Crawls Backward (When Alarmed)

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Stuffing the Circuit Board - Tweed Bandmaster Pro Super Clone

Now it's on to stuffing the board for the Bandmaster clone build.

In all of the Fender tweed amps, there is some under-the-board, subterranean wiring.  The last couple of these I built, I did this wiring as I went along.  This time, I think I've wised up and decided to do the that wiring first. 

It's a pretty easy matter to look at the layout diagram and see what goes where.  I didn't solder these connnections yet, but I bent them around the eyelets so the wire would stay in place.

I started at the left end - the filter cap end of the board.  One change I made from the 'stock' Fender circuit is a bias pot.  I dropped the value of the first resistor the bias voltage 'sees' from 6.8K to 4.7K, and I have a 50K adjustable pot after the diode, then a 15K resistor after that.  I think I'll have enough range to be able to bias the output tubes with this set up.

While I was wiring it, I set the bias adjust so the combined resistance of the pot and the 15K resistor is right about 56K - which is the stock Fender value.  That should be a safe starting point when I bring the amp up to full power for the first time.

You can see how I wired all this above, and you can see two of the main filter caps in place.


There are two resistors I needed to put in before I could connect the third filter, so I put them in place.

These are the 56K feedback resistor and the 1.5K cathode resistor off the phase inverter tube, fwiw.

Except for the power amp and bias section, I'm using all carbon composition resistors.

The picture on the left is the underside of the board where I tied all of the filter cap grounds together.  I'm going to run a lead from the eyelet on the right (it's on left when the board is face up) to a single ground point for all of the power supply, main AC, and output tube cathode grounds. 

On the input side, I'll run the preamp, tone control, preamp power filter, and other input-side grounds to their own ground point on the other, far side of the chassis.

This is to separate the power supply and input grounds as much as possible to cut down on potential hum as much as possible.  None of this is 'new' practice - you can read about this as good wiring practice going back to the Moyer and Wostrel radio books in the 1920s. 

Here's the main filter caps in place.  I try to keep the leads as tidy as possible, make good physical connections to the eyelets, and make clean solder joints.  Again, nothing new, but I believe good workmanship and good practice helps make the best sounding amp possible.

 
 
 
 

Post a Comment 1 comments:

  • alansaki said...
    December 20, 2012 at 11:39 PM
    Great article nice posting thanks for the sharing this.Great blog!Thanks a lot for taking the time to discuss this,
    PCB

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