OK, I haven't researched the topic, because I reasoned that the collective intelligence already has the answer.
Having obtained OTs from discarded '50s radios/hifi systems, where the output taps are 2ohm for 2 X 6V6 , is there any caveat consideration of adding say a 10watt resistor to equal a 8ohm speaker load?
Thanks in advance.
Is resistance just resistance?
Moderators: pompeiisneaks, Colossal
Re: Is resistance just resistance?
I assume you don't want to/have room to parallel two 4-ohm speakers to get your 2-ohm load. Couple of issues: resistance and impedance are not quite the same thing;resistors and inductors will not behave the same way at different frequencies, so just adding a parallel resistance isn't exactly the same.
At any rate, 10 ohms is not the right number anyway: 4||4=2; 8||2.7=2.02. In each case, a portion of your output power will be expended heating up the resistor instead of making sound (half of it in the 4||4 case; more in the 8||2.7 case).
A better solution is simply to use a 4-ohm speaker and be done with it. Your will lose a little power versus the "correct" load, but nothing compared to the loss of adding the resistor. If the transformer is well-designed, there will be no issues. It would also be useful to know the specs of the original application: primary impedance and plate voltage. There are many different "correct" impedances for a pair of 6V6s, depending on use.
At any rate, 10 ohms is not the right number anyway: 4||4=2; 8||2.7=2.02. In each case, a portion of your output power will be expended heating up the resistor instead of making sound (half of it in the 4||4 case; more in the 8||2.7 case).
A better solution is simply to use a 4-ohm speaker and be done with it. Your will lose a little power versus the "correct" load, but nothing compared to the loss of adding the resistor. If the transformer is well-designed, there will be no issues. It would also be useful to know the specs of the original application: primary impedance and plate voltage. There are many different "correct" impedances for a pair of 6V6s, depending on use.
Last edited by Firestorm on Fri Sep 07, 2012 9:19 pm, edited 1 time in total.
Re: Is resistance just resistance?
Timely discussion! See my thread <https://tubeamparchive.com/viewtopic.php?t=19042> I'm building at 50-watt 1987 style, with a Fender '59 Bassman reissue OT <http://www.tubesandmore.com/products/P-TF36485> which has only 2ohm output secondary. Planning to push 4ohm speaker cabs. (I don't have any 2-ohm loads). Hoping all goes smoothly. Comments?