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Author Topic: Heathkit AT-1  (Read 2400 times)
AB2MA
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« on: February 27, 2008, 07:04:24 PM »

I'm replacing the power transformer in my AT-1.The transformer I have has a hv of 596 volts with a 295v tap.The other windings are 5 volts and 6.3 volts.According to the manual the hv on the 5u4 is 430vac and the hv on the 6ag7 is 220v.Will the higher voltage of the new transformer hurt anything?Thanks,Stan
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KA5N
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« Reply #1 on: February 28, 2008, 09:21:08 AM »

The transformer in the AT-1 is 430V-ct-430V in other words 430 volts each side of center tap.  Does the transformer you want to use for replacement have 596 V-ct-596 volts or is it 0volts-295volts-596 volts?  If so then the DC voltage will be low, not high because it is 295v-ct-295v.
How did you determine that your transformer would be a replacement?  
Allen
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AB2MA
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« Reply #2 on: February 28, 2008, 11:22:50 AM »

I measured voltage across the two red leads and it was 596 volts.Measured from either red lead to a single red-yellow stripped wire(which I believe is the tap)is 295 volts.So I believed it to be a 596-295-596.Was my thinking correct?I picked this transformer because of physical size and seems to be closest to the voltages I need of all the transformers I have on hand. Tnx,Stan
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AB2MA
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« Reply #3 on: February 28, 2008, 12:11:01 PM »

Just a correction,I believe it to be 596-0-596 not 596-295-596.Stan
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KA5N
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« Reply #4 on: February 28, 2008, 12:31:06 PM »

The red leads are the start and end of the winding and the red/yellow lead is the center tap so it is  295-0-295 and would supply only about 68% of the required voltage.  The AT-1 would probably function after a fashion but the power output would be less than normal and some circuit changes might be necessary to get the 6AG7 to oscillate properly.
Need to keep looking.
Good Luck
Allen
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AB2MA
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« Reply #5 on: February 29, 2008, 06:11:30 AM »

Thanks Allen,I'll keep looking.If I do find a tranformer with more than 430v will it hurt?Would I have to increase voltage ratings on some components?Stan
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KA5N
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« Reply #6 on: February 29, 2008, 09:00:07 AM »

Hi Stan,
If you find a transformer that is like 20-30 more volts it should be fine.  You can also add a small filter choke (choke input) which will reduce the rectified voltage a bit if necessary.  A transformer with 400-0-400 up to about 475-0-475 should be workable. The current rating should be about 150 ma.  You can find new transformers (Radio Daze for example) which may work, but they come with a healthy price tag and you have to be careful that the dimensions are close enough to fit.
Hope you get this Heathkit back in operation.  I still remember when they came out back when I was a teenager.
73 Allen
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W5KCM
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« Reply #7 on: May 08, 2008, 06:01:52 PM »

Hi Stan, just thought I would throw in my 2 cents worth. I picked up an AT-1 at a local hamfest. It was mostly in parts in a cardboard box. It was missing a bunch of parts including the main power transformer. I put out an appeal on QTH.com looking for AT-1 parts. I got several good responses. A fellow in Kentucky had a now old stock transformer type Merit Coil and Transformer model P-2954. It has 375-375 center tapped HV secondary @ 150ma, 5 VAC @3 A & 6.3 VAC CT @5 A. The HV winding was a little low for the AT-1 but it works well. The only thing is that I had to fabricate some small brackets for the mounting. It is a different style of mounting type transformer. I finally finished my AT-1 project about a month ago and have been making some contacts with it on 80 meters CW (lots of fun). I have some photos of my AT-1 project on my Yahoo Flicker site. Here is a link to this site if you want to take a look.
http://www.flickr.com/photos/wb5kcm/sets/72157603797664318/
Let me know how your project is going.
73, Randy, W5KCM
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AB2MA
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« Reply #8 on: May 09, 2008, 06:37:10 AM »

Nice AT-1 Randy.I found a transformer at QTH.COM also,(thanks W1GEE)and put the AT-1 together.I've been having alot of fun with it.Thinking of trying to modulate it now.Two questions if you don't mind,1)what paint did you use for the cabinet and 2)did you find a place too copper coat the chassis? Tnx,Stan WB3EIM
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W5KCM
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« Reply #9 on: May 16, 2008, 07:19:58 PM »

Hi Stan, sorry about the delay, I dont check this forum very often. What I did on the chassis was clean it real well with some steel wool. After that it still did not look too good, too much discoloration of the copper. I picked up some type of bright copper looking spray paint at Home Depot and painted the chassis with several coats. I really liked the way it came out. Some of the photos look more gold than copper color but it looks really like very bright copper. I really did not find the exact match for the cabinet so I picked up a can of hammered dark grey spray paint. Came out real nice but not original. If I can find the original color, I may go back and repaint the cabinet. This fellow is making vinyl overlays for the front panel.
http://www.hayseedhamfest.com/
As you can see my front panel has some extra holes that have been patched. I am going to put on one of his vinyl overlays on the front panel and then I will call it done. If you need more info on the pain let me know, the spray cans are out in my shed and I will get the exact color and brand on them if needed. Glad to hear yours is doing well. 73, Randy, W5KCM
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