[mike s]

On Friday, May 6, 2011 3:55:16 AM UTC+1, flipper wrote:


Most AC radios did since you could eliminate the cost of a power
transformer entirely by running series heater strings and half wave
rectifying AC for B+. And you could also run them off DC.

The Vortexion guitar amplifier I'm currently restoring had series heaters, four CL33 output valves in parallel push pull and two EF40, the first as a pentode and the second wired as a triode to drive the output valves through a phase-splitter auto-transformer.
To make it safe-ish the inputs are isolated with a transformer and none of the internal metalwork can be touched if the back panel is in place. Even so, I believe there were casualties from these types of amplifiers and guitar amps soon adopted power transformers as standard, whereas in the UK radios, TVs and other consumer electronics were often "AC/DC" through the 1950s and beyond. This guitar amp was probably made in 1947 or 1948.

http://mike.wepoco.com/Home/retro-ge...vortexion-eg20

I'll add some more photos and schematics at the weekend if I get time. It now has four EL33 for the output and a new PSU with transformer and silicon rectifiers.

[Alejandro Lieber]

On 05/06/2011 07:15 AM, mike s wrote:
On Friday, May 6, 2011 3:55:16 AM UTC+1, flipper wrote:


Most AC radios did since you could eliminate the cost of a power
transformer entirely by running series heater strings and half wave
rectifying AC for B+. And you could also run them off DC.

The Vortexion guitar amplifier I'm currently restoring had series heaters, four CL33 output valves in parallel push pull and two EF40, the first as a pentode and the second wired as a triode to drive the output valves through a phase-splitter auto-transformer.
To make it safe-ish the inputs are isolated with a transformer and none of the internal metalwork can be touched if the back panel is in place. Even so, I believe there were casualties from these types of amplifiers and guitar amps soon adopted power transformers as standard, whereas in the UK radios, TVs and other consumer electronics were often "AC/DC" through the 1950s and beyond. This guitar amp was probably made in 1947 or 1948.

http://mike.wepoco.com/Home/retro-ge...vortexion-eg20

I'll add some more photos and schematics at the weekend if I get time. It now has four EL33 for the output and a new PSU with transformer and silicon rectifiers.

Here in Argentina we have 220 volts A.C.

Many tube radios from the forties to the fifties, were american circuits
for 110 volts A.C., so there was a special supply cable sold here that
had 3 conductors: 2 for the 220 volts that were rectified to 300 volts
as +B, and the third conductor that was very resitive, I think some 70
ohms per foot that was used to bring the 220 volts to 110 volts needed
for the filaments that were wired in series. This cable, from the mains
to the radio, got hot, as it had to dissipate nearly 16.5 watts for 150
mA filaments.

I remember building one of these radios with the tubes 12BE6, 12BA6,
12AV6, 50C5 and 35W4.

I also built a ham radio transmitter with a filament transformer but the
300 Volts +B came directly from the mains using a half wave silicon
rectifier. Only two tubes were used: a 6V6GT oscillating by means of a
crystal in 3.597 MHZ (80 meters) modulated through a transformer by a
6AQ5 fed directly from a carbon microphone. Plenty of fun, with a
coverage of more than 500 miles at night.

--
Alejandro Lieber LU1FCR
Rosario Argentina

Real-Time F2-Layer Critical Frequency Map foF2:
http://1fcr.com.ar

[John L Stewart]

Here in Argentina we have 220 volts A.C.

Many tube radios from the forties to the fifties, were american circuits
for 110 volts A.C., so there was a special supply cable sold here that
had 3 conductors: 2 for the 220 volts that were rectified to 300 volts
as +B, and the third conductor that was very resitive, I think some 70
ohms per foot that was used to bring the 220 volts to 110 volts needed
for the filaments that were wired in series. This cable, from the mains
to the radio, got hot, as it had to dissipate nearly 16.5 watts for 150
mA filaments.

I remember building one of these radios with the tubes 12BE6, 12BA6,
12AV6, 50C5 and 35W4.

I also built a ham radio transmitter with a filament transformer but the
300 Volts +B came directly from the mains using a half wave silicon
rectifier. Only two tubes were used: a 6V6GT oscillating by means of a
crystal in 3.597 MHZ (80 meters) modulated through a transformer by a
6AQ5 fed directly from a carbon microphone. Plenty of fun, with a
coverage of more than 500 miles at night.

--
Alejandro Lieber LU1FCR
Rosario Argentina

Real-Time F2-Layer Critical Frequency Map foF2:
http://1fcr.com.ar[/quote]

In the 1930's before the original AA5 of 12SK7, 12SA7, 12SQ7, 35L6 & 35Z5 became available some radios ran straight off the 110 volt line running heaters at 300 mA.

But 39, 36, 38 & 12Z3 or 6A7, 6B7, 77, 43, 25Z5 heaters didn't get you 110 volts. The required dropping resistor often showed up in the line cord which got warm.

Cheers, John