Mark IV with 6V6's and 2-2x12's

[itsjonduhh]

hey all i've been curious about my mark's future setup. right now it still has the stock 6l6's, but someone is selling me a quad of nos 6v6's and i've been confused about the impedance situation.

the manual says to halve the impedance and use the 4ohm tap into an 8ohm cab when using 6v6's. if i have 2-8ohm cabs creating a 4ohm load, a 2ohm tap would be the ideal one to use no? think it would be safe to use the 4ohm outs into the 2-2x12's?

thanks.

 

[MrMarkIII]

Keep reading.
Further down, under the picture of the power tubes, the paragraph headed "SPEAKER JACKS".

"Two 4 ohm jacks are provided and should be used when you wish to run two 8 ohm speakers or cabinets... If, for example, you run two 4 ohm cabinets - each plugged into a 4 ohm jack - the amp would "see" 2 ohms as the total load. And while this will not cause immediate damage, it will result in shortened power tube life. Mis-matching on the high side is always preferable..."

If you're running 6V6s, it would be safer to re-wire the cabs to 16 ohms each (series instead of parallel), then plug each cab into a 4 ohm jack. As the manual states, these jacks are parallel, therefore the total load would be 8 ohms. Yes, the "4 ohm" labels are confusing, and at this point should be ignored. THOSE TWO "4 OHM" JACKS ARE PARALLEL. Whatever the impedance of the two cabs connected, the total impedance will be one-half of one cab.
The formula is (A times B) divided by (A plus B).
8 x 8 = 64
8 + 8 = 16
64 divided by 16 = 4
The manual is saying that when running 6V6s, it is better to DOUBLE the total speaker load, i.e., an 8 ohm speaker into a 4 ohm jack.
The manual is telling you to DOUBLE the impedance, not halve it.
Using the two 8 ohm cabs will be "normal", but the 6V6s will wear faster.
Hope this helps.

 

[itsjonduhh]

wow thanks that really helps a lot. i guess i have trouble deciphering the difference between halving and doubling impedances. need some work on that :lol:

but basically the safest thing to do would be to rewire each cab in parallel before using the 4ohm taps?


oh, i was also curious about the "parallel out" on the rear of the cab does? it seems to be the better idea to use the 2-4ohm taps off the transformer, but just don't know exactly what happens if you connect the cabs directly to each other.

 

[MrMarkIII]

wow thanks that really helps a lot. i guess i have trouble deciphering the difference between halving and doubling impedances. need some work on that :lol:

but basically the safest thing to do would be to rewire each cab in parallel before using the 4ohm taps?


oh, i was also curious about the "parallel out" on the rear of the cab does? it seems to be the better idea to use the 2-4ohm taps off the transformer, but just don't know exactly what happens if you connect the cabs directly to each other.

Well... you want to re-wire the 8 ohm cabs in series, so that each cab is 16 ohms.
Daisy-chaining the cabs is identical to connecting each cab in parallel.
Two 8 ohm cabs daisy-chained = 4 ohms. Hook the whole daisy-chain to a 4 ohm jack. NO, you can't use the other speaker jacks, unless you are ready to go down to 2 ohms.
Remember, mis-matches change the sound. It becomes more compressed, more "distant". Some like it, some don't.
Go to Mesa's website and download the Lonestar manual. At the end there are numerous examples of speaker wiring diagrams.

 

[itsjonduhh]

haha thanks, you made me laugh. i'll double check what i read and am turning to the manual pdf's now.

cheers

 

[itsjonduhh]

hey sorry to be a pain but i need some confirmation whether or not i'm thinking this correctly. there are 2-16ohm speakers wired in parallel to create an 8ohm load, as far as i know.

if i wired each cab (2-16ohm speakers) in series, the load would be 32ohms for each cab. so 32 x 32 = 1024 / 32 + 32 = 16 ohm total. i hope i'm correct there.

so... for the 6v6's it should be going into an 8ohm load (that's double the impedance right i believe). and i wanna say i would be fine using each of the 4ohm taps into each cab.

sorry i don't know why i'm so bad with this :?

 

[MrMarkIII]

hey sorry to be a pain but i need some confirmation whether or not i'm thinking this correctly. there are 2-16ohm speakers wired in parallel to create an 8ohm load, as far as i know.

if i wired each cab (2-16ohm speakers) in series, the load would be 32ohms for each cab. so 32 x 32 = 1024 / 32 + 32 = 16 ohm total. i hope i'm correct there.

so... for the 6v6's it should be going into an 8ohm load (that's double the impedance right i believe). and i wanna say i would be fine using each of the 4ohm taps into each cab.

sorry i don't know why i'm so bad with this :?

You are correct, sir!

 

[itsjonduhh]

woo!