12 volt preamp

[beamnet]

Hi guys,

I got this cute miniature 6ag5 tub from a friend i traded with.

googling for an application i came across a radio citcuit using it in a 12 volt application.

Just out of curioity i powered up mu 12 V dektop supply and plugged some resistors 'n caps in my breadboard.

Within a short time i was hearing audio, after a bit tinkereing i am hearing GOOD audio.

Looks all cool on the scope. Don't know how to measure distortion, but it sounds teriffic.

Now i am suspecting there is some drawback, else we would all hook tubes to low voltage supplies.

Could anybody enlighten me why this isn't done more?

I am thinking: 12 lead acid battery and make a hummless phono!

 

[eVITAERC]

This IS being done and is already a very famous approach in the headphone amplifier scene. The most notable implementation mates it with a buffer output and is called the Millet Hybrid Amplifier.

 

[lineup]

12 Volt is maybe to overdo it.


But there are a few tubes that do reasonably well at lower voltages.
Say between 50-100 Volt.
But some values of performance will not be optimal.
What will suffer I do not know, as I am no tube expert.

One tube that can run a bit lower (than 200 Volt) is 6DJ8/E88CC/6922.

Here is a thread about same topic:
Running tubes at lower voltages

 

[owen]

Nope, these are tubes designed for 12V operation - typically for car radios!

Thought about finding some, but in the end I have too many other things to do!

Owen

 

[beamnet]

which tubes?

Bas

 

[eVITAERC]

For 12v single triodes we have the 12AE6A, 12FK6, and 12FM6.

These are all designed for car operation and can thus run well off a 12v SLA.

 

[Eli Duttman]

The 6GM8/ECC86 is a LOW voltage relative of the 6922. It's a fine Dutch product.

 

[316a]

Hi ,
I don't know about the space charge valves mentioned earlier but the ECC86 looks like a safe bet . Otherwise if you can stretch to 50v or so , miniatures such as 3S4 are a possibility and there are many subminiature types that run at low voltages . Steve Bench has a battery phono stage on his site , maybe a good reference ?

cheers

316a

 

[rcavictim]

I have a bunch of NIB 12CN5 and was thinking of a battery amp myself. These are IF pentode but ought to work at lower frequencies I'd think. You can actuallly get 4.5 mA plate current happening with 12 volts B+. Here's data on this baby. http://www.nj7p.org/Tube1.php?tube=12cn5

 

[lineup]

The 6GM8/ECC86 is a LOW voltage relative of the 6922. It's a fine Dutch product.

6GM8 is tube design especially for 12 volt supply ( in car battery operation ).
At plate 12 Volt will run like 2.5 mA
At plate 6 Volt will run like 0.8-1.0 mA


I guess that when plate 6 Volt, the supply is 12 Volt
and anode resistor is like 5 kOhm
and cathode resistor 1 kOhm

Heater is 6.3 Volt / 330mA

 

[marziom]

hi... this is my first post here....

i have a box of 3A4 they are power pentode (DHT!) for radio operation....

 

[Giaime]

Hello Marziom,

do I know you?