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 Post subject: Heathkit T-3 health check
PostPosted: Jul Thu 11, 2019 2:26 am 
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Joined: Mar Sun 25, 2018 10:50 pm
Posts: 190
Location: 07960
I have a T-3 that I recently tried powering up through my dim bulb tester. At first the 40W bulb dimmed, but then a few seconds later it started to glow increasingly bright, so I cut the power. Would it be a safe assumption that there's a shorted cap somewhere and I should just do a recap before powering up again?


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 Post subject: Re: Heathkit T-3 health check
PostPosted: Jul Thu 11, 2019 2:58 am 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8748
Location: Long Island
You may only be seeing the normal increase in current as the tubes warm up and start drawing current.

Without knowing the history of the unit it is hard to say what to do next. Unless you know that it was working and in use recently, you have to open it up and inspect it. Do the parts look original, or very old? Then it’s very likely the paper and electrolytic capacitors are bad and should be replaced before further attempts at powering up are made. But don’t stop there. This was a kit so you cannot just assume it was ever right to begin with. Try to find a copy of the manual and make sure it is wired as it should be, correct parts and tubes in the right places, no wiring mistakes, and no mods or hacks by previous owners. These are great signal tracers and it is well worth the time to make sure yours is 100% right.

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 Post subject: Re: Heathkit T-3 health check
PostPosted: Jul Thu 11, 2019 4:05 am 
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Joined: Feb Fri 22, 2008 3:28 am
Posts: 470
I had an IG-72 Heathkit audio generator that hadn't been used for some time. I powered it up and it seemed to work OK, for a few minutes that is. The transformer failed on the high voltage winding, and got super hot fast. You might try your dim bulb test with the rectifier tube removed to see if there might be a transformer issue.


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 Post subject: Re: Heathkit T-3 health check
PostPosted: Jul Fri 12, 2019 12:31 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11698
Location: Powell River BC Canada
The T-3 has an interesting wiring layout.

Don't try this unless you understand the circuit.

Tape up the power cord plug.




Power the T-3 from your dim bulb tester, to the
wattmeter load outlet on the front panel.

If all is well, after the dim bulb load is shunted out,
you can use the T-3 wattmeter, to measure it's
power consumption.
Attachment:
Heath T3 partial.JPG
Heath T3 partial.JPG [ 130.54 KiB | Viewed 265 times ]
Attachment:
Heath T 3 Wattmeter loop back.jpg
Heath T 3 Wattmeter loop back.jpg [ 160.16 KiB | Viewed 254 times ]
Attachment:
Heath T 3 Wattmeter loop back Tape up the power cord plug.jpg
Heath T 3 Wattmeter loop back Tape up the power cord plug.jpg [ 198.55 KiB | Viewed 251 times ]

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de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
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 Post subject: Re: Heathkit T-3 health check
PostPosted: Jul Fri 12, 2019 2:25 am 
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Joined: Mar Sun 25, 2018 10:50 pm
Posts: 190
Location: 07960
Thanks Chris108, CurtisL, and radiotechnician. Since this T-3 does look untouched since it was originally assembled and I know nothing of its provenance, I'm leaning toward going ahead with a recap and inspection of all the connections. I would, however, like to confirm that the transformer is ok before digging in. I've read recommendations like that of CurtisL to pull just the rectifier tube and power up with the DBT, but then I've also read folks saying that you should pull all of the tubes to remove the filament loads.


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 Post subject: Re: Heathkit T-3 health check
PostPosted: Jul Fri 12, 2019 4:06 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11698
Location: Powell River BC Canada
My T-3 draws a bit less that it should.

About 50 years ago, the 6X5 burned out, and I replaced it with two diodes.

Money was tight then.

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de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Heathkit T-3 health check
PostPosted: Jul Fri 12, 2019 10:18 pm 
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Joined: Feb Fri 22, 2008 3:28 am
Posts: 470
Pulling all the tubes before any DBT is a good idea. I just noticed the rectifier was a 6X5; I've heard stories of those damaging transformers due to shorts. Most of my Heathkits use the 6X4 which I think is a bit more robust.


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 Post subject: Re: Heathkit T-3 health check
PostPosted: Jul Fri 12, 2019 10:34 pm 
Member

Joined: Sep Thu 23, 2010 6:37 am
Posts: 11698
Location: Powell River BC Canada
The 6X4 is more robust because it it more modern.

The T-3 is so ancient it used surplus WW2 tubes. They had to include a
procedure in their VTVM to overcome 6H6s with emissions that were so
different between the sides as to need an alternate wiring to get the
AC balance to work.

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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