Hi, first post, I've been reading the old forum all nite and am getting itchy to try one or two basic mods and maybe bias. I have a question for someone smarter than me (not hard!), what do each of the preamp numbers mean? ie. V1, V2 etc and what does each position do. Also, would you gain greater differences by changing component values as per your mods or does mix and matching valves make as big a difference?
Anyway, hope someone can shed a bit of light on this dull old mind!! Oh yeah, I have a 22h.
Cheers Jase
Last edited by Jase01 on Wed Feb 20, 2013 6:04 pm, edited 1 time in total.
Usually the numbers refer to the tubes simply counting from left to right. V1 being the tube farthest from the power section.....v2 being the next etc. The V1 tube is usually the first preamp tube. The first stage of amplification after the signal enters the amp. Don't assume that a given "v number" has a defined function because that will vary with amp design. All the v designation tells you is a tube's location in a given amp.
Ok, so its better do component mods then? Did a little reading while waiting, is V1 usually where your gain and tone comes from and will running a hotter valve in the the phase inverter (last slot, yes?) push the power valves harder? Sorry for my ignorance, I'm trying to get a better grasp on this before I tackle any mods.. Cheers for your help!
Usually, the first valve gets the instrument signal level up a bit so it can get through the tone controls without being degraded too much. Then there might be any number of extra valves after that for gain, or even just to drive things like reverb and effects loop sends/returns. Then the last one is the phase inverter which does indeed drive the power tubes.
Hotter or cooler valves will affect all the stages because they change the signal level. It's impossible to say where a hot valve might be good because it depends so much by amp design, I would say that there's not insane differences between preamp valve strengths - if you want to seriously increase the gain of your amp its better to mod the circuit. If you want to decrease it though,something like a 12au7 is often a good substitute. But as to which position it'd be best in, again that just depends on the amp and where you think it sounds best.
Thanks, I think maybe I posted this in the wrong section! I just found a dedicated Jet City page. Maybe someone could move this? So I see Cirrus it's not going to be as straight forward as I was hoping...Oh well, give something to learn, I appreciate the help from you guys keep it coming if you can think of anything else that might help!
My advice - go with a new set of tubes and then adjust bias on any JCA amp before making judgements on what to do about gain or tone. That change alone will make a world of difference. Speakers are the next thing to look at, then probably the depth knob.
The JCA50 I run has the smaller tubes running from left to right (V1 through V5), which lead logically from the input through to the power section. I'm pretty sure all other JCA amps are set up the same, but I can only speak to the one I know.
I asked Edge11 if he was thinking about bringing his mod thread this way. He responded that he was going to wait and see. There's a new group of guys going nuts on that thread right now, and it'd probably be hard to do anything at this stage that wouldn't be a demotivator - plus, they're probably the only thing active at HCAF , and they'd probably send Anderton over to kill me as his last act.
, and they'd probably send Anderton over to kill me as his last act.
