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Output Tranny ?

mrmojorisin

Member
Messages
1,332
I am looking for a replacement output tranny for a single ended class A EL84 amp. I need 4, 8 and 16 ohm secondary taps. My question concerns the primary impedance.

When I look at the EL84 data sheets, output impedance is listed at 5200 for SE class A operation. So I figure I want a 5200 primary on the output tranny to match this. I know this will maximize power transfer, etc.

But why then when I call and speak to tranny manufacturer's are most of them recommending a 9K tranny for use in the single ended class A EL84 application?

While this will give less power output than the 5200 output tranny, does it improve tone? If so, why?

Appreciate the help / insights.
 

rooster

Member
Messages
2,119
5200 ohms at the voltage you're running it at, or at some other voltage spec'd on the datasheet? That makes a difference.

rooster.
 

mrmojorisin

Member
Messages
1,332
The EL84 data sheet shows 5200 output impedance at a voltage of 250V, against a max plate voltage of 300V.

I plan to oversize the output tranny (15w min) which should be more than enough margin for a single EL84 application.

So, I still wonder what primary impedance to look for in the output tranny. SHould I buy one at 5200, or 9000 as one tranny mfg recommends, or 7-8K as is used in the amp currently?
 

phsyconoodler

Member
Messages
4,305
a Hammond 125ESE OT has multiple impedance taps so you can choose whichever one floats your boat.Being a 15 watt rated OT it will make your amp sound bigger too.
 

syxxstring

Member
Messages
304
So if I put a 125ese in my Valve Jr. Could I install a heavy duty switch to go between Clean & Low and Loud & Nasty?
 




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