info on fender twin reverb, please!

[dragonworks]

The rectifier tube cuts half the ac wave changing it to a dc wave which in turn is smoothed out by the power supply filter capictors then fed to a resistance divider network distributing the proper voltages to the proper circuits, so, if you have a rectifier tube and its missing the amp wont work. Anywho, thats the basics of a power supply. If you can identify the amp model no. you can look at its schematic and get all the info you are requesting. You should be able to follow the power line in then to the proper tube socket in the power supply to identify a rectifier tube. It should be tied to the biggest capicitors in the amp. If you dont know a cap from a map, stop in Radio shack and look at the different components, caps, resistors, transistors, etc and be able to go home and recognize the difference in the amp. The capicitors in the power supply should be "electrolitic" and thexe have a tendency to "leak" as they become older and this can cause problems, motorboating etc.

 

[MONTE]

If your in a pinch for money, just mark the tubes and the sockets so you know where they go and take the tubes to a shop. Most reputable shops will check the tubes for you and let you know if they need replacing or not. I do it all the time for customers! Just because tubes are old does not necessarily mean they are bad. Remember, they're VACCUM tubes.

Also, not hackin' on ya Dragon but caps usually don't leak (although they can). Usually the electrolyte dries out from age. Similar to what happens to a car battery that's been sitting around too long. The motorboating sound you describe is usually because as the cap dries out it no longer filters the AC content off the DC line. and the DC needed for proper plate voltage to the tubes is effectively lowered. Also, sometimes when caps dry out the "windings" of paper insulated film inside the cap can arc to each other causing all sorts of pops, snaps, etc.

 

[fenix]

If you get round to replacing the power tubes make sure you get it biased, on the newer Fenders it is relatively easy but on the old ones it was a pain, but it will increase your tube life.

Clive

it only needs biased if you are changing tube types. if you replace an old 6L6 with a new 6L6, it doesn't need rebiased!

 

[Lt. Bob]

That's not correct. First, you can't change tube types without making some changes to the circuit (mostly resistors). If you don't, a different type tube won't work properly. It MIGHT work, but not well. Simply changing bias is not enough to use a different type of tube. Second.. new tubes can have a different plate capacity and definately should be rebiased for best performance and sometimes even with the same tubes as they age it can be useful to rebias them to compensate for aging.

 

[dragonworks]

Not hackin on ya monte but thats why "leak" was in quotation marks. Its a metaphor for just the problems you describe. When I suggested where to get tubes, these are not used tubes but new older stock still in the box. Granted you wont get matched sets but you might wind up with never used before sylvanias or GEs, etc.

 

[lucid]

sorry, but i got to learn somehwehre... but what does biasing mean?

 

[dragonworks]

There is a negative voltage applied to one of the grids on the output tubes so it runs at optimum. If I remember from looking at the schematics I think the twin I looked at is -64 volts, I am not sure. But if this voltage is not set where it is supposed to be you will not get your best performance from the tubes. Someone will come along and explain this better than I.