"Superfly" - submini tube version of Doug H's Firefly

[kristoffereide]

Will this do? http://no.mouser.com/Search/ProductDetail.aspx?R=RLH0912-101KBRLvirtualkey65210000virtualkey652-RLH0912-101KBRL

[Taylor]

I think that works, but it is surface mount. This is the one I was going to use:

http://no.mouser.com/Search/ProductDetail.aspx?R=RLB0712-101KLvirtualkey65210000virtualkey652-RLB0712-101KL

[frequencycentral]

Looks pretty similar to the one I used, and the one in the photo on the PDF that I got the SMPS schematic from: http://www.ledsales.com.au/kits/nixie_supply.pdf

[Taylor]

Got my tubes - Yowza. I didn't realize how truly tiny these guys are. I know they're "submini" but I was expecting something about as big as my pinky.

I ordered an OT15PP from here. It's bigger, for better bass response, and it comes with end bells so it's a little prettier than the Hammond 125 series. It's actually a little cheaper too. We'll see how it goes. I'm pretty excited about this project.

I'm planning to put a solid state clean boost with EQ in there, and possibly tack an L-Pad to the end so I can have separate control of preamp saturation, power saturation, and actual volume.

Rick, you mentioned adding another power section in parallel for more output. Have you tried that or do you have any further thoughts on it? I'm definitely interested in a little more clean volume than I think it will have stock. Would it be as simple as duplicating the power section, using the signal at pin 2 of the 7327? I still know next to nothing about tube circuits, so I don't know if buffering is necessary, or...?

I'm guessing the stock SMPS couldn't handle this, so maybe I'd have to wait until Cliff Schect's power supply mentioned in the Subzero thread is working.

[frequencycentral]

Rick, you mentioned adding another power section in parallel for more output. Have you tried that or do you have any further thoughts on it? I'm definitely interested in a little more clean volume than I think it will have stock. Would it be as simple as duplicating the power section, using the signal at pin 2 of the 7327? I still know next to nothing about tube circuits, so I don't know if buffering is necessary, or...?

I'm guessing the stock SMPS couldn't handle this, so maybe I'd have to wait until Cliff Schect's power supply mentioned in the Subzero thread is working.

I've tried it with single ended designs and it does work, certainly increasing volume. But double the tubes doesn't seem to equate to double the volume. Haven't tried it with a self split design like this one though. I believe that parallel output sections also half the output impedance. Yes it should be as simple as just duplicating the power section and using teh signal at pin 2 of the 7327.

Yeah, it's questionable as to if the SMPS will actually power a third tube - not too sure. I suck at math, prefering to just try it and see if it works, so I don't tend to bother calculating current draw and such. 

BTW - you managed to track down some 7327? Where? How much?

[Taylor]

BTW - you managed to track down some 7327? Where? How much?

Nope, I'm going to try 6111 instead, I was just saying 7327 for simplicity's sake, since it's what in the schematic.

[Taylor]

I want to add a boost with EQ to this. I've got the circuit all figured out and made a layout, but I began to worry if I'm about to do something stupid...

Will it mess things up if I take the 9v from the power jack to power the opamp in my EQ? In other words, does the SMPS need to be power by its own isolated supply, or can I share 9v between the SMPS and booster?

Also, I'm a little unsure how to hook up my transformer. Anyone know of a calculator for figuring out which taps to use for various loads? This is my xfmr's schematic:

http://www.musicalpowersupplies.com/resources/_wsb_522x355_OT15PP_SELL_SPEC.gif

and I'm using an 8 ohm speaker.

[Cliff Schecht]

Black to ground, yellow to 8 Ohm speaker "+" lead. Speaker "-" lead goes to ground.

[Taylor]

Thanks Cliff! Should I use the blue or brown leads on the primary?

[Cliff Schecht]

That depends, what does the actual design call for? A higher impedance (the 8k windings) will increase your gain slightly while reducing headroom. If you're going for a dirty sound, try the 8k (brown) leads first.

[Taylor]

Ok, cool. It's not marked in the schem, but I'll just try both and see what I like.

Anyone have any thoughts about the power supply issue?

I want to add a boost with EQ to this. I've got the circuit all figured out and made a layout, but I began to worry if I'm about to do something stupid...

Will it mess things up if I take the 9v from the power jack to power the opamp in my EQ? In other words, does the SMPS need to be power by its own isolated supply, or can I share 9v between the SMPS and booster?

[frequencycentral]

Anyone have any thoughts about the power supply issue?

I want to add a boost with EQ to this. I've got the circuit all figured out and made a layout, but I began to worry if I'm about to do something stupid...

