Current draw of an Express

[rooster]

I need to buy an AC to AC isolation transformer for my studio because I have (even after replacing AC grounding rods to Hi-Fi specs) and whatnot, there is something that arrives as line noise at various times in the day. Maddening and not a big deal to some but if I can remove it I'm in.

So there's a site that let's you calculate the current draw of tube amps and I'll list it here:

https://www.thesubjectmatter.com/calcptcurrent.html

Using the easy to use entry options of plate voltage, tube type, etc., the calculations I arrive at for a 50 Watt Marshall (or TW Express) is approx. 4.0432 amps. This seems about right but then again, maybe a little high? What throws me is the current draw of the filament supply. Does it really take almost 4 amps of current to run the filaments in a pair of EL34 and 3 12AX7s?

Current Draw, 50 watt Marshall.JPG

[sluckey]

Does it really take almost 4 amps of current to run the filaments in a pair of EL34 and 3 12AX7s?

Yes, but that only equates to 0.2A at 120V on the mains.

[xtian]

Most of my 50 watt amps pull 0.5A at 120vAC, and closer to 1A when running hard. That's 60-120watts.

[rooster]

Thanks for this response. Real Life experience is best, of course. My options are a 2.25A isolated AC/AC vs. a 9A version. One's half the price of the other so I guess I can buy the 2.25 amp version.

[sluckey]

Line noise will pass right through an isolation transformer as if it were not even there.

[rooster]

Hm, this is not what I am hearing from audio guys, sluckey. In fact they say this is the biggest reason they buy such a device. From the manufacturer:

<<Get complete protection for sensitive devices and prevent power disruption with Tripp Lite's Isolator IS1000 Isolation Transformer. Featuring an internal isolation transformer with Faraday Shield, the IS1000 completely isolates equipment from line noise that can cause incremental but devastating equipment damage. Its 680-joule surge suppression rating protects equipment from surges and spikes caused by utility power disruptions and the operation of nearby equipment on the same circuit. Its 6-ft. power cord allows for flexibility during installation, while its built-in circuit breaker prevents dangerous circuit overloads. Its 1000-watt capacity allows it to be used with a variety of sensitive equipment. Its 4 widely spaced NEMA 5-15R outlets accommodate bulky transformers, and its lighted power switch offers convenient, one-touch power control. For peace of mind, the IS1000 features a rugged, all-metal housing.>>

[rooster]

Hm, this is not what I am hearing from audio guys, sluckey. In fact they say this is the biggest reason they buy such a device. From the manufacturer:

<<Get complete protection for sensitive devices and prevent power disruption with Tripp Lite's Isolator IS1000 Isolation Transformer. Featuring an internal isolation transformer with Faraday Shield, the IS1000 completely isolates equipment from line noise that can cause incremental but devastating equipment damage. Its 680-joule surge suppression rating protects equipment from surges and spikes caused by utility power disruptions and the operation of nearby equipment on the same circuit. Its 6-ft. power cord allows for flexibility during installation, while its built-in circuit breaker prevents dangerous circuit overloads. Its 1000-watt capacity allows it to be used with a variety of sensitive equipment. Its 4 widely spaced NEMA 5-15R outlets accommodate bulky transformers, and its lighted power switch offers convenient, one-touch power control. For peace of mind, the IS1000 features a rugged, all-metal housing.>>

And on the smaller amperage model:

<<Tripp Lite Isolator series isolation transformer-based power conditioners offer complete line isolation, continuous noise filtering and enhanced common mode surge suppression
Supports combined loads up to 250 watts continuous/2.1A at 120V
Isolation transformer with Faraday Shield offers 100% isolation from the input AC line
Neutral to ground bonding at the secondary eliminates common mode noise and provides an isolated ground reference for sensitive equipment
Isolation transformer design serves as an inexpensive alternative to the installation of dedicated circuits and site electrical upgrades
Removes EMI/RFI noise, utility switching transients, background spikes and power problems generated by other on-site loads, utility grid-switching and related surges
Line isolation with additional surge suppression components offer continuous line filtering of a full range of power line noise in all modes
Continuous transformer filtering with no wearable parts reduces surges in the worst of power environments to harmless levels
Includes 2 widely-spaced NEMA5-15R output receptacles, 6 ft power cord, circuit breaker overload protection and lighted power switch
Rugged all-metal housing ships ready for upright tower or wallmount installation>>

[rooster]

A follow up, I also borrowed a device that measures AC current. I plugged a High Power Tweed Twin and a Super Reverb into it, turned them on, and they measured 1.4A. I turned off the HPTT and had a reading of .7A on the SR by itself. So thanks again for the help sluckey and xtian.

[sluckey]

That Tripp-Lite unit is much more than just a simple line isolation transformer that I thought you were referring to.