Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Diverted on October 25, 2023, 10:08:22 am

Title: Impedance/build question
Post by: Diverted on October 25, 2023, 10:08:22 am

Hi all, quick question:
If I have an output transformer rated at 6.6K center tapped w/4, 8 and 16 ohm secondaries, designed for 6V6s and using the 8 ohm winding into an 8 ohm speaker ...
If I were to swap the 6V6s for 6L6s and rebias, would I use the 4 or 16 ohm winding for them? I always get confused on which way to go.

Reason I'm asking: I want to build a marginally higher power Princeton Reverb-ish circuit. I am using a power transformer rated at 300-0-300@173ma, and a 30w 6.6K output transformer. I plan to do the Stokes mod (higher B+ to phase inverter), add in a mid pot and that's about all I would change except for some unrelated changes, like a slower tremolo speed etc. I'm hoping for up to 15W w/6V6s and maybe 22-25 or so with 6L6s and a re-bias.

Thanks.

Title: Re: Impedance/build question
Post by: tubeswell on October 25, 2023, 10:33:24 am

6L6s, switch 8R speaker to the 16R tap (reflecting 3k3 Pr Z)


Or, break it down

6k6:16 = 412.5:1 Z, 412.5 x 8 = 3k3

6k6:8 = 825:1 Z = etc

6k6:4 = 1650:1 Z = etc

Title: Re: Impedance/build question
Post by: Greenwichpaul on October 25, 2023, 10:45:25 am

Edit: we are now in alignment. 8 ohm speaker on 16 ohm tap would reflect 3.3k to the OT primary

Title: Re: Impedance/build question
Post by: tubeswell on October 25, 2023, 10:46:28 am

4am math

Title: Re: Impedance/build question
Post by: Diverted on October 25, 2023, 12:38:11 pm

Thanks for the explanation! I will not have to ask this again! I understand the math, much appreciated.