Amph T00b Questions

[marnold]

(For those of you who are new, here's why you spell it "amph." (http://www.thefret.net/showthread.php/403-quot-With-this-amph-I-get-no-screaming-solos-quot))

Anyway, I'm in the process of getting my Jet City JCA22H retubed. I called a tech in Green Bay about getting JJ EL84s put in and biased. That will happen sometime next week. After that, I'm going to turn my attention to the preamp tubes. A couple of general questions:

My amph has five preamp tubes: V1 is the primary gain stage for both channels, V2 is a secondary gain stage for the overdrive/SLO channel, V3 is half for a gain stage for both channels while the other half is a cathode follower, V4 is for the effects loop, and V5 is the phase inverter.

I assume the biggest tone differences would come from V1 and V2. Is that accurate? I had all JJs in my old JCA20H and was quite happy with that. JJs are a bit darker which actually works quite well with this amph which tends to be pretty bright.

Does it really matter what I put in V4? It would seem as long as it's a functioning 12AX7/ECC83 it really wouldn't contribute much to the tone of the amph. Or am I way off on that?

Does a balanced phase inverter really matter? All the tube sales sites seem to think so, but just about everything else I've read indicates it's not worth the upcharge, at least in a guitar amph.

V1 and V2 have tube covers on them. Are they really necessary? Do they just unscrew or is there something else you need to do.

Inquiring minds want to know!

[tonebender]

I always run 12AT7's in the V1 slot, especially an amps 20W or less. It seems to give me more clean headroom. Don't know why, read it somewhere, tried it and it works for me. As for the other slots, I've never experimented or heard anything about changing the type from what comes stock. I usually do try to upgrade all tubes from Chinese to better tubes. Hope this helps.

[marnold]

I always run 12AT7's in the V1 slot, especially an amps 20W or less. It seems to give me more clean headroom. Don't know why, read it somewhere, tried it and it works for me. As for the other slots, I've never experimented or heard anything about changing the type from what comes stock. I usually do try to upgrade all tubes from Chinese to better tubes. Hope this helps.

Eurotubes had recommended a 5751 for the same purpose. Someone else on The Gear Page had put a 12DW7 to accomplish the same thing. Apparently that tube is half 12AX7 and half 12AU7. Might be an interesting thing to try since there isn't a ton of clean headroom on it to begin with. Of course, that's not the point of this amph in the first place. :rockon:

[marnold]

Well, I figured out how to get the tube covers off. I just needed to spin them until the tab on the cover lined up with the slot on the chassis and they popped right off. I wanted to check the first two tubes, particularly V2, because I thought the overdrive channel was getting too noisy. It seemed to be glowing brighter than the others. I replaced it with one of the original preamp tubes from my JCA20H and the extra noise went away. Pays to have a spare.

[marnold]

I got the new power tubes put in today and the amp was biased properly. Any thoughts on my other preamp questions?

Thus far it seems like removing the tube covers has not resulted in any additional noise.

[Robert]

The tube covers are safe to remove.

"Tube shields are those little metal cylinders you find over the small tubes in your amplifier. They're used to reduce the chance of picking up hum and noise. Sometimes they're also used to hold the tubes securely into the tube sockets. Tube shields have an adverse affect on the tone of most amps. Here's the reason why. The tube has an element called a "cathode" which gives off electrons. Electrons are attracted to a positive charge and repelled by a negative charge. The cathode is in the center of the tube element called the "plate". The plate has a positive charge which it uses to attract electrons. OK, so now we have a cathode flowing electrons to the positive plate and all is well. Then we install a tube shield that connects to the chassis which is negative in relationship to the plate. Confused? So are the electrons that see this negative charge past the positive plate. Also the plate and the shield form a small value capacitor.

To test this for yourself, start with the tube shields off. That way you won't be dealing with hot tube shields later in this test. Warm up the amp and play, listening to the tone with a critical ear. Next put the tube shields back on. Be careful, the tube shields will be cool but the tubes will be hot. Do not change any settings on the amp or guitar and listen to the tone again. I rest my case. If your amp makes too much noise or does any nasty tricks with the tube shields off, do put them back on."

[marnold]

"To test this for yourself, start with the tube shields off. That way you won't be dealing with hot tube shields later in this test. Warm up the amp and play, listening to the tone with a critical ear. Next put the tube shields back on. Be careful, the tube shields will be cool but the tubes will be hot. Do not change any settings on the amp or guitar and listen to the tone again. I rest my case. If your amp makes too much noise or does any nasty tricks with the tube shields off, do put them back on."

Thanks for the info, Robert. I think I'll try this some time. I assume that since you have this in quotes that you got the information from someone else?

