If you haven't seen this; a starting point...
I've owned a JoLida 502B since 2001. I assume at least some of what I did will benefit your 302. Absolutely - upgrading the stock tubes is a place to start. I went to various KT88s in place of the Sovtek 6550s. Not sure what the 302B comes with stock. Talk to the folk at the TubeStore to get some ideas. I also upgraded the power cord and put in a HiFi Tuning Fuse. All these changes made a positive difference. My system is posted under Budget-minded so you will find additional details there. I recommend trying some of Herbie's AudioLab "Tenderfeet" underneath your amp. I found placement on a cutting board and better isolation seemed to tighten up the bass. Response Audio is another modder/upgrader to consider. Hope this helps.
I had one of these and it sounded great. Here is what I did: I got more bang for my buck by upgrading the stock 12AX7's and the 12AT7 (I think)tubes with amperex or mullards first. Then I upgraded the stock power tubes (El34's) with Mullard reissues (bigger soundstage but the reissues had reliability issues so I was using the stock powertubes while looking for a deal or real Mullards when I was forced to sell the amp. I used this amp with Spendor small floorstanding speakers and I found it very enjoyable and non-fatiguing to listen to.
Hi Marty, I have the Jolida 502brc. Based on my experience, I would replace the tubes, and make sure you have adequate power, ie. decent power cord, no issues with electrical system. I just added four dedicated circuits, and while doing so we noticed that the neutral return going to the pole had frayed with only a few strands intact. I don't know if it was the neutral, the dedicated circuits or the whole panel update, but wow, what a difference. I am nervous about the mods myself. If you try new tubes and don't like them, you can always put the old ones back in.
Thanks all for the advice. I decided just to upgrade the tubes for now. I bought
EH6CA7, RFT 12AT7, and RFT 12AT7. I am really looking forward to hearing how they sound compared to the stock tubes.
Re: upgrades -- the only thing I did so far was put in a better power cord. Power supply in the house is ok. Still need to rewire the house for three prong outlets so I am still using a dinky converter from Rite-aid for the plug.
One of these days I may do one of the more expensive mods but for now, figured I would rather swap tubes ($150) rather than a mod that would run up to $600. Maybe in a couple of years.