Firefly tube amp attempt

[maiko]

Ok so after i got the charge pump built and sorted out i set the voltage to 130v.

I built the amp according to the point to point setup but mine on a pcb.    (cant get the turret board)

B1=130 b2 125 b3 120

checked everything wire the heaters to 12.6 v and with the amp set to standby turn the power on.  the heaters lit up.  and after about 2  mins i switch the stanby off but no sound.

followed everything in the build guide all pots set to zero boost to off.  nothing.

by the way my power supply transformer is a 2 amp 12-0-12 ct.    power for the charge pump is regulated trough a 7812 ic and the heaters are regulated to a lm317 set to 12.6v

Gradually i notice the output voltage of the max1044 keeps dropping i mean until even with all the stages it only produces 30v.   

I dunno how the guys who built this amp around the chargepump what voltages were they running or etc.      Right now im soo tempted to use a isolation transformer 220 primary and 110 secondary.

btw the mains in my country is 220v

[thomasha]

Hi,
could post some other voltages? Plates, cathodes and so on.

One thing with the max1044 is the current it can deliver. I imagine that a firefly would need more than the 10mA specified, unless you change the 12au7 cathode resistor to reduce current.

What kind of capacitors are you using at the charge pump?Are they low ESR fast switching? And is the value big enough to handle the current requirements?

Some pics could help also.

The ideia of using an isolation transformer is very good, at least until you got the amp circuit working.
cheers

[GibsonGM]

It's probably the OT drawing a lot of current. I bet the charge pump could power the preamp stuff.  If you disconnect the last cap prior to the output (C7 on my schem...), you will probably find OK B+.    Be careful if you 'monitor' this with an amp to audio probe, check the output level first!

As said, if you can try it with an isolation transformer first, that would be best, to assure it all works properly.

[sajy_ho]

It's definately the MAX1044 chip. It is rated for max 20mA output, and you are pumping 12V to 130V; so the max output current will be 12/130 * 20 minus losses, leaving less than 2mA for the amp! That's too shy..

If you want to stick with the charge pumps, you better change the IC to LT1054(100mA outpu), but still you cannot raise the B+ higher than 105V in the case of Firefly. So here's my offer; Build a SMPS around 555 or MAX1771 chip and have fun varying the B+ using a little trimmer.

Here's the one that I used in my FF, it can put out max 170V with the FF:https://db.tt/NqrEqe1L

If you want the actual voltages in the schem without a transformer, the only thing I can think of is the MAX1771 SMPS or a flyback converter...

[amptramp]

Charge pumps are not efficient and have voltage limitations.  Here is an amplifier schematic using simple parts that offers efficiency and low cost:

http://diyaudioprojects.com/mirror/members.aol.com/sbench101/BatteryPoweredAmps/3vHiFi.gif

[maiko]

Thanks for all the replies will try the isolation transformer.

as soon as time permits and update accordingly.

as soon as i figure the amp works will try into the smps ps. 

[duck_arse]

on the topic of the smps, specifically the nixie driver - does anyone else use the 7555, or does everyone stick with the 555?

[PRR]

Can you find a *solid* 30V or so supply? Some old printers had a 30V or 48V DC power pack. This beast would "run" on three or four 9V batteries in series.

The Firefly won't scream with 30-50V but it should pass signal enuff to fill a room.

If it don't, measure voltages on all tube pins. Preamp plates should be "roughly half-way" to B+ (so at 30V, maybe 10V to 20V). Power stage plates at near full B+. Cathodes nearer 1V or a part-Volt (except power tube cathodes may be a bit over 1V). Grids at zero (+/-100mV). "Close" is probably OK. "Way out" means look for missing/extra connections in that area.

[maiko]

Can you find a *solid* 30V or so supply? Some old printers had a 30V or 48V DC power pack. This beast would "run" on three or four 9V batteries in series.

The Firefly won't scream with 30-50V but it should pass signal enuff to fill a room.

If it don't, measure voltages on all tube pins. Preamp plates should be "roughly half-way" to B+ (so at 30V, maybe 10V to 20V). Power stage plates at near full B+. Cathodes nearer 1V or a part-Volt (except power tube cathodes may be a bit over 1V). Grids at zero (+/-100mV). "Close" is probably OK. "Way out" means look for missing/extra connections in that area.

