5V4 vs 5U4 rectifier in my Scott Super XII

[Y2K Bruce]

When I acquired my Scott Super XII, it had a 5U4 rectifier. My repairman however put in a 5V4 when he went through the electrical repairs, as that is what the schematics show. I understand the 5U4 runs a 3V filament voltage vs 2V on the 5V4 tube and thus may overload the transformer.

 

HOWEVER, the Super XII owners manual specifically mentions the 5U4 was being used by Scott as a running change in lieu of the earlier 5V4 due to tube improvements. My tube socket does NOT say the correct tube.

 

Is there any easy way to tell which should be used in my radio ? It seems to play fine with either as the rectifier.

[Thomas Peters]

As you have found out, it works with either one. I have tried both types in my two chassis Super XII, with no difference in performance.

As to overload, I don't think so. Rather with a filament rated for a slightly higher voltage, it will last longer since full voltage is not applied.

By the way, what version is your Super XII?

[Y2K Bruce]

Hi Thomas-Thank you for the reply. How can I tell which version of the Super XII I have ? its a single chassis set and has 5 knobs.

[Norman S Braithwaite]

Filament voltage is not an issue.  Both use 5-volt filaments.  The filament current requirements are different however, the 5U4 using 3-amperes vs 2-amperes required by the 5V4.  Use of a rectifier that requires higher filament current adds to the load that must be handled by the power transformer.  Generally transformers used on radios were designed to handle at least 10% more load than required (probably more like 20% or greater) to accommodate unknown conditions (higher line voltages, filter capacitor leakage as a result of aging, etc).  The usual limiting factor for transformer design is heat dissapation.  If there are no other reasons that the chassis may draw more current than when new, there should be no problem using a 5U4 tube.  The 5U4 tube can handle higher B+ voltages and B+ current than the 5V4 tube and is therefore less likely to fail in operation or switching but, since it is directly heated (no cathode) it may introduce hum.  If the power transformer becomes too hot to hold your hand upon (140F +/-), use the 5V4 tube.  If there is no problem operating the set with a 5V4 tube, I would recommend using it.

Norman

[Thomas Peters]

Thank you for clearing up the 5U4/5V4 question, Norman.

If authenticity is your concern, either would be correct, since it is a factory designated substitution.

Based on your description, your Super XII should look like the sample in the Scott News for September 1938, ie., single chassis electronics. Mine looks like the one pictured in the Scott News for March of 1939, ie., separate chassis for power transformer and rectifier tube.

This one here also has a "bezel board" with extra unused holes. Picture a board like used with a Masterpiece or the "improved 1940 Super XII" shown in the one sheet posted on the info website.

Antenna hook up is also different from the earlier Super XII, as shown in the manual. Its antenna terminal strip is like what a Masterpiece utilizes.

[Y2K Bruce]

Interesting variant you have. I have put the 5V4 back into my set and it seems to play the same either way.

It's running on a variac set to 105V and the transformer is nice and slightly warm to the touch after 4 hours of operation today. I plan to install it into the "Heron" cabinet I recently acquired from 'Willie' and have been test driving it for a week now.

[David C. Poland]

The evolution of the Super XII seems to have 3 versions.

Initially, the single 12 tube chassis with 4 controls plus 2 speed dial. Next with an 11 tube receiver and an outboard power transformer and rectifier on a small chromed chassis, but same 4 controls controls plus 2 speed dial.

The third version Super XII has the same small outboard 1 tube rectifier/power transformer chassis, but has 2 additional controls so it looks like the 14 tube Scott Masterpiece. One additional control is a radio-phono switch --- t he other - a variable sensitivity switch. To differentiate the late Super XII 11 tube receiver from the 11 tube Masterpiece receiver check for unshielded 6V6's behind the tuning condenser. For the Masterpiece, the 6V6's were relocated on a 3 tube power supply with the 5U4.

[Thomas Peters]

Version one and two, I am acquainted with, however, number three is another story.

Anybody on this board have an "improved 1940 Super  XII", of which they could  share some chassis and/or cabinet shots?

[David C. Poland]

Thomas,
Here is a photo of my late Super XII on the shelf having the additional 2 controls (no wood panel). Broadcast and 3 SW bands, no red TV band on this example. The 1 tube power supply sits to the right. Unrestored, but complete and I have the 12 inch speaker with 5 pin plug. Speaker 5 pin socket on the back of the receiver chassis. Again, the easy tip off for this variant of the Super XII is the pair of 6V6 output tubes without tube shields, located behind the tuning cap cover on the back of the receiver chassis.

The second photo is my unrestored Scott Masterpiece on the shelf (has the wood panel) for which i have the 3 tube amp. I have the 12 speaker with octal plug.

This late Super XII variant is easily mistaken for the Scott 14 tube Masterpiece receiver. Both are somewhat rare. Same black Stradivarius dial. Both have 11 tubes on the receiver chassis, but all the tubes across the back of the Masterpiece should have tube shields. Some differences in function of the 6 control knobs. My Scott Masterpiece has the optional red band for pre war TV audio broadcasts. The Scott Masterpiece has a 3 tube amp using 6V6's and the octal speaker socket.

My early single chassis Super XII is in a Braemer. Any of the late 1930's cabinets would be correct (Accousticraft, Braemer... and also larger cabinets Warrington, etc, or any of the phono combination credenzas same as you might see with a Phantom.

[Thomas Peters]

Thanks for posting these photographs, as they are most informative!

It is interesting to see the further development of the same chassis.

My version 2 is currently situated atop of a short modified book cabinet, ala home made Napier.