- Make sure you use 18-gauge speaker cable with straight 1/4 inch plugs and not your standard guitar instrument cable. I used two Yorkville Sound - Standard Series Speaker Cable - 18G - 5 foot cables.
- Ensure you match the impedance on the amp and cab. Start off with 16 ohms on both the amp and cab and set the cab to mono.
Steps to control the 6505 / similar high gain tube amp squeal
- Switch any gain pedals (overdrive, distortion) you might have going into the amp.
- Turn down your post-gain down to a soft but audible level.
- Start increasing the pre-gain from zero up to where you can get a nice crunch without sacrificing tone and before you start to sound too compressed. On the 6505 the sweet spot is midway at 5 where you get enough of growl without sacrificing your tone too much.
- Now that your pre-gain is set, you can crank up the post-gain to a level that works. Get those ear buds out cause it gets pretty loud!
- Make sure that your gain settings on all pedals as well are kept low to avoid the squealing.