The JFETs require 6 to 7 volts minimum at the drain, so at least 10-11 Volt rails.
thanks for the information.
I was thinking of making a smaller amplifier to test and for low volume music.
The normal F5 can give 50W peaks and is 25W normal power class A and needs a 300VA transformer.
A 2x12V 100-150VA transformer should give 16V rails.
This should give 9W normal power with 18W peak capability.
I think the correct bias would be 0,75A.
Heat dissipation per channel is 24Watts so the needed heatsink would be 0,84°C/W for 20°C difference.
I hope my thoughts are correct.
I was thinking of making a smaller amplifier to test and for low volume music.
The normal F5 can give 50W peaks and is 25W normal power class A and needs a 300VA transformer.
A 2x12V 100-150VA transformer should give 16V rails.
This should give 9W normal power with 18W peak capability.
I think the correct bias would be 0,75A.
Heat dissipation per channel is 24Watts so the needed heatsink would be 0,84°C/W for 20°C difference.
I hope my thoughts are correct.
Not a half bad idea actually, for 12W dissipation each, one could even use the TO-220 version of the 19N20C/12P20, an FQP pair does ~€2.25 at DK.
Ah, well how about that!
I remember finding your article about "tuning transformers" some years ago and have been using the technique ever since with remarkable results, and I wanted to thank you for that "little gem" - thank you.
Pity the website is plagued by that irritataing advertising.
I remember finding your article about "tuning transformers" some years ago and have been using the technique ever since with remarkable results, and I wanted to thank you for that "little gem" - thank you.
Pity the website is plagued by that irritataing advertising.
Drifting bias
I am having a problem on one of the channels. This was working fine for over a year when all of a sudden one channel developed this problem. I changed the adjustment pots based on suggestion from this forum, and it worked for a few days of extended testing and listening. But now it's doing it again. The bias voltage on the output resistors dropped from .575 to about .400 at first but now it is all over the place. The other channel is rock-steady.
Do you think the thermistors themselves could be a problem? I know, I know. I could change them and see. But unfortunately, due to the beauty of my chassis layout, I have to take out the power supply and the big caps out first to get at the amp board. So iterative troubleshooting is a bit of a pain. Some pointers would be helpful.
Thanks
UV
I am having a problem on one of the channels. This was working fine for over a year when all of a sudden one channel developed this problem. I changed the adjustment pots based on suggestion from this forum, and it worked for a few days of extended testing and listening. But now it's doing it again. The bias voltage on the output resistors dropped from .575 to about .400 at first but now it is all over the place. The other channel is rock-steady.
Do you think the thermistors themselves could be a problem? I know, I know. I could change them and see. But unfortunately, due to the beauty of my chassis layout, I have to take out the power supply and the big caps out first to get at the amp board. So iterative troubleshooting is a bit of a pain. Some pointers would be helpful.
Thanks
UV
i have a good quality of toroidal transformer with 2x36vac 500va
and i want to use them in my F5
questions:
1. is that possible to regulating the 2x36vac into 2x18vac without loosing the current? anyone have the schematics for this?
2. if regulating is possible, should it placed before the filter caps (the 15000uf), or after?
thanks.
and i want to use them in my F5
questions:
1. is that possible to regulating the 2x36vac into 2x18vac without loosing the current? anyone have the schematics for this?
2. if regulating is possible, should it placed before the filter caps (the 15000uf), or after?
thanks.
Hi,
I don't know that schematic, could work. But you would need adequate heatsinks for it. In fact you need twice the heatsinking capability than the original amp for your amp+ps.
At least here in europe the main factors for the costs on an amp like this are the heatsinks and the transformer. I think you will get a cheaper and better amp if you buy an adequate transformer.
Best regards
Flo
I don't know that schematic, could work. But you would need adequate heatsinks for it. In fact you need twice the heatsinking capability than the original amp for your amp+ps.
At least here in europe the main factors for the costs on an amp like this are the heatsinks and the transformer. I think you will get a cheaper and better amp if you buy an adequate transformer.
Best regards
Flo
One cannot easily regulate AC voltage.
We generally adopt converting the AC to DC and regulate to the required voltage.
Starting a project with the wrong transformer is silly.
Buy the correct transformer, or select a project that will work properly with the transformer you have.
BTW,
you have 19Vac tappings on your transformer, but the VA available is ~18% of the total. i.e. 90VA from each of the two 19Vac windings, (if the wire to the 55Vac taps is the same as the wire in the remainder of the winding).
We generally adopt converting the AC to DC and regulate to the required voltage.
Starting a project with the wrong transformer is silly.
Buy the correct transformer, or select a project that will work properly with the transformer you have.
BTW,
you have 19Vac tappings on your transformer, but the VA available is ~18% of the total. i.e. 90VA from each of the two 19Vac windings, (if the wire to the 55Vac taps is the same as the wire in the remainder of the winding).
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