#1
I've noticed that my preamp tubes have little metal covers over them, and I was wondering if there's a reason for that. I've seen plenty of amps that don't have covers on their preamp tubes and some that do have covers. What are the point of them?
#2
I'm no expert, but from what I've heard they are to help reject RF interference and that sort of thing. Some amps have them only on the V1 tube, which would seem to make sense by that logic.
#3
Quote by Charley2715
I'm no expert, but from what I've heard they are to help reject RF interference and that sort of thing. Some amps have them only on the V1 tube, which would seem to make sense by that logic.


That does make sense, and was what I thought they would be for. I read an argument on another forum about them affecting tone, though, and now I'm wondering if it's true or if they're full of crystal letuce.
#4
hey dude!

i've taken them off of every amp i've owned and never had any problems. i like to be able to see my tubes and visually inspect them. if a tube lights up really bright that is a bad sign.

i say, leave them off unless you are having interference problems.
#5
A lot of combos have them, I always assumed they were to keep the tube from working itself loose since the tube are hanging upside down rather close to a pulsing speaker. Haven't heard the rf thing before but it makes sense.
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#6
The ones you see on preamp tubes are faraday sheilds to cut out inductive noise. That's why you see them on the tubes operating with the lowest signal levels - ie V1.
The bigger valves that isn't such an issue, heat dissipation matters more. That's why they have simple spring systems to hold the valve in place. On small signal valves interference is the biggest issue, on large ones heat dissipation is more important. That's why there is a mixture of the two methods of doing it in your amp.
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#7
i read an article in a book about improving tone by removing the covers to improve tone. cant find the article ATM, but it said something about the cover screwing with the electron flow from cathode to plate in the tube. the plate attracts electrons because it is held at a positive voltage in respect to the cathode, but the cover being negative (or grounded, because its connected to the chassis) repels the electrons, so they get "confused" baasically. *shrug

it did also mention something about possible increased hum do to interference. but the sunn solarus im using right now has no covers, and is quieter than the other guitarists fender bassman, which has covers (this could obviously be caused by quite a number of things besides the tube covers tho)

if i find the article, ill post it here.


i did take the tube covers off in his amp recently to test the theory, and it did seem to improve the tone, but i didnt a/b it.
#8
The need to shield the tubes has a lot to do with their physical location in the chassis. A good design puts the smallest signal tubes as far away from the power transformer as possible. The closer it is to the PT the greater the need for shielding.
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#9
Well, all 6 of my preamp tubes are sheilded, and they lie directly behind the front baffel in a row going lengthwise across the amp, with the one on the far right (facing the front of the amp) being 2 tubes deep.

So, like this:

Back of amp
_________ O
O O O O O
Front of amp

(The underscores are just to align the last tube)

What SGRocker400 was saying is basically what I was reading, but all this talk of electron activity was getting me suspicious of some Crystal Lattice theory going on

I mean, the negative/positive attraction/repulsion thing makes sense, but I wasn't sure how much actual effect it has on tone.
Last edited by Blktiger0 at Feb 15, 2012,
#10
Take them all off and see what happens. Your amp will look cooler too

If you detect a problem, put them back on. I have a little vid doing this and swapping a tube if you are interested. You may have to pull the chassis out - not sure. If so, make sure it is unplugged and you DON"T touch the underside (open facing chassis' can kill if you stick your hands in there). Grab it by the transformers and slide it out just enough to reach the preamp tubes better.

Then take some pictures for me before you put it back in

Because you do gig, make sure the tubes are seated (pushed down) real good and get some spare tubes too.
#11
I have broken 2 pre-amp tubes putting the damn covers back on. I leave them off now. I don't see them grounded on my cheap ass Blue Voodoo so I don't know if it's an interference thing or to keep them seated(Always assumed this). They had O-rings to stop vibration on the chassis.
#12
You broke the tubes? How were you trying to fit the covers? With a hammer?
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#13
Quote by Cathbard
You broke the tubes? How were you trying to fit the covers? With a hammer?



No- the spring broke the top of the tube.
#14
Never heard of such a thing. My guess it was already cracked and wasn't long for this world anyway. I've broken them on purpose before, it wasn't an easy task.
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#15
Quote by Cathbard
Never heard of such a thing. My guess it was already cracked and wasn't long for this world anyway. I've broken them on purpose before, it wasn't an easy task.




I can picture it now...

