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Step 12Routing, and other tips...
Routing
This turned out to be significant for my amp. The tone signal wire was routed beside the filament heater loop (the wire had a funny kink in it, which indicates that it was originally routed elsewhere.) The yellow wire in the photos is the heater circuit.
Signal wires should be separated from the heater circuit, especially if it's an AC loop, like this one. It's a prime source of hum.
Any long reaches, such as output to the transformer should be in twisted-pairs. A twisted-pair signal wire performs nearly as well as a fully-shielded cable.
If the hum persists, perhaps a ground-loop is at fault. Point-to-point wiring should utilize 'star grounding,' in which loops are avoided.
Oh, oh, Don't try this at home, Kids!:
One way to chase down hum is to move the components around while the amp is live. A wooden stick can be used to adjust position.
Don't use a pencil! Don't cross wires and short them! If you're smart, don't do this at all....
Other tips
--Testing with the speaker in the cabinet has a significant effect on the sound. An unenclosed speaker will have more treble (and likely not be as loud, too.)
--While on the subject of speakers, be very careful with screwdrivers, etc. around the speaker(s). Depending on the size, a new speaker will set you back $30 to $300 USD (reconeing is another option, but better to just avoid the issue.)
--Connecting two speakers in parallel reduces resistance, increasing the load. If both speakers are 4 ohm, then the load becomes 2 ohm! This is perilously close to a 'hard short.' A tube power amp can probably handle the current, but if you're messing with a transistor power amp, beware!
Even if the amp circuitry survives, there's a good chance you'll blow the output transformer if the speaker isn't close to spec...
This turned out to be significant for my amp. The tone signal wire was routed beside the filament heater loop (the wire had a funny kink in it, which indicates that it was originally routed elsewhere.) The yellow wire in the photos is the heater circuit.
Signal wires should be separated from the heater circuit, especially if it's an AC loop, like this one. It's a prime source of hum.
Any long reaches, such as output to the transformer should be in twisted-pairs. A twisted-pair signal wire performs nearly as well as a fully-shielded cable.
If the hum persists, perhaps a ground-loop is at fault. Point-to-point wiring should utilize 'star grounding,' in which loops are avoided.
Oh, oh, Don't try this at home, Kids!:
One way to chase down hum is to move the components around while the amp is live. A wooden stick can be used to adjust position.
Don't use a pencil! Don't cross wires and short them! If you're smart, don't do this at all....
Other tips
--Testing with the speaker in the cabinet has a significant effect on the sound. An unenclosed speaker will have more treble (and likely not be as loud, too.)
--While on the subject of speakers, be very careful with screwdrivers, etc. around the speaker(s). Depending on the size, a new speaker will set you back $30 to $300 USD (reconeing is another option, but better to just avoid the issue.)
--Connecting two speakers in parallel reduces resistance, increasing the load. If both speakers are 4 ohm, then the load becomes 2 ohm! This is perilously close to a 'hard short.' A tube power amp can probably handle the current, but if you're messing with a transistor power amp, beware!
Even if the amp circuitry survives, there's a good chance you'll blow the output transformer if the speaker isn't close to spec...
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