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Heathkit C3 Condenser Checker Restoration and Parts Recommendations
Heathkit C3 Condenser Checker Restoration and Parts Recommendations
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Old 14th June 2018, 06:34 PM   #1
spaceistheplace is offline spaceistheplace
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Heathkit C3 Condenser Checker Restoration and Parts Recommendations
Default Heathkit C3 Condenser Checker Restoration and Parts Recommendations

Grabbed this for next to nothing in perfect cosmetic condition and figured it an interesting enough piece to attempt to restore as a learning exercise.

The cord had been cut for reasons unknown. I figure with all those old caps in there it might be wise to do some replacements before powering it back up again.

So, I went through the manual and began putting together a parts list.

Edit: Uploaded the parts list as an attachment rather than in-post as it was rendering strangely.

However, couple of problems I ran into:

1. Heathkit's manual doesn't specify voltages on the caps. From what I gather some of the caps are substantially overrated for their purpose.

In the unit these are the voltage ratings on the caps:

.2uf - 2x .1uf 400V
.01uf - 400V
.05uf - 600V
2uf - 200V
.25uf - 500V

One part in particular that a replacement is proving difficult to find is the two 8uf 475V Mallory Polar Electrolytics. Can't seem to find a replacement except at 8uf 450V and wondering if that's sufficient.

2. Heathkit says 1/2W Carbon Comp unless otherwise specified, but unsure if let's say a 1/2W CMF55 replacements are adequate, given that carbon comps from what I gather had higher voltage ratings.

Would I be better upping the resistor values to 1W? Metal oxide seem to have better voltage ratings than the metal films.


3. Curious what you all would recommend for the pots as well.


Slowly I'm learning (life is full these days), but always want to proceed with caution when high voltages are involved.

Full manual can be found here.

As always, grateful for any guidance / suggestions.
Attached Images
File Type: jpg C3-1.jpg (171.5 KB, 48 views)
File Type: jpg C3-2.jpg (120.1 KB, 49 views)
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Old 14th June 2018, 09:01 PM   #2
Enzo is offline Enzo  United States
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First, odd things like 8uf caps were common 60 years ago, but not in recent decades. 10uf is just fine or even 22uf.

HAve you cleaned the pots?

The 0.05uf is from mains to chassis. I'd remove it and install a three wire grounded power cord myself.

I have no reason to second guess their voltage ratings. In my shop I'd be reaching for 630v film caps anyway.

I wouldn't sweat resistors, metal films would work just fine. If 1 watt makes you comfortable, the difference is just a few cents.

I have a similar Eico 950B I built some 55 years ago, I dearly love it, and it has seen use all these years. I recently passed it down to a younger tech who rebuilt it as you are doing, and it now sits on his bench.

You have found a really great old piece of gear that is useful as well. Many DMMs these days measure capacitance, but in repair work I am way more concerned with leakage, and these old testers will put actual voltage on the caps.
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Old 15th June 2018, 06:56 PM   #3
PRR is offline PRR  United States
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Manual and restorer-notes can be downloaded:
Heathkit C 3 Condenser Checker (manual) : Free Download, Borrow, and Streaming : Internet Archive

As the notes say, it begs for 3-pin conversion for user safety.

The 8uFd shown with 410V "could" get 466V on start-up. This assumes the 500V AC peaks at 707V DC, and the 47K vs 22K-string splits 1/3 to 2/3. Obviously when all is warm this cap should be nearer 410V. Even allowing higher wall-voltage today, I'd use a 450V if handy, though 500V is commonly available in guitar-amp parts. The 8uFd is not critical, use 10uFd, or even 4.7u or 22u if you have a heap. The two "8uFd" should probably be nominally the same, though wide mis-match won't do any harm.

I'm not following all the DC/AC relationships. Up to 0.05 (0.047), I'd use 400V rating. Having gone that far, it would only be a few bucks to do 600V throughout the film caps.

The 2uFd is noted "precision". It should be more accurate than you want to measure to. They probably gave you a 5% cap and claimed 10% on the whole thing. While you can buy better caps now, you can VERY cleaply buy digital meters of better precision. So I would treat this as a nostalgic folly and Good Working Tool, not any kind of micrometer theodolite chronometer. Buy a couple 2% 1uFd 600V caps and go for it.

Last edited by PRR; 15th June 2018 at 07:04 PM.
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Old 15th June 2018, 09:43 PM   #4
Enzo is offline Enzo  United States
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Yeah, accuracy is only relative. The measurement is made visually nulling the magic eye tube and looking at the knob pointing to the printed scale. 5% would be lucky.
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Old 16th June 2018, 04:30 AM   #5
spaceistheplace is offline spaceistheplace
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Heathkit C3 Condenser Checker Restoration and Parts Recommendations
Yes I was not concerned as much with accuracy as voltage ratings on the caps and resistors.

As has been said this is more a curiosity and an interesting project. Iím not expecting to come out the other end with a piece of Keysight kit.
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Old 16th June 2018, 06:40 AM   #6
spaceistheplace is offline spaceistheplace
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Heathkit C3 Condenser Checker Restoration and Parts Recommendations
Quote:
Originally Posted by PRR View Post
Manual and restorer-notes can be downloaded:
Heathkit C 3 Condenser Checker (manual) : Free Download, Borrow, and Streaming : Internet Archive

As the notes say, it begs for 3-pin conversion for user safety.

Thanks those restorer notes will come in quite handy. Lots of useful tidbits.

I will of course update to a grounded IEC.
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