Cath: WHAT IS THIS?!?!?! YOU AREN'T A NOS JJ!!! DEATH TO YOU, DEMON!!!

*squeezes tube as hard as possible with hand*

Cath: WHY. WON'T. YOU. DIE?

*gets hammer*

Cath: Seriously? This thing is ridiculous...

*stares at it with his pure hatred*

Tube explodes.

Cath: MUHWAHAHAHAHAHAHAHAHAHAHAHAHA!!!

I think I will go ahead and pull them off, then take some beautiful pictures for 311
#16
I took them off, and it did sound a little bit more clear than before, but it could all be in my head.

The biggest surprise that I got from all of this was this:



It has Tung Sol's in V1 and V2! I almost shit...

Granted, the rest of the tubes were all Ruby, but I was quite surprised by that...

Here are the rest of the pics:











I tried to pull the Chassis out after I took the covers off just to see if I could, but it was pretty damn stuck...

Also, the little red and black wire for the fan hangs down near the V6 preamp tube and V1 power tube. Should I be concerned about it touching them?
Last edited by Blktiger0 at Feb 15, 2012,
#17
Tung Sols are kinda whatever tubes , the Rubies are probably better depending on the specific label on them. Whats the code on the Rubies?

EDIT: those Egnater labled 12ax7s are triple mica, very interesting. I didn't know anyone was still making triple mica tubes.
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Last edited by Flux'D at Feb 15, 2012,
#18
Quote by Flux'D
Tung Sols are kinda whatever tubes , the Rubies are probably better depending on the specific label on them. Whats the code on the Rubies?

EDIT: those Egnater labled 12ax7s are triple mica, very interesting. I didn't know anyone was still making triple mica tubes.


I wanted to put Tung Sol's in V1 and V2 anyway, but replace the rest with JJ's and maybe a JJ 5751 in V6. It just saved me some money of buying two more tubes as backups.

The Power Tubes are 6L6GCMSTR

The Preamp Tubes are 7025ss/12ax7a

Both are Ruby except the two Tung Sol in V1 and V2
#19
Aren't there more codes than that? Ruby can be rebadged just about anything. To tell what they are you'd need all the codes surrounding the 12AX7. I'm not really up on Ruby codes though. Iirc they aren't as logical and obvious as groove tubes. I like the way GT do their tube labels, you can tell at a glance what they actually are. Well, it gets a bit more complex with their Russians ones because there are three different ones (and they are a bit cryptic about it) but the others are blatently obvious. Like with a GT a JJ would be GT-12AX7-S, S being for Slovakia, ie JJ.
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#20
Those are Ruby "Silver Special" tubes, highly regarded as far as recently made stuff. They're like a more musical Chinese tube with better low end definition. Those are definitely a better tube than the Tung Sol.
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Last edited by Flux'D at Feb 15, 2012,
#21
Yes, very interesting.

Thanks for the pics too. Looks like you've got a bit more room in there then I was thinking. Worst case you could remove some of the power tubes to get to the preamp tubes. I personally would pull all of these tubes out and spray some contact cleaner on the pins and work each one in and out a bit. Tung Sols are good tubes, just a bit bright. Too bright for me. I like the darker tone of the JJ's. I'd get one Phillips 5751, maybe 1 NOS 12AX7 and then the rest JJ. The Ruby STRs are good tubes I hear but I'm not sure about about the GCM part.


Congrats again dude....cool amp
#22
What's the whole Triple Mica thing?

Also, what are the qualities of the Silver Special tubes? In terms of EQ and whatnot.

The reason I like Tung Sols is they add some brightness to the amp, which I like. I wouldn't use an entire set of them, just one or two in V1 and V2. I plan on getting JJ's for the rest, like I said.

Also, just wondered if you guys saw my question at the end of the post with the pictures about the wires touching/being close to the tubes
#23
Quote by 311ZOSOVHJH
Yes, very interesting.

Thanks for the pics too. Looks like you've got a bit more room in there then I was thinking. Worst case you could remove some of the power tubes to get to the preamp tubes. I personally would pull all of these tubes out and spray some contact cleaner on the pins and work each one in and out a bit. Tung Sols are good tubes, just a bit bright. Too bright for me. I like the darker tone of the JJ's. I'd get one Phillips 5751, maybe 1 NOS 12AX7 and then the rest JJ. The Ruby STRs are good tubes I hear but I'm not sure about about the GCM part.


Congrats again dude....cool amp


Thanks!

