Robert,

You are correct. An OT is basically an impedance matching device. Tubes are high voltage, high impedance, low current devices. Speakers are low voltage, low impedance, high current devices. The OT bridges the tubes and the spearker(s) to produce sound.

An OT is made of two coils of wire, the primary winding which connects to the tubes and the secondary winding which connects to the speaker. These coils surround a ferrous core. The core is made up of individual laminations that are physically separated by lacquer.

The OT has an effect on tone due to its composition. The composition of the wire and the gauge have an effect as do the composition of the laminations. Also the primary impedance will have an effect on tone. A particular set of tubes wants to "see" a particular primary impedance. For example amps using a pair of 6V6 tubes in push pull can use from 6K-8K for the primary. Not that the OT does not have an impedance of its own. Rather the speaker (connected to the secondary) reflects back the primary impedance to the tubes. For example if an OT has a impedance ratio of 1000:1, that means an 8 ohm speaker will reflect back an 8K impedance on the primary. If you plug a 4 ohm speaker into the same circuit, you get 4K reflected back to the primary. That is why it is important to match the proper speaker to the proper tap.

Some OTs are made for hifi use, they will produce the entire frequency range from 20hz to 20khz. These types typically do not saturate as this is bad from a hifi perspective. Guitar amp OTs are generally not "hifi" and will not produce such a wide band response. Some of them are more prone to saturation, others not so much. The classic example of saturation are Marshall amplifiers, particularly the plexis and metal panel models. The OTs in the aforementioned saturate when pushed hard and create the classic Marshall sound. Fender, OTOH, has OTs that are less prone to saturation. That's why Fenders never sound like Marshalls when cranked.

"Good" for an OT is very subjective. Some of the best makers of OTs are: Hammond, Heyboer, Mercury Magnetics, Schumacher, Triad, and a few others I'm forgetting. Generally, most of the OTs made in Canada, Europe, and the USA are pretty good. Those made in Asian countries aren't as good. Again, it comes down to the materials used in construction.

A rectifier is a device that changes AC to pulsing DC. The filter caps then smooth this out so that the tubes can use this filtered DC. Originally rectifiers were vacuum tubes. These had advantages and disadvantages. Then solid state rectifiers were invented. They are much more efficient, but also have advantages and disadvantages.

HTH,

tung


Quote Originally Posted by Robert
I don't know much about output transformers. Can someone educate me a bit?

I have read an output transformer takes the signal from the tubes and transforms them into impedances and power suitable for your speakers. Seems like that wouldn't affect the tone much, but many people say the do.

So how much does an output transformer affect the amp's overall sound?

How do I know if an amp has a good one or not?

And what is a rectifier and what does it do?