OT - Finished my FireFly :)

[sir Franc of SOSCASTOA]

I finished my FireFly yesterday and WOW what a sound for 1.5Watts
This thing rocks

Haven't got a cabinet for it yet, because I need to find just the right speaker to make a nice combo. So it's just a chassis now, plugged into a 150W Celestion (of a Marshall 1912 cab).

If you are interested, pics are on my site, soundbits will be there soon!

Thanks Doug for the design and Paul for the inspiration for the chassis layout!

http://amps.soscastoa.com

[jimmy]

that looks GREAT!!! well done and enjoy your amp  

say if i accidentally plugged a 4 ohm speaker into my firefly which is set up for an 8 ohm speaker, and then it suddenly stopped working, would anything have exploded, or have i knocked something loose?

i pray for the latter.  :oops:

cheers
Jim

P.S. sorry for hijacking your thread! i hope you dont mind

[sir Franc of SOSCASTOA]

I think something is indeed loose or maybe you smoked a resistor, tube or something else.
It is always best to match speaker to tranny impedance, but it will not just stop working if you connect 4ohm to a 8ohm output.

Did it go out with a bang? Smoke? Flash?

Check if all tubes are secure in their sockets, maybe replace them. See if they at least heat up.
Check your B+ voltages (careful!)

Oh and check your fuse

Worst case, if you indeed smoked the output tran, replace it (it is not *that* expensive), but it wouldn't be the first thing I'd suspect.

Franc.

[jimmy]

thanks for the help!!

yeah when i plugged it into the speaker it was waaaay quieter than usual. then it just didnt go when i plugged it back into the 8 ohm speaker. my DMM is out of batteries haha, so that why i hope its something simple.

by the way, your way of making boards is GENIUS. i dont know why i didnt think of that.

cheers
Jim

[sir Franc of SOSCASTOA]

Well, I wouldn't worry too much, let us know what you find out

Thanks for the compliment. It was the first board I made like this and I liked it a lot. Only next time I will make it a little less wide so modern resistors will fit. I used the dimensions of the JTM45 board I have, but I won't do that next time

[Doug H]

Looks great! Nice clean build.

I hope it sounds good. BTW, I think the original estimate of 1.5W is off. I think it may actually be less than .5W clean, but I need to settle that once and for all...

Thanks for sharing the pics.

Doug

[Doug H]

that looks GREAT!!! well done and enjoy your amp  

say if i accidentally plugged a 4 ohm speaker into my firefly which is set up for an 8 ohm speaker, and then it suddenly stopped working, would anything have exploded, or have i knocked something loose?

i pray for the latter.  :oops:

cheers
Jim

P.S. sorry for hijacking your thread! i hope you dont mind

I doubt you did any serious damage with the 4 ohm speaker. I originally had the FF set up for 8K Zpri on the output transformer and ran it a long time like that with no problems. You probably have a loose connection somewhere. If you didn't smell smoke or see an arc it's probably something minor. Just inspect it closely and check it with your meter. Sometimes it's a good idea to just reflow all the solder connections. Cold solder joints can drive you nuts.

Doug

[sir Franc of SOSCASTOA]

Oh well, 1.5W, .5W who's counting

Never really cared much for showing off the amount of Watts my amps have.
As long as it sounds good and is loud enough/quiet enough for your purpose it's fine.  

All I know is this amp can be loud enough to get the neighbours call the police ;)

[sir Franc of SOSCASTOA]

And it sounds really great.

I instantly went into an AC/DC mood with that boost gain switched on and both volumes halfway

And I can't hear any hum or hiss or whatever! I'll make some soundbytes soon.

[Doug H]

And it sounds really great.

I instantly went into an AC/DC mood with that boost gain switched on and both volumes halfway

And I can't hear any hum or hiss or whatever! I'll make some soundbytes soon.

Wow, you did better than I did then! I noticed that somewhere in all the mods my star grounding scheme went awry. So I am planning on taking a little time and cleaning that up. I hope that cures some of my noise issues when the cascode is switched on.

As far as the wattage is concerned, I think I'm going to reword the blurb on my site to say it is "shouting volume" and just leave it at that.

