For the technically inquisitive folks, the file below shows some graphs comparing the performance difference between the old efx loop and the new one.
The graphs show the frequency response of the loops without cables attached and the frequency response with 50ft of standard guitar cable (30pF per foot capacitance) and the effects of the high frequency response. There are also graphs showing noise analysis comparisons.

While the 5751 driven efx loop has been a staple in almost all our amps since 2005, it was time for a redesign. This is partly due to issues with some effects units and partly due to the difficulty of obtaining 'quiet' 5751 new production tubes. I now reject 2 out of every 3 I buy. 

So....the new loop uses an NOS 12AU7 high current tube. This tube is way more capable of driving long cables with much less High frequency roll off due to cable capacitance.  The signal to noise ratio is also much improved from the 5751 based design.

The send control on the back of the amp has always been able to be used as a master volume control for the entire amp, with 'unity' being at the 11 O clock position. The new system also allows this control to be used as a master volume for the entire amp, the 'unity' position is now 2 O clock, giving much more available range to bring the overall volume down if required.

This new loop will feature on all amps from serial number 151106 onward.

Please note it is not possible to just put a 12AU7 in the current loop, it will potentially cause damage.

I will be taking amps in for upgrades to this new loop from the beginning od December. Cost is $150.00 plus shipping and includes the NOS 12AU7 as well as an entirely new loop circuit. Please email me at alan@carolannamps.com to schedule your amp in if you want to take advantage of this new loop.

We have just added the ability to register your amplifier online. It doesn't matter if you purchased the amplifier new or used, there are definite benefits to registration.  you can register your amplifier here

We have vastly expanded our upgrade options for almost all the CA models. This allows players to update to current specifications or upgrade their rig without having to trade up. Please visit the upgrade section of our website to view the options that are available to you.