Short HOW DO MIC CABZ - ¯\(°_o)/¯

[Glenn Fricker]

Would that go to 4 or 16?

 

[guitarguru777]

Cuts it in half ....

16 = 8
8 = 4

EDIT:
Just re read this let me be a bit more clear ..

If your cab is 16ohm set your amp to 8. If your Cab is 8 ohm set your amp to 4

 

[topsoul182]

I already knew about the impedance change, but i just wasnt sure if it mattered which to pull. I already did it and no problems at all thanks!

 

[Sloan]

Hi,
The formula is pretty straightforward,

R=Sqrroot(Zin/Zout), or R^2=Zin/Zout

Where : R = Ratio
Zin = Impedance "seen" by the OT's primary
Zout = Load impedance

The output impedance of six 6L6s in parallel push-pull operation is in the 1.7 KOhm range, and, since your OT has two taps ( 4 and 8 Ohms ) we can calculate the transformer's ratios.

R(4) = Sqrroot(1700/4) -----> 20.6

R(8) = Sqrroot(1700/8) -----> 14.6

By removing two tubes you raised the impedance "seen" by the primary winding ( remember OT don't have an inherent impedance of their own, they have ratios ) to about 2.5 KOhms, so, by reversing the formula to solve for the output impedance we have (for the 4 Ohms tap):

Zout(4) = Zin/(R^2) -----> 2500/425 = 5.8 Ohms

While, for the 8 Ohms tap we have :

Zout(8) = Zin/(R^2) ----> 2500/213 = 11.7 Ohms

So, while it's true that the power transferred from the primary to the secondary will not be at its maximum due to the slight mismatch, it's still advisable to use the 4 Ohms tap IMHO ( connecting the 8 (now 11.7) Ohms tap to a 4 Ohms load would result in worsening the mismatch ).

Hope this helps

Best regards

Bob

http://music-electronics-forum.com/t18102/

 

[guitarguru777]

uhhh .... my head hurts