It seems to have taken me a long time to get this far but I am almost finished with my Express build. A few wires and some housework and I think I will be ready to plug in and begin checking some stuff out.
If anyone can find something that might benefit from a revisit or that is clearly wrong..... I'm all ears and I won't be offended
I haven't posted pics before so hopefully I get this right.
Its not a kit but ther is plenty of help from Allyn (chassis), Dana (boards) and Moose (iron)
100 ohms...... I hope not. I'll double check. The pics are not quite as clear as I was hoping and I can't tell by looking at it. Whatever they are, they are 5% though not 1%
Thanks for the feedback.
I verified the resistors on the power tube cathodes were 1ohm.
Checked the heater wiring again and all that was good.
Fired it up tonight with some old tubes and all looks to be working.
Used a short crappy lead under a flourescent light with no bottom cover on. Hisses but I expected a lot worse. Does not hum. Checked voltages but didn't have the chance to do much else.
I will post more as it happens.
Thanks for all the help so far.
The wire from your treble cap (500pF) is wired to the Mid pot and not the treble pot. The lug that you have it wired to should have no connection.
Allyn
I don't think I would use 1 ohm resistors to ground on my Power Tubes. I know you think that is an easy way to check bias current but, people have had problems with that in the past. Also, the wattage ratings on thos resistors is a little small.
pin 1 and 8 on EL34 should be connected directly to ground..
the 2 resistors 1ohm are important if you use a PT that has 0/+6.3 V to create a virtual 0 to ground (and in this case the 2 1ohm are connected to the heaters pins). if you use the 3.15-0-3.15 you have the center connected to ground.
In order to bias the amp I used the method of -30V as per Trainwreck pages.
If you want you can refer to the common used ceriatone layout and the pics of francesca.
Allynmey wrote:I don't think I would use 1 ohm resistors to ground on my Power Tubes. I know you think that is an easy way to check bias current but, people have had problems with that in the past. Also, the wattage ratings on thos resistors is a little small.
I think that the biggest problem with those as installed is that over time the connection between the steel screw and the aluminum chassis can weaken, causeing a very small arcing to occur and with arcing; heat. This will destroy the resisitor. I run mine to a solder strip and then a wire from there to the main cap ground. Solid connection all the way. But let's say for sake of arguement that really flailing on those tubes, in full feedback we get the tubes to pull 300ma. I squared times R equal watts right? So .3*.3= .09 times 1 equals .09 watts. It's pretty hard to get a 1 ohm resistor hot. My guess is failures in this area are due to arcing.
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Allynmey wrote:I don't think I would use 1 ohm resistors to ground on my Power Tubes. I know you think that is an easy way to check bias current but, people have had problems with that in the past. Also, the wattage ratings on thos resistors is a little small.
What exactly is it that makes this a bad idea?
On some amps like the Komets and Others that use them for a Bias point, usually no problem, I use silicon 3W 1 Ohm 1% there. The TW's and other high gain amps are just looking for something to offer a better ground path and thus, noise introduction to the circuit. I just wouldn't use those 1 Ohm 1/2 or 1 watt 10% resistors there. I like using my Compu-bias from Mission amps. It allows me to see Plate voltage, Current Draw and Plate Dissipation all at once. They all change as you change the Bias and it is helpful to watch the relationships as you set the Bias.
560]http://i297.photobucket.com/albums/mm24 ... G_0015.jpg[/img]
I will get that fixed. 
