I plan to rebuild an old preamp. I don't know if rebuild is the right word since I plan to replace just about everything but the cabinet and transformer. It's my first tube project.
I would like to integrate the phono headamp with the preamp. It's not a necessity, but is my goal for now. But I'll keep it to the preamp for now. It will be based on the 6267/EF86 (or similar tube) in triode connection. The problem is that the transformer has 290 V and I need 250 at most, as I understand it.
What's the best way to get the voltage down to, say, 225? A resistor should do it. But is there a better way? I guess what I ask is, is there a way to not just burn energy, or to burn as little as possible?
A search here might give me the answer. But I doubt it. I'm completely in the dark here. So don't hold back on the details.
Well, I have a few phono headamp question as well. I'm considering one of these: EF86 preamp (in Japanese; image is 1/3 down the page) and EF86 pre.
Any opinions/input? Also, they have 12.6 V filaments. My preamp has 6.3. Would it work with these? Why different voltages for the same tube?
I would like to integrate the phono headamp with the preamp. It's not a necessity, but is my goal for now. But I'll keep it to the preamp for now. It will be based on the 6267/EF86 (or similar tube) in triode connection. The problem is that the transformer has 290 V and I need 250 at most, as I understand it.
What's the best way to get the voltage down to, say, 225? A resistor should do it. But is there a better way? I guess what I ask is, is there a way to not just burn energy, or to burn as little as possible?
A search here might give me the answer. But I doubt it. I'm completely in the dark here. So don't hold back on the details.
Well, I have a few phono headamp question as well. I'm considering one of these: EF86 preamp (in Japanese; image is 1/3 down the page) and EF86 pre.
Any opinions/input? Also, they have 12.6 V filaments. My preamp has 6.3. Would it work with these? Why different voltages for the same tube?
Questions-
Are you comfortable with working with lethal voltages? Tube amp voltages can kill.
Is the 290V directly from the transformer or is that what the PS is putting out currently after rectification and filtering?
What type of rectification are you planning on using? If the PTX puts out 290VAC and you use tube rectification you'll have no problem getting down to the voltage you are after.
Adding an additional RC (resistor/capacitor) section to the filter will also drop the voltage and filter the power supply further.
Answers-
Most tubes that have 12.6V filaments can be operated on 6.3V, the inverse is not true. Of course current draw will double. The method is to tie together two of the pins, often 4 and 5 and connect the 6.3V to the combined pins and pin 9. (Those numbers are tube dependant.)
Are you comfortable with working with lethal voltages? Tube amp voltages can kill.
Is the 290V directly from the transformer or is that what the PS is putting out currently after rectification and filtering?
What type of rectification are you planning on using? If the PTX puts out 290VAC and you use tube rectification you'll have no problem getting down to the voltage you are after.
Adding an additional RC (resistor/capacitor) section to the filter will also drop the voltage and filter the power supply further.
Answers-
Most tubes that have 12.6V filaments can be operated on 6.3V, the inverse is not true. Of course current draw will double. The method is to tie together two of the pins, often 4 and 5 and connect the 6.3V to the combined pins and pin 9. (Those numbers are tube dependant.)
Thanks for the reply and concern.
Comfortable? No. Secure? I would say, yes, but wary. (I just fried an SMPS, though I wasn't at risk, so I know what the consequenses can be.) Rest assured I will take any and all precaution. The preamp section is very minimalist with few things to get lost in. I wouldn't touch a big power amp, at least not yet.
I haven't looked into the details. For now I only assume the voltage is too high. I haven't gotten as far as to rectifier. My problem isn't follow some schematics, but to make practical use of it, like making small changes to make it fit my needs. I ask here in order to get some basic grasp on the fundamentals. It's very difficult to seek meaningful information when you can't even crawl.
Let's put it this way, how would I go about to get the 310 V of the PSU in the first link down to 290 V?
I don't expect to start this until after the summer. By then I hope to have it all, design, material and some very basic, but useful, knowledge.
Comfortable? No. Secure? I would say, yes, but wary. (I just fried an SMPS, though I wasn't at risk, so I know what the consequenses can be.) Rest assured I will take any and all precaution. The preamp section is very minimalist with few things to get lost in. I wouldn't touch a big power amp, at least not yet.
I haven't looked into the details. For now I only assume the voltage is too high. I haven't gotten as far as to rectifier. My problem isn't follow some schematics, but to make practical use of it, like making small changes to make it fit my needs. I ask here in order to get some basic grasp on the fundamentals. It's very difficult to seek meaningful information when you can't even crawl.
Let's put it this way, how would I go about to get the 310 V of the PSU in the first link down to 290 V?
I don't expect to start this until after the summer. By then I hope to have it all, design, material and some very basic, but useful, knowledge.
As a first step, I highly recommend ordering Morgan Jones' book "Valve Amplifiers".