The more I play it and spend time with it, the more I love it. I'm pretty happy I got this instead of the Jet City, although I would still like to try one myself.

It is pretty damn spacious in there I was able to reach around/over the power tubes to get the covers off. I'm thinking I might get a JAN Phillips 5751 for V6 and do JJ ECC83's for everything but V1 and maybe V2. Some recent playing with the Presence, Treble, and Volume, and I don't really think I need anything brighter, but I'm not sure I would want it darker either. I'll still be trying both a Tung Sol and a JJ in V2. Hell, I'll probably take an entire day to just experiment with the preamp tube positions. First I've gotta get the extra money to spend on some tubes, though

I Googled the Ruby Tubes, and in an old Harmony Central thread, they said that they are relabeled Shuguang 6L6's, then I got this off of DougsTubes:

The Ruby 6L6GC-MSTR is from the Shuguang factory. It's thicker glass envelope and sturdy construction is designed to work in the most demanding applications. It it packed with lots of punch and a sweet tone, very musical. Philips STR copy. This Ruby tube is a re-labeled Sino, Chinese and Shuguang - it's all the same.


I have absolutely no knowledge of that brand whatsoever, if someone would like to enlighten me
#24
They are the cheapest tubes on the market pretty much. I haven't tried their 6L6's but I do have a quartet of their EL34's in my JCM900 and they are surprisingly good. No SED or anything but certainly decent. I'd rank them a fair way above Sovtek tbh.
Shuguangs seem to be getting better all the time. Give them time and they'll probably be one of the best, if not the best tubes out there. I suspect that's what is going to happen to Chinese stuff in general. I remember quite clearly when Japanese stuff was crap too.
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#25
It looks like those Ruby preamp tubes are actually JJ's

http://www.musiciansfriend.com/accessories/ruby-ecc83-12ax7a-preamp-tube

http://elderly.com/accessories/items/12AX7ACZ.htm

and a few other sites had the same description as Musician's Friend

Although from these two, they look to be Shuguangs:

http://thetubestore.com/chinese12ax7.html

http://www.fryette-users.com/forums/showthread.php?2688-Question-for-the-tube-experts....Ruby-7025SS-12AX7A-Chinese

I would say with how recently I bought this amp and because Musician's Friend would probably be pretty up-to-date with their descriptions, it would be a JJ, but it looks more like the Shuguang

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I'll let you guys decide.
#27
Quote by steven_ferns84
Ruby rebrands JJ,SED & Chinese made stuff.

If you want to experiment with different preamp tubes then this looks like a good deal for modern tubes: http://www.tubesandmore.com/scripts/foxweb.dll/moreinfo@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?item=T-12AX7-SET

10 different pre types for $100. its missing some popular sovtek stuff but its got most of the chinese stuff.


My only problem is that 3 of the tubes are rebrands, and I don't want to spend that much money on tubes when I might only like 2 of them. We'll see, though. I'm more concerned about finding out hwhat the rubies in my preamp are. If they're JJ's, that saves me some times and money, and if they're Shuguangs, I know how those sound now and have those to play around with.
#28
The valve in your picture is definitely a Shug.
If you are sticking it in a head then I'd suggest that you try a JJ ECC803. They aren't quite as middy as a JJ ECC83S. They are a little more sparkly. The ECC803 is the same design as the old long plate Teslas. They are a low noise variant. Their only drawback is that they tend to be more microphonic which can be an issue in a combo but normally not a problem in a head. Very nice lively valve. A tiny tiny bit less gain than an ECC83S.
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#29
Quote by Cathbard
The valve in your picture is definitely a Shug.
If you are sticking it in a head then I'd suggest that you try a JJ ECC803. They aren't quite as middy as a JJ ECC83S. They are a little more sparkly. The ECC803 is the same design as the old long plate Teslas. They are a low noise variant. Their only drawback is that they tend to be more microphonic which can be an issue in a combo but normally not a problem in a head. Very nice lively valve. A tiny tiny bit less gain than an ECC83S.


The picture above of just a valve is a Shug for sure...I just got it to compare to the other pictures on the first page. Did you mean the pictures from my amp or the one above with the white background?

I'm thinking I'll grab 2 803's 3 83S's, one more Tung Sol, and a JAN Philips 5751 and play with all of those in different positions, with either JJ 6L6's or =C= 6L6's in the power section. That one just depends on what I want to spend. Maybe I'll go insane and spend $400 on NOS 6L6's...