Silverface Vibro Champ Re-Tube

[Musicalfish]

My beloved Vibro Champ (AA764) is in need of a new power tube (it has started glowing blue) and I am going to the store tomorrow to buy one but I don't know what to ask for (in terms of bias, brand, etc.) I like my breakup to start around 5-6 on the dial, so not too early or too late. Also, I am a bit strapped for cash now so I can only afford to replace the one tube. Is it ok to replace one now and the other 3 tubes (2x 12AX7 and 1x 5Y3) later? Thank you in advance for helping me with these questions.

[Citizen_Insane]

Read this, or do a Google search for blue glow:

http://www.kcanostubes.com/content/blue-glow-tubes

 

It doesn't necessarily mean the tube is bad. If you are going to replace it, you should replace the rectifier 5Y3 and the power tube at the same time.

[Wyatt]

Avoid the Groove Tubes 6V6GT-R and the Sovtek (they are the same tube). The Electro-Harmonic 6V6EH is an ok tube, but Tung Sol And JJ are the current best new production 6V6GTs. The JJ however is larger, and has higher output, it's more of a 6V6/6L6 hybrid. If you can't get either of these two from you local shop, buy them online.

 

Power tubes wear out faster than the rest. Preamp tubes can outlast them several times over.

 

Rectifier tubes replacement schedules are debated, but in most amp designs a good, New Old Stock (NOS) American tube will last a hobby-guitarist for a decade or a lifetime. Which is good, because the only REAL 5Y3G(T)s available are all NOS or used North American tubes. There are NO modern production tubes that met the correct specs. You stick a Sovtek 5Y3 in that Champ and you'll run though power tubes (and maybe worse).

[Musicalfish]

Hmm, well the blue glow criss-crosses the glass like an x, twice, across the tube from each other. Would it be safe to just leave the tubes for now? What specific 12ax7s and NOS 5Y3 would you recommend? Also, how would the salesman know which tube to give me? Doesn't it have to be a certain bias, or something? (Sorry I don't really understand tubes that much...)

[Musicalfish]

Oops, I take that back. The blue glow is an hourglass shape on one side and a line across. Judging by pictures I found on google of good blue glow it looks fine and normal. An interesting thing i noticed is that that blue flickers with the vibrato on the amp! Cool, huh?

[Wyatt]

 

Hmm, well the blue glow criss-crosses the glass like an x, twice, across the tube from each other. Would it be safe to just leave the tubes for now? What specific 12ax7s and NOS 5Y3 would you recommend? Also, how would the salesman know which tube to give me? Doesn't it have to be a certain bias, or something? (Sorry I don't really understand tubes that much...)

 

 

Any NOS 5Y3, don't spend a fortune for RCA, any good tube from a reputable dealer will work. They can be had for around $15.

 

You can't choose the bias point off the shelf. In fixed-based amps, you install the tube, measure the voltages, and then adjust the bias. To be really exact, many anal techs use an oscilloscope that allows them to bias the tube exactly where it needs to be. But most of us us ballpark figures then dial it in a little by ear.

 

However, you amp is cathode-biased. As long as the voltage stays in the right range, any good 6V6GT should be plug and play. That's where the NOS 5Y3 comes in, using a Sovtek 5Y3 will bump up the plate voltages by 25 to 40 volts and can run a 6V6GT way too hot.

 

To get into a confusing subject. Groove Tubes has something called a "hardness" factor...supposedly, a low number means the tube runs cleaner and a high number means it breaks up earlier. In reality, they are just tubes that had a proclivity to be bias cold or hot or in between in the 1/2 second they took to test the tube. But these only fall into these cold/hot ranges in the average "non-adjustable" fixed-biased amps (amps with no bias pot, the bias is set by fixed-value resistors). But in "adjustable" fixed-biased amps, you can adjust the bias to make any of these tubes bias cold, hot or just right.

 

Blue glow is common, and not a bad thing per say, but it can be indicative of a leaky tube. If you blow a fuse or something in the future, I would replace the tube.

[NinjaModder]

Oops, I take that back. The blue glow is an hourglass shape on one side and a line across. Judging by pictures I found on google of good blue glow it looks fine and normal. An interesting thing i noticed is that that blue flickers with the vibrato on the amp! Cool, huh?

 

Yeah! It is awesome!

 

I also noticed that the harder I play the more my EL84s light up in my Egnater. Tubes are wonderful.

[billy budapest]

If you like, PM me with your budget for a 5Y3 and a 6V6. I have some really nice used 50s/60s RCA and Sylvania rectifiers, plus some GE Blackplate 6V6s.