1 mF?
Hi,
With 1 mF at the input no surprises there.
I don't use a simulator but common sense tells me I'd use a 4700mf (or thereabout) for C1.
I don't know what the limit for the LM317 is at its' output,I mostly use the ubiquitous 7812 and put anothor 4700 mF at its' tail with
excellent results.
I think the max A rating for the 7812 may be 2A though.
I'll need to check that Amp rating.
Cheers,
Hi,
With 1 mF at the input no surprises there.
I don't use a simulator but common sense tells me I'd use a 4700mf (or thereabout) for C1.
I don't know what the limit for the LM317 is at its' output,I mostly use the ubiquitous 7812 and put anothor 4700 mF at its' tail with
excellent results.
I think the max A rating for the 7812 may be 2A though.
I'll need to check that Amp rating.
Cheers,
RELIGIOUSLY.
Hi,
Usually I only used voltage regs for heaters.
Although some people here (in the tube section) suggested (quite fervently) that for heaters it was better to regulate current rather then to keep voltage constant, I confess I was very skeptical and still am to this very day.
Since I haven't tried it,I won't pass judgement...frankly I always thought the heaters to consume whatever current they needed...no more no less.
Yes,but you can combine both virtues and keep voltage constant in the process,I'd say?
Cheers,
Hi,
Usually I only used voltage regs for heaters.
Although some people here (in the tube section) suggested (quite fervently) that for heaters it was better to regulate current rather then to keep voltage constant, I confess I was very skeptical and still am to this very day.
Since I haven't tried it,I won't pass judgement...frankly I always thought the heaters to consume whatever current they needed...no more no less.
Yes,but you can combine both virtues and keep voltage constant in the process,I'd say?
Cheers,
Hi guys,
Surprise here, I thought the heater supply was pretty good. Can this be the source of the hum? I do have another 2 1000uF/63V caps so I could easily experiment. I do use the LM317 as a current regulator for 450mA.
If I use Schottky diodes, what do I need as heatsink? I guess I have to skrew the diodes onto somekind of heatsink?
And another thing about the diodes, if I want to use them for the biascircuit, the heater of the driver and the 300B heater, I need a minimum of 150V and 3A to be on the safe side. The diodes you specified are rated to 45V max I think.
Ralph
Surprise here, I thought the heater supply was pretty good. Can this be the source of the hum? I do have another 2 1000uF/63V caps so I could easily experiment. I do use the LM317 as a current regulator for 450mA.
If I use Schottky diodes, what do I need as heatsink? I guess I have to skrew the diodes onto somekind of heatsink?
And another thing about the diodes, if I want to use them for the biascircuit, the heater of the driver and the 300B heater, I need a minimum of 150V and 3A to be on the safe side. The diodes you specified are rated to 45V max I think.
Ralph
Ralph,
Yes, they are only suitable for heaters.
General "rule of thumb" for rectifiers is to go for at least 2 x the rated voltage.
As for current, the bias circuit takes almost none. There's only the capacitor chargeup at power-on.
Yes, your heater rectifier and regulator circuit is good, but just near the edge of not working. Hence my suggestion to either raising the value of C1, or changing to Schottky.
You will not need a heatsink fot the 12v supply schottky's, but you can if you want for neatness.
You will need to heatsink the 5v 2a schottkys.
Heatsinking:
This is not a big deal like it is for these class A SS amps.
However, our conditions are different.
Probably, you'll want to mount them under chassis, as they are not very "valve like".
In that case, you may not be able to use convection to cool effectively. Conduction will be the best option.
Now, it depends on your chassis thickness. If it is thick: =>2mm, I would bolt directly to it. If thinner, then bolt the devices to a thicker piece of aluminium, and then bolt that to the chassis.
In fact I would suggest the same piece could be used for the 5v regulator - now that will put out some heat.
Cheers,
Yes, they are only suitable for heaters.
General "rule of thumb" for rectifiers is to go for at least 2 x the rated voltage.
As for current, the bias circuit takes almost none. There's only the capacitor chargeup at power-on.
