New Build - Express

[Colossal]

Yeah, it is a trick not to spin the turret. I put the turret board on the drill press and line up the center of the turret in the laser crosshairs. You need a sharp #33 bit to pull it off. Then you just slowly drop the bit into the turret a hair at a time, just easing the material out. A #33 bit (which is the same size for cutting the hole in your board to mount a double turret) will leave a nice margin around the turret (a little more than 1/32") if you center it exactly (and that's pretty easy to do when you drop the bit into the turret and start cutting -- it self centers). I have a depth gauge on my drill dress that will tell how far the chuck has been lowered so I don't go too far and bore out the whole turret LOL. If you go too deep then it might bite in and start spinning the turret which causes swearing.

[Big Jim]

+1 on Colossal's trick drilling the turrets....I thought I was the only one who resorted to those tactics.... I find a few extra gentle taps with the staking tool also helps keep it from spinning if you have to open up a turret a little. My drill press is a cheapie, but with a sharp drill, and a little patience, it's pretty easy to do.

[angelodp]

Its the little things.....

[Picker]

I don't think I would ever bother with drilling out the turrets. I'm quite happy using it for one or two and wrapping whatever wont fit.

[M Fowler]

I have never drilled out turrets and Dave not sure how you keep it from spinning.

The new ones from www.Turretboards.com are larger then normal. I don't find them larger myself; however.

Mark

[amplifiednation]

I have been wrapping those suckers! They look prettier when using the top but I like knowing I have a good mechanical connection so the heat, and the solder, flows. Then the top is a nice easy spot to throw a grid or plate line

[Picker]

I have another question.

For the PS resisters, I ordered what was on the BOM which shows as 9.1k 2W resistors. However, what I received is 9.1k 3W.

Am I okay using the 3W ones? Or should I go back and try to get 2W?

Thanks

[funkmeblue]

3 watt are fine

[surfsup]

3W are better than 2W (handle more heat and supposedly quieter) but they might be larger/longer so may not fit as well, but they can hang off the side. Not a biggie, unless you planned your amp to have all the components in nice neat tidy order and mountings...

[Picker]

Next issue:

I'm not sure I understand what to do with the 25k Bias resistor. It is hard to tell from the Build guide exactly what is going on with this... There is a cluster of 3 turrets and I assume one leg goes to each turret - from there one leg goes to the 47k resistor and it looks like the other two just go to ground. However the Build Guide shows an arrow labled as "Wiper" and I wasn't sure what was meant by this.

The schematic shows two legs going to ground, but one of them shows an arrow pointing to the center of the resistor. what does this mean?

[NickC]

Next issue:

I'm not sure I understand what to do with the 25k Bias resistor. It is hard to tell from the Build guide exactly what is going on with this... There is a cluster of 3 turrets and I assume one leg goes to each turret - from there one leg goes to the 47k resistor and it looks like the other two just go to ground. However the Build Guide shows an arrow labled as "Wiper" and I wasn't sure what was meant by this.

The schematic shows two legs going to ground, but one of them shows an arrow pointing to the center of the resistor. what does this mean?

Wiper is the middle position of a potentiometer.

"an arrow pointing to the center of the resistor" is the schematic symbol for a potentiometer .... the arrow is the pot wiper.

[img:640:220]http://sound.westhost.com/pots-f6.gif[/img]

http://sound.westhost.com/pots.htm

[Picker]

I'm not in front of it right now, but I'll see if I can determine which lead is the "center".

Since they are both going to ground, should I jumper them together and send one lead to the ground? or is there a reason why they a shown with separate leads going to ground?

[NickC]

I'm not in front of it right now, but I'll see if I can determine which lead is the "center".

Since they are both going to ground, should I jumper them together and send one lead to the ground? or is there a reason why they a shown with separate leads going to ground?

Looking at the Express schematic ...... there is the VR6 25k bias adjustment pot .... VR means the pot is wired as a variable resistor ...... the wiper (center position on pot) goes to ground ....... one leg of the pot (the input side) connects to R31 47k ...... the other lug of the pot connects to ground.

The layout diagram show the two ground connections from the trim-pot run to a ground point along with the ground side of C21 .... then a wire runs from that junction to chassis ground with the mains safety ground.

See lower right hand quadrant:

https://tubeamparchive.com/files/tw_exp ... 18_635.pdf

[Picker]

By the "center" I wasn't sure which you meant. Right now I am using the leg that looks like it is coming out of the center of the bottom, but you may have meant the 'center as I turn the pot. Hope I'm doing this right.

There is also a silver tab (top left in the picture) that stops the pot from spinning past 360 degress. This is opposite of what I am using as the center/wiper leg, so I think it is right.

[IMG:799:531]http://i54.photobucket.com/albums/g94/r ... C_0880.jpg[/img]

[NickC]

By the "center" I wasn't sure which you meant .................

You can use your meter to determine the Resistance between the legs and the wiper, and the relationship between them.

Here is some good info on pots:

http://www.geofex.com/article_folders/p ... tscret.htm