there is no reasons whatsoever to use battery to bias power tubes, since a negative voltage can be achieved way easier with simple diodes.
I wouldn't mind using a 9V battery to bias tubes in a phono stage, at the condition to remember to change the battery every 5 years.
I wouldn't mind using a 9V battery to bias tubes in a phono stage, at the condition to remember to change the battery every 5 years.
They are well heatsinked as I designed it to use the CCS and the batteries were an afterthought. Without the batteries the CCS is between 12V and 70V depending on the tubes. For 6V6 I use LM317, and for the higher bias voltages I use a TL783.
And another transformer... I'm using an SMPS for the heaters so I can't even use a sextupler. I don't like the idea of obtaining bias from the B+ transformer as there is no bias tap and a voltage divider from -500V makes me uneasy. Plus the main reason is that it's more efficient, makes less heat, and gives more B+ to the tubes.
As for a phono stage I've found the best results using the CCDA topology with a passive filter in between.
Battery bias of an output tube is not for the faint of heart.
It is not worth it, unless it is implemented properly.
No current draw from the batteries, method to limit the current on the output tube,
prevention of thermal runaway, and easy (and instant) visual monitoring of the output tube current.
If you have enough B+ then just use self bias; if not, then use fixed adjustable bias or battery bias.
I took a very small area chassis that was only 1 inch deep. I added a large SE output transformer; choke input power supply; 3 upright electrolytic capacitors; a 2A3, a dual triode tube, large power resistors to drop the 6.3VAC down to 2.5V (at 2.5A); a hum balance pot, a resistor and 1 mA meter to monitor the 2A3 current; other miscellaneous parts; and 5 each 9V batteries in series.
This was all that would fit on the chassis.
There was no room to use 2 diodes, 2 more electrolytic caps, 1 resistor, and 1 pot in order to have fixed adjustable bias.
It is not worth it, unless it is implemented properly.
No current draw from the batteries, method to limit the current on the output tube,
prevention of thermal runaway, and easy (and instant) visual monitoring of the output tube current.
If you have enough B+ then just use self bias; if not, then use fixed adjustable bias or battery bias.
I took a very small area chassis that was only 1 inch deep. I added a large SE output transformer; choke input power supply; 3 upright electrolytic capacitors; a 2A3, a dual triode tube, large power resistors to drop the 6.3VAC down to 2.5V (at 2.5A); a hum balance pot, a resistor and 1 mA meter to monitor the 2A3 current; other miscellaneous parts; and 5 each 9V batteries in series.
This was all that would fit on the chassis.
There was no room to use 2 diodes, 2 more electrolytic caps, 1 resistor, and 1 pot in order to have fixed adjustable bias.
one thing that battery bias is good for is the power on/off/on bias drop which damages triodes and causes premature failures.
Fix bias tubes can fail prematurely when each time you turn off the amplifier the bias (-) falls before the B+ , which switch the tube outside max parameters. This is very important and should be the emphasis of fix bias designs which surely results in lower harmonics and better performance.
Fix bias tubes can fail prematurely when each time you turn off the amplifier the bias (-) falls before the B+ , which switch the tube outside max parameters. This is very important and should be the emphasis of fix bias designs which surely results in lower harmonics and better performance.
Also, if the B+ powers up before the fixed bias supply, that is not good for DHTs.
Battery bias is always there, both at power up, and at power down.
Battery bias is always there, both at power up, and at power down.
A bias tap is just a wire attached to the winding and brought out. You can use the lead going to the rectifier in the same way. Lots of amps create bias off of the HV A/C lead and divided down.
I suppose I could use a string of zener diodes or something but the batteries are just easier, especially with the CCS.
I use this arrangement.
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How to precisely adjust battery voltage for battery bias
My favorite battery is 18650 type Li ion cell. These cells are used in laptop computer batteries. Typically a throwaway laptop battery has a few good cells, so these cells can be had cheap or even free. The nominal voltage is 3.7 V, with the range of 3.2 V (fully discharged) to 4.2 V (fully charged).
Li ion cells have very low self-discharge rate within their working range. A partially charged cell (anywhere from 3.5 to 4.0 V) will keep steady voltage for at least a couple of years. So, a string of 10 cells can be precisely adjusted to any voltage between 35 and 40 V by manually charging it to the desired voltage point.
Using Li ion batteries, one should be aware that discharging below 3.0 V will kill the cell, and charging above 4.0 V will shorten cells's life. A Li ion cell cycled between 3.5 V and 4.0 V and not abused by over-current will last for 20-30 years.
My favorite battery is 18650 type Li ion cell. These cells are used in laptop computer batteries. Typically a throwaway laptop battery has a few good cells, so these cells can be had cheap or even free. The nominal voltage is 3.7 V, with the range of 3.2 V (fully discharged) to 4.2 V (fully charged).
Li ion cells have very low self-discharge rate within their working range. A partially charged cell (anywhere from 3.5 to 4.0 V) will keep steady voltage for at least a couple of years. So, a string of 10 cells can be precisely adjusted to any voltage between 35 and 40 V by manually charging it to the desired voltage point.
Using Li ion batteries, one should be aware that discharging below 3.0 V will kill the cell, and charging above 4.0 V will shorten cells's life. A Li ion cell cycled between 3.5 V and 4.0 V and not abused by over-current will last for 20-30 years.
Agreed it's a great battery, but to get 27V they would take a lot of chassis realty...
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