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Can someone explain the meaning or the reasoning behind the dual impedance OT?

I see in online schematics that lots of simple, single-ended amps use a basic transformer (think the 5F1 Champ uses a 5k primary, but I can't remember). I see on the Trinity Tramp schematic in the Resource page that it's transformer is 5k/2.5k on the primary and 4/8/16 ohm on the secondary side. Why is that? Is it to work with different output tubes?

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Ding ding ding! We have a winner!

EL34s like 2K5 primary impedance for example while 6V6 and 6L6GC like 5K primary impedance.
That's not to say you can't run a EL34 at 5K. 2K5 is optimal and will give the best power and headroom performance but 5K will work. You'll get a different tone and probably not as good performance as if you ran it at 2K5. Look at the TC-15 if you want to see multi primaries on the OT and switching between them.

Check this document out from the Resource section: viewtopic.php?f=12&t=779

Obviously 4/8/16 on the secondary allows you to use any speaker/speaker combination you want.

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http://pdfelectronics.com

Thanks. Wasn't sure, but I thought it made sense.

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I checked out that thread, but I am a little confused.

1. I don't see EL34 in the single ended table.

2. Why do the same tubes show up twice at 5k and the next row?

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1. EL34 = 6AC7. British vs North American name

2. As I hinted at before there is not one optimal primary impedance for a tube. It can be run at a variety of impedance's depending on the voltage level and also what you want to get out of the tube (tone/power/distortion).

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Originally we wanted to keep it really simple and stick to one impedance and one speaker impedance, but we felt the additional versatility outweighed the expense.
so for the reasons kurtlives explained, we did it right!!

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks!

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Well kind of yes and no. US-made 6CA7s are actually beam tetrodes built to have similar electrical characteristics to EL34s (which are pentodes). They sound somewhat different, with a later breakup and stronger bass. Sometimes you find European-made EL34s that have been relabelled as 6CA7s for the North American market. In that case those are true power pentode EL34s. In any case, 6CA7s are interchangeable with EL34s. Likewise KT77s are also tetrodes with similar electrical characteristics to EL34s, although they can handle slightly higher power dissipation. And the same rule applies that they're interchangeable with EL34s.


Very true. Although I designed that power stage to run EL34s with a 2.5k load, you can actually try both 2.5k and 5k and see which you prefer the sound of. The Tramp's OT is pretty rugged and can handle it.

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Great tones come in small glass jars!

I actually spec'd. The 0T and PT to handle the big tubes like these as we knew people would want to play! They can definitely handle it!

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Good point, I often forget about this!

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http://pdfelectronics.com

However, the gist of what you said is still completely valid.

I also just read the page about recommended load impedances http://trinityamps.com/phpbb/viewtopic.php?f=12&t=779 , and was horrified to see that it refers to the 6AQ5, 6V6, 6L6, 807, 5881 and 6550 as pentodes. They're all actually beam tetrodes. Big difference - although probably of very little interest to the average guitarist.

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Great tones come in small glass jars!