Here is a chart I made in response to a question about direct 12ax7 substitutions. There are more than most people realize. The RCA manual designates the pinout as "9A", so I've included all "9A" pinout tubes here.
I've included all the industrial and military designations of these tubes also (where applicable), and arranged them in order of amplification factor. I did not include European designations like ECC83, etc. Hope this helps someone with their experimentation. As for which of these will work in certain applications, you'll have to do more research and conduct your own experiments. Generally, if a 12ax7 is called for in a certain position in one of your amps, probably any of these tubes will work as a drop-in substitute. The lower the amp factor, the less gain you'll get from that stage, which might be desirable. If the stage is a cathode follower and calls for a 12AT7 or 12AU7, subbing a 12AX7 or another of these tubes might create issues. I encourage you to experiment. This would actually make for a nice video comparing as many of these as possible. I think I have most of them in my tube collection already. If you'd like to see a video like that, let me know.
This is a video response to Tone Priest's question about modding a Hiwatt clone build. If you are a paid member here on Locals and have tech or other questions, I'll be happy to give you a similar video response when I get time! Thanks so much for all your continued support.
This was the full jam session on the Gibson L1 I did recently. As you probably know, I usually will jam for a while on something and then pick a few highlights to show in a final video. A ton of stuff got edited out. It's not all great, but it's not all bad either. I find it kind of soothing, this quiet acoustic stuff. I'm never sure where the mood will take me.
I made this quick video the other day for a friend and figured I'd post it here as well. He wants to get started in slide, so I was quickly showing him some open tuning concepts to make the transition to slide a bit easier. Kind of like learning slide without a slide.
This video won't go live until Saturday morning. I figure Saturday and Sunday mornings are pretty good times for long-form videos because people are probably settling in with a coffee somewhere, maybe doing a hobby, or having breakfast, so they aren't in doom scrolling mode just yet. But for my Locals peeps, I'll give you the link early in case you got more time on Friday. Don't say I never did anything for ya! ;)
Hi guys. I built a Hiwatt DR504 - that's not a sentence I had on life's bingo card. Anyway, since it's a clone and not a priceless antique, I want to tinker with it.
1st thought is I want to change the Brilliant input to Marshall spec. The Bril channel would otherwise not get used except for maybe jumpering channels. It's pretty thin and shrill in stock form. It currently has a 220k plate resistor, 2.2k cathode and a .47 bypass cap. I'm thinking we change that to 100k / 2.7k / .68uf and ditching the bright cap.
The other thing I was thinking was: since the Hiwatt's master volume is -> right after the tone stack -> makeup gain stage -> then the phase inverter, what if we replace the master volume pot with a fixed grid stopper & leak of some values and install a post phase inverter master volume? I don't know how useful this would be. The amp is LOUD and it is CLEAN. Cranking the preamp volume all the way up doesn't get you much crunch and the little you get is kinda just blocking ...
