#1
I recently got a fender pro junior, but during shipping one of the EL84s had broken... Is it safe to run this amp with 1 EL84 until i get a new one? (probably like a week or so)

Also the single EL84 is slightly glowing blue near and inside the metal thing in the tube amp.... I read blue glow is usually normal but i'm worried i did this by playing it a few times with only 1 power tube...

Anyways... Please help. Thanks!
GEAR

Guitars
Danelectro Double Cutaway 1959 reissue, Jay Turser Vintage Series Strat

Pedals
Danelectro Reel Echo, Crybaby Wah, Boss DS-1

Amplifiers
Orange Crush 30w
Fender Pro Junior
#2
Should be fine using one tube. You're just driving one half of the output transformer, though, so the sound may not be as good with both tubes. Not sure if you understand why there are two tubes, but one tube drives the positive half of the signal's cycle and the second drives the negative half. With half of the signal present, like I said, the sound quality may not be the same.

Blue glow is normal and somewhat desirable in audio tubes. Don't worry. It will be fine.

One last thing - be careful pulling out the old, broken tube. There are some high voltages inside of that amp - stored in the power supply capacitors. These high voltages can exist for weeks, even after the amp has been turned off and unplugged. Coming into contact with these voltages could certainly make your arm hurt, or worse - kill you.
Last edited by KG6_Steven at Jun 13, 2010,
#3
Ahhh.

Wouldn't it put more strain on the one tube or possibly mess up the transformer....

Sorry to be a bug, its my first tube amp... I got a lot to learn heh.
GEAR

Guitars
Danelectro Double Cutaway 1959 reissue, Jay Turser Vintage Series Strat

Pedals
Danelectro Reel Echo, Crybaby Wah, Boss DS-1

Amplifiers
Orange Crush 30w
Fender Pro Junior
#4
Nope. Absolutely not. Picture it like this. The output transformer has a center tap. The output from one tube feeds one half of the transformer's input. The output from the other tube feeds the other half. At any given time, only one tube is on, or conducting. When the first El-84 is conducting, the other is in cut-off and is not producing a signal. If you're familiar with a sine wave and we draw a horizontal line through its middle - the upper half would be fed by one tube, and the bottom half fed by the other. Only one tube is ever "on" at a time, so each never "feels" or "sees" the output of the other. This is why you can get away with removing one output tube and powering the amp. Remove one tube and the other could care less that it's gone. In fact, this is a troubleshooting technique we use to troubleshoot tube amps. Would I take my amps out and gig like this? Probably not. As I already mentioned, the sound isn't going to be the same - you're missing one half of the sine wave, or signal. But if you really want to play it with one output tube missing, it won't harm the amp, remaining good tube or the output transformer.
Last edited by KG6_Steven at Jun 13, 2010,
#5
Thank you Steven, your great... and you definitely know whats up.

You should be on the who to listen to list.

Anyways, moving on. If you have any experience with pro juniors, maybe you could recommend a brand for me to replace the stock sovtek/groove tube one(s) with.... I was probably going to buy JJs based on people telling me they are good... But I've never used any other tubes except when i randomly play amps at shops and stuff.

If its any help, I can try and tell you what type of tone I like... (If that matters when buying tubes....)
GEAR

Guitars
Danelectro Double Cutaway 1959 reissue, Jay Turser Vintage Series Strat

Pedals
Danelectro Reel Echo, Crybaby Wah, Boss DS-1

Amplifiers
Orange Crush 30w
Fender Pro Junior
#6
You're welcome. I've been an electronics tech for several years, which helps.

You're too kind!

No experience with Juniors at all. I'm running Peavey, Rivera and Mesa here at the moment. As you're aware, tubes from different manufacturers will each have a unique sound. Heck, even tubes from the same manufacturer can tend to sound different. I've done some experimentation with different output tubes in my Mesa Lonestar and finally settled on a pair of 6V6 from Groove Tubes. I mostly use the reviews from Tube Depot and some of the other tube vendors to find the approximate sound I'm seeking. What type of sound are you looking for? I don't consider myself an expert on tube tone specifics, but perhaps can get you in the ballpark. I like JJs, Groove, Sovtek and some others. Don't forget a lot of your tone shaping can be done by swapping out the right 12AX7 tubes.

Lastly, is the bias on your amp fixed or adjustable? If you start playing around with different output tubes, if it's adjustable, you'll either need to have the tools to adjust your own, or get friendly with a local repair tech. Expect to pay around $50 to have a local tech adjust your bias, if it's not fixed, like on my Mesa and Peavey.

Forgot to mention, if you have the budget, consider the NOS tubes. NOS means New Old Stock. These are tubes from the 1950s through about the 1970s that are considered to be so much better quality than the brand new tubes being produced today. The quality control on tubes back then was vastly better. Unfortunately, tube quality has not improved in the 2000s. The only bad news is, these old tubes are in limited supply and command a high price. The other bad news is, counterfeiting is quite common. Take a new tube, remove the label and stamp on a label matching a tube from the 1950s and the price just went up big time. Unfortunately, it doesn't do the same for the quality.
Last edited by KG6_Steven at Jun 13, 2010,
#7
I'm pretty sure its fixed, says something here on the manual about not having to bias to switch tubes... biasing is... like if im switching from the EL84s to like 6v6s or for each set of EL84s you would have to bias?

