Transformer Current Rating

Littlewyan · Post by **Littlewyan** » Wed Apr 16, 2014 6:32 pm

If I used a Full Wave Rectifier on a Centre Tapped Transformer, would the current rating of the transformer double? As I'm only effectively using one winding at a time. As looking at the Marshall PTs Available from various companies they are only rated at 150Ma, which for EL34s is nowhere near enough.

Phil_S · Post by **Phil_S** » Wed Apr 16, 2014 7:10 pm

Littlewyan · Post by **Littlewyan** » Wed Apr 16, 2014 7:16 pm

So why on earth are the Marshall PTs rated at 150Ma? I used a 288Ma PT for my Express.

M Fowler · Post by **M Fowler** » Wed Apr 16, 2014 7:31 pm

http://ampgarage.com/forum/viewtopic.ph ... ransformer

Littlewyan · Post by **Littlewyan** » Wed Apr 16, 2014 11:09 pm

Jesus Fowler I hope you were referring to the Current Calculator on that thread. VacuumVoodoo's post just drained me, too much info at once! Am I right in saying that he is basically saying to get max clean output from the valves a properly designed PSU is required? So Marshall's use of an underrated PT may have been intentional?

M Fowler · Post by **M Fowler** » Thu Apr 17, 2014 5:20 am

I thought it was a good link.

Basically stating 150mA classic tone MCI transformer is good for 50w.

VacuumVoodoo · Post by **VacuumVoodoo** » Thu Apr 17, 2014 6:35 am

Littlewyan wrote:Jesus Fowler I hope you were referring to the Current Calculator on that thread. VacuumVoodoo's post just drained me, too much info at once! Am I right in saying that he is basically saying to get max clean output from the valves a properly designed PSU is required? So Marshall's use of an underrated PT may have been intentional?

How do you eat a whole elephant?
Slice by slice....

VacuumVoodoo · Post by **VacuumVoodoo** » Thu Apr 17, 2014 6:36 am

multiple post, forum reported "debug mode"

VacuumVoodoo · Post by **VacuumVoodoo** » Thu Apr 17, 2014 6:36 am

multiple post, forum reported "debug mode"

Gaz · Post by **Gaz** » Thu Apr 17, 2014 9:37 am

I know your standard of living is high, but I didn't realize you were eating elephants up there!

Littlewyan · Post by **Littlewyan** » Thu Apr 17, 2014 9:58 am

Right, so basically 150mA is fine, it just means I will get sag, which is probably part of the early Marshall sound. However if I want my Amp to have maximum headroom and produce maximum clean Output then I should use a better Transformer?

I also often hear that only one valve is conducting at a time, is this taken into consideration?

analogdino · Post by **analogdino** » Mon Apr 21, 2014 10:41 pm

In class B, yes, they conduct alternately. In class AB the conduction overlaps during each cycle. In class A they both conduct through the whole cycle... and the box gets even hotter!
Cheers,
Roger

The Amp Garage

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