Just started on a new valve amplifier.
It is about 100 watts using quad el34.
It has lots of gain to amplifier the guitar signal.
It has bass and treble controls.
A phase splitter into 4 el34's.
I am using fixed bias so I don't lose power in the cathode resistors.
Power supply is just CRC and gives 340 volts DC.
Fixed bias supply is half wave rectified AC into a capacitor and preset.
Circuit is pretty big and doesn't come out well on a screen.
However here is the pcb layout.
It is about 100 watts using quad el34.
It has lots of gain to amplifier the guitar signal.
It has bass and treble controls.
A phase splitter into 4 el34's.
I am using fixed bias so I don't lose power in the cathode resistors.
Power supply is just CRC and gives 340 volts DC.
Fixed bias supply is half wave rectified AC into a capacitor and preset.
Circuit is pretty big and doesn't come out well on a screen.
However here is the pcb layout.
An externally hosted image should be here but it was not working when we last tested it.
The 807 can indeed be run at higher voltages than other 6L6 family members but not at the full 30W dissipation of the 6L6GC! The anode is rated for 25W and 600V max. Another thing to watch is the screen rating: 300V max (400V trilde connected).
You might want to think about having an adjustable bias supply. Today's tubes vary quite a bit. Also, they are quite different from vintage tubes.
Agree with Parafeed, it will be hard to get 100 watts at that voltage but going from 100 down to 70 watts is only a drop of 1.5dB, so you mostly will lose clean headroom. Depending on what you want the amp to do this might or might not be an issue. If you are going for overdrive/distortion, no big deal. If you want good cleans at loud volumes, maybe might want to up the B+ to low 400s at least.
Agree with Parafeed, it will be hard to get 100 watts at that voltage but going from 100 down to 70 watts is only a drop of 1.5dB, so you mostly will lose clean headroom. Depending on what you want the amp to do this might or might not be an issue. If you are going for overdrive/distortion, no big deal. If you want good cleans at loud volumes, maybe might want to up the B+ to low 400s at least.
nigelwright7557,
I suppose that you looked after the circuits made from Marshall, Orange or Hiwatt. If not already, do it...
Search for the Hiwatt DR103 (the best IMHO), Marshall 2203, Orange 120 schematics, search also for the specs of their OPT (you can go to tubetown.de for that). You will notice that all these amps share an HV at 440-460VDC and pl-to-pl load of circa 2K.
A+!
I suppose that you looked after the circuits made from Marshall, Orange or Hiwatt. If not already, do it...
Search for the Hiwatt DR103 (the best IMHO), Marshall 2203, Orange 120 schematics, search also for the specs of their OPT (you can go to tubetown.de for that). You will notice that all these amps share an HV at 440-460VDC and pl-to-pl load of circa 2K.
A+!
I used to have a Simm-Watts 100 watt PA amplifier.
I had a look through the circuit for that.
The Simm-Watts is fixed bias too.
I have put a lot of effort into the pcb to ensure no ground loops and that I have minimal track lengths especially around the input.
This is my second go at a 100 watt valve guitar amp, the previous version didn't have enough gain so I have added another 12ax7 gain stage.
I had a look through the circuit for that.
The Simm-Watts is fixed bias too.
I have put a lot of effort into the pcb to ensure no ground loops and that I have minimal track lengths especially around the input.
This is my second go at a 100 watt valve guitar amp, the previous version didn't have enough gain so I have added another 12ax7 gain stage.
Some of the VIAS are way to small, especially on the heaters..and GND return for output tubes.... During a "fault event" those vias will open...
I suggest a GND plane for noise reduction....use a POLY-POUR-PLANE, aka, Polygon-Pour .... this is for shielding only...not for return currents..
The AC HEATER lines should be placed over each other and around a GND plane to reduce field...
Make sure to follow guidelines for creepage distances and dielectric thickness for the voltages you are working at...
Download a PDF copy of IPC 2221A-C and you will find all the info in there in for guidleines..
http://sisko.colorado.edu/CRIA/FILES/REFS/Electronics/IPC_2221A.pdf
I suggest a GND plane for noise reduction....use a POLY-POUR-PLANE, aka, Polygon-Pour .... this is for shielding only...not for return currents..
The AC HEATER lines should be placed over each other and around a GND plane to reduce field...
Make sure to follow guidelines for creepage distances and dielectric thickness for the voltages you are working at...
Download a PDF copy of IPC 2221A-C and you will find all the info in there in for guidleines..
http://sisko.colorado.edu/CRIA/FILES/REFS/Electronics/IPC_2221A.pdf
The vias are all 60/40 thou of inch.
They have terminal pins in the holes so should be OK for output valve heaters.
The preamp heaters is only 600ma so should be OK.
I tried to reduce vias where I could.
There are so many tracks there wouldn't be much of a ground plane.
I did have a problem with noise on the previous version so this time made the front end very short and tight this time around.
They have terminal pins in the holes so should be OK for output valve heaters.
The preamp heaters is only 600ma so should be OK.
I tried to reduce vias where I could.
There are so many tracks there wouldn't be much of a ground plane.
I did have a problem with noise on the previous version so this time made the front end very short and tight this time around.
If you don't want to increase the SIZE of your VIAS, then over lap the traces and add more VIAS....figure 4 to 6 more VIAS...
The thinnest track is 75 thou so I could increase the size of the via's a bit from 40 thou.
I have added ground plane on both sides of pcb, there was a bit more spare room than I thought. I only added ground plane to front end to stop ground loops from output stage.
I have added ground plane on both sides of pcb, there was a bit more spare room than I thought. I only added ground plane to front end to stop ground loops from output stage.
An externally hosted image should be here but it was not working when we last tested it.
I'm trying to understand why you go to all the trouble of doing this. It seems as though PCB amps' whole purpose is to save money on mass production costs. If this is a one-off, is there a reason for doing it this way? Not knocking it, it's cool that you want to do something different, just wondering if there is an advantage for doing this or just that this is your preferred way to do it. I have to admit, this takes another level of skill to pull this off. It's just from my point of view, this is a whole lot of extra work. But I'm old school, I like point to point, turret boards, etc, but this old dog might want to learn a new trick.
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