Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on June 30, 2019, 10:01:18 am
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Been reading about PT specs but can’t find info on exactly what determines the overall rating, 160mA, 180mA, 200mA, etc. Big bottles need higher ratings, regarding the PT windings what determines this rating. Is the sum of current draw for each secondary added to determine what rating is needed?
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Try looking at this. Plug in different tube types and preamp tube count to see how the
Current draw changes. Gives a good ballpark on what type a PT is needed per situation
https://thesubjectmatter.com/calcptcurrent.html
Joe
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> PT specs but can’t find info on exactly what determines the overall rating, 160mA, 180mA, 200mA, etc.
To design a PT is like designing a pickup truck. A 1-ton truck has bigger axles, springs, frame than a 1/2-ton truck. A high-current winding has fatter wire; and for the same voltage, fatter iron to handle the higher power.
If you are asking about what pre-made PT to buy for a given tube(s) and plan: look in the tube-book and find a similar Suggested Condition. Add plate and screen current. Add 10% to cover your small-tubes.
Also: figure out what Popular Brand amp works the same tubes at the same output, and buy the Replacement iron (PT and OT) for that. Couple 6L6GC working hard? That's a 2x6L6 Fender "40W-50W" and the iron is readily available.
> Try looking at this.
On quick-check it gives reasonable values for push-pull. In SE it assumes full Pdiss(max), which is probably fair for many guitar amps, though if planning a "small" amp you might run cooler.