Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: DrewB on October 05, 2020, 03:15:18 pm

Title: How loud is a Firefly amp supposed to be? Is this normal?
Post by: DrewB on October 05, 2020, 03:15:18 pm

I just completed a Firefly Rev 3 build (omitted the Standby switch) and am thinking it should be louder when it's all the way up. I can talk over it running through a Celestion Greenback, though it's almost at conversation level.

Plate voltages (12AU7): ~ 240VDC
Cathode voltage drop: ~ 22VDC
Cathode resistor: 470R

Power transformer is Hammond 269EX and output transformer is Hammond 125A.

Title: Re: How loud is a Firefly amp supposed to be? Is this normal?
Post by: shooter on October 05, 2020, 03:59:35 pm

my math is coming up ~ 10W of heat
2 tubes?
believe the tube is ~3W max?

Title: Re: How loud is a Firefly amp supposed to be? Is this normal?
Post by: PRR on October 05, 2020, 04:10:18 pm

A Firefly may not be over 1 Watt clean audio output. But in a Greenback that should be over 95dB SPL in a home room, and that's SHOUT, not conversation.

The Hammond 125A has way too many wires to connect different ways.

Title: Re: How loud is a Firefly amp supposed to be? Is this normal?
Post by: DrewB on October 05, 2020, 05:30:43 pm

Bonehead mistake: I missed a ground to the grid on V3b and didn't catch it on my first check-through.