[L0rdGwyn]

My favorite part(s) of the entire build! There is just something about using batteries within these types of devices .. when I first used batteries to hear what fixed bias sounded like compared to cathode bias in my amps circuit, firstly the sound quality amazed me but IMHO there is elegance in its simplicity, especially when it does such a good job.

When it can be used, battery bias is great. Not really practical for power stages however as the bias currents will be all over the place. Not a problem with low power gain stages however since the tubes are not typically biased near their maximum plate dissipation. A conventional negative bias supply with adjustable bias preferred for power stages.

I love to make my dry joke about changing the batteries so the amplifier doesn't lose power, but I controlled myself when I posted that pic. Every once in a while someone falls for it

 

[g0ldl10n]

When it can be used, battery bias is great. Not really practical for power stages however as the bias currents will be all over the place. Not a problem with low power gain stages however since the tubes are not typically biased near their maximum plate dissipation. A conventional negative bias supply with adjustable bias preferred for power stages.

Right now I have a single 9V batter in series with an adjustable negative voltage regulator - 1 regulator splitting its single negative out into two separate lines, then both in series with its own 9V battery, then tied to each grid of the output tubes - will give me a bit more overhead if needed for certain tubes and acts as a sort of fail safe in the event the regulator stops regulating - at least there should be -9V biased at all times - but so far the negative voltage regulator is only responsible for about 22% of the total negative voltage applied to the grids right now and the plate currents (which I am actively monitoring each tube live) and both are very stable. Only fluctuating within 1mA range.. seeing it range from 40.5mA to 41.5mA (both tubes in this range). I guess if the performance of this continues this way, a battery in series along with a negative voltage regulator even if the batteries are doing majority of the lifting is fine in/with certain scenarios/power tubes.

I love to make my dry joke about changing the batteries so the amplifier doesn't lose power, but I controlled myself when I posted that pic. Every once in a while someone falls for it

 

[L0rdGwyn]

Right now I have a single 9V batter in series with an adjustable negative voltage regulator - 1 regulator splitting its single negative out into two separate lines, then both in series with its own 9V battery, then tied to each grid of the output tubes - will give me a bit more overhead if needed for certain tubes and acts as a sort of fail safe in the event the regulator stops regulating - at least there should be -9V biased at all times - but so far the negative voltage regulator is only responsible for about 22% of the total negative voltage applied to the grids right now and the plate currents (which I am actively monitoring each tube live) and both are very stable. Only fluctuating within 1mA range.. seeing it range from 40.5mA to 41.5mA (both tubes in this range). I guess if the performance of this continues this way, a battery in series along with a negative voltage regulator even if the batteries are doing majority of the lifting is fine in/with certain scenarios/power tubes.

If you have some adjustability in the negative supply that's good, but you might want to eventually get a supply that has enough negative voltage available to send the tube to cutoff i.e., no current (or close to it), then use a potentiometer as a voltage divider to adjust bias. So you can turn the tube down from no current up to your desired bias current, and a little higher to account for tube aging. And include fuses for safety in case the negative supply were to fail for some reason.

 

[g0ldl10n]

If you have some adjustability in the negative supply that's good, but you might want to eventually get a supply that has enough negative voltage available to send the tube to cutoff i.e., no current (or close to it), then use a potentiometer as a voltage divider to adjust bias. So you can turn the tube down from no current up to your desired bias current, and a little higher to account for tube aging. And include fuses for safety in case the negative supply were to fail for some reason.

I have been waiting to order Merlins book on power supply designing until I felt ready, and now that I have gotten to this point of basic understanding as well as execution with my working prototype circuit, I ordered it today and is scheduled to arrive Friday. I am not sure how in depth it will go into bias supplies, but regardless, I know my current power supply is probably not ideal and likely has a lot of room for improvements, so I am highly anticipating its arrival. I think that book could be more profound (or at least just as) to me than the other one already has been, I am very excited!

 

[g0ldl10n]

And it arrived!

Taking a look at subjects of each chapter I believe this book will be extremely helpful, as I have many questions pertaining to all of them still.

 

[L0rdGwyn]

Got some parts in today for my HY69 final build. Nothing too interesting, except for maybe the umbilical connectors. Using these 11-pin mil-spec Amphenol connectors. Pricey, but very high quality and rated for 1kV.



Wanted to check these out in person before finalizing chassis plans. Going to do raw DC for the filament, B+, and bias supplies in the power supply chassis and keep the regulators in the amplifier chassis, meaning raw DC will run over the umbilical, which will be shielded. For the sake of keeping high ripple currents out of the amplifier chassis (which is a potential source of noise), I've added an additional RC filter to my raw DC boards for the B+ and bias supplies. I will be using regulated DC for the input tube heaters as well, and probably floated some +30-40V above ground. I'm going to keep the heater regulator in the power supply chassis and run the regulated DC over the umbilical to the amplifier chassis as it is not imperative that it be ultra low noise for indirectly heated tubes.

Layout and chassis plans are maybe 80% done. Still waiting on the Simpson meters and a new custom mains transformer with a bias winding and some 7VAC windings for my heater regulator. Bias point for HY69 will be 400V / 55mA. New output transformers are 7K:100ohm/32ohm. Should be pretty interesting when it's all done, a three chassis beast, but it will sound great and be very low noise.

Oh and I will be getting rid of the blue ClarityCaps everyone hates LOL new PCBs designed for Vishay film caps that will go inside the chassis.

 

[triod750]

I will be getting rid of the blue ClarityCaps

Loverly!! Beautifying!!!

 

[L0rdGwyn]

Loverly!! Beautifying!!!

Turns out they were sitting right where I want the bias pots to go, and with the extra real estate inside without power supply parts, plenty of room to move the caps indoors. But switching to Vishay as they are easier to fit and work well on a PCB.

Oh I also got this thing. I commissioned a rotating walnut cassette holder from a guy on Etsy. Came out really well! Also doubles as a cat deterrent on top of my speakers

 

[triod750]

Turns out they were sitting right where I want the bias pots to go, and with the extra real estate inside without power supply parts, plenty of room to move the caps indoors. But switching to Vishay as they are easier to fit and work well on a PCB.

Sometimes you are just lucky!!

 

[mjstealey]

Oh I also got this thing. I commissioned a rotating walnut cassette holder from a guy on Etsy. Came out really well! Also doubles as a cat deterrent on top of my speakers

Once they figure out that it rotates it will go from deterrent to worlds best speaker top cat toy

 

[L0rdGwyn]

Sometimes you are just lucky!!

Sometimes you name your cat Lucky. He's the one that likes to jump on the speakers. He was a street cat so he pays humans no mind.

 

[triod750]

He owns you, as cats do