Restoring Fender Deluxe Reverb Silverface or Blackface amp part 3 – resistors
In common with all Fender amps they are mounted in the case “upside down” the valves hang at the bottom for east access. The trade off with this design is that heat rises so all the heat from the tubes/valves rises and it cooks all the components over time. A silver face amp is a minimum of 35 years old and so the components have taken a lot of cooking. I mentioned in part 2 relacing the electrolytic capacitors and now we need to look at the resistors. In these amps the resistors are a type called carbon composition. we dont need to understand the physics of going on but what happens with carbon composition resistors is that their value increases over time. They can go way out of tolerance and this of course makes the amp sound deteriorate and in the worst case stop working all together.
The hottest place in the amp is where the output valves are located. This is where parts get cooked most and are mostl likely to be high in value.The two 6V6’s in the delue Reverb. These are biasing resistors and are 5 watt 470 ohms. Take a multimeter and measure the resistance . In my amp one was 472 ohms. Still like new. the other was at 617 ohms. It was way high. I replaced both of them with new 470 ohm modern metal film resistors.
If you want to check out resistor values and the tolerance here s a link which will help
http://www.electronics2000.co.uk/calc/resistor-code-calculator.php
a simple first test is to check the resistors on the tag board. It does not take long. as they are in circuit the vlaues might read a little it lower than the actual value. In this first pass look for any that are high in value. Unsolder one side of any resistors that looked too high in this first test and check them again. any out of specification , change them. Also do not forget the resistors in the metal can where the big lectroltic power supply capaciitors are . I found these to get the most stress and these tend to go high.
There are quite a number of resistors in the amp so I will leave you to test them. ! Part 4 will cover fiing the vibrato. The vibrator often become weak with age too and this is an easy fix.
