Trinity Amps Trinity Tweed Amp, Builder'S Manual, Page: 59 / 77

Version 3.2 Page: 59
Defective internal grounding
There are potentially lots of places that must be tied to ground in the internal wiring. This varies a lot
from amp to amp. If one is broken loose or has a poor solder joint or poor mechanical connection, it
can show up as hum. Note that modified amplifiers are particularly susceptible to this problem, as the
grounding scheme that the manuFacturer came up with may well have been modified, sometimes
unintentionally. With the amp unplugged, open and the filter capacitors drained, carefully examine the
wires for signs of breakage.
Hiss
Some noise or hiss is normal. These amps are supplied with Carbon Composition resistors similar to
the original. This style of resistor has inherent noise. If this amount of hiss is bothersome, you will need
to replace the resistors in the signal chain with Metal Film resistors.
Metal Film Resistor Substitutions
If you really want to eliminate hiss, use metal film resistors where the signal level is small and the
following amplification is high - a classical description of an input stage. The input to an amp should
probably have a metal film plate resistor to minimize noise.
Substitute them on the grid resistors in all but output stages because the signal level is typically too low.
Substitute them on the Cathode resistors. They typically only have a few volts across them, and they're
often decoupled with a capacitor, both of which would minimize the carbon composition resistor
distortion (AKA Mojo).
The best place to use CC's is where there's big signal - plate resistors, and ideally the stage just before
the phase inverter. The phase inverter would otherwise be ideal, with plate resistors carrying the highest
signal voltage in the amp, but phase inverters are often enclosed in a feedback loop. The feedback
minimizes the distortion the resistor generates.
Squealing/Feedback
Squealing usually occurs when there is coupling between the input and output stages. The positive
feedback causes the amp to become an oscillator. Vary the volume and tone controls to see if it affects
the oscillation.
That will tell you if the coupling is occurring before or after the control. Sometimes the problem can be
solved by minor changes to the wiring (moving output wires away from input wires, shortening
excessively long wires, etc.).
Use shielded wire on the input jack to help a hum or squealing problem.
Ensure the shielded wire goes on top of the board, not underneath it.
If all that doesn't work reverse the output transformer leads Yellow & Black, on pin 3 on 6V6 V3, V4.
Explanation from s2 Amplification: One of the primary leads is in phase with one of the secondary
taps. In a high gain amp, this phase relationship needs to be maintained.