Hello, I’m going to make a little 5F2A but I want it to be as clean as possible. Any suggestions for changes to the circuit? I was thinking of just a lower gain preamp tube or a lower value plate resistor on the second stage.
Thanks
Changes to an 5F2A for more clean headroom
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Changes to an 5F2A for more clean headroom
old user username was steveo
Re: Changes to an 5F2A for more clean headroom
remove bypass cap on the cathode of the first gainstage?
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Re: Changes to an 5F2A for more clean headroom
12AY7 for the first tube
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Stevem
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Re: Changes to an 5F2A for more clean headroom
First built it stock but with a 5AR4 in place of the 5Y3, and also change the 470 ohm on the cathode of the output tube to 500 or 520 ohm 5 watt.
If that's still not good enough then hook up your scope and tone genorator, drive the amps input with 150 me and then look to see which gain stage starts to clip first.
Many times the output tube clips first and the best way to deal with this and still have good touch and feel out of the amp is to either lower the gain on the drive signal to the output or put in a master volume or a voltage divider after the coupling cap off the plate of the driver.
Basically what I am saying is if you like the feel of the amp before it clips then removing the bypass cap on the first gain stage or swapping that tube out for a 12AY7 will effect that feel and not for the better.
A lot also hinges on how much mids your pickups have, how close they are to the strings and just in general how hot they are.
If that's still not good enough then hook up your scope and tone genorator, drive the amps input with 150 me and then look to see which gain stage starts to clip first.
Many times the output tube clips first and the best way to deal with this and still have good touch and feel out of the amp is to either lower the gain on the drive signal to the output or put in a master volume or a voltage divider after the coupling cap off the plate of the driver.
Basically what I am saying is if you like the feel of the amp before it clips then removing the bypass cap on the first gain stage or swapping that tube out for a 12AY7 will effect that feel and not for the better.
A lot also hinges on how much mids your pickups have, how close they are to the strings and just in general how hot they are.
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Not screaming like the passengers in his car!
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Re: Changes to an 5F2A for more clean headroom
Cool, thanks. I see mentioned a master volume or voltage divider. How do these little amps react to a master volume before the power tube?
old user username was steveo
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Stevem
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Re: Changes to an 5F2A for more clean headroom
I much prefer with any amp, but especially small ones to not have a master .
It’s much better to just pump the amp thru a good load attenuator if a SPL reduction is needed.
The use of a master volume to me is to really only allow you to set the ratio of preamp distortion to output stage distortion, and since your goal is to have the minimum amount of that I see no need for such in your build.
Any amp will always sound more natural without that crutch in the circuit.
Just play with your levels of gain from stage to stage that works best for having good cleans and also good feel.
With any preamp stage besides removing or added a bypass cap on the cathode you can play around with the value of the plate or cathode resistor by up to 25% before you need to mess with the power supply voltage feeding that stage.
The main thing you will find from playing around with all 3 tubes is that for the best cleans to take place before clipping steps in is to have a tube biased such that it achieves saturation and cut of at the same level of drive signal.
The great thing about a 3 tube single ended amp of any wattage is that it’s so easy and quick to play around with that in one afternoons time you will have a good feel for what changes will head you in the direction to get to your needs.
Also don’t forget that the value of the interstate coupling caps and the amount of low end they pass down stream will have a big effect on when clipping takes place.
So messing around with these will be time well spent also.
It’s much better to just pump the amp thru a good load attenuator if a SPL reduction is needed.
The use of a master volume to me is to really only allow you to set the ratio of preamp distortion to output stage distortion, and since your goal is to have the minimum amount of that I see no need for such in your build.
Any amp will always sound more natural without that crutch in the circuit.
Just play with your levels of gain from stage to stage that works best for having good cleans and also good feel.
With any preamp stage besides removing or added a bypass cap on the cathode you can play around with the value of the plate or cathode resistor by up to 25% before you need to mess with the power supply voltage feeding that stage.
The main thing you will find from playing around with all 3 tubes is that for the best cleans to take place before clipping steps in is to have a tube biased such that it achieves saturation and cut of at the same level of drive signal.
The great thing about a 3 tube single ended amp of any wattage is that it’s so easy and quick to play around with that in one afternoons time you will have a good feel for what changes will head you in the direction to get to your needs.
Also don’t forget that the value of the interstate coupling caps and the amount of low end they pass down stream will have a big effect on when clipping takes place.
So messing around with these will be time well spent also.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Changes to an 5F2A for more clean headroom
You could try a good 5751 instead of a 12AX7. I think it has a gain factor or mu of 70.
I changed the coupling caps in mine to .0022uf rather than the stock .022uf to get rid of the excessive sub-tones as well. Getting rid of the unwanted low-end did the most for me in terms of cleaning up the amp a bit.
I changed the coupling caps in mine to .0022uf rather than the stock .022uf to get rid of the excessive sub-tones as well. Getting rid of the unwanted low-end did the most for me in terms of cleaning up the amp a bit.
Last edited by lightfoot on Wed Apr 26, 2023 10:23 am, edited 1 time in total.
Re: Changes to an 5F2A for more clean headroom
I built a small 5f2 with diode rectifier 6v6 and 12ax7 that a friend bought and took to another builder and they loved it only thing they did was add mini toggle for bypass boosting. Thanks to rj for PT.
Mark
Mark
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Re: Changes to an 5F2A for more clean headroom
Cool build, Mark. I like that old Stancor PT.
Re: Changes to an 5F2A for more clean headroom
Solid State rectifier to maximize B+ (Hint: The empty socket hole can also be used to parallel a second output tube for more power)
No cathode bypass cap on V1b and have adjustable NFB.
PT that can handle 6L6, 6550, and/or KT88.
Ultralinear output transformer. (You can put this on a switch, FWIW)
That's more or less the most you're going to squeeze out of it.
No cathode bypass cap on V1b and have adjustable NFB.
PT that can handle 6L6, 6550, and/or KT88.
Ultralinear output transformer. (You can put this on a switch, FWIW)
That's more or less the most you're going to squeeze out of it.
It's true i've lost my marbles and i cant remember where i put them
Re: Changes to an 5F2A for more clean headroom
Solid State rectifier to maximize B+ (Hint: The empty socket hole can also be used to parallel a second output tube for more power)
No cathode bypass cap on V1b and have adjustable NFB.
PT that can handle 6L6, 6550, and/or KT88.
Ultralinear output transformer. (You can put this on a switch, FWIW)
That's more or less the most you're going to squeeze out of it.
No cathode bypass cap on V1b and have adjustable NFB.
PT that can handle 6L6, 6550, and/or KT88.
Ultralinear output transformer. (You can put this on a switch, FWIW)
That's more or less the most you're going to squeeze out of it.
It's true i've lost my marbles and i cant remember where i put them
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youtubeexhile
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Re: Changes to an 5F2A for more clean headroom
A simple and easy way to increase the clean headroom is to increase the pre-amp voltage.
Just swap the 22k dropping resistor for a 10k.
All transformers are different but for illustrative purposes this took my voltages from 268 in the preamp to 286.
To complete the transition to a clean machine also drop the V1A cathode bypass cap down to 4.7uf. This trims low end allowing the amp to make a hair "more" clean output.
Just swap the 22k dropping resistor for a 10k.
All transformers are different but for illustrative purposes this took my voltages from 268 in the preamp to 286.
To complete the transition to a clean machine also drop the V1A cathode bypass cap down to 4.7uf. This trims low end allowing the amp to make a hair "more" clean output.