It is basically *the* textbook for DIY on tube-based amps and preamps. And he devotes a section to power supply design, as well.
Very well written, and very clear for a beginner. I learned quite a bit from it...and am now embarking down the road of building my first preamp.
Also, check out the Power Supply Designer software: PSUD2. Available at www.duncanamps.com This software will allow you to play with power supply components (transformers, capacitors, inductors/chokes, and resistors) to achieve the voltage you need. You'll learn a lot about how to configure a power supply just from playing around with that software.
It is basically *the* textbook for DIY on tube-based amps and preamps. And he devotes a section to power supply design, as well.
Very well written, and very clear for a beginner. I learned quite a bit from it...and am now embarking down the road of building my first preamp.
Also, check out the Power Supply Designer software: PSUD2. Available at www.duncanamps.com This software will allow you to play with power supply components (transformers, capacitors, inductors/chokes, and resistors) to achieve the voltage you need. You'll learn a lot about how to configure a power supply just from playing around with that software.
I will scrap the original transformer and get one suitable for my needs. I held on to it because it's there and I wouldn't have to try fit another.
I will use this PSU, or something very close to this. I might use diodes instead.
Anyone that would like to offer his thoughts on it? Ideas for bypass caps? Tube or diodes?
I'm planning to use the Elna Cerafine 47uF/500VDC and
220uF+220uF/350VDC. Any ideas for the 225uF cap? Chokes? Transformer?
I will use this PSU, or something very close to this. I might use diodes instead.
Anyone that would like to offer his thoughts on it? Ideas for bypass caps? Tube or diodes?
I'm planning to use the Elna Cerafine 47uF/500VDC and
220uF+220uF/350VDC. Any ideas for the 225uF cap? Chokes? Transformer?
phn said:
Don't be too quick to do that. First of all, it's not really clear what you have. As others have asked: are the voltages you've quoted unrectified AC (straight from the transformer wires) or DC voltages you've measured from the existing ps?
If they're AC measurements of the unloaded transformer, then those numbers will go down when the transformer is loaded with a functioning circuit.
In any case, a higher voltage isn't necessarily going to be unusable. It might work fine as-is, or you might just need to increase the plate load resistor of the EF86 a little.
Very often a particular power transformer is used simply because it happened to be available. The voltages written on the schematic are those that the builder happened to end up with. They might have been just as happy (or even happier) with something else.
Actually, there are now fewer details.
I have this Leak preamp I don't use. But instead of selling it I decided to have fun with it. (This may make sense to nobody but me. That's enough for me.) Also to turn it into a very good preamp. This is pretty much the preamp I want. I have no questions concerning the preamp, other than possibly the voltage.
I haven't checked the trafo in the preamp, but measured the output of the Leak power amp, 290 V. (It's moded, so don't think about the 125mV input.) Thinking about it, Lundahl should be able to supply me chokes and, if needed, trafo if I email the schematic.
I have also come to the conclusion that I will not be able to fit a phono headamp in the small Leak cabinet with those chokes. Which is fine.
The GZ32/34 may also be a problem. The Leak cabinet is quite small and I think it will be very hot in there. So maybe diodes will work better.
I have this Leak preamp I don't use. But instead of selling it I decided to have fun with it. (This may make sense to nobody but me. That's enough for me.) Also to turn it into a very good preamp. This is pretty much the preamp I want. I have no questions concerning the preamp, other than possibly the voltage.
I haven't checked the trafo in the preamp, but measured the output of the Leak power amp, 290 V. (It's moded, so don't think about the 125mV input.) Thinking about it, Lundahl should be able to supply me chokes and, if needed, trafo if I email the schematic.
I have also come to the conclusion that I will not be able to fit a phono headamp in the small Leak cabinet with those chokes. Which is fine.
The GZ32/34 may also be a problem. The Leak cabinet is quite small and I think it will be very hot in there. So maybe diodes will work better.
Why not sell the Leak which is probably collectable and worth more than you suspect and build one entirely from scratch? You won't have to make the compromises otherwise required.
There are now lots of resources on line for making nice front panels and custom chassis or off the shelf chassis are fairly readily available.
There are now lots of resources on line for making nice front panels and custom chassis or off the shelf chassis are fairly readily available.
No complaining or anything. But this is why I was hesitant to bring up the brand name.
Today the Pont One/Varislope Stereo regularly brings about €100. That's what I would expect to get from this "collectible." I was actually thinking of naming eBay as one of the things I hate in the "Things I hate" thread."
This is what I hate about eBay: "Thanks to the enthusiast community's high demand for hard-to-find vintage audio, these electronics products retain their value and make a solid investment."
Great, now I have to compete with some investor that banks his retirement on that hard-to-find tube or Ortofon PU!
