junction of the self bias resistor and the concertina cathode resistor.
By the way, the marked Ohms values are not equal on the schematic 21.2k for the plate, and 22.7k for the cathode (again, not including the 0.76k self bias resistor).
Use matched 22k resistors, and match the Rg resistors of the output stage grids too)..
Post #27 and the schematic is STILL wrong and uncorrected, in spite of numerous warnings.
Top EL34 is STILL being driven from an HV node and not from cathodyne plate, Pin 1
Makes anybody trying to help feel discouraged.
Top EL34 is STILL being driven from an HV node and not from cathodyne plate, Pin 1
Makes anybody trying to help feel discouraged.
"Numerous warnings" 🤣.
"STILL". What are you talking about?
Post #27 was in response to a request from another member
That sketch was made weeks ago, and that pic was taken weeks ago! I'll amend it in due course. Is that ok with you? I haven't done anything with this for days. I very much appreciate people helping me and I'm responding to their questions. I posted a pic showing the output stage because someone asked to see it. I don't always have the amp or the drawings in front of me. It's just a picture I had on my phone. This is a hobbyist forum, the clues in the name. I've stated several times that I don't expect everything on my schematic to be accurate, I've never attempted to draw one before!
Where you not once a beginner yourself?
You´ve been warned about your important error in posts # 10 - 13 - 14 -30
Does it count as "numerous?
"Still" means you have been warned about the error since post#8, so 18 posts earlier ... yet you don´t even acknowledge it .... let alone correct it.
Does that solve the problem?
Not my problem, it´s you who are asking for answers.
Cool, it would be fine if you said something like "oh, I know there is an error, can´t edit the picture now" or something to that effect.
Otherwise you don´seem to care and that certainly affects will to help.
Still am! On many issues!!!
Always happy to have my errors corrected 🙂
Take care friend.
The choice of language alone, "warned" . I've been advised. I haven't been warned. You're taking about a mistake on a drawing. And one by someone who's openly acknowledged, from the outset, that they're a newcomer to electronics at that. You need to chill out and get a grip, mate.
I saw the situation regarding the coupling cap/HT node as far back as post no 10. I clicked the like button. Some of the information shared in the subsequent posts by other forum members is quite technical and needs time to be digested and properly understood.
I haven't spent much (if any) time in front of the amp since then. I certainly haven't done any drawing.
As I've already explained, when I posted the drawing again in response to jcalvarez it was a photograph I already had taken weeks ago. As I've also already told you, I'm not always at home so can't access my drawings or be in front of the amp.
Are you familiar with the phrase 'wind your neck in'?
How I choose to acknowledge people's advice or input is up to me. You don't get to dictate that to others.
I saw the situation regarding the coupling cap/HT node as far back as post no 10. I clicked the like button. Some of the information shared in the subsequent posts by other forum members is quite technical and needs time to be digested and properly understood.
I haven't spent much (if any) time in front of the amp since then. I certainly haven't done any drawing.
As I've already explained, when I posted the drawing again in response to jcalvarez it was a photograph I already had taken weeks ago. As I've also already told you, I'm not always at home so can't access my drawings or be in front of the amp.
Are you familiar with the phrase 'wind your neck in'?
A good rule?
Anybody asking for help in the Tubes/Valves threads, then . . .
Help Us to Help You.
As far as I know, all advice here is given freely.
There is no hourly wage, and no salary paid to those who post answers (both right answers and wrong answers).
Just my opinions
Anybody asking for help in the Tubes/Valves threads, then . . .
Help Us to Help You.
As far as I know, all advice here is given freely.
There is no hourly wage, and no salary paid to those who post answers (both right answers and wrong answers).
Just my opinions
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JMFahey,
Building a phase splitter using load resistors that are +/- 10% does not encourage that circuit to work very well . . .
unless there is lots of global negative feedback to cover over the un-balanced signals.
It is nice to have a schematic that lists the actual values. In some cases it leads to troubleshooting some of the problems expressed in a post.
Building a phase splitter using load resistors that are +/- 10% does not encourage that circuit to work very well . . .
unless there is lots of global negative feedback to cover over the un-balanced signals.
It is nice to have a schematic that lists the actual values. In some cases it leads to troubleshooting some of the problems expressed in a post.
6a3sUMMER I take your point..but I'm not entirely sure it applies in this case.
I'm always polite, curious and respectful of anyone who is the same to me. I provided a schematic which was drawn to the best of my abilities and openly acknowledged that it was a work in progress. I'm putting effort in on my side, I done expect to be spoon fed. Although I can quite well understand how it must be frustrating to the likes of yourself when people do expect this.
I have no issues with yourself at all.
I hit the like button in your posts in acknowledgement. I understand that there is no obligation to provide help and that people are doing so out of a sense of community and kindness. I think that's brilliant as I'm extremely appreciative when people are able to provide answers to my questions. I'm not sure what it was in particular which made you think I am of a different mindset to you in this?
There are however always a minority of knowledgeable people on most forums who feel they have a right to speak to people in a way which is rude and condescending (not you). I have no time for this whatsoever and reserve the right to object to it. Whether they are providing answers or not, there's no need for this sort of behaviour. People who present themselves in such a way serve only discourage people from asking questions. Which is a DIY forum all all about? Nobody is obliged to help others, if people are not able to conduct themselves in a courteous and respectful way, they should save their energy.
The question I posed was about voltage on the grid of the cathodyne. Which, as I now thanks to members input, is supposed to be there. I now from that that I need to go away and do more reading on cathodyne PI's. That's it..job done really. I'm grateful for the further information and will make use of it all in due course 👍
Thanks to everyone for your help.
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