Time to re-tube my amp... any advice?

[VAiN]

Hey guys, I have an original 'block letter' 5150 Half-stack that requires some re-tubing...

My plan is to go with Russian tubes - I'm thinking Sovtek. And what's up with the 'bias'? Is that something that the repair guy can dial in? I'm open to any and all ideas/recommendations... what do you all suggest?

[jhale667]

Yep, the bias can (and should be if you don't know how) be set by the tech that ends up working on your head. The new Sovtek tubes are supposed to be cool, but haven't tried them yet personally...

[Nitro Express]

The regular Peavey 5150 heads have a fixed bias so there is nothing to adjust. You just buy a matched set of tubes and plug them in. What I do is spray the pins of the new tubes with Deoxit before plugging them into the sockets. Doing this helps clean the electrical contacts. My main amp is a 5150 II and I'm running Electroharmonix 6L6 tubes in it and it sounds great.

The 5150 amps are purposely biased cold for power amp reliability and so the tubes last longer. You don't need to worry about biasing these amps. You just plug a new set of tubes in. The power section doesn't effect the tone as much as let's say an old Marshall. On the 5150 the tone is generated more in the preamp so experimenting with different kinds of preamp tubes, especially the first three in the preamp will make a HUGE difference in your tone. Speakers make a huge difference as does setting the EQ and Resonance controls.

The old block letter 5150's are being sought out more by collectors. I would hang onto the amp and leave it stock. As years go by they will be even more sought after. What's nice is preamp tubes are cheap and easy to replace and you don't need special equipment to customize your sound. These are amps that you can tweak just with the knobs and finding the right tubes and speakers and work wonderful for high gain to classic rock. They do best with weaker pickups and tend to prefer humbuckers. They love PAF style humbuckers.

[VAiN]

Thanks for the info guys... So in your opinions it's cool to go with the Sovteks all around? I'm leaning towards those for sure...

[Nitro Express]

Sovtek and Electroharmonix are two brands owned by Matt Mathews. Matt is one of the biggest importer of tubes and what he does is import Russian tubes, test, match and package them in sets. He and Hartley Peavey are long time friends and in fact, Peavey buys their tubes from him. Either brand should work fine. Svetlana are good tubes as well. Most the tubes on the market today are made in Russia.

[Nitro Express]

No problem running Sovteks. Just make sure you have a matched set of them. All tubes draw current differently so what they do is test them and combine sets of like tubes. If your tubes are mismatched you will get crossover distortion and your amp will sound like shit. On the 5150 I would lean towards the 6L6 instead of the 5881. The 5881 is a military grade tube and very reliable but they don't sound as warm as a 6L6 in a 5150.

[Nitro Express]

Here's a pretty good short article on what bias is.

http://www.tubedepot.com/whisbipo.html

[Nitro Express]

In high school, I had an old Fender than had an adjustable bias. How I changed the tubes and biased it was I turned the pot until the plates on the tubes glowed red and then I would play my guitar through it and slowly adjust the voltage to where it still sounded good but the tube plates were no longer glowing. That's the poor man's way of doing it but with a 5150 you just plug new tubes in. They are pretty much fool proof amps very reliable. Mine went down a flight of stairs on a coaster cart. The cheapo plastic grill on top broke but the thing still worked. Unless you are diming the shit out of it, the tubes will last for years. 5150's are as maintenance free as tube amps get. I've never even had to clean the pots. They never have gotten scratchy on me yet. So as far as the electronics go. Bulletproof.

[Nitro Express]

Even techs with a sine wave generator and oscilloscope plug a guitar in and fine adjust the bias to ear. In fact, some amps like a Marshall sound better bias a little warmer to where you get a tad bit of crossover distortion on the sine wave. All biasing does is make sure the tubes aren't running too hot. That's all it is.

[Nitro Express]

I have an old philco radio that is still running on the original Tung-Sol tubes from the late 1938's. The thing still fires up and works and as far as I know, those tubes were put in at the factory. Tubes can last longer than people think.

[VAiN]

Thanks a lot for the info, I do appreciate it. I'll go with 6L6 Sovteks and see how that feels/sounds!