Making a preamp cabinet, including RIAA, from scratch is something I have been considering, seriously. Money is no factor. Fun is. Having that said, this is still up in the air. In the meantime, feel free to voice your opinions on that PSU.
Today the Pont One/Varislope Stereo regularly brings about €100. That's what I would expect to get from this "collectible." I was actually thinking of naming eBay as one of the things I hate in the "Things I hate" thread."
This is what I hate about eBay: "Thanks to the enthusiast community's high demand for hard-to-find vintage audio, these electronics products retain their value and make a solid investment."
Great, now I have to compete with some investor that banks his retirement on that hard-to-find tube or Ortofon PU!
Making a preamp cabinet, including RIAA, from scratch is something I have been considering, seriously. Money is no factor. Fun is. Having that said, this is still up in the air. In the meantime, feel free to voice your opinions on that PSU.
I second what Sherman said here. PSUD is very good and will answer a lot of your power supply questions for you. Before you spend any money, download the program and play with it. It is very educational and will demonstrate that a lot of options are avalible to you with the transformer you already have.
good luck
BZ
good luck
BZ
I third 
that opinion on PSUD, I find it accurate enough in day to day use not to have resort to the laborious calculations I used to have to do when not using a regulated supply in order to end up with the supply voltage I wanted. I was good at this, PSUD is at least as good or even better, and far easier.
that opinion on PSUD, I find it accurate enough in day to day use not to have resort to the laborious calculations I used to have to do when not using a regulated supply in order to end up with the supply voltage I wanted. I was good at this, PSUD is at least as good or even better, and far easier.
Thanks guys.
I have tested the PSU software. The Valve Amplifier book will come later.
Last couple of questions. After that I hope to start buying the stuff I need.
What's the benefit of the GZ32/34 compared to diodes? Please try to be objective here, whatever that means. Below you can be as subjective as you want. In fact, I expect you to be.
The PSU schematic says 225uF/350V. The designer of the amp says, "For general rectification I used a Philips Electrolitic (16+225µF) bypassed with Xicon 0,470µF/630Vdc caps."
I googled for Philips electrolytic(s). It didn't produce any useful hits. I will use the Elna Cerafine 220+220uF. And I was originally planning to use an Elna Cerafine 47uF. But maybe 47uF is too high, using 16 as reference. Any recommendations for the "max 50uF" and 225uF caps? I was thinking Black Gate VK 22uF/350V for the max 50uF cap.
Finally, when I simulate this circuit in the PSU Designer II using a SS bridge, I need to use 190 V to get a few volts above 240. I use default Ohm values. (With a 5-Ohm load, it's a bit over 230 V.) Does this mean a 190-0 transformer? I mean, that's very far from the 180-0-180 transformer in the GZ34 schematics. Not even this tube newbie believes the GZ34 consumes 170 V. So what is going on here?
I have tested the PSU software. The Valve Amplifier book will come later.
Last couple of questions. After that I hope to start buying the stuff I need.
What's the benefit of the GZ32/34 compared to diodes? Please try to be objective here, whatever that means. Below you can be as subjective as you want. In fact, I expect you to be.
The PSU schematic says 225uF/350V. The designer of the amp says, "For general rectification I used a Philips Electrolitic (16+225µF) bypassed with Xicon 0,470µF/630Vdc caps."
I googled for Philips electrolytic(s). It didn't produce any useful hits. I will use the Elna Cerafine 220+220uF. And I was originally planning to use an Elna Cerafine 47uF. But maybe 47uF is too high, using 16 as reference. Any recommendations for the "max 50uF" and 225uF caps? I was thinking Black Gate VK 22uF/350V for the max 50uF cap.
Finally, when I simulate this circuit in the PSU Designer II using a SS bridge, I need to use 190 V to get a few volts above 240. I use default Ohm values. (With a 5-Ohm load, it's a bit over 230 V.) Does this mean a 190-0 transformer? I mean, that's very far from the 180-0-180 transformer in the GZ34 schematics. Not even this tube newbie believes the GZ34 consumes 170 V. So what is going on here?
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I realize now that I hadn't studied up enough on the subject when posting my questions. So I'll give it a final go here.
I think I have taken the design as far as I can. I have these things left:
Am I doing right when I add a 68k resistor as load? There's a 68k resistor on the preamp power input.
Will the splitting of the PSU into two 20H chokes change the characteristics? As I understand it, it shouldn't. The problem is that my understanding might be faulty.
In the end my question is: will this design give me the 230 V I need?
I think I have taken the design as far as I can. I have these things left:
Am I doing right when I add a 68k resistor as load? There's a 68k resistor on the preamp power input.
Will the splitting of the PSU into two 20H chokes change the characteristics? As I understand it, it shouldn't. The problem is that my understanding might be faulty.
In the end my question is: will this design give me the 230 V I need?
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