Getting more voltage out of tube heater filament?

[blues_mang]

Ok, maybe this the wrong question to ask, but here goes. A while back I started a thread about wanting to add a digital reverb circuit to the Firefly amp. See the thread here: http://www.diystompboxes.com/smfforum/index.php?topic=100941.0. I also wanted to add a switching circuit so that I could use a remote footswitch to turn the reverb on and off which I worked out in this thread: http://www.diystompboxes.com/smfforum/index.php?topic=101347.0

The issue I'm having is powering everything (or getting 9V where I need it). I originally had planned on getting power from the heater filament of the tubes. I can get power from it, but I don't think it's enough to power the 2 circuits (reverb and switching). I'm only getting 6V at both and I don't think it's enough, because when I have everything turned on, I'm not passing any signal once it gets to the switching circuit. I only get loud hum. If I disconnect the input and output from the switching board and connect them together, then I get sound. I've triple checked all my wiring. I've also tried bypassing the switching circuit and run straight to the reverb circuit, and I still only get hum. This leads me to believe that I'm not getting enough power to either boards so that they will correctly.

So, can I get more voltage out of the filaments or is there a better way to power this internally (I don't want to use a second power source or stick a 9V battery in)?

[Pojo]

I'm assuming you rectified the filament voltage to DC? I wouldn't see why you couldn't just use a CMOS voltage converter to double it such as the max1044 or the tl7660 to bring it up above 9V.

[R.G.]

Can't tell what you're doing without a schematic.

[merlinb]

Sounds like you need a voltage doubler.

[teemuk]

He may or may not need one. The digital circuit is probably happy with a good regulated 5V supply, which can be easily derived from a rectified filament supply.

The opamps may need higher voltages for headroom, but regardless they should be perfectly happy running from a 9V single-supply. At least many effect pedals don't seem to bother...

Either way, the low supply voltage surely doesn't explain why the thing obviously doesn't work.



R.G. is right: We should see a schematic to figure out what the OP is doing wrong. ...not to mention, usual inclusions of the " DEBUGGING - What to do when it doesn't work" -thread.

[blues_mang]

Ok, here are the schematics:

For the switching circuit...


For the reverb circuit...
The schematic can be found here: http://1776effects.com/wp-content/uploads/2014/05/Rub-a-Dub-Deluxe-BOM.pdf

For the Firefly circuit...
The schematic can be found here: http://vintageusaguitars.com/misc/Firefly%20PCB%20Guide%208.pdf

As for trouble shooting, here's what I have done so far: I've built the entire firefly amp circuit exactly to specs and confirmed that it works. I've built the reverb circuit and confirms that it works outside of the amp. I am now running the input from the input jack to the switching circuit using the schematic above and the perfboard layout from the thread I linked to above. From the switching circuit out, to the reverb and from the reverb out to the in of the Firefly circuit In. I pass signal from the input jack to the in, but once I even touch the end of the wire to the switching circuit in or the reverb in I get really loud hum. I'm just thinking out loud now, but could it be a ground issue? In order to get the voltage from the tube filament, I've run the positive from pin 2 (I think) and the negative from pin 7 (I think). Might be vice versa. I'm using that negative wire as the ground for the 2 circuits. If I only run one wire, I don't get any voltage, so I assume both are needed, but maybe this is not correct. Hope this enough information for now. I can provide more later if need be.

Thanks.

[R.G.]

Ok, here are the schematics:

Actually I meant the schemo of what you're doing to make the voltage, not the other pieces that you're using. As an example:

In order to get the voltage from the tube filament, I've run the positive from pin 2 (I think) and the negative from pin 7 (I think). Might be vice versa. I'm using that negative wire as the ground for the 2 circuits. If I only run one wire, I don't get any voltage, so I assume both are needed, but maybe this is not correct.

We'll need a schemo of the heaters from the transformer to the tube, any rectification and filtering of the heater voltage, and then how you're making 9V from it.

For instance, I can't tell from this if you are trying to put 6V or 12V AC into the circuits, or if it's being carefully rectified/filtered/regulated, etc.

It is likely that there is a grounding problem, but I can't tell any more about it from your description.

The forum seems to be in the middle of a run of people saying things like this "hey, I hooked pin 7 of my Megablaster up to the footswitch, and now it doesn't work! What could be wrong?" A schematic of the part you're messing with goes a long way toward helping us help you.

[blues_mang]

Ok, when I get home tonight, I will make a diagram showing the wires coming from the Firefly board to the switching circuit and reverb circuit and post it. I can answer some of the questions in the meantime:

I'm not rectifying or filtering the heater voltage at all. My understanding was that you get around 6V directly from the heater so I'm was just tying into the pins of the tubes directly on the board. I'm trying to put 9V (preferred) to the circuits, but I'm finding out that 6V is about the max. the tubes are putting out on the heaters.

Like I said, I'll make a diagram to better explain my situation and post it later on.

[davent]

The Firefly schematic shows the heaters running VAC, you'll fry your chips if you try to power them without rectifying the 6VAC to get VDC first.

