The tubes in my 5150 combo - question

[EVHwannabe]

Okay, I know less about tubes than just about anyone, so I'm looking for some info from anyone...
I popped the back off my 5150 combo (singature not block letters and not II) to see what tubes were in there. The two power tubes (a sticky says they are 6LCGC (or is it 6L6GC)) don't have any writing or logos on them. They do have a stickers close to them that say "30.8" and "30.9". I presume that has something to do with their bias setting ???
The 5 preamp tubes are labeled as 12AX7s. The odd part is that the 1st, 3rd, and 5th have no writing on them, no logo, no nothing. The 2nd and the 4th have a "JJ" logo on them. My uneducated guess is that all the tubes came from the factory with no writing or logos on them, and whomever owned it before me replaced two of the preamp tubes with JJs. Why would they just replace two, and why every other one (unless it is just a coincidence that those two flamed out)?

Does anyone have any insight into these amps, or into tubes in general that might shed some light? I guess ultimately, I'm trying to decide if it's worth hauling this 85 pound monster to Uncle Albert's to have it looked at to see if it would sound better with new tubes.

Also, the thing has a ground switch on the back that can be in a "+" position, a "0" position, or a "-" position. How do I know which to choose? Thanks and sorry if these questions have been answered before, as I didn't do a search first... [img]/images/graemlins/crazy.gif[/img]

[jazzman]

Re: The tubes in my 5150 combo - question

I don't know what tubes your amp came with. If you like the way it sounds now, find the same tube and make sure the plates look the same. From my own experience, I've always matched the tubes that have the same plates so it would sound the same. Different tubes from different makes do sound different. It don't matter about markings. If the tube is the same number, and the plates are the same, they should be close. The only tube so far I've seen that is different is the Sovtek 12AX7 LP and LPS. These look identical but the filement is different. Therefore, they sound different. At least to me.

I think the older 5150's used to use NOS chinese preamp tubes. I can't remember which one's they used for power. I wouldn't haul any amp anywhere just for tubes.

I'm pretty much a wacko when it comes to tubes. I hear a big difference between makes of tubes. Now may be a good time to try some different tubes. Just keep the old ones for reference.

[nonamemx]

Re: The tubes in my 5150 combo - question


I dont know a whole lot about tubes, just that a matched set will probably sound better than a bunch of goofy ones [img]/images/graemlins/laugh.gif[/img]


and *i think* the ground switch is meant to help control noise levels (all the gain can create enough hiss on its own) some buildings are wired weird, and how you determine the setting is just flip it to whatever quiets the amp the most efficiently.

[Cleveland Metal]

Re: The tubes in my 5150 combo - question

The sticker apparently are the Bias voltages. That is good to have.

My 5150s did well with Tesla/JJ tubes all around, power and preamp. I prefer SED Svetlana now but the Tesla JJs were great.

Call tubestore, give them the bias numbers for the power tubes that you have, they'll match them up, and get JJ preamp tubes and you'll be set!

Many people will replace just what is acting up. hence your mismatched tubes. Do it right, replace them all.

[Cleveland Metal]

Re: The tubes in my 5150 combo - question

With those bias numbers, just pop in the tubes, and no biasing needed. 5150s aren't bias-able without a mod anyways.

[EVHwannabe]

Re: The tubes in my 5150 combo - question

so you just grab them and pull them out? Nothing to unhook or unscrew or anything??

[jazzman]

Re: The tubes in my 5150 combo - question

Pretty much. It's more work to change a light bulb.

[nonamemx]

Re: The tubes in my 5150 combo - question

Just dont bend the prongs!