Yes, your heater rectifier and regulator circuit is good, but just near the edge of not working. Hence my suggestion to either raising the value of C1, or changing to Schottky.
You will not need a heatsink fot the 12v supply schottky's, but you can if you want for neatness.
You will need to heatsink the 5v 2a schottkys.
Heatsinking:
This is not a big deal like it is for these class A SS amps.
However, our conditions are different.
Probably, you'll want to mount them under chassis, as they are not very "valve like".
In that case, you may not be able to use convection to cool effectively. Conduction will be the best option.
Now, it depends on your chassis thickness. If it is thick: =>2mm, I would bolt directly to it. If thinner, then bolt the devices to a thicker piece of aluminium, and then bolt that to the chassis.
In fact I would suggest the same piece could be used for the 5v regulator - now that will put out some heat.
Cheers,
Ralph,
The output voltage of your transformer must be a little high. That's good news this time.
What I don't believe is the ripple (AC) value on the input to the regulator. It's bound to be higher. Possibly your meter is getting upset by the DC present. If you have a capacitor spare (100n upwards), try connecting in series with the meter probe, and try again.
Cheers,
John
Then there's nothing to worry about.
The output voltage of your transformer must be a little high. That's good news this time.
What I don't believe is the ripple (AC) value on the input to the regulator. It's bound to be higher. Possibly your meter is getting upset by the DC present. If you have a capacitor spare (100n upwards), try connecting in series with the meter probe, and try again.
Cheers,
John
Hi John,
No panic here
About the B+ I don't have high voltage caps laying around to experiment with so it's a little difficult to change the B+ supply on short notice. One option is find me a 1uF/700V cap to change for the existing 2uF/700V. I'm not very sure what will happen, but the B+ will be lower I guess Another option is to keep what I currently have. In this update ampschema I've written all the measures values. As you can see, the amp runs now at 56,4 Watt. Main concern right now is the hum.
http://www.homepages.hetnet.nl/~rjonkers/amp.jpg
Ralph
No panic here
About the B+ I don't have high voltage caps laying around to experiment with so it's a little difficult to change the B+ supply on short notice. One option is find me a 1uF/700V cap to change for the existing 2uF/700V. I'm not very sure what will happen, but the B+ will be lower I guess
Another option is to keep what I currently have. In this update ampschema I've written all the measures values. As you can see, the amp runs now at 56,4 Watt. Main concern right now is the hum.http://www.homepages.hetnet.nl/~rjonkers/amp.jpg
Ralph
Hi Ralph,
I agree that there is no need to panic about the dissapation.
However, you should bring it down for the long term, if you want the valves to live long.
To check whether 1uF is OK, why don't you borrow the 2uF from the other channel, and wire them in series?
Hum: it's almost certainly the heaters. We've been over that.
Cheers,
I agree that there is no need to panic about the dissapation.
However, you should bring it down for the long term, if you want the valves to live long.
To check whether 1uF is OK, why don't you borrow the 2uF from the other channel, and wire them in series?
Hum: it's almost certainly the heaters. We've been over that.
Cheers,
John,
I even tried 416V @ 134mA (55.7 Watt at -80V bias), the OPTx are specified for 140mA. There's no buzzing at all from the chokes. Maybe I should try something in between, like 1.2uF or 1.5uF, so it gives me just a little bit of voltage. I like to get to something in the area of 465V @ 120mA.
Cheers
I even tried 416V @ 134mA (55.7 Watt at -80V bias), the OPTx are specified for 140mA. There's no buzzing at all from the chokes. Maybe I should try something in between, like 1.2uF or 1.5uF, so it gives me just a little bit of voltage. I like to get to something in the area of 465V @ 120mA.
Cheers
Hi Ralph,
The tube and transformer will perform best near to the specified current. But, the tube will last longer with lower dissapation.
It's your decision. Some people say they can hear subtle differences with different voltage / current combinations.
Who knows....
The tweaking's part of the fun.
As long as there is no noise from the choke, you can have any suitable value of capacitor.
Remember that the mains voltage can vary during the day, and at different locations. Consider the tolerance when you choose your value.
