Vacuum Tubes and 110 / 115 / 117 / 120 / 125 volts

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If you visit the antiqueradio.com forum you will see the issue are:
1. manufacturers spec transformers in wattage handling pretty close to maximum, so when the line voltage increases the heat of the transformer can then exceed what the winding insulation can handle.
2. B+ can get excessive, if line voltage goes up 10 volts, say nameplate is 115 VAC and the receptacle supplies 125 VAC, that is ~8% increase. If the B+ was designed for 300 VDC, now the transformer and rectifier will produce 324 volts. Not too bad, but if 350 VDC designed, it is now 378 VDC, close to ratings of 400 volt electrolytics. Really close if the bean counters made them install 375 VDC electrolytics!

FIlament voltage was never thought to be a problem. 6.3 design is now 6.8.

Now, if the nameplate is 110 VAC, woops, now that's over a 12% increase and the B+ is very over spec. The 6.3 filament is just 7 volts.
 
Not only is higher AC line voltage a problem for vacuum tubes, it's a problem for the power transformers in vintage and legacy audio equipment. With higher AC line voltage the transformers can saturate. The hi-fi people think that it's a DC offset causing the hum & buzz, but it's a high line voltage problem.
 
ggunn said:
I have several guitar amplifiers that are powered by vacuum tubes. Tube amps rule!
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And Eddie Van Halen (RIP) used a Variac to lower his tube amp's voltage to help achieve his original sound. :). I also have 2 Marshall amps but no talent to make good use of them.
 
drcampbell said:
The original motivation for not using a transformer wasn't savings; it was so the radio could operate on either 110v AC or 110v DC.
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My parents had a 'portable' tube radio with a red plastic case. There was a spring-loaded switch inside that the power plug held when running it on the internal 90v battery.
That battery was also the source of my first electric shock. 😯


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ggunn said:
I have several guitar amplifiers that are powered by vacuum tubes. Tube amps rule!
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I used to build them for my guitar-playing buddies when I was in high school. One of them took top prize in a state-wide vo-tech competition. It was basically 2 complete Fender Showman circuits that could be bootstrapped together to yield 160 watts.
I used to find bars that were scrapping out old Rock-Ola jukeboxes to get the power transformers.

The orange glow of 8 6L6GCs in a dark room was a beautiful sight!
 
OldBroadcastTech said:
Largest tube I ever dealt with was the 4CX15000A used in a Harris FM-20 ( 20 kW) transmitter


Filament was 6.3 volts at a whopping 160 amps, leads from filament transformer to tube socket were # 2 welding cable (to get the flexibility needed to hook it up.

Plate volts were 7800 at 2.9 amps for 17.5 kW output.........separate 3' W x 6' L x 5' H cabinet for the HV supply
alone.
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Those Harris transmitters used to be built in my hometown.
 
LarryFine said:
My parents had a 'portable' tube radio with a red plastic case. There was a spring-loaded switch inside that the power plug held when running it on the internal 90v battery.
That battery was also the source of my first electric shock. 😯


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I though people were nuts when they would lick 9V battery terminals to see if they still had a charge. This one would leave a mark. :LOL:
 
OldBroadcastTech said:
Largest tube I ever dealt with was the 4CX15000A used in a Harris FM-20 ( 20 kW) transmitter


Filament was 6.3 volts at a whopping 160 amps, leads from filament transformer to tube socket were # 2 welding cable (to get the flexibility needed to hook it up.

Plate volts were 7800 at 2.9 amps for 17.5 kW output.........separate 3' W x 6' L x 5' H cabinet for the HV supply
alone.
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And don't forget to kill BOTH power inputs when servicing. My mentor forgot, and took a chunk out of the shorting stick when he was making sure the capacitors were bled off.
 
drcampbell said:
Many collectors prefer to preserve their antiques in original condition. Which doesn't preclude using a voltage-dropping power resistor external to the device instead of a buck transformer.


