Universal SE Amp Driver Board

[Curious_George]

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[John Warren]

One would also require a filament supply (VAC or VDC?), 350VDC supply that may also be on a PC board.  There's also power transformer, OT transformer, chassis/cage.  Are the tubes mounted to the PC board? or is the board for component and wire management only? 

[Curious_George]

Hi John,

I have attached my preliminary layout. I am trying to keep the pcb as small as practical while giving me enough room for signal, low voltage and high voltage traces. It is a challenge as you know. I know you have done a lot of pcb layout so feel free to offer advice if you want. I not an expert at pcb layout, but am at an intermediate level. 

 

The driver and rectifier tubes will be mounted on the pcb. The output tubes will be chassis mounted. I have provisions on the pcb for DC filaments.

[No.4]

I wanted to build a get set go, but by the time I got around to it Shannon was no longer selling boards. Real bummer. I did build a clementine which has been my daily driver for many years now. Great designs.

[Curious_George]

20 hours ago, No.4 said:

I wanted to build a get set go, but by the time I got around to it Shannon was no longer selling boards. Real bummer. I did build a clementine which has been my daily driver for many years now. Great designs.

I'll probably get the boards made even if I don't get commitments here. I'll eventually sell the boards somewhere. I was just trying to help DIYer's easily build a nice SE amp. 

 

I don't desire a PCB, I prefer point-to-point, but since I am getting them made, I would use one. 

[captainbeefheart]

Looks good, I'm sure you meant 1.1mA and not .0011mA as .0000011*1800 does not equal 2v

 

 

I know you are already deep into the design but you may consider just doing and end all driver board that can drive grid current.

 

AC couple the common cathode stage to the follower and reference the follower cathode and grid to a negative supply. Swap to a 12DW7 that way there you have a high mu triode for gain and a better follower for a driver.

 

Or better, use one 12AX7 for both channels and then use two Mosfet source followers for the grid drive. I tried about a bazillion different tubes including high gm types and even high'ish gm power tubes like EL84/6BQ5 as a follower. The EL84 worked the best but it's just very wasteful in my opinion and doesn't do nearly as good as a job as a Mosfet. The latter requires no heater current, no heater to cathode ratings to adhere to, and best of all they are cheap and last forever. I know some people complain about having solid state parts in their tube amps but the Mosfet follower has slightly less than unity gain and is transparent. I.e. It doesn't add anything negative to the sound. It's just a buffer.

 

 

[Curious_George]

14 hours ago, captainbeefheart said:

Looks good, I'm sure you meant 1.1mA and not .0011mA as .0000011*1800 does not equal 2v

 

 

I know you are already deep into the design but you may consider just doing and end all driver board that can drive grid current.

 

AC couple the common cathode stage to the follower and reference the follower cathode and grid to a negative supply. Swap to a 12DW7 that way there you have a high mu triode for gain and a better follower for a driver.

 

Or better, use one 12AX7 for both channels and then use two Mosfet source followers for the grid drive. I tried about a bazillion different tubes including high gm types and even high'ish gm power tubes like EL84/6BQ5 as a follower. The EL84 worked the best but it's just very wasteful in my opinion and doesn't do nearly as good as a job as a Mosfet. The latter requires no heater current, no heater to cathode ratings to adhere to, and best of all they are cheap and last forever. I know some people complain about having solid state parts in their tube amps but the Mosfet follower has slightly less than unity gain and is transparent. I.e. It doesn't add anything negative to the sound. It's just a buffer.

 

 

Hey Cappy - I wanted to keep this particular design simple. It can technically drive some grid current, but not much. My intention is to get DIY'ers to build and gain experience (if new in the hobby) to build a SE amp. A lot of people can build from a schematic and PCB vs a schematic & point-to-point wiring. 

 

No doubt there are alternate circuits that can be used here, but I am already slightly larger than the orignal Get*SET*Go PCB and I did not want to design a "hybrid circuit". 

 

I know you prefer to drive grids positive for the headroom, but awhile back you did a poll on how much power we actually use when listening, I believe your results surprised a lot of poeple and the power used was quite low in most circumstances. If this is the case, then for a lot of tubes used with this driver circuit, we should have plenty of power without going to A2. I love A2, but this driver PCB was not designed with that in mind this time around. 

 

 

 

[captainbeefheart]

2 hours ago, Curious_George said:

Hey Cappy - I wanted to keep this particular design simple. It can technically drive some grid current, but not much. My intention is to get DIY'ers to build and gain experience (if new in the hobby) to build a SE amp. A lot of people can build from a schematic and PCB vs a schematic & point-to-point wiring. 

 

No doubt there are alternate circuits that can be used here, but I am already slightly larger than the orignal Get*SET*Go PCB and I did not want to design a "hybrid circuit". 

 

I know you prefer to drive grids positive for the headroom, but awhile back you did a poll on how much power we actually use when listening, I believe your results surprised a lot of poeple and the power used was quite low in most circumstances. If this is the case, then for a lot of tubes used with this driver circuit, we should have plenty of power without going to A2. I love A2, but this driver PCB was not designed with that in mind this time around. 

 

 

 

 

You're probably right in that as long as you have say 5 watts or more most of the guys here with big horn speakers shouldn't be hitting grid current too often unless playing loud dynamic music.

 

For me it's not so much about the extra power, it just to eliminate the time it takes to recover from getting near 0v on the grid. The coupling cap charges up and you get a bias shift then it all needs to recover. With 2 watt or less amps I feel grid drive is a great insurance policy for great sound.

 

I have helped many people with their systems and after analyzing lots of systems of people using SET amps I found that one of the major issues was AC coupling the power stage. It's when the beer starts to flow and the volume goes up past where they normally listen at is when their SET amps run into this issue so I found it best to just go grid drive that way there if the amp is used to close to it's maximum headroom it will still perform decent enough. I know some will say just get a more powerful amp but a lot of us really find a tube or an amp that we really like the sound of and don't want to change. We just want to improve the amp we have to work better under tougher conditions.

 

 

[henry4841]

Do not expect an answer because I am almost sure the original poster has moved on. At least I have not seen him in months. As far as CBH, well let's just say he is no longer here either. I miss Curious George but I am sure he has his reason for not participating lately. Very knowledgeable guy. 

[Marvel]

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