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Old 16th March 2006, 09:56 PM   #1
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Default Just acquired HEATHKIT W4-AM-*picture*

Link and pic of amp here:

http://www.heathkit-museum.com/hifi/w4-am.shtml

First, I'd like to hear opinions if you know about this amp.
This amp is in great shape but when I fired it up, the fuse blew.

I was told that replacing the caps would probably cure the amp completely. The problem is that I don't what caps it uses!

Has anyone else gone through this maintenance that ca offer advice/parts list?

Thanks,
Dominick

PS-Its my first tube and I cant wait
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Old 16th March 2006, 10:15 PM   #2
Trout is offline Trout  United States
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I Had one of those for a bit, For sure you will need to replace that Can Style Multisection eyectrolytic. Even if it tested marginally, It can and will be a problem down the road.

AES is a fair source for those metal can caps in many cases they are exact matches. though not especially cheap. Mallory FP Style Can Caps

Instantly blowing a fuse might be something more serious though. Bad Rect Tube, Shorted transformer and on and on. Mine had a bad can cap and a blown resistor.

Trout
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Old 16th March 2006, 10:25 PM   #3
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dominik22,

Here is a link to the schematic:

http://www.geocities.com/free_schema...schematic.html

Caps to be replaced:

- All electrolytics {power supply }
4 * 20 microF 450 Volts
2 * 20 microF 350 volts

Coupling caps to be replaced:

All...

Tubes:
All tubes 2 * 6SN7 - 2 * 5881 - 1 * 5Y4G

Resistors:
All cathode and Anode resistors ; plus verify all the others...

Good DIY.

Alain.
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Old 16th March 2006, 11:22 PM   #4
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Thanks for the help!

Dominick
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Old 8th April 2006, 08:30 AM   #5
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Default Same Problem

One of my Heath 44-AM amps started blowing fuses as well. I brought it to a shady shop in Toronto and they guy said the transformer was shorted. 2 questions;

1. How can I verify this with a multimeter
2. What options do I have for a replacement?

Cheers,
Noah
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Old 8th April 2006, 11:39 AM   #6
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If the fuse blows INSTANTLY, it's a shorted transformer or rectifier (probably socket). Shorted cap wouldn't blow fuse until the rectifier warms up.

Hammond makes replacement transformers - about $80 - or you can try for a used one if you want to keep the appearance original.
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Old 8th April 2006, 12:49 PM   #7
SY is offline SY  United States
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Terminatorx, disconnect all leads and check the primary and secondary coil resistances for dead shorts. The secondary should be checked from center tap to each end- the values should be within 15% of one another. Check resistance from each lead to the case- it should be open circuit. (an analog ohmmeter works best here)

Now CAREFULLY connect the primary to the AC line using a series fuse (or, what I use, a 60W light bulb). Load the secondary with a voltmeter. Apply power. If the fuse pops immediately (or the light bulb lights), you've got a bad tranny. If it doesn't and you get a high value of voltage (for this tranny, end to end will be something like 700V), the transformer is likely OK.

edit: This test exposes LETHAL voltages. If you have ANY doubts whatever about your abilities or experience, don't do it! Death is very permanent.
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Old 8th April 2006, 09:16 PM   #8
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Your edit came too late...Now I am dead! Thanks for the help!

Dominick
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Old 9th April 2006, 12:35 AM   #9
Sherman is offline Sherman  United States
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Don't join the club!

http://www.ibiblio.org/Dave/Dr-Fun/df9510/df951017.jpg
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Old 12th April 2006, 09:12 AM   #10
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Thanks for the info. 3 quick follow up questions;

1. Any idea where I can find an original tranformer, or a W4-AM for parts?

2. should I attempt to rewind the transoformer?

3. If I replace the transformer with a 3rd party unit, will I need to replace the transformer on the other mono-block to ensure they both sound the same?

Cheers,
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