Hey I Actually do.  I will try this just to test the circuit.    Thanks  running 110 was kinda intimidating me actually    you know thinking what if theres a problem and it kills me. hehehe

[PRR]

Don't get killed, please.

25V is generally recognized as "safe for finger contact". That's conservative. I don't like poking 30V or 40V, it stings. But it is unlikely to kill, especially if all in one hand. Don't get BOTH hands in there... a basic rule of safety. This also means rubber shoes on wood floor and don't be touching metal with the other hand, so no sneak-path from hand to foot through *chest* (heart). Ideally, set your meter clips with power OFF, hands off, power on, take readings.

[maiko]

Well i tried the 30v ps.   Voltage seemed stable and would not drop but still no life.

on the process of reviewing all hook ups now.

[maiko]

Some pictures by the way.

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The image below shows my pcb that i patterned from the point to point wiring.  Since i did not have access to the turret board i built it like this.   Ive checked the traces over and over and am confident there is no error in the board.    Its patterened after the V3

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The output transformer is a valiant (local brand here) has taps for 4  8 and 16 ohms.   
is enthusiatically rated at 80watts but i doubt it as physical size of it is too small

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[PRR]

> Voltage seemed stable and would not drop but still no life.

Again: measure voltages on all tube pins.

Like: there's water in your neighbors' houses, not at your sink. Drill holes in your pipes to find where you have water and where you don't have water. OK, that technique is messy in water pipes, but easy in electric systems. I gave rough guide above. For 30V supply, you expect 10V-20V at Plate, more like 1V at Cathode, and (usually) practically Zero at Grid. Like you might expect water flow of 30 in the street main, 10 at your house main, 1 at your bathroom faucet. Anything very different is A Clue.

[maiko]

@PRR

Sorry about that.  Though about getting voltages but kinda confused me you mean i take voltages of for example pin 1 against pin 6 (anode) pin 2 and pin7 (Grid) pin 3 and pin 8 (Cathode)

[bluebunny]

Connect your black lead to ground and leave it there.  Now (carefully) touch your red lead to each of the valve pins in turn and report the readings.

[maiko]

Connect your black lead to ground and leave it there.  Now (carefully) touch your red lead to each of the valve pins in turn and report the readings.

Gotcha.   Will report tommorrow.   Thanks for all your replys

[maiko]

hey guys

Got the voltages. . . there seems to be something really bad or has gone wrong cause some pins are zero.  i took voltages for pins 1,2,3,6,7,8 only 45 and 9 are heaters and they do lit up

12ax7 1              12ax7 2              12au7

pin 1 26.5           pin 1 26.5           pin 1 30.5
pin 2  0              pin 2   0             pin 2 0
pin 3  0              pin 3   0              pin 3 .8
pin 6  0              pin 6   26.5          pin 6 30.5
pin 7  0              pin 7   0              pin 7  --to ground
pin 8  0              pin 8   1.2            pin 8 30.5

b1 30.5 b2 29.5 b3 28.9(29 practically)

[maiko]

Sorry that its on its side

[PRR]

Thanks. I like functions, not pins, so I added that.

>          12ax7 1              12ax7 2              12au7
>  P2      pin 1 26.5           pin 1 26.5           pin 1 30.5
>  G2      pin 2  0             pin 2   0            pin 2 0
>  K2      pin 3  0             pin 3   0            pin 3 .8
>  P1      pin 6  0             pin 6   26.5         pin 6 30.5
>  G1      pin 7  0             pin 7   0            pin 7  --to ground
>  K1      pin 8  0             pin 8   1.2          pin 8 30.5

12AU7, we expect full supply voltage on Plates (DC drop in transformer is very small). Not on cathodes. And very odd that the two cathodes, pins 3 and 8, are probably(?) tied together but show different voltages? (Otherwise "7 - to ground" makes no sense.)

12AX7 2 pin 8 K1 at 1.2V shows some life, except I would expect a much lower voltage.

Please put a link *in this thread* to the specific schematic you are using. (I'm lame and can't be running to other threads or Google.)

[maiko]

This si the one

https://robrobinette.com/images/Guitar/Deluxe_Micro/Firefly_Schematic.gif