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

[bbmonster]

Is the 47uf capacitor (after the B+ and 22k resistor) not needed anymore since you are using an smps? It's not placed anywhere on the perf layout.

Thanks.
-Bernard

[frequencycentral]

Is the 47uf capacitor (after the B+ and 22k resistor) not needed anymore since you are using an smps? It's not placed anywhere on the perf layout.

Thanks.
-Bernard

Well spotted! That cap is in the original Firefly schematic to minimise ripples in the B+2. However a 47uF 250v cap was far too huge for my enclosure of choice, so I left it out. Probably bad practice on my part, but I'm still sleeping nights. 

[Mick Bailey]

Rick,

I'm convinced that you shouldn't be getting such a big drop on the B+ side and I still think this is down to the current rating of the 12v supply. The Nixie PSUs place a high instantaneous demand on the supply which is very much higher than the average current draw that you would expect from adding up the current demands of each tube and other associated losses.

[frequencycentral]

Thanks Mick, I'll do some more experimenting. I'm also planning to change out that 2.2uF cap in the SMPS for a higher value. I have another issue which may be connected, if I have the amp at maximum volume (pretty loud!) and use it with a high gain pedal I get some whining, which goes away if I turn the volume down a touch. I haven't forgootten I owe you a couple of NE5532's - the ones I had were bad, so I've ordered some more.

[frequencycentral]

Someone asked by PM for some idea of how big it is, so here's a photo for scale, together with some internationally recognised household items:

[Ice-9]

Rick , that is one nice piece of kit.

[frequencycentral]

Rick , that is one nice piece of kit.

Thanks Mick - I'm really proud of it too. Definately one of the coolest things I've ever built. With the volume set at 10 or 11 o'clock it's clean and easily loud enough for home use. Cranked it's bloody loud. Cranked with a high gain pedal driving it it's antisocial. Enough to get the steely stare from Mrs FC. 

[Taylor]

I'm thinking about building one of these; it looks like it's a very cool little amp. I have a couple of questions that will reveal my noobishness with anything tube.

What power rating do the caps and resistors need to be? Can I just use the regular 1/4w Rs and 16v caps as in pedals?

Where does this fall on the danger continuum between stompboxes and standard tube amps? "The 200v enough to (sting/hurt/kill)" - please select one. After turning it off and unplugging it and leaving it for a few minutes, is it safe to poke around in there?

Any thoughts on using it for bass? I'm not looking to replace my 100w tube head, but I imagine the stock design might be a tad anemic in the low end since it's meant for guitar.

[frequencycentral]

What power rating do the caps and resistors need to be? Can I just use the regular 1/4w Rs and 16v caps as in pedals?

All the resistors are 1/4 watt. The 2.2uf cap in the SMPS needs to be 400 volt rated. Other than that, no special requirements.

Where does this fall on the danger continuum between stompboxes and standard tube amps? "The 200v enough to (sting/hurt/kill)" - please select one. After turning it off and unplugging it and leaving it for a few minutes, is it safe to poke around in there?

(sting/hurt/kill) - but you'll know about it. It's 200 volts DC though, so it tends to cause you to flinch away, as oppossed to AC which make you hold on. I've never received a shock when fiddling with it when it's turned off though.

Any thoughts on using it for bass? I'm not looking to replace my 100w tube head, but I imagine the stock design might be a tad anemic in the low end since it's meant for guitar.

I'll try it with bass tomorrow. My bass is active though, so it's output is hotter than average. My initial thoughts would be that crunch that is pleasing for guitar is not neccesarily desirable for bass - unless you wanna sound like Lemmy. Also, the OT, Hammond 125A is a little light at the low end compared to it's bigger brothers in the Hammond range.

[Taylor]

Cool, thanks for that detailed reply. I use active basses as well, so that's no problem.

What OT would you recommend? Looking on ebay, it seems like they're all around the same price, so should I just go for the 125D?

[frequencycentral]

What OT would you recommend? Looking on ebay, it seems like they're all around the same price, so should I just go for the 125D?

I don't know, I'm no expert, though my understanding is the bigger ones have a better bottom end as well as higher wattage rating. Bear in mind the 125D is physically a lot bigger too.

[Mick Bailey]

The little 3.5w output transformers sold by RS Components are very good, but perhaps a little too big for the size of enclosure used by Rick. They work exceptionally well in the original firefly and have a good range of impedance combinations. Trouble is with the exposed connections in an 'open' amp.

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=3.5w+transformer&x=0&y=0

I asked OEP for a price to run off a quantity of these with flying leads exiting at the bottom, but they never responded, despite my interest in a production run. Guess they've got too much business to want any more.

Much of the bass also comes down to which speaker you use. For guitar work if you hook one of these up to a Celestion G12H in a semi-open back cabinet the bass and lower-mids are incredible.

[Taylor]

Can't seem to find 6021wa or 7327 tubes anywhere. Anyone know a source? Or should I just go ahead with underrated tubes as mentioned in the first post?

[frequencycentral]

Can't seem to find 6021wa or 7327 tubes anywhere. Anyone know a source? Or should I just go ahead with underrated tubes as mentioned in the first post?

In the UK, both these suppliers have 7327:

http://www.langrex.co.uk/

https://secure25.securewebsession.com/bel-tubes.co.uk/shop/index.php?osCsid=4347fe0759098c28188fd5ed43ba0219

Never used them myself, only came across them recently.

Personally I'd 'risk' underrated tubes - but that's just me.

[punkin]

I'm sorry...if I've missed I apologize. What is the volume pot value you're using here? I'm assembling my Mouser parts list. I've just got to build this thing.

Steph

[frequencycentral]

I'm sorry...if I've missed I apologize. What is the volume pot value you're using here? I'm assembling my Mouser parts list. I've just got to build this thing.

Steph

1M log, it's marked as 'Gain' in the schematic on page 1 for some bizzarre reason that I can't explain right now.

Don't forget a little heatsink for the IRF740, and some thermally conductive paste.

I had an interesting experience with the trimpot last weekend. I was adjusting it, my hand slipped and I somehow put too much pressure on it. The amp started to hum. Debugging showed that trimmer was no longer able to adjust the B+, which was at 270v. I changed out the BC547 for a new one and all was good again. Presumably the pressure I put on the trimpot somehow sent lots and lots of volts to the BC547 and it blew. So it's probably worth socketing the BC547. The BC547 acts as a regulator, momentarily shutting down the 555 when the voltage set by the trimmer is reached, so that a constant voltage is maintained.

[punkin]

Great tips! Thanks!

[frequencycentral]

A guy on another forum did this PCB layout. I haven't gone over it with a fine tooth comb, but it looks to be heavily based on my perf layout. It would be worth checking over thouroughly before anyone builds it.

[frequencycentral]

^
^
^
Here's the PnP for that PCB layout:

[kristoffereide]

What part is "L1"? I can't find anything that is measured in "H" if you know what I mean...


EDIT: Nevermind