[merlinb]

but I'm finding out that 6V is about the max. the tubes are putting out on the heaters.

The tubes don't produce the voltage, the use it. The transformer produces the voltage (which is AC).

[R.G.]

Oh, dear. There may be some Darkness Emitting Diodes (DEDs) in there now.

[blues_mang]

Aha, therein lies the problem. One must read carefully ... the article I was reading about powering from tube heaters, I totally mis-read and though it said 6V DC. I see now, that it is 6VAC. This could definitely be a problem. Well, at least one of the circuits had a power protection diode. Now let's see how much I fried.

Anyone point me in the direction of ways to rectify VAC to DC?

[Jdansti]

There may be some confusion about what you are calling a "filament". Here's the pin out for the 12ax7 and 12au7:



Which pin number(s) are you calling a filament?

Also, could you post a link to the article you referenced?

[R.G.]

Aha, therein lies the problem. One must read carefully ... the article I was reading about powering from tube heaters, I totally mis-read and though it said 6V DC. I see now, that it is 6VAC. This could definitely be a problem. Well, at least one of the circuits had a power protection diode. Now let's see how much I fried.

This is one of the big dangers in popularizing a technical disclipline down for hobbyists - all that messy, time-consuming background learning that gets left out really is needed in some cases.

Anyone point me in the direction of ways to rectify VAC to DC?

My general advice to people about effects is to read Geofex.com. In this case, the particular thing you're looking for is
http://www.geofex.com/Article_Folders/Power-supplies/powersup.htm

[Jdansti]

After reading RG's last post and looking at the Fire Fly schematic, I think I now understand what you're trying to do. No offense intended, but let me restate what I think the original post title should have been:

Corrected Title: How to get 9VDC from the 6VAC that supplies the heaters on my Fire Fly amp?

The confusion for me was where you said "getting more voltage out of the tube heater filament.

I recommend reading RG's article and letting some people smarter than I show you how to:

1) Rectify your 6VAC to 6VDC
2) Double the 6VDC to 12VDC
3) Regulate the 12VDC to 9VDC

Carry on.

[R.G.]

Good one John.

@OP:
Since you already have 6Vac, you might even use the "AC-ness" of the filament supply to do a doubling or tripling rectifier directly from the 6Vac. This will be complicated by however the 6Vac is grounded - and it will be grounded somewhere. But still, using some diodes and caps might get you enough DC to make 9V out of.

[PRR]

Collect all facts.

The FireFly is a small tube amp. Heater supply is 6V _AC_ and nominally center-tapped (either hard or with resistors) and also _raised_ to a positive voltage.

This is a very messy thing to try to derive more than a trace of grounded DC power from.

Which is a shame, because the 6VAC winding has more than ample current for your heaters.

There's already 8.8V DC inside the 'Fly: the output cathode sits at +8.8V. There is only 20mA here, so you can't steal more than 1mA-2mA without problems, and 20mA if you really re-rig it.

So your op-amps could sneak power.

The BTDR-3H needs 5V (DC) at _1_Amp_ (100mA). This is a LOT. (And unaccountable... we can run a tablet-PC with many more bits and frills with less power than that.)

The suggested Hammond 269EX PT has no additional windings (just 380VCT and 6V).

I considered a radical change. Cut-up the PCB so the heaters can be fed 12V _DC_. This can potentially remove all heater-induced hum. The 12VDC could also power the opamps, and the regulator for the digi-delay. But the required filter-cap sizes, for good doubler-action and low ripple, just get absurd.

Get a 9V wall-wart and hide it inside the amp.

[blues_mang]

Well, I was away for the weekend and just got a chance to read all the comments. This is why I come to this forum...to learn something. To answer John's question, about which pins I was mistakenly calling filament (I meant heaters) is pins 4 & 9. I was previously running wires from these pins to power a LED light strip to "back light" the inside of the amp which I thought was providing DC based on suggestions I received back when I first built this. I can't find the article again, it was over a year ago.

So after reading the GEOFX article and the comments above, it's looking like my 2 options are to rectify and filter the 6V AC coming from the tubes which would still only give me 6V DC. This is enough for the reverb circuit, but likely not for the op-amp on the switching board or taking PRR's advice and wiring (and hiding) a wall wart inside the amp which I could wire directly to the main 120V AC in and is already doing the rectifying and filtering and will provide 9V DC to the spots I need it.

I'm thinking of going with choice number 2 and just use the wall wart inside the amp. I may just rob the x-former from a wall wart and re-house it in an enclosure and mount it inside the amp cabinet. Then just run wires to the chassis for sake of room inside the chassis.

[davent]

You need one lead connected to pins 4 & 5, the other lead connected to pin 9 when powering the heaters with 6v. The way you described the wiring, only one of the two triodes has the filament working.

Chances are the wall wart has no filtering after the bridge so you'll need to add some of your own.

[blues_mang]

You're right. I cracked one open and the only thing inside it was a transformer. I'll add some filtering.