Cheers,
The tube and transformer will perform best near to the specified current. But, the tube will last longer with lower dissapation.
It's your decision.
Some people say they can hear subtle differences with different voltage / current combinations. Who knows....
The tweaking's part of the fun.
As long as there is no noise from the choke, you can have any suitable value of capacitor.
Remember that the mains voltage can vary during the day, and at different locations. Consider the tolerance when you choose your value.
Cheers,
Hi John,
A lot of things to be done, and I don't have much time during the week. But I am in no hurry
On Friday I'm going to buy some nice PIO's to use in the B+ supply. I think I end up somewhere between 1uF and 2uF for maximum flexibility. That's the easy part.
Then we have the hum. Most likely it's from the 300B filament. If I disconnect the interstage (and skip the driver circuit) the hum stays. Like to try two things: balance the cathode resistor with some kind of pot between the trafo and so minimize the hum. I have a spare 100 ohm/4W pot that I could use, but haven't figured out how to do it correctly. Other thing I like to try is DC on the filaments.
Then the interstage. Remember that I loose the highs when I swap the bias and the grid? I don't think that should happen. Like to check the interstages with someone with a oscilloscoop.
Finally the enclosure. I have this nice wood enclosure but it's not made 100% according to my measurements (1.5 mm different) so it won't fit. Need to work that out as well. And I have to order some aluminium tops. Goal is to have it all done somewhere next month. But as you said: tweaking is part of the fun
Cheers, Ralph
A lot of things to be done, and I don't have much time during the week. But I am in no hurry
On Friday I'm going to buy some nice PIO's to use in the B+ supply. I think I end up somewhere between 1uF and 2uF for maximum flexibility. That's the easy part.
Then we have the hum. Most likely it's from the 300B filament. If I disconnect the interstage (and skip the driver circuit) the hum stays. Like to try two things: balance the cathode resistor with some kind of pot between the trafo and so minimize the hum. I have a spare 100 ohm/4W pot that I could use, but haven't figured out how to do it correctly. Other thing I like to try is DC on the filaments.
Then the interstage. Remember that I loose the highs when I swap the bias and the grid? I don't think that should happen. Like to check the interstages with someone with a oscilloscoop.
Finally the enclosure. I have this nice wood enclosure but it's not made 100% according to my measurements (1.5 mm different) so it won't fit. Need to work that out as well. And I have to order some aluminium tops. Goal is to have it all done somewhere next month. But as you said: tweaking is part of the fun
Cheers, Ralph
Winding matters...
Ralph,
Bifilar, is a winding technique where the primary and secondary wires are wound at the same time, together. This gets maximum bandwidth without too much sectionalizing. It is only usefull for 1:1 transformers.
The only drawback with this method is that the winding connecting phase is important.
Sectionalizing, is where the winding bobbin is split into sections. There is a seperate winding in each section. The windings are connected in series or parallel to obtain the right impedance.
The winding connecting phase is less important with this technique.
Your output transformer will be sectionalized. It must be.
There will probably be 4 sections. Each section will have a primary winding, and a secondary winding. The primary's are connected in series, while the secondarys are connected in parallel. This technique reduces the capacitance between wires carrying different signal potentials, and reduces the number of turns required.
Cheers,
Ralph,
I think that happens with your Interstage transformers because the windings are "bifilar".
Bifilar, is a winding technique where the primary and secondary wires are wound at the same time, together. This gets maximum bandwidth without too much sectionalizing. It is only usefull for 1:1 transformers.
The only drawback with this method is that the winding connecting phase is important.
Sectionalizing, is where the winding bobbin is split into sections. There is a seperate winding in each section. The windings are connected in series or parallel to obtain the right impedance.
The winding connecting phase is less important with this technique.
Your output transformer will be sectionalized. It must be.
There will probably be 4 sections. Each section will have a primary winding, and a secondary winding. The primary's are connected in series, while the secondarys are connected in parallel. This technique reduces the capacitance between wires carrying different signal potentials, and reduces the number of turns required.
Cheers,
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