Rather than starting a new thread, I decided I'd just add to this one. I have one of the earlier DSL5C amplifiers. As I mentioned in my Introductions thread, I play live with this amp. I essentially use it as a head and run to an external speaker in an isolation cabinet that I built. There, the speaker is mic'ed to the PA. Currently, I'm using a Celestion G10N-40, But @Micky 's mention of a 12" WGS Green Beret has me interested....I've gotta look into that. Anyhoo...I changed my PI valve to a JAN Philips 5751, versus the stock ECC83. Additionally, I changed the stock V1 to an Electro Harmonix 12AX7. I tried a Sylvania 12AX7 valve in the V1 slot, too. Results? I tried the 5751 swap in the phase inverter first, before changing any valves in V1. The difference is very slight. You won't notice a night-and-day difference. There really was no tonal change, per se, that I could detect. However, there was less fizz on the Ultra channel. I want to say that a Stratocaster is more usable with this amp now, as the 5751 takes just a touch off the spikiness of a Strat bridge pickup. I've also done the steel plate mod to the bridge pickup of my Strat, so...there's that. As for the V1 swaps, when I swapped in the Sylvania 12AX7 I couldn't hear a meaningful difference between that and the stock ECC83. The Electro-Harmonix 12AX7, however, seemed like it added just the slightest touch more harmonics. Again, it wasn't a super-obvious change, but it help this amp "grow up" a little more. I'm leaving it in. My next task is to acquire a 12" speaker and build a new enclosure for it. I've been planning on a Greenback, but I'm curious about this Green Beret. What are the positives about that?