Pribek

Warning! Amp stuff-too much deep geeking for most.

Today, I changed the power tubes on my amp and biased the new ones. The amp is a Fender Hot Rod DeVille 4X10.

When I had my tube problem over the weekend, I did a little snorting around the web and ended up at “The Unofficial Fender Hot Rod Deluxe Owner’s Guide”. Which, is a good place to find stuff about any Fender amp in the Hot Rod series. One thing I found out there was that the stock tubes in this amp, Groove Tubes 6L6Bs, were not the optimum type tube for this amp.

Stock Groove Tubes 6L6Bs

Now, there is a lot of discussion about these tubes. Justin Holton at The Unofficial Fender Hot Rod Deluxe Owner’s Guide, says that the tubes that should normally go in the amp are 6L6GCs. Justin seems pretty knowledgeable about these amps so, I took his word. The thing is, he strongly recommends setting the bias if you do replace the stock tubes with 6L6GCs. The bias point controls the amount of electrons passing through the grid to the plate inside the tube. It’s like setting the idle on a car.

So, I want to get 6L6GCs and I need to set the bias. Now, I can leave the amp with somebody to set the bias but, there are some issues.

1. If I leave the amp, I have to make sure I can get it back for the weekend and it’s two trips to town.
2. It’s going to cost something.
3. If the bias point is set when the tubes are new, what happens after they’ve burned in for a couple of weeks?

I went back to Justin’s site to see what was involved in setting the bias and, for this ,it’s pretty simple. The only thing I lacked was a multi-meter which, costs about what it would to get the bias set.

I had to stop at Wal Mart anyway to pick up a prescription so, I figured I’d get one there. Wrong. I’m standing in the electronics department and there’s a guy there in a Wal Mart costume watching cartoons on one of the TVs. I ask him and, he’s on a break but, he leads me over to another area and points to to a gal that’s standing by three other women in Wal Mart costumes and they are all on break. Can’t answer a question because they’re all on break. So, I went to Radio Shack and probably paid more and, had to give up my phone number but, nobody was on break.

Anyway, I went to Hoover Music in Springfield and talked my buddy Richie Rebuth who, aside from being a genuine guitar slinger type of guy, plays a Tele with Joe Barden pick-ups like I do and, he’s way in to all of the deep geeking guitar stuff. He sold me a set of Svetlana 6L6GCs and I was on my way back to the Winnebago.

Setting The Bias

This turned out to be real simple. If you have one of these amps go to the aforelinked Unofficial Fender Hot Rod Deluxe Owner’s Guide for a detailed description.

Here is the bias control.

It’s that little blue knob there. See that yellowish looking glop on there? It’s like a kind of temporary glue. Richie says they do that because they really don’t want you messing with it. Anyway, you turn that to set the bias.

This is the bias point.

Bad picture but, it’s that little dab of solder on the corner of the green board. The positive lead from your multi-meter goes on that little spot. Once again go to Justin’s site for details but, you get your reading and adjust the knob until you get the desire read-out.

New Svets Glowing

As soon as I plugged in I noticed quite a difference in tone, for the better. I don’t know if it’s because the stock Groove Tubes aren’t really the right ones or, maybe they were biased wrong or these new tubes are just a good match for the guitar. Don’t know. The amp is singing now though and I’m digging it.