Help with JTM-45 impedance questions...

[retro]

HI,

I have a JTM-45RI head going into a 1936 cab with two 8 ohm speakers wired in
parallel at 4 ohms.

I am wondering what the differences would be if I wired the cab in series at 16 ohms and switched my output impedance.

And I have read and heard this before:

"Output Impedance. The standard JTM reissue output transformer has a primary of about 6.5k, which is about 65% higher than your typical two-tube Marshall iron in an EL34 amp (e.g. 50w plexi). If you want more of an aggressive sound, set the selector one notch higher than the load, i.e. set it at 16-ohms for an 8-ohm cabinet, which tends to make the tone much more Marshally. It has been said that using the impedance selector in this manner will make the amp louder and it will sound less constricted."

So I am wondering if I shouldn't just switch the impedance on the head to 8 ohms going into my 4 ohm cab.

Would someone be kind enough to let me know if the quoted material is an accurate statement and is there any reason or benefit to rewire my cab to 16 ohms?
T.I.A.

[Reinhardt Amps]

I cant vouch for the Marshall RI Iron, but I like the tone better with the trannies Im currently using when I run it set up at 3.4 k instead of the 6.6. IOW, set up using the mismatch. I do know some people prefer it with the normal setup as well.

[kindburro]

Retro......By simply running your JTM-45 RI at the 8 ohm setting into your existing 4 ohm load you will be halving the primary impedance of your O/T down to around 3.3K. With a four ohm load and amp set at four ohms your are hearing/feeling the upwards impedance match of 6.6K.
The amount of negative feedback thru the circuit may change depending on where the wire for this part of the circuit is attached. If it's going to the 8 ohm tap in theory it should be equal no matter what setting is used.
You may want to try rewiring your speakers in series for 16 ohms and set the amp at 16 just for a comparison if it's easy to do.
All older JTM-45's using the Radio Spares O/T were set up for use with the 6.6K primary and fixed output at 16 ohms. Heads ran into 4 X 12's wired at 16 ohms. Combo used 16 ohm speakers wired parallel for 8 ohms.
Later JTM-45's used a Drake O/T with an 8K primary and secondary was selectable at 4/8/16. Many used these amps in combo form set at 16 ohms running into an 8 ohm load. The JTM-45 sounds punchier this way with a more pronounced midrange crunch. At a standard 16 ohm/16 ohm load you have more of a Hi-Fi type sound to me, less efficent power wise and less midrange. Either can be cool and it's very subjective. All up to the player, the rig and type music. The upwards impedance match can be usefull in keeping volume in check while cranking an amp.
Best to all,
Greg G.

[retro]

Thanks guys...

I appreciate it.