Matching Your Output Transformer

Does it have to be exact?

Matching your output transformer to your output tube does not have to be an exact fit. 5K ohm Transformer to 4K ohm output tube? Yup. 10 watt transformer to a 2.5 watt output tube? Overkill, but sure. If you’re unsure then just get as close as you can within reason. Here are some options with variations. https://crunchytubeamps.com/product-category/electronics-components-parts-transformers/

What are the effects of a mismatch?

A higher ohm (impedance) output transformer can shorten the life of your output tube but also increase the output in watts into the speaker. Too high impedance will cause your output tube swing past high voltage limits and damage or destroy your equipment:( A lower impedance output transformer can lower unwanted distortions but decrease the output in watts into the speaker. Too low impedance will cause your output tube to swing past plate power dissipation limits and damage or destroy your equipment:(

Find the Impedance of an output tube

A simple search can find a calculator online. here’s one: https://www.vtadiy.com/loadline-calculators/loadline-calculator/, but I tend to search thru the data sheets here: https://frank.pocnet.net/. Wanna get crazy with a grounded grid biased dynamically coupled triode 6B5 single ended output for 5.2 watts? https://frank.pocnet.net/sheets/127/6/6B5.pdf Use this 7K ohm output transformer, and this power transformer: https://crunchytubeamps.com/product/single-ended-output-transformer-5w-7k%cf%89-0-4-8%cf%89-or-10k%cf%89-0-4-8%cf%89/ https://crunchytubeamps.com/product/270v-0-270v-3-15v-0-3-15v-0-6-3v-0-12v/. Want to build on budget? try a 6W6GT for 3.8watts RMS! Use these: https://frank.pocnet.net/sheets/127/6/6W6GT.pdf https://crunchytubeamps.com/product/5k-5w-single-ended-output-audio-transformer-with-4-or-8-ohm/ https://crunchytubeamps.com/product/40w-r-core-audio-transformer-40va-180v-0-180v-0-6-3v2/.

Go experiment

Now that you’re armed with matching your output transformer knowledge, pick a tube, grab a transformer, and build an amp. Not sure about a preamp? read my last article https://crunchytubeamps.com/use-the-preamp-tube-of-your-choice/. Just remember to discharge those caps after you unplug for testing and go build an awesome amp!