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Isolation transformer

 
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pattycakes77



Joined: 17 Jan 2008
Posts: 2093
Location: Cedar Rapids, Iowa

PostPosted: Sun Oct 02, 2016 7:50 pm    Post subject: Isolation transformer Reply with quote

Next week I have a guy who is going to sell me a Montgomery Ward Airline 9001b amp. It needs tubes for sure because they are missing, this will be a little something to tinker with. Did a quick search and I've seen mention of the potential of electrocution if plugged direct into a wall outlet. So, do I buy an isolation transformer or modify the amp itself to safely play through it?

Thanks.
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statorvane



Joined: 21 Aug 2003
Posts: 1950
Location: Upstate New York

PostPosted: Sun Oct 02, 2016 11:30 pm    Post subject: Reply with quote

Buy an isolation transformer. What is the B+ for that model? I am guessing around 220-240 volts?
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Mr. Clevername



Joined: 08 Dec 2006
Posts: 2450
Location: San Francisco, CA

PostPosted: Mon Oct 03, 2016 11:34 am    Post subject: Reply with quote

I know you can wire one in because somebody did it to an old Kent I have.

Actually doing stuff like that is way over my pay grade, so no practical tips from me, sorry!
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BrightKJ



Joined: 13 Sep 2008
Posts: 342
Location: Midlothian, VA

PostPosted: Mon Oct 03, 2016 2:07 pm    Post subject: Reply with quote

If you don't know what you're doing with the transformer, find somebody who does. It's not worth electrocuting yourself because you weren't sure and just guessed and hoped for the best. Be safe!
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pattycakes77



Joined: 17 Jan 2008
Posts: 2093
Location: Cedar Rapids, Iowa

PostPosted: Mon Oct 03, 2016 5:11 pm    Post subject: Reply with quote

BrightKJ wrote:
If you don't know what you're doing with the transformer, find somebody who does. It's not worth electrocuting yourself because you weren't sure and just guessed and hoped for the best. Be safe!


Exactly. If there is electrocution involved, I'm out. I didn't know if you could just plug into a gadget and be safe or if modifying the actual amp was the safest way to go. I know a guy out in Davenport (AM Guitars) that would be my go to guy for the actual work if it's even worth it.
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Mr. Clevername



Joined: 08 Dec 2006
Posts: 2450
Location: San Francisco, CA

PostPosted: Tue Oct 04, 2016 9:56 am    Post subject: Reply with quote

I found a plug-in isolation transformer on Ebay quite a few years ago. It's ancient, and very, very heavy.
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WildIowa



Joined: 06 Mar 2004
Posts: 490
Location: Henderson IA

PostPosted: Wed Oct 05, 2016 5:59 pm    Post subject: Reply with quote

I have several old tube amps but only one, an old Ariatone, is as you describe. They are actually more of an old AM radio design and quite unstable and even dangerous I don't even know if they have any transformers whatsoever. One of my earliest boyhood memories in the early 60's was reading an article about a kid who was sitting in a metal lawn chair in wet grass and he was toasted when he picked up a guitar...I suspect it was hooked to one of these types of amps.

They are usually very low power, maybe 3 to 6 watts, and I wonder if they are even worth the hassle of trying to mod them to the point they are acceptable. Kinda funny and weird conversation pieces...I was thinking about digging in to the Ariatone but not sure it is worth the time and hassle, very low power, weird tubes and crap tone no matter what you do. Not really a gigging amp maybe some recording possibilities as a novelty.

Just be darned careful!
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Mr. Clevername



Joined: 08 Dec 2006
Posts: 2450
Location: San Francisco, CA

PostPosted: Thu Oct 06, 2016 10:58 am    Post subject: Reply with quote

I've always called them record player amps because they look just like what was inside old portable record players. My Kent was the first amp I ever had. Some of them can be great practice/recording amps, but NOW they say they're unsafe.

Oh, it's buzzing? Just turn the plug around . . .
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tangelolemon



Joined: 26 Jan 2009
Posts: 2691
Location: Brooklyn, NY

PostPosted: Thu Oct 06, 2016 3:37 pm    Post subject: Reply with quote

These are known as "series heater" amps, because the filaments of the tubes are all in a series, like a string of christmas lights.

If you add up the filament voltages (first number) of the tubes, you'll see that they add up to about 110 or 117, which is the line voltage. They did this so that they could skip the expensive (heavy) power transformer. Sadly, it also makes the amp very dangerous.

Get a plug-in isolation transformer and you'll be all set.
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pattycakes77



Joined: 17 Jan 2008
Posts: 2093
Location: Cedar Rapids, Iowa

PostPosted: Fri Oct 07, 2016 5:50 pm    Post subject: Reply with quote

Thanks for the info everyone. I picked up the amp last night, probably over paid but it was cheap enough. Going to look through my hoard of tubes to see if I have what it needs otherwise it's another $50 for new ones.

Any recommendations on a decent plug in isolation transformer? Maybe something that won't break the bank?
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