Basically the tone im looking for is psychadelic/60s/surf/grunge.... I'm constantly drenched in reverb.

Think 60s meets late 80s/90s grunge. In a garage. o_o


edit: on the topic of nos tubes, thanks for finally explaining those... for the longest time i thought they were a brand you simply had to put in your silvertone if you wanted to sound good. xD

.... and on the topic of silvertone... Gawsh I wish i had a silvertone.
GEAR

Guitars
Danelectro Double Cutaway 1959 reissue, Jay Turser Vintage Series Strat

Pedals
Danelectro Reel Echo, Crybaby Wah, Boss DS-1

Amplifiers
Orange Crush 30w
Fender Pro Junior
Last edited by manipulator70 at Jun 13, 2010,
#8
Yeah, I think Fender uses a color scheme for their output tubes. What this means, is since they use fixed bias, you need to make sure you install output tubes in the same bias range as the ones currently installed. Install something that's too far out of spec and either the sound will suffer, or you'll wear out the new tubes in a jiffy. Wherever you decide to buy your new tubes, make sure they are aware that you're buying them for a Fender Junior and the color on the base of the existing output tubes. This doesn't apply to preamp, or 12AX7 tubes.

You're on the right track with the concept of biasing. More specifically, bias is:

Take two 6L6GC tubes. One of them will require a specific plate current, while the other may require something different. The bias basically determines how hard the tube works. Set the bias too low and the tube operates cold. It'll sound poor. Set the bias too high and the tube operates hot. It may sound good, but will quickly wear out, as it is operating outside of its design specs.

Some amps are designed to accept different tube types, such as 6L6, EL-34 and/or 6V6. This requires not only a different bias voltage, but different operating voltages as well. So, it's kind of the same, but more involved.

When I think of surf music, I think of lots of reverb. Grunge and Psych suggest some growl, or snarl. Personally, if it were me, I'd swap out the dirty channel 12AX7 for something with a hotter output. I don't have the schematic for that amp in front of me, but there should be a gain stage tube in there somewhere for that channel. That tube is going to drive your distortion. Replace it, or the first tube in the dirty channel with something hotter and you'll make a big change for about $15 or $20. To complete the transformation, replace the output tubes with something a bit more gain and it should sound pretty nice.

http://www.tubedepot.com/

I'd be tempted to try their Sovtek EL-84. You might want to try contacting them via e-mail to see what they recommend. They are quite knowledgeable - I've bought several tubes from Tube Depot.
#9
Ok wait a sec... Will any EL84 be good to go in my output section? Or will it have to be a certain color coded EL84 that matches my amps bias?

or is that for when im changing types, like from EL84 to 6v6?

Also, would that mean I could have a EL84 that runs cold or a EL84 that runs hot and have to find the correct one for my amps biasing? Or is that all EL84s have a certain biasing, while all 6v6s have a different one, and my amp is biased for EL84

Edit: Ok my other tube just crapped out I think.... I was playing and it slowly got quieter.... Then the tube just stopped lighting up and no volume.... Must have got mucked up in shipping, both the EL84s were out of the socket when i received the amp... T-T
GEAR

Guitars
Danelectro Double Cutaway 1959 reissue, Jay Turser Vintage Series Strat

Pedals
Danelectro Reel Echo, Crybaby Wah, Boss DS-1

Amplifiers
Orange Crush 30w
Fender Pro Junior
Last edited by manipulator70 at Jun 13, 2010,
#10
The bias range of the replacement EL84 must match that of the original tubes supplies by Fender. Groove Tubes used to have a color coding comparison on their website - not sure if it's still there, or not. If it isn't, it shouldn't be too hard to find it somewhere on the web. Fact is, Groove Tubes is now owned by Fender. Which should make it even easier for you. On the base of your EL-84, it should have a color that identifies the bias range. The color means a certain numeric value. If using Groove Tubes, you'd match that color to their line of tubes and then order that color. You'd have a perfect match and life would go on. If you order from a vendor like Tube Depot, you need to tell the amp you're buying tubes for and the color on the existing tube. They will know how to match that with what you're buying and supply you with the correct tube.

So, just for clarity - this is something you need to do anytime you replace the EL-84 tubes in your Junior with another set of EL-84 tubes. The colors, or bias range, must match up to provide the electrical qualities, or a mismatch will occur.

Although the bases of some tubes are identical, the electrical functions are not. Some amps are designed to accept different types of tubes (EL-34, 6V6 or 6L6GC in the same socket) and others are not. For example, my Mesa will accept all three types I just mentioned. I have to change the position of a switch on the back of the amp and then make sure the right type of tube is installed. Even for that installation, since that amp uses fixed bias, I have to make sure all of the tubes I buy for it operate at the same bias level. If I happened to have a quad of 6L6 tubes with a higher or lower bias setting, I would not use them, since it could cause problems.

So, when I buy tubes, I make sure that they are a matched pair or quad. That means the vendor has tested them and verified their bias requirements. Remember, tubes from the same batch will have different bias requirements. Most of them have test equipment for checking these values. Once determined, they mark the tubes. This is how they can create matched pairs and quads.

Hope this helps answer your questions. If you have any others, just ask.

If that amp was brand new, I'd contact the store and have them make it right.