Amp Mods and Soundclip

[Davefx]

If anything is an inspiration for a "first amp project", this certainly IS!!
I can imagine how this thing would sound through my 4-12 Marshall greenback cab!  I'm sure it would drive it, although at even less power, due to the 16 ohms of the cabinet.

 Your playing kicks butt, Doug!!!!!

Dave

[Doug H]

If anything is an inspiration for a "first amp project", this certainly IS!!
I can imagine how this thing would sound through my 4-12 Marshall greenback cab!  I'm sure it would drive it, although at even less power, due to the 16 ohms of the cabinet.

 Your playing kicks butt, Doug!!!!!

Dave

Thanks, Dave.

Actually, if you use the hammond 125 series output transformer, you can wire it to match the impedance of your 16 ohm speaker cabinet. It has multiple taps for different impedances.

Doug

[Alex C]

Hey, I'm fairly new to tube amp building (only the AX84 P1).  I'm very interested in the firefly, but I have a question about the PT.  
How critical is the 207 volts?  What I mean is, how far can I deviate from that (up or down) before I change the operation of the amp?
Mouser sells Hammond PTs that are close (190, 225v).  I can't seem to find an isolation transformer at Mouser, and I'd like to use just one anyway (not a separate filament transformer-the Hammonds include a 6.3 tap).

Is it a problem if I use a 225 volt PT instead?  I don't know enough to know what that would do to biasing, etc.  Thanks.

Alex

[Doug H]

Is it a problem if I use a 225 volt PT instead?  I don't know enough to know what that would do to biasing, etc.  Thanks.

Alex

Do a search at ax84. I addressed this question over there at one point. I'm thinking you're probably better off going with the 190 than the 225 for this amp. You don't want to exceed 300v across the 12au7 plate. You may have to drop it down a little or use a bigger cathode resistor with the 225v whereas you can probably use it as is with the 190v.

Doug

[Alex C]

Hey Doug, thank you very much.  I'll use the 190v Hammond and the two-diode rectifier like the P1.  I'm really excited about this project; I've heard nothing but great things about it.  Thanks again!

Alex