My First Express Board

[DaveWell]

Hi Everyone !

I'm starting a New Project

My First Express !

Comment (good or bad) Are Welcome !

Thank's to all of you help me with this Project !

Dave

[M Fowler]

Good looking boards

Mark

[NickC]

I am no expert, so please forgive me if I'm wrong on this ...... but shouldn't that power resistor be bolted to the chassis as a better heat-sink than the board material used in the rectifier and bias supply board (IMG_0816)?

[M Fowler]

The 1k/25w cement resistor shown in original Trainwrecks were mounted to the board without problems. I see no problem with this case resistor bolted to the board rather then chassis.

Mark

[NickC]

The 1k/25w cement resistor shown in original Trainwrecks were mounted to the board without problems. I see no problem with this case resistor bolted to the board rather then chassis.

Mark

Good to know! Thanks Mark!


Dave,
Those boards certainly do look nice and tidy!

[DaveWell]

Thanks ! for the info and comment !

[Richie]

Looks like you have a 470k in the PI cathode, you need a 470ohm. The 470k will kill the amp from having much sound.. also put the 47pf cap between the 100k and 82k PI plates. other than that it looks really good


Oh, the main board looks a little wide. Don't know what chassis you are using, but make sure when you mount it, you have clearance fro the input jack, that it doesn't hit the board.

[DaveWell]

Yes, i put a 47pf on new pic ,

Thanks ! i'll check for the 470 ohm, don't want to Fry the amp !

In a 1/2 watt will fit or must be 1W ?

[Richie]

Yes, i put a 47pf on new pic ,

Thanks ! i'll check for the 470 ohm, don't want to Fry the amp !

In a 1/2 watt will fit or must be 1W ?

Well it wouldn't fry the amp not having that correct value there, it just would not have much sound. In The real wrecks that section did use a 1 watt 470 ohm. but many other amps use the exact same PI values,and those found in fender and marshalls use 1/2 watt. You should be fine using 1/2 watt 470 ohm there.

[M Fowler]

Also, make sure if your using traditional TW cap stack that you have enough board room it can get very tight quickly.

[martin manning]

The 1k/25w cement resistor shown in original Trainwrecks were mounted to the board without problems. I see no problem with this case resistor bolted to the board rather then chassis.

As I recall metal cased resistors are not capable of their full power rating unless they are attached to a heat sink of some kind. Does it need the full 25W? Probably not, but I would be inclined to put a U-shaped piece of aluminum under it, and put a couple of washers on each mounting bolt between the aluminum piece and the board.

[Mark]

As I recall metal cased resistors are not capable of their full power rating unless they are attached to a heat sink of some kind. Does it need the full 25W? Probably not, but I would be inclined to put a U-shaped piece of aluminum under it, and put a couple of washers on each mounting bolt between the aluminum piece and the board.

This what I was thinking, the resistor won't be rated at 25 watts with the correct heatsink, as shown in the link it is actually a 9 watt resistor above 25 degrees C.

http://www.arcolresistors.com/wp-conten ... sheet6.pdf

Richie is correct about the 470K resistor, you've made an error which you must rectify.

[hans-jörg]

Hello,
beautiful boards.
But please check values and connections of the first 3 component!
The first cap and resistor are parallel, means both sides are tied together, but not with the big 0,47µf tube side - why such big? Shouldn´t be there something like 0,02µf?

Hans-Jörg

[Littlewyan]

I've used one of those 1K 25W Chassis Mount resistors and its absolutely fine. I mounted mine on screw turrets to raise it from the board to give it some airflow and stop it from ever possibly burning the board material. I've felt it after playing for 20minutes and it just gets a bit warm but no where near too hot to touch.

Doing the maths, say you have approx 10mA being drawn by the Pre Amp Valves and 60mA being drawn by the screen grids when playing full blast (Usually 50mA I believe) then.....

.07A * 1000Ohms = 70V
70V * .07A = 4.9W

Without a heatsink that resistor is rated at 9Watts so I don't see an issue with using that resistor.

[DaveWell]

The .47uf is in parallel with the 1.5K

I put a 3 position Switch for bypass

My way to add voicing in pre-amp.
Position 1 : 25uf + 1.5K
Position 2 : 1.5K
Position 3 : .47uf + 1.5K

I'm not going to put the "Bright Switch"



Add washer under the 1K 25W resistor is a goos Idea !

Gonna change (for sure ) the 470K for a 470 ohm.... My mistake (Thanks Richie !)