Should an old type z have a loud hum? All the voltages are correct.
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Some do, some don't. The laminations may be floating loose some ... they can be tightened/clamped down with dis-assembly.
Thanks I'll take a look inside.
Jake
Easier said than done.
Go slowly and take pics if this is your first time opening a Z or V.
Jake-
Be very careful too - even though these transformers put out up to 24 volts, it is still enough to cause a dangerous shock. When in doubt, take the unit to a qualified service station, especially if the unit has other damage (i.e. cracked cord or plug).
-John
Rob, wanna confirm this one?...as I've heard the early small badge ZWs had loose laminations while the later large badge{type R?} had a solid pack....this makes repacking the older units easier to supposedly hit nearly 300 watts by cramming more plates in....so says a ZW rebuild guy from the local train show. Loose packs can hum...my small badge ZW starts to hum after 45min to an hour of constant use, but it's nothing loud or annoying.
Well, the ZW is a completely different transformer to use and work on. jp says he has a Type Z.
You are close on the ZW. All Type "R" models had riveted laminations, but so did those made before the "R", how far back is not really clear as they were running changes in production.
Your ZW guy is, well, let's say "mistaken" or "misinformed". A ZW is rated for and will put out 185-190-195(maybe for extreme examples) watts continuously. The 250/275 is the input rating, so the imaginary 300 watt ZW output would be reflected by about a 400 watt input. If he's talking about the input alone, the "modification" is meaningless without output numbers, as a fully loaded ZW will draw more than 300 watts easily for short periods. Also, there is no "room" for cramming in more plates.
Clamping/gluing loose laminations in a ZW does quiet them down and they may run marginally cooler.
Obviously, the ZW Rebuild guy was trying to puff up his rebuilds to make them seem more valuable. However, as Rob says, he's full of something, and it's not facts. 
Z's are sort of pre ZW's. They all have laminated c shaped layers loosely slid into the core from left and right - no rivets. There are screws that restrain the core that you can tighten but they have limited effect. They all hum at least a little.
The Z is complicated to take apart and to get back together than a ZW. There are many variations of Z's with basic improvements starting in pre war until the end. Like a ZW they have 4 rollers, the Bakelite breaker and the same terminals that fail over time like a ZW. The core is similar to the early ZW's. The one advantage over a ZW is the higher voltage.