Doug

[sir Franc of SOSCASTOA]

[

Wow, you did better than I did then! I noticed that somewhere in all the mods my star grounding scheme went awry. So I am planning on taking a little time and cleaning that up. I hope that cures some of my noise issues when the cascode is switched on.

As far as the wattage is concerned, I think I'm going to reword the blurb on my site to say it is "shouting volume" and just leave it at that.

Doug

Shouting Volume, yes that will be great. Although I don't know if my shouting is as loud as this amp

Don't know if I did anything really smart, really good, or if I am just lucky.
I twisted the heater wires, put them against the chassis away from all the other wires. Did the extensive star grounding, used new parts and almost new JJ tubes.

Come to think of it, maybe the size of the chassis helps also. If you use a really small enclosure to squeeze everything in, components are bound to interact.
My chassis has the dimensions of a Marshall JTM45 chassis.
Which gave me plenty of room to work in and maybe less hum

Either way, I am happy with it.

[Ansil]

in the process of making another one, as soon as i get all my parts laid out at the shop.  should be moving in this weekend.

and i am going to start up my new version.

i got a butload of 12ax7 style tubes so i am going to do two 12ax7's for preamp and use two 6dx8's for the powerampsection, and use the other half to split it hmm i gues like a pahse inverter.

still tyoing with the idea of adding a standbyswitch to the pentode side so i can have a low power jammer and a slightly louder jammer

[Paul Marossy]

Very nice work, sir Franc.  

I'm glad that you could make use of my chassis layout (and thanks for helping me get it straightened out)

I don't know where I got the 1.5 watt number from... I thought that I saw that somewhere on Doug's site. Hey Doug, if you get an official number for the wattage, let me know. I'll update my webpage accordingly.

Just a quick question for all you Firefly builders: Now that I have my heater running on 6.3 volts instead of 12.6 volts, I noticed that the 12AU7 gets really hot. Is that normal? Class A runs pretty hot, right? Just for kicks, I'm thinking that I could put a small DC fan inside my enclosure to keep things a little cooler. I could run it off of the 6.3 volt heater supply, through a full wave rectifier. Anyone try installing a fan in their Firefly? I thought that I remembered someone here talking about doing that...

[sir Franc of SOSCASTOA]

Well, I like my tubes when they are hot

Tubes are meant to get hot and in fact I think actively cooling your tubes will affect the sound of the amp. I would say, make sure there is free are flowing so the tubes can get rid of their heat, but do not actually blow cold air towards the tubes.

[Doug H]

Very nice work, sir Franc.  

I don't know where I got the 1.5 watt number from... I thought that I saw that somewhere on Doug's site. Hey Doug, if you get an official number for the wattage, let me know. I'll update my webpage accordingly.

Just a quick question for all you Firefly builders: Now that I have my heater running on 6.3 volts instead of 12.6 volts, I noticed that the 12AU7 gets really hot. Is that normal? Class A runs pretty hot, right? Just for kicks, I'm thinking that I could put a small DC fan inside my enclosure to keep things a little cooler. I could run it off of the 6.3 volt heater supply, through a full wave rectifier. Anyone try installing a fan in their Firefly? I thought that I remembered someone here talking about doing that...

Paul, I originally had 1.5W on the schem. I think it's more like half a watt clean.

Yes, the 12au7 will get very hot. I just built another amp with an octal power tube (6v6) and it gets pretty hot too. The power tubes handle a lot of current and, well, power...  So they generate some heat. That's why it's important to have good ventilation.

Doug

[Paul Marossy]

OK. I wasn't too worried about that 12AU7 getting so hot, it is just a little unusual to me because I am used to AB push-pull type amps with EL34 or 6L6GC tubes and the preamp tubes in these types of amps run pretty cool in comparison.

So, a 1/2 watt clean. What about when in boost mode and cranked? It sounds like it's more than 1/2 a watt... maybe around 1 watt? I'm not sure how to calc that out.  :oops:

If I actually put a fan in this amp, I will have it draw the air across the tubes rather than blowing air across them. I wouldn't be moving very much air when it's running on ~6 volts anyhow.  But, it would be really quiet and I figure a little more air movement in the enclosure couldn't hurt.