Ultra Linear Output Transformer

[david90678]

Hi everyone,

I am considering building an amp of my own, based on an 18W Marshall, and my guitar dealer advised me to look into Ultra Linear Output Transformers, so, what can you tell me about this type of operation in the power stage of an amp?

Many thanks,

David

[burnsy]

Take a look at www.ampmaker.com. I made their 18w amp which is based on the Marshall circuit and it sounds brilliant. Barry at Ampmaker was able to supply everything and is a very helpful guy.

[MKB]

IIRC, an ultralinear amp has an additional pair of taps that connect to the screen grid of the output tubes. There are basically 5 wires from the primary, two for the output tube plates, and two for the output tube screen grids. This configuration is popular in very high power amps (the Marshall Major is ultralinear, as well as many early Sunn and late seventies Fender amps).

The reason for it is the power tubes are operated in semi-class A mode, which gives you a lower output impedance and lower distortion. But you also get the benefit of higher output power for a given tube and plate voltage than you would with the tube in class A, like you would with a pentode configuration.

FWIW, I haven't heard or seen many good comments on older ultralinear guitar amps. The Fender ultralinears are not highly regarded. However some of the Dr. Z amps, like the Route 66, are ultralinear. YMMV.

The good thing is if you buy an ultralinear output TX and you don't like the tone in that configuration, you can simply disconnect the ultralinear TX taps from the output tube screens and run the screens to a normal supply filter configuration. Just because your TX has ultralinear taps does not mean you need to use them.