The original motivation for not using a transformer wasn't savings; it was so the radio could operate on either 110v AC or 110v DC.
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Wow First time that I ever heard about this tube type being able to run on AC or DC. My dad had a 3/8" hand drill made in the 1950's that label said it could run on AC or DC. Had a universal motor where one line wire was connected to a winding then thru a brush to the armature thru the second brush & other winding. Still have a RCA tube Manuel with over 300 pages of specs & tube drawings that I purchased back in the 1960's. The only other thing that comes to my old mind that can operate on AC or DC were older model Danfoss VFD'S ( VLT 6000 model ) . They had two terminals think marked #81 & 82 where you could attach DC to. At a continuing education class awhile ago they told us that Japan was looking into running DC in buildings to supply computers and anything else that uses DC. Stated it would save on power & Air conditioning.
 
garbo said:
Wow First time that I ever heard about this tube type being able to run on AC or DC. ...
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All-American 5-tube radios contain a half-wave rectifier. Half the time when plugged into DC, the filaments will light up but the radio won't play. It's then necessary to unplug it, turn the plug over, and plug it back in the other way.
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garbo said:
... My dad had a 3/8" hand drill made in the 1950's that label said it could run on AC or DC. Had a universal motor where one line wire was connected to a winding then thru a brush to the armature thru the second brush & other winding. ...
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That's still true of universal motors, though advertisers put a whole lot less emphasis on that capability today because DC receptacles are so much less common, and today's switches in cheap tools probably aren't up to the task of switching DC.

Not only will they run on AC or DC, but also on every AC frequency ever used for power distribution. 60 Hz, 50Hz, 25 Hz, 400 Hz, whatever. No matter what the frequency, (including zero Hz) the current in each winding in a series-wound motor will necessarily be the same, resulting in the magnetic phase angle being determined only by the mechanical design of the motor, not inductive reactance.

garbo said:
... The only other thing that comes to my old mind that can operate on AC or DC were older model Danfoss VFD'S ( VLT 6000 model ) . They had two terminals think marked #81 & 82 where you could attach DC to. At a continuing education class awhile ago they told us that Japan was looking into running DC in buildings to supply computers and anything else that uses DC. Stated it would save on power & Air conditioning.
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In a complex machine with many motors accelerating & decelerating simultaneously, a significant amount of power & energy can be saved by putting all the VFDs on the same DC buss. The braking energy extracted from one motor can be used to power another motor instead of being dissipated in a braking resistor.

San Fransisco's cable cars use a similar concept. A hundred (~?) cars share the same cable. The uphill-bound cars get a boost from the downhill-bound cars, the brakes get a rest, and the whole line is run on a single, thousand-horsepower (~?) motor. It's a mechanical cable, but the same energy-sharing concept.
 
grich said:
I though people were nuts when they would lick 9V battery terminals to see if they still had a charge.
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It was THE method for testing those 9 volt batteries in transistor radios back in the early 60s. Still do it today. I get wild looks from younger people who grew up on small stuff being powered by AA and AAA cells when I remove the 9 volt battery from non-functioning test equipment and lick it.

Like using a Wiggy, it works!
 
Frank DuVal said:
It was THE method for testing those 9 volt batteries in transistor radios back in the early 60s. Still do it today.
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So do I. I can tell when a 9V battery is not dead but nearly so by the degree of sensation.

But don't put a live one in your pocket with loose change! :D
 
In a previous life I worked for a Motorola 2-way shop.

My boss had an iron-clad rule that batteries being given to a customer be in factory or we-provided cardboard packaging........no 'bare batteries' were ever to be handed to a customer.

The reason was that a police officer in a nearby city took one out of its package and put it in his jacket pocket along with his car keys......this was a portable radio battery, 15 volts 600 mAh NiCad.

He was lucky....the keys were between the battery and his rib cage, so he got off 'easy'....three broken ribs, a punctured lung and a shirt and jacket....if the battery had been toward his body he probably would have died from Cadmium poisoning.
 
(topic drift alert)
drcampbell said:
San Fransisco's cable cars use a similar concept. A hundred (~?) cars share the same cable.
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Since the rebuild in the 1980s, there have been only three lines running on four "ropes" (1 1/4" wire rope). IIRC no more than maybe 6-8 cars on a single rope at once. (For technical content- each rope is driven by an 510HP motor and moves about 9.5MPH.)
 
Alot of buildings in s.f. had a leg from the same feed in buildings for the d.c. elevators... big buildings even had the actual feeders enter and exit. Large, scary cables w/ very crappy insulation...
 
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