I ended up ordering preamp tubes from Tube Depot today. They had JJ 12AX7s for $9.95 which is the cheapest I've seen them anywhere. I got five of them, one is balanced. Don't know if that's necessary or not but for $2, I wasn't too concerned. I also got a JJ 5751 which I'm going to try in V1. If nothing else, at least I'll have a spare 12AX7.

In the future, I intend to pick up some random 12AX7s as I have opportunity and trying them in V1 and V2. I know I really liked JJs in my old JCA20H so I suspect it will be the same story here. Unfortunately, it's almost impossible to find tubes around here.

[Spudman]

When you swap tubes let them stay in place for an extended time rather than pulling them right out if you don't like what you hear. I've found that as the tubes get played there are some changes that happen with the sound. I think that method would give you a truer sense of what they'll sound like down the road too.

[Robert]

Thanks for the info, Robert. I think I'll try this some time. I assume that since you have this in quotes that you got the information from someone else?

I ended up ordering preamp tubes from Tube Depot today. They had JJ 12AX7s for $9.95 which is the cheapest I've seen them anywhere. I got five of them, one is balanced. Don't know if that's necessary or not but for $2, I wasn't too concerned. I also got a JJ 5751 which I'm going to try in V1. If nothing else, at least I'll have a spare 12AX7.

In the future, I intend to pick up some random 12AX7s as I have opportunity and trying them in V1 and V2. I know I really liked JJs in my old JCA20H so I suspect it will be the same story here. Unfortunately, it's almost impossible to find tubes around here.

Yeah I found that info somewhere online... I think it is correct though.

[marnold]

Got my preamp tubes from Tube Depot today! That was fast via USPS. I put the 5751 in V1. One thing that struck me is that it became even quieter and it wasn't noisy to begin with. Some of the shrill/ragged high end is gone. I guess JJs are the way to go with Jet City amphs, at least to my ears. I don't know how much the 5751 really affected things. I guess I'll have to put my spare 12AX7 in there and see what the difference is. Seems to have made a good amph even better.

[Monkus]

great !

[marnold]

It's thread resurrection time! I had not been happy with the tone of my amph for a little while so I decided to pull out the 5751 and replace it with the extra 12AX7 I bought at the time. I like it better now, although I can't necessarily quantify why. I went back and forth between the two with my two guitars at various levels of gain. The 12AX7 just sounded better to me. I'll keep the 5751 around for future reference.

One of the reasons that I wanted to try the 5751 was to see if it would give the amph more clean headroom. Surprisingly, it didn't. Where it was noticeable was on the high end of the gain scale. Completely diming the preamp gain ("9" is the highest on these Jet Citys, unlike the actual Soldanos that really do go up to 11) was about the same as it was on 6-7 with a 12AX7, which would make sense since the 5751 is supposed to have 30% less gain.

[Eric]

Interesting notes. I sold my Jet City combo a while ago when I realized I had no occasion to turn it up and was playing more bass than anything anyway. Now I have a kid (almost two) and use any spare noisy time to play drums. But I guess on some level it's nice to just plug into a tube amph and go. I'm glad to hear that your devotion to your Jet City amphs has not waned.

[marnold]

Interesting notes. I sold my Jet City combo a while ago when I realized I had no occasion to turn it up and was playing more bass than anything anyway. Now I have a kid (almost two) and use any spare noisy time to play drums. But I guess on some level it's nice to just plug into a tube amph and go. I'm glad to hear that your devotion to your Jet City amphs has not waned.

Nope. I'm really happy with this one. However, if I were to get an amph in the future it would probably not be a Jet City, not because they are bad, but because they no longer are associated with Mike Soldano. Quite frankly, his designs are what drew me to this in the first place. Having said that, I have no intention on getting a new amph unless the "magic smoke" would ever come out of this one.

[deeaa]

5751 for me often sounds kinda cold, suppose it depends on amp design though.

I don't even have an amp these days save for a couple of tube preamps...Amplitube for me only. I should maybe some day try a few different toobs in those pre's.

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[Eric]

5751 for me often sounds kinda cold, suppose it depends on amp design though.

I don't even have an amp these days save for a couple of tube preamps...Amplitube for me only. I should maybe some day try a few different toobs in those pre's.

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Yeah, me too -- just a Pod. I guess I have a powered speaker though, so that's kind of like an amp. Still, the idea of buying an amp at this point seems a little odd.

[Robert]

I liked my Jet City that I had. Good to hear you're rocking yours!

Deeaa, so you sold your JVM? I still have mine! I had to get it repaired (again). It's sounding quite awesome now.

[deeaa]

Yeah I did, didn't see the point of keeping it as I only play the drums with the band now. And for recording my Amplitube rig is much more convenient.

I do use a separate laptop and powered speakers for it, never was happy with using it only in my DAW.

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