On the FireFly, is there any specific make and model on the main power transformer and heater supply transformer? I thought I remembered someone talking about this, but I can't seem to find it...

I've got my chassis all ready for point-to-point and I am going to build the enclosure while I'm waiting for parts. This is going to be fun! I'm ready to roll!  

Hey Paul,

Please post your results as I'm thinking of making a firefly

cheers
Ben

OK, I will. I've messed with tube amps some, but this will be my first build. It's not too complicated of build, so I think it's a good starter project.

I'm doing a preliminary chassis layout right now. I have a 14"x6.5"x2" chassis I pulled from a piece of _____ Crate amp. I'm going to recycle it. I need to figure out the physical placement of the transformers most of all. The ones that Doug used look fairly small in size and I would like to use something similar.

Quote from: Paul MarossyOn the FireFly, is there any specific make and model on the main power transformer and heater supply transformer? I thought I remembered someone talking about this, but I can't seem to find it...

I asked about the transformer(s) and was told that I needed one that would do 200V. Since then I've been hunting and haven't been able to find something that I am sure will work.

I just don't know enough about spec'ing transformers, so I probably need part numbers.

If someone who's built one could go to Antique Electronics' web page and pick 'em out, that's the amount of hand-holding I need.

Hey, I built the Firefly with the Hammond 269EX, which can run at 190V, based on Doug's recommendation.  It includes a 6.3V tap for the heaters, and it works just fine.  I'm having some trouble with oscillation at some settings, but those on which it works sound incredible!  Listen to Doug's new sound clips and let your jaw drop.  This thing sounds awesome.  Build this amp immediately!  

Alex

The Hammond 269ex is available at Mouser //www.mouser.com
and Antique Electronic Supply  //www.tubesandmore.com  .

I believe it's a few bucks cheaper at Antique Electronic Supply.  Hope that helps.

Alex

Thanks for the tip Alex.

Looking at the specs found at http://www.tubesandmore.com on the Hammond 125A output transformer, it doesn't quite do the full range of audio - 150Hz to 15kHz. That's OK on the high end since the highest harmonics a guitar can produce is around 3kHz, but the low end of guitar is 82Hz. So, that would mean a reduced bass response, right? But, the transformer they suggest, the P-T1627SE does. But at $98, I think I can live with the 125A.  

Also, on that Hammond 269ex, the secondary is center-tapped. I assume that the center tap is not used?

Yes, the center tap is not used.   I'd say I could live with the 125 A also.  

Thanks, Alex!

That's just what I needed to know.

I wonder what the differences are between the 125E and 125A.

It's going to be hard getting used to paying upwards of $30 for a single component.

Wow -
I've been thinking about an amp in the back of my mind for a while.. and was thinking that the Firefly would be a good place to start..

but I never thought it would sound like THAT... the sound clip on the rev 3 (doing the EVH licks) sounds AMAZING.. it's the 'brown sound'.. it's amazing..

good work as usual, Doug... and I think a Firefly build is in my NEAR future.
"-)

As you go down the alphabet, the wattage ratings increase.

a = 3 Watts
b = 5 Watts
c = 7 Watts
d = 10 Watts
e = 15 Watts

The basic difference is more iron and thicker wire.

The best prices I've seen on Hammond trannys is from http://www.angela.com  (It was hard to get used to people here calling transistors as trannys after coming from tube land). Great cap selection there too. Check out the FastCaps!!!

For power, there's a lot of flexability. You could use a 115/230 step up/down transformer too. The higher the voltage, the cleaner the sound. The only thing you might have to adjust is the cathode resistor on the 12AU7.

Best of luck on your FireFly! I will be surprised if you don't end up loving it!

Take care,
-Peter

So if I used a 125d instead of a 125a, would I get more power just like that, or would some circuitry have to be adjusted?

You need larger tubes to get more power. The wattage is rated like a resistor.... use too much and you let the blue smoke out.

If you use a larger transformer, you can use different tubes. If you use the 125A, you are fairly stuck with lower power.

The 125C would be a good choice for a self-split EL84 amp. If you want to experiment, I would get a larger transformer like the 125D or E, as that will keep all of your options open.

Take care,
-Peter

So low wattage tubes + 125E will make no difference except that I could throw more power at it in the future if i wanted to. Okay makes sense... :? Got to get my head around all this new info though.

Here are some transformers that will work:

Power:
---
Mouser Stock No: 546-186B120
Mfr. Part #: 186B120
Mfr. / Suppler: Hammond


Description: Hammond Power Transformers
115/230, 6VA,120VCT (50ma)

$ 10.53

You will need 18ma for the output stage and few more ma for the
preamp. Something that puts out 50ma gives a good safety margin.

----

Filament:
---

Mouser Stock No: 41FD010
Mfr. Part #: 41FD010
Mfr. / Suppler: Hi-Q


Description: HIQ Heavy Duty Power Transformers
TRANS FIL 6.3V 1A
Product Category: Power Transformers

$ 4.79

You will need about 900ma for the tube filaments (300ma x 3 tubes),
so 1A should cover it.
---

So for approx $15 you can get a separate filament and power
transformer for it. Not bad, since I paid $14 for my surplus
transformers and thought that was a good deal.

---

If you want a combination filament and power transformer try this:

http://www.tubesandmore.com/new/scripts/silverware.exe/moreinfo@d:/df
s/elevclients/cemirror/ELEVATOR.FXP?item=P-T269EX

B+ will be a little lower but it should be okay.

---

For an output transformer I used a hammond 125a. I like it because
the 22.5k primary Z sounds real good (and I think its easier on the
tube).


So you have some options for transformers. I need to put this info up on my site.

Doug

Quote from: Alex CHey, I built the Firefly with the Hammond 269EX, which can run at 190V, based on Doug's recommendation.  It includes a 6.3V tap for the heaters, and it works just fine.  I'm having some trouble with oscillation at some settings, but those on which it works sound incredible!  Listen to Doug's new sound clips and let your jaw drop.  This thing sounds awesome.  Build this amp immediately!  

Alex

Thanks!

If you're having oscillation problems, check your layout. It should not squeal at all on any setting.

Doug

Quote from: Alex CYes, the center tap is not used.   I'd say I could live with the 125 A also.  

If you have the center tap you can wire it as a full wave rectifier instead of a bridge and save 2 diodes.

Doug

OK, I have one more question:
The 1uF caps on V1a and V1b, can I use a 50V cap there?
And the 10uF cap on V2a, a 50V cap there as well?

As a side note, I used to want to get one of those Allen Amp kits, but I just don't have the extra $1000-1200 right now. But, this project should satisfy my desire to build a tube amp, and is something I can actually use. The other thing I like about the FireFly project is that I can design the layout and choose what parts I want to use for it. I already have the layout designed, I just have to decide what transformers I want to use.

Quote from: Doug H
If you're having oscillation problems, check your layout. It should not squeal at all on any setting.

Doug

I didn't mean to imply that the circuit is the problem!     I that's what it sounded like though.  I asked a few days ago about the squealing problems and everyone told me how much it would depend on the physical layout of the components.  I just haven't had time to get in there again.  I was trying to say that besides my own problems, the amp is sweet!  Sorry for the misunderstanding.  

Alex

So how would you go about selecting where the tubes/transformers go? :? I mean after you drill holes etc it's kindof a pain in the ass to move stuff around.