Lead Dress Q's

[benoit]

1. From what I gather, unless B+ is really really smooth (and maybe even then) you don't want signal wires crossing. So looking at the chassis from the rear, the power tube grid wires and bias supply run from the top left of the preamp board back under the board, under the PS board, and to their respective destinations. B+ leads coming from the right side of the PS board can run either down between the two boards further toward the rear of the chassis than the grids/bias or if they're further toward the front than the chassis-front edge of the preamp board they can run around. Where I run into problems is with v1 and v2 B+. If they run along the front of the preamp board they'll cross the presence pot wires. If they run along underneath the board they'll cross the wire from the power amp in jack. In short: help!

2. I drilled the holes for my OT leads to come through the chassis straight down from the OT. Is this a bad idea? Should I do another hole closer to the imp. selector? Seems like the hole for the primaries would be fine since they just have to run from under the PS board to the power tube plates.

3. In some pics I see a 5-lug terminal strip mounted just to the chassis-rear side of the PT. The clearest pic I can find (bradon's 80s build pics from the files section) shows the outer terminals connected to the heater supply (in this case, one wire to pin 3 of the right most power tube and one to pin 7 of the next one over. From the lug connected to pin 7 is a diode (I think) to the next lug in, and on the lug connected to pin 3 a resister to the next lug in from it. from these inner lugs two wires appear to run to the power LED. Am I correct on this? If not, what is this circuit? Also, what is the resistor value and why? Will this work ok for a fender-style lamp?

[tubedogsmith]

Just run your v1 and v2 supply wires under the board. The main concern is routing them around the eyelets so you don't accidently melt the insulation later.
Your fine on the hole for the OT leads.
The LED circuit your talking about is for the power lamp. I think ic-racer has this detailed on a few of his schems. A fender style lamp would work fine in your amp but not with this particular circuit. The Fender style amp works straight off the heater tap with no need to reduce voltage or convert to DC.
All this said, the closer you can stick to copying the real thing the better off you are until you get a real understanding for what you're doing. Dumble had/has a lot of great ideas and cool ways of doing things.

[ic-racer]

Except for the small difference listed below, from what I can tell on the HRM, this setup is the same as #124. This is my #124. The LED leads are purple and green. The resistor is 330r.

The only subtle difference from what I can tell in the HRM is that physically the resistor and the diode are swapped in position and the LED leads are on the far ends with the heater leads in the middle (and diode flipped around) But the function and values are the same

[ic-racer]

duplicate

[Guitarman18]

benoit wrote:

3. In some pics I see a 5-lug terminal strip mounted just to the chassis-rear side of the PT. The clearest pic I can find (bradon's 80s build pics from the files section) shows the outer terminals connected to the heater supply (in this case, one wire to pin 3 of the right most power tube and one to pin 7 of the next one over. From the lug connected to pin 7 is a diode (I think) to the next lug in, and on the lug connected to pin 3 a resister to the next lug in from it. from these inner lugs two wires appear to run to the power LED. Am I correct on this? If not, what is this circuit? Also, what is the resistor value and why? Will this work ok for a fender-style lamp?

https://tubeamparchive.com/download/file.php?id=2757

Are you looking at the purple wire from pin 7 (furthest left 6l6) and the red wire from pin 2 (heaters)? In which case this is for the LED that requires a dropping resistor and diode, as can be seen in the D'lator power supply diagrams. Check out this link, about half way down by UltraHookedOnPhonix.

https://tubeamparchive.com/viewtopic.php?t=4837

The other thing to look out for is on the next set of power tubes are 100ohm resistors coming off the heaters to ground. This is to create the artifical centre tap I believe. (forgive me if you already know this but I have just been looking at this, trying to figure out where this little set-up was.

Cheers, Paul.

[benoit]

Just run your v1 and v2 supply wires under the board. The main concern is routing them around the eyelets so you don't accidently melt the insulation later.
Your fine on the hole for the OT leads.
The LED circuit your talking about is for the power lamp. I think ic-racer has this detailed on a few of his schems. A fender style lamp would work fine in your amp but not with this particular circuit. The Fender style amp works straight off the heater tap with no need to reduce voltage or convert to DC.
All this said, the closer you can stick to copying the real thing the better off you are until you get a real understanding for what you're doing. Dumble had/has a lot of great ideas and cool ways of doing things.

Ok, but there is a signal run that b+ will definitely cross if I run under the board, as well as OT secondaries. You're saying this isn't a problem? In the real thing are the B+ wires pulled tight so they don't actually rest on the bottom of the chassis?

[tubedogsmith]

there's no way to avoid wires crossing each other. If you run them perpendicular to each other you should be fine. I run them tight to the board.

[Funkalicousgroove]

Fold your b+ wires under the board and zip tie them together at 90 degrees, the only signal wires they should cross are shielded- Quiet as a mouse

[benoit]

Fold your b+ wires under the board and zip tie them together at 90 degrees, the only signal wires they should cross are shielded- Quiet as a mouse

The one in particular I was worried about is the power amp in jack to the .02uF (would that be the PI coupling cap?). In all the pics I've seen that wire runs straight from the chassis-front side of the board, under the board, to the power amp in jack. Also, doesn't the preamp out wire come straight from the OD relay? I haven't seen shields on these.

Also, I'm a little unclear as to what you mean by "zip tie them together at 90 degrees." So they fold under the board... then zip tie where? Right where they go under? Or did you mean zip tie them to the wires they cross?