The 6X4 is the rectifier for the reverb amplifier. You've given me some important information in that you are not satisfied with the stereo cartridge. Perhaps the sound is fine and it's just that particular source. Have you tried it with an iPod, computer, CD player, etc? if you feed the tape input or phono input it should knock your socks off.
I'm listening to it right now and I'm blown away by how great it sounds. The sound just shimmers with the reverb, they really hit a home run with that feature. Speaking of that when I took the reverb unit off to clean the contacts it had a made by Hammond Organ company label inside it. Really first rate quality equipment.
I will be posting pics over the course of the next week along with some videos of the unit in operation. It has exceeded my hopes and expectations. The sound is fabulous.
A quick summary of the work I pergormed this week: recapped the power and reverb amps, recapped the tuner. Restrung the tuner as the string was broken. Tested and replaced all bad tubes. Cleaned every tube socket and and switch. Changed every light bulb. Disassembled front dial glass assembly's and cleaned everything. Removed all old grease from tuner dial indicator slides and regreased. Lubed all bearings and shafts and contact points. Cleaned all three chassis's. Changed speaker crossover capacitors.
I still need to finish the cabinet, I'll be going over it with Howard's. I think I'll also repaint the silver knobs, as most of the metalized finish is worn off the plastic. I'll be giving the record changer a servicing as well although I have high hopes for it as it still works from new. As for the tubes, I installed a set of the Russian EL84's in the amp with a matched pair of GE 12AX7's, sweet.
Pat