Current Ratings for amp and Power Transformers

[Gtr0]

Thanks, this book I have. The EL34 example given is for a 40W stage with cathode bias and very high (60mA) idle current. So it is not comparable to the other 55W fixed bias examples. But if you add max plate (143mA) and screen (44mA) currents and multiply with supply voltage (450V), you get 84W DC power consumption at full power. This again confirms that DC power demand with class AB is always a little higher than twice the output power, meaning a power conversion efficiency of 84/40= 48%.

I'm trying to follow but I do not see a reference to a specific wattage in the RCA tube manual - or are you referring to the mullard data sheet?

Could you elaborate? Not sure if I understand.

You don't need a "voltage doubler" (I actually don't like this term being used for the Marshall type fullbridge rectifier with CT) to get 500VDC. The "voltage doubler" circuit would work just the same without the center tap (but you would need at least 600V rated filter caps). Without the CT everybody would call the circuit a standard fullbridge rectifier. The center tap only balances the voltages across the stacked filter caps, otherwise no net current flows through the center tap.

Sorry, that is the term that stuck with me - but I understand it to be a fullwave bridge rectifier. IS the term 'voltage doubler' specific to this particular design? or is it just a misnomer?

Perhaps the PT current ratings are something to do with the 690V PT being intended for a 2 diode full wave rectifier whereas the 350V PT is for a bridge rectifier? Hammond states in their “Design Guide for Rectifier Use” that the DC current available from a 2 diode full wave rectifier is 1 x Transformer RMS current. i.e. 150mA for the 50W PT. For a bridge rectifier they say the DC current available is 0.62 x Transformer RMS current. i.e. 260mA for the 100W PT. Neither transformer is rated to supply enough DC for continuous full power output (250mA DC for 2 EL34 at 50W)

This is where I was going, but not educated enough to articulate it properly. But I be tryin.

When comparing have you look for which working classes of service data refer to.
The information you provide (page 353) is for PP class AB1 (two tubes).
For zero signal and small signal levels, the amplifier work in class A, and when the signal increase the amplifier will work in class AB and accordingly the anode current will be proportionally higher.
When designing a power amp, all data refers to max values.

[ATTACH=CONFIG]55470[/ATTACH]
https://archive.org/details/RCA_RC-30_1975 (pages 25-38)

I was looking for the 'worst case scenario'...

basically I am worried that these transformers aren't up to the task. I have a 100 watt Marshall type amp that I often play and you dare not touch the power supply after playing for 30 minutes, it'll burn your finger to the bone.

[Helmholtz]

Sorry, that is the term that stuck with me - but I understand it to be a fullwave bridge rectifier. IS the term 'voltage doubler' specific to this particular design? or is it just a misnomer?

"Voltage doubler" is often used to characterize this Marshall circuit. Actually a voltage doubler is a somewhat different circuit:
https://en.wikipedia.org/wiki/Voltage_doubler
The Marshall circuit can be interpreted as a variant of a voltage doubler if you start from the AC voltage across one of the primary halves. But I think this makes understanding unnecessarily complicated. It is much more straight forward to look at it as a standard bridge rectifier fed from the total primary, having an additional center tap for balancing the filter caps.

[Helmholtz]

I'm trying to follow but I do not see a reference to a specific wattage in the RCA tube manual - or are you referring to the mullard data sheet?

My RC-30 lists the wattage of 40W in the last line of the 6CA7/EL34 specs as "Maximum-Signal Power Output".

[Helmholtz]

I was looking for the 'worst case scenario'...

That's a good designer's approach. But that means that you want a PT that supports 500mADC or around 230W (not including heater power) secondary power for a 100W amp. Obviously the point of PT manufacturers is that full power is only demanded for some small (not specified) fraction of time. So they specify only a "typical" or average secondary AC current. This seems quite arbitrary and is certainly not really satisfactory.

[vintagekiki]

Tube Datasheets

https://drtube.com/en/library/tube-datasheets
Tube Datasheets

https://drtube.com/datasheets/el34-philips1969.pdf
For EL34 Philips lists the wattage from 45W to 90W depending on the power supply voltage.

[Gingertube]

I use this a lot.
http://tdsl.duncanamps.com/tubesearch.php
Links to datasheets plus summary operating conditions.
Example:
http://tdsl.duncanamps.com/show.php?des=EL34

Cheers,
Ian