Will it mess things up if I take the 9v from the power jack to power the opamp in my EQ? In other words, does the SMPS need to be power by its own isolated supply, or can I share 9v between the SMPS and booster?

I don't think that would be a problem. BTW, you mention 9 volts? Maybe it's not clear on the schematics (because the SMPS schematic says 9 volts), but I run mine from 12 volts. Appears to make little difference to the SMPS, but it does mean that the two tubes heaters in series work nicely. You also mentions using two 6111, you'll find that you don't get so much gain with a 6111 in the preamp position as you would with a 6112 (gain of 20 versus gain of 70), but a 6111 should work fine in the power section, albeit that it may be 'overvolted', as the 6111's stated max is 150 volts. But don't let that put you off, I have run them at 200 volts.

I'm just getting round to thinking of doing a version using full size tubes but staying with a SMPS, I have 12AU7 and 12AX7 on hand, but am quite tempted by ECC99. I just got the parts to experiment with some different SMPS designs. I think I'd go for the same size enclosure too!

[Taylor]

I think there's some confusion because of all the tube numbers being bandies about (the PCB layout specifies different tubes from the ones either of us is using). I am using a 6112 in the preamp and 6111 in the power position, just as you suggest. These were the only usable subminis I could lay hands on that you mentioned would work.

I did notice that you power everything on 12v, but I had planned to use 9v because I happen to have lot of 9v supplies and no 12v. I didn't think this would be a problem since, as you mention, the Nixie supply schem says 9v in. Buuuut, I see your point with the heaters. I'll grab a 12v supply.

[Taylor]

I'm pretty close to finished with my build, but I just realized that the IRF740 is backwards in the PCB layout. Rick has it right in his perf layout, of course. I realized this just as I was about to connect the power to my build. No fires yet.

I was going to fix it myself and upload the new file, but for some reason, my DIYLC won't open the file (maybe because I use the Mac version?) so I can't.

[Taylor]

I'm getting lots of nasty digital noise, and intermittent signal. I'm sure the signal thing is some bad joint somewhere, but what about the switching noise?

I can hear it sometimes through the speaker and sometimes there's a buzzing coming out of the circuit itself. Also, my nominal 12v seems to fluctuate when I tweak the B+ trimmer. Any idea where I should be looking for the problem here?

[maarten]

If you hear buzzing from the circuit itself instead of out of your speaker, it might be the transformer you are hearing - this would suggest a bad connection from the transformer to the speaker.
Maarten

[frequencycentral]

Hi Taylor - Just curious about your 12 volt supply. Is it regulated? Strange that the 12 volts should fluctuate as you adjust the B+ trimpot. Also, what amperage is it rated at? Mine is 750ma, though I'm thinking of getting a higher rated supply as I think it would give me a higher B+. I've found with that SMPS that it hums if you ask too much of it. With the supply I'm using 190 volts is fine, but any higher and I get hum. I really only get whine if I use a high gain pedal maxed out into the amp, and then only at close to the amp itself being maxed too.

Have you got a heatsink on the IRF740? As without adequate thermal dissipation the MOSFET will heat up and the point at which it introduces hum into the circuit will be lower - which will mean you'll need to lower the B+ with the trimmer. If it's not heatsinked, and with thermally conductive gel, it will evetually burn out I believe.

So, providing the MOSFET is well heatsinked, find a point at which it doesn't introduce hum, then tweak it back by a further 5 volts just to allow to the heat rise from prolonged use.

However, if you're getting switching noise even at low volume there something else wrong somewhere - is the 555's timing cap the correct value?

The intermittent signal would suggest a bad joint as you suggest. Bedtime now in the UK - so until tomorrow!

[punkin]

Anyone found a toroidal transformer for US power as in the YouTube demo? I've been doing some poking around but can't seem to find one. I really like the extra small compact layout.

[Taylor]

I bought a new regulated 1amp supply. Finally got sound! Then I got smoke.

I haven't yet figured out what part smoked, but I now have a very smelly broken amplifier. I don't think it's the MOSFET, I did have it heatsinked. Could it be the tubes? You said originally that you thought it was ok to over-volt these 6111 tubes, but now I'm wondering if I've toasted the tube.

I found some 7327 in America, was just about to gripe about 12 dollars per, until I looked on your UK supplier's site, who sells them for 12 pounds apiece, which is like $19. I guess I'll bite the bullet. Hope I find some use for these 6111s down the road...

[frequencycentral]

Probably the inductor, maybe the MOSFET, unlikely the tubes. The best way to set up the SMPS it to make sure it works with the trimpot anticlockwise at its lowest voltage and gradually step it up. Monitor the voltage at all times. Do you have another inductor? Maybe also consider a higher rated one.