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Old 20th December 2009, 02:53 AM   #1
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Default hafler psu caps

Anybody know how to determine the relative "goodness" of the original Hafler 10K caps or must we assume they need replacement.
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Old 20th December 2009, 03:20 AM   #2
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how old is the amp?

dave
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Old 20th December 2009, 03:53 AM   #3
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when in doubt change em out
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Old 20th December 2009, 02:19 PM   #4
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Quote:
Originally Posted by planet10 View Post
how old is the amp?

dave
Not sure. It's a dh-200. The manual was copyrighted in 1980. I got several of these from ebay for my HT. They seem to work OK. When I hang the scope on the caps I see a pretty typical sawtooth. It would be nice to have a simple go/no go test.
Dennis
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Old 20th December 2009, 06:05 PM   #5
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Well, they are at least 20 to 30 years old.

Go ahead and replace them. While you are at it, here are some fairly inexpensive upgrades for a DH200.
1. Attach some thermistors on the Power supply (the start up is hard on the Hafler switch)
2. fabricate a heavier bus on the PS caps (rather than the small wire that is currently there).
3. Attach (parallel) small bypass caps on the PS caps.

These are all documented on this forum - do a search.

If you are more adventurous, then,
4. there a few other caps that can be upgraded and bypassed. Again, search the threads. Also check the bias and re-set to factory specs.

These are fairly simple and will clean up the bass a bit (#3) and make the mids a bit clearer (#4).

My suggestions are quite affordable.
Good luck.
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Old 20th December 2009, 07:52 PM   #6
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wich capacitors recommend for an upgrade like that?
wich brand, model?
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Old 20th December 2009, 09:24 PM   #7
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Some how I knew replacement would be the consensus. For those who might be interested, I found a guy on ebay selling 18K Hafler replacement caps for $50 a pair. I found a capacitor upgrade kit for the pc board as well. Just search Hafler in electronics. Thanks