Need a bit of direction...

[Flatted Fifth]

Hi there, I just got a "Blues Forever" tube set from Torres Engineering in the mail, along with the bias installation kit for my '95 Fender Blues Deville. I realized soon after opening the package that I'm in the dark when it comes to tube amps.

I'm looking for advice on how to install these tubes and bias kit safely, and to pick up a good bit of knowledge on the way. I've always been the "do-it-yourself-if-possible" kind of guy, and if it's not unreasonable to try to do this, I want to.

Looking forward to working on this little project of mine...

Danny

[TweeDLX]

Do a search on this forum for "Cap draining". Always drain the filter caps (those are the big cylinders either in a case underneath, or on the circuit board) before you go "inside" the chassis. Installing the tubes is easy, just pop them in. I don't know what your kit is, but I'm assuming it's a mod to give you external access to an adjustable bias pot. Those usually have a wire from the Standby switch to the pot (with a resistor) and another from the pot to the bias tap. The bias tap can be at one end of the circuit board, or on a small seperate circuit board of its own. Start looking at the schematic for your amp to figure out where this stuff is. Do a web search for "schematic symbols" to help you understand it. Try here: http://en.wikipedia.org/wiki/Electronic_symbol

Mikehttp://www.thegearpage.net/board/images/icons/icon7.gif

[Nolatone Ampworks]

+1. Make sure you have NO lack of understanding as to the safety procedures when fooling with the innerds of your tube amp. You can find most anything you need by searching this forum. A lot of great info about bias and many other topics on Randall Aiken's site, http://www.aikenamps.com

Or just google.

But don't guess at the safety thing. It's a bad gamble.

[Flatted Fifth]

This is the Bias Kit I got...

http://www.torresengineering.com/fenbluesdevn.html

I actually took my amp over to my neighbor who knows electronics (he actually gave me his soldering iron a couple years ago), and he talked to someone he knows, and it doesn't sound like there's anything in the chassis that will do any damage besides the filter caps, which we drained. Oddly enough when we plugged in the amp and got it running, the filter caps were showing their respective values, but once we straight unplugged it, those values dropped to almost nothing. I was under the impression that these caps held a lethal charge for some time after you turned off the amp...

Ah real quick, does it matter how you put the tubes back in? There are holes for all kind of orientations.

[TweeDLX]

This is the Bias Kit I got...
http://www.torresengineering.com/fenbluesdevn.html
Ah real quick, does it matter how you put the tubes back in? There are holes for all kind of orientations.
Unless you have some new sort of bastard tube sockets (which I doubt) http://www.thegearpage.net/board/images/icons/icon7.gif , you can actually look at the sockets and see how the tubes are oriented. The power tube sockets have a little notch that corresponds with the little ridge on the gizmo in the center of the bottom of the tube. Just line 'em up and insert. The pre-amp tubes should have a little gap in the pins that lines up with the gap in the socket holes. I usually just gently press and rotate the tube until it goes in. It may remind you of your early experiences with sex...http://www.thegearpage.net/board/images/icons/icon10.gif No dinner required...
One thing to keep in mind...any of your pre-amp tubes is interchangeable with one of the others. It won't necessarily sound the greatest to switch them around, but it's good to know. 12AX7, 12AT7, 12AY7, 5751, 12AU7, 12AV7 (maybe a couple more...) will all work in those sockets. You can swap them around without fear of damaging the amp.

Mike

[Flatted Fifth]

So I just got in from finishing with my project...almost. I got everything done except to actually set the bias. I need to go out and by a more reliable multimeter than what my neighbor had. So I'll go out tomorrow to do that, and I'll also need to swap out the resistor on the bias pot to a higher ohm to get the bias right...

...anyway, I'm tired. Night all, and thanks!

[Flatted Fifth]

I'm sitting down and revisiting some stuff that wasn't going quite right when I went through this the first time...

So I did the mod, which was pretty clever actually. They have you install a 1 ohm resistor onto pin 8 of the left-most power tube, so the resistor is the connection between the tube socket and circuit board. Then you connect a wire to the lead of the resistor/pin near the tube socket, and you solder a bias monitor test probe jack to the end of that wire. Then you clip the existing bias supply (resistor R87), and attach a wire to the top lead, which goes to a 10k bias pot.

You have to play around with the resistors that you have on the bias pot since they're made for different ranges, but the problem is I'm not getting a correct reading when I connect to the test probe jack and the chasis.

I should be getting somewhere between 28 to 35 millivolts and I'm only getting about 1.

The amp actually works, it just distorts even sooner than it was before. I tried biasing by ear by just replacing the first resistor on the bias pot with the highest value I had, and it didn't make the amp any less hot.

The more I think about it the less it seems any one out there would be able to help me from this description alone, but I appreciate anything I can get.

Ah and here's an interesting bit of information, it may be something wrong with my Blues Deville or maybe it's just the design but the filter caps are nowhere near lethal when the amp is turned off. It's less than 10 V for each one. They charge up a little when the amp is turned on, but they don't become dangerous until you go off of standby. Once you do the supposedly 350 V filter caps jump to only around 235 V, which I know will still kill you, but it's just less than 100 V less than what it should be for some reason. The two 500V caps are running at 420V and 380V respectively. I don't really need to know why these caps are running at less than they're supposed to, but if anyone knows I wouldn't object to hearing.

Looking forward to some replies...I learned a LOT with this little experiment.