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Discussion Starter · #1 ·
Hi all, I am just curious about engine numbers and have not found a good explanation why some carry the AC designation while others don't. l understand the AW is add whistle, and I think the DC is for direct current when included in the engine number, but since the vast majority are intended to run on alternating current, is seem odd that the AC is for alternating current. This comes about particularly because I was looking at the 342 vs. 342AC. I think the 342 may be a DC only, and the 342 AC could be either? However this 'logic' breaks down when I look at my entry level 300AC, which I am nearly positive does not have a DC alternative, nor any added features. Also, most of the engines carry no designation, so why just some? Any explanation would be appreciated!
TimmyD
 

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We need to begin with the motor design. Initially in 1946 all Gilbert engines had universal, open frame, series wound motors. These run on either AC or DC, hence "universal" in the name of the motor. In 1947 Gilbert introduced DC motors. these were just the old universal motor with a permanent magnet for the field in place of a field winding. They run on DC only, AC power will cause armature failure in a time period measured in seconds. Unfortunately Gilbert chose to not add DC after the engine number of the engines that were built with the DC motor, who knows why???!!! Therefore engines numbered 332 or 342 made beginning in 1947 through 1950 can have either a universal motor or a DC motor. There were some engines with DC after the number, these were the 332DC, 334DC and the 342DC. These always have a DC motor. In 1949 Gilbert began numbering some engines with AC after the number, for example 322AC. All this meant was it had a universal motor. But all 322's had a universal motor.

The only engines ever built with a DC motor were Northerns and 0-8-0 Switchers.

The use of suffixes came to and end with the introduction of knuckle couplers. A 302 or 302AC became just a 303 when built with a KC. The 332AC became a 336. In 1957 Gilbert adopted a 5 digit numbering system but that is a story for a different post.
 

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Discussion Starter · #3 ·
Thanks Tom! So from what I understand, the AC suffix really means very little; AC does stand for Alternating Current, meaning a universal motor, but does not really mean much since most engines have no suffix and are the universal. A DC suffix assures DC motor, but engines without the DC suffix may have a DC motor if they are X-8-X wheel wheel configuration making them Northern's or Switchers. No X-6-X or X-4-X wheel configuration engines were ever made with a DC motor. If I come across an engine with a magnet as opposed to a field, it is DC and applying AC current to it will ruin the armature in a matter of seconds if it was not already ruined by the previous owner. Is the armature run in a DC different than the ones run in universals? I am curious as I am interested in finding an old 342 or 343 switcher if I can find one in my price range, which will be unlikely. But if so it will likely be non-running, and if it happened to be a DC with a bad armature, I am wondering how challenging finding a replacement armature is. Also just curious and enjoying learning from you guys, thank you for sharing your wealth of knowledge! Also, are those of you running DC's using AF transformers and rectifiers or more modern DC power supplies? Also, any thoughts on why DC was introduced in the first place? Do the DC's offer more power at a given voltage than the AC? Just wondering as the universal motor technology seems to me to be very robust and pretty powerful. Just curious about the logic behind the DC.
Thanks again and hope you all have a wonderful day!
TimmyD
 

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The DC motor armatures are different than the Universal motor armatures. The only real difference is is the universal armature has about 1.5 Ohm resistance and the DC armature has about 2.5 Ohm resistance, to compensate for the lack of the Field resistance in the formerly series wound motor.
Way back in 1954 my dad bought a Gilbert AlNiCo DC field from a 332 DC motor and swapped it into my 322AC with no other changes. That engine ran great for a number of years. It is possible to make that swap and use the original armature. There are two different DC armatures, so if the armature is also swapped the correct one must be used. The early DC armature has no oil slinger and is 1/16" shorter than the later armature with the oil slinger.
As far as power, the easiest DC supply is an original transformer with a cheap 10A DC bridge rectifier and a DPDT switch for direction control. By cheap I mean under $5.
The only real issue is the open frame universal motors used in Gilbert (and Lionel) engines are three pole designs. These are not inherently smooth running. Modern can motors with 7 poles are way better, especially for smooth, low speed running. The best way to get optimum low speed performance from a three pole universal motor is to use a power supply that outputs a chopped AC waveform. I use the MRC AH101 for this reason. The downside is the motor may be noisier and engines with built in horns/whistles cannot be used because the higher frequency harmonics make them sound continuously.
I believe Gilbert introduced DC postwar for several reasons. One, Gilbert had to develop a DC motor anyhow for their HO line so it was easy to scale that up for S gauge. Two, the AlNiCo permanent magnet material became cheaper and more widely available after the war. Three, it offered positive direction control over the engine and eliminated the need for the troublesome and expensive reverse unit. The DC line was eliminated in S for several reasons. First, with the Korean war AlNiCo again became controlled and expensive. Second, AC was just too pervasive in the non-scale toy train world so the DC engines were not big sellers. Third, there were no cheap, high current, DC supplies. Look at the expensive vacuum rectifier tubes Gilbert had to use in their #14 and #16 rectiformers. Anyone with AC trains had to buy one of those or a bulky and expensive #15 selenium disc rectifier just to run their DC engine. AC track power was easier and cheaper for toy trains.
 
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