Out go the cathode's resistor and cåp - In goes the BATTERY

[mooreamps]

With rechargeable cells: would it work to power the heaters with a digital power supply such as this Nokia 5.7 volt @ 800mA

I don't know. 5.7 volts maybe enough to light up the tube, but barely enough to light up the tone.

-g

[CRU JONES]

5.7volts not enough to light up the tone? How much do you need to do that?


You could crack open the nokia and get the app. notes on whatever switching supply is used and mod it to 8 volts, that will light your tone up!

Kidding aside, I wish I regulated my heaters with a LM317 instead of a LM7812.6 so I could test this out.

[Guitarist]

5 Volts might be the reason I sold an ADA MP1 complete with the 3 tube mod. It sounded cold but I'm sure it was other other reasons too.

I tried the battery on the worst possible amp, a Carvin ts100 which has as many gain stages as a Fender preamp. A Boogie rack poweramp has one less. Carvin held things back with a 22K cathode resistor which was a HUGE change.

[mooreamps]

5.7volts not enough to light up the tone? How much do you need to do that?

6.0 volts min.

Kidding aside, I wish I regulated my heaters with a LM317 instead of a LM7812.6 so I could test this out.

If you do, I recommend you run your heaters at 12.6 volts instead of 6.3. At 6 volts, I don't think the lm317 is that stable.

-g

[Guitarist]

I figured out where the hum was coming from. I had to add 100 Ohm resistors to float the heaters from ground. As this was rectified and regulated DC (has to to bring Volts down to 12) that got floated as well.
pin 4 +'ve, 5 neg, 9 n.c.

The batteries expand the bass as the analyzer suggests. Not EQ'ed. Tube is a 12au7.

Fender pre in a Dunlop volume pedal! I'd post an sound sample if it was possible here. I'm going to move the batteries into a Marshall as this is too clipped.

[tedmich]

No it does not. The thermal noise generated by the cathode resistor across the very high 1 meg ohm input impedance of the gain stage, is the major contributor to the hiss factor of the gain stage. I know this because I am currently writing a doc thesis on the subject. Secondly, I would imagine quite the opposite, with the open bandwidth of the led, allows for a fuller , fatter tone and quite honestly my intent of the gain stage is a flat frequency response; thus allowing any tone shaping to be done inside the tone stacks.

-g

huh? I thought all cathode bypass diodes/zeners/LEDs had to have ~100nF snubbers across them to avoid switching noise when the stage is overdrive, while "thermally noisy" resistors never do?

I am interested in trying the "oddwatt" LM338 CCS bias configuration on an EL84 PP, but have diodes on gainstage cathode bypass been used in any guitar amps that I'd know?

I may well be confused here, as my dissertation was on an unrelated subject

[mooreamps]

huh? I thought all cathode bypass diodes/zeners/LEDs had to have ~100nF snubbers across them to avoid switching noise when the stage is overdrive, while "thermally noisy" resistors never do?

No, because the diode / led is always forward biased, there-by they never "switch". Further, I would imagine the zener would be even noiser than the resistor, and thus not recommended.

I am interested in trying the "oddwatt" LM338 CCS bias configuration on an EL84 PP, but have diodes on gainstage cathode bypass been used in any guitar amps that I'd know?

I don't know, but I have read it is currently being tried by others. I do use the led's in my power amp stages, but more for the bite function, not for biasing. If used only for biasing, then it would not be compatible with my electronic power brake.


-g





[/QUOTE]

[Guitarist]

I can add that after comparing an LED to a battery, the LED totally sucked. Meaning harsh and biting —even sitting at the bottom of a tube. Kind of what I used to suspect; a tone killer but the glow was cool and reminded you that the mains were on

I soldered in a few batteries (scratch the end caps, dabbed resin and added the wire to pin 3/8 and the local/star ground) and they really clear the amp up. No BS! Alike changing to a fine quality tube, new pickups or _____.
They caveat is that you don't get the bass shaping that .47uF caps, etc. deliver (mentioned prior) and so your stuck with full bandwidth. I auditioned them through a Hiwatt, a couple different 4x12s, Planet Waves cable and a nice axe. They are staying; the head is well ventilated but I'll keep an eye on them for unlikely leakage.

Try one sometime, if you don't hear good things and potential—I'll buy you a beer. Must be 19 or over and claim prize in Vancouver BC.

[mooreamps]

this is what happens when people attempt to reverse engineer my design work. You have to change the input and output coupling values to get the proper gain bandwidth thru the gain stage.


-g

[tedmich]

I can add that after comparing an LED to a battery, the LED totally sucked. Meaning harsh and biting —even sitting at the bottom of a tube. Kind of what I used to suspect; a tone killer but the glow was cool and reminded you that the mains were on

I soldered in a few batteries (scratch the end caps, dabbed resin and added the wire to pin 3/8 and the local/star ground) and they really clear the amp up. No BS! Alike changing to a fine quality tube, new pickups or _____.
They caveat is that you don't get the bass shaping that .47uF caps, etc. deliver (mentioned prior) and so your stuck with full bandwidth. I auditioned them through a Hiwatt, a couple different 4x12s, Planet Waves cable and a nice axe. They are staying; the head is well ventilated but I'll keep an eye on them for unlikely leakage.

Try one sometime, if you don't hear good things and potential—I'll buy you a beer. Must be 19 or over and claim prize in Vancouver BC.

why not use an "ultra capacitor" as the battery:
Long-life capacitor suits battery backup apps
you could wire it to charge when off and play until it needed juice

or use these:


$4500/pair

(not kidding->kidding)

[mojo2001]

As a more prominent, recent, and hi-tech example of battery bias, I had a mid 60s Neumann record cutting system where where the preamplifier had a bias battery in the cathode of the input tube.


Clearly they were going for optimal performance and this wasn't some audiophile experiment. I am in the crazy end of the audio biz so I understand and appreciate what that DIY madness is all about, but you know those German engineers weren't simply freaking out with funky hookups.


This preamp was nothing to sneeze at and the whole rack of gear was insanely well built, 2" I- beam frame, hammertone silver....beautiful. Amps were PP EL156. That thing was nice.

[Guitarist]

Well these rechargeable batteries on the cathode are still really working well for me. I know it's unconventional;( But they consistently up the gain and clarity every time.
Note, with the full frequency present I usually have to pay extra attention to the the DC blocking cap. Also the plate resistor may need to be larger say 1 or 2 watts (I sometimes use 47K or lower) to accomodate the extra "power".

? If one takes a 9 Volt rechargeable apart, will one cell have enough mA to run well in a typical tube circuit? These would be AAAA

Some specs:

9v - 595mAh
Aaa- 1150mAh

[CRU JONES]

Guitarist,

This is interesting! I'm glad you are still experimenting with this.

Each cell in the 9V will have the same current as the battery as a whole. The voltage will be less.

595mAH is a ton for a NiMH! are those NiCD cells?

I guess I don't know much about NiCD, but NiMH will usually have 7 or 8 cells inside that equal 1.2V to 1.4V apiece. With 100mAH to 450mAH each.

Trickle charging is done at C/10 or less (59.5 mA or less!) , so those cells will be more than enough for any bias current that a 12au7 would be run at!

Thanks again for this idea, I put a 9V in a 6sn7 output stage of a rackmount amp. I only just remembered now that it is still in there!

Cheers!
Cru

[Rhodesplyr]

Well, early tube amplifiers did use batteries for bias. They also used batteries for the B+, and they used batteries for the heaters. They used batteries for the whole thing. it was only later as houses were wired for power that they changed over to line voltage.

Enzo, I have an inherited Atwater Kent radio of just that type. My theory is that my ancestors used it till the first set of batteries ran down and then didn't know quite what to do. Other features include a ~10" high-impedance speaker (no output transformer) with a cone made of a very thin piece of wood. Yes, I'm sure. It's wood. Tubes are Cunningham brand.

[Merlinb]

Well these rechargeable batteries on the cathode are still really working well for me. I know it's unconventional

Have you tried putting the battery in series with the grid leak instead of in the cathode circuit? That would practically eliminate all battery current, allowing the cathode to be grounded. (Basically fixed bias for preamp tubes).

LEDs used for biasing do switch off if the tube is driven to cut-off, hence the need for a bypass cap or current-feed resistor.