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Old 8th July 2007, 04:26 PM   #1
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Default Hammond 2XX vs 3XX Power Tranny Questions

OK... quick background.. plenty of tube building experience... but I've never used a Hammond Transformer. I have an old homebrew amp on my bench that the 50 year old power tranny finally gave up on. I need a replacement transformer. I have been looking at the Hammond 272JX because it's specs fit the bill nicely. However, I've been reading on the tube section here and read "the 2 series are bad, you must get a 3 series they are so much better" over and over and over. One poster even said the 2 series had knockouts in the bell, which the 3 series dont. OK, here's the kicker, I have the Hammond catalog in front of me right now. And the only spec difference is the extra taps for the universal primary and bias tap. Everything else is the same, including the knockouts in the bell housing. So what gives? What's the real difference?
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Old 8th July 2007, 05:03 PM   #2
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The 300 series is rated for 50/60 hz where as the 200 series is only rated for 60 hz. In order for a transformer to run at rated specs at 50 hz, it needs to be about 20 % larger than the same transformer that is only rated for 60 hz, for the same specs.
Basically, the higher the AC frequency the transformer will work at, the smaller it can be, because its efficiency goes up with higher frequencies.
What this means applied to the 200 and 300 series transformers at 60 hz (USA, Canada, and I think Japan line frequency) the 300 series will run much cooler at 60 hz at the given load, because the core is about 20% larger.
Hope this helps... Daniel
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Old 8th July 2007, 05:06 PM   #3
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The "300" series can be used on 50 Hz as well as 60 - that means more primary turns, and 20% lower flux density on 60 Hz. Less likely to buzz, less inrush current, and of course larger physical size and higher cost for the same rating.

Do you need 50 Hz or 240V? Use 300 series. 200 series may win on size though... will 300 series fit?
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Old 8th July 2007, 05:08 PM   #4
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There are several differences. If you look at the size chart, you'll see that the 3** series is a core size or two larger. The 3** series has very versatile dual 100-110-120v primaries, which can really help you get the secondary voltages you need. The 3** series also has a bias tap on the HV secondary, in case your amp has 'fixed' (negative supply) bias.

About 50% of the 2** trans I used developed mechanical hum (an overall problem with Hammond) when used at anything above about 50% derating, and all got too hot to touch for more than an instant.

Your amp, your call; but I don't even look at the 2** transformers any more. The pro series aren't that much more expensive.

Aloha,

Poinz
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Old 9th July 2007, 02:33 AM   #5
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Thanks everyone.. the larger size/running cooler makes sense... I guess what I'm struggling with here is that it appears to me these are made with the same cores (across the series - not necessarily the 272JX vs 373JX), same bell housing construction, etc... so I don't see why the 200s are buzzing and the 300s aren't. I don't need universal, I don't need negative bias... and the transformer would be running at about 50% of it's rated capacity. I have decided to go with the 300 just because there must be something to all the comments on the forum here, but in the back of my head it just seems like the other would fit the bill nicely too at 2/3 the price.
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Old 9th July 2007, 03:03 AM   #6
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Listen, Daddyo,

Make how you like. The 3** trans is made with one size up core, has no knockouts (euw!) in the bells, and the adjustable primary may end up (how do I know this, hm?) being more useful than you dream right now.

Look at the difference in price. You want the best for your dozens (hundreds) of hours of sweat equity, or you don't think this is value?

Up to you,

Poinz
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Old 9th July 2007, 05:36 PM   #7
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even if its the same core size, designed for 50 hz, and the no of turns can be different, all that still affects buzzing ( magnetic B) ability

its to do with volts ( same? ) , frequency (50 hz capable better ), core size, no turns, even if core size is the same, more turns will mean lower b, meaning lower heat and buzzing, and of course, more turns, means more copper, longer to wind, more money.
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Old 9th July 2007, 05:50 PM   #8
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I've used the 2xx series transformer on several projects and haven't had any mechanical buzzing issues. They do seem to run a bit hot though.
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Old 9th July 2007, 10:09 PM   #9
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Quote:
Originally posted by Poindexter
Listen, Daddyo,

Make how you like. The 3** trans is made with one size up core, has no knockouts (euw!) in the bells, and the adjustable primary may end up (how do I know this, hm?) being more useful than you dream right now.

Look at the difference in price. You want the best for your dozens (hundreds) of hours of sweat equity, or you don't think this is value?

Up to you,

Poinz
OK, several points to address here - the Hammond catalog shows and specifies knockouts on BOTH models. That's 200 and 300. Why does everyone keep saying they don't have knockouts? I can't find an image of one that doesnt when searching images.google.com? That was one of my original questions. As for dozens of hours - not hardly, more like 30 minutes - less time than spent in this forum. All im doing is replacing a failed transformer. The circuit has an autobias feature I did - so I don't even have to bias the tubes. As for the universal primary - it won't be useful - I don't need it. Not to single you out per see, but it is posts like POINZ's here that made me ask in the first place, because they seem to be saying things without anything that backs it up. It sure shows knockouts on hammonds site too:

Look at the 300 page
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Old 9th July 2007, 10:29 PM   #10
MikeR is offline MikeR  United States
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Default Knockouts

I have two of the Hammond 300 series transformers and neither has knockout plugs. They are also a nicer finish than the 200 series. It's more satin than gloss and looks thicker.

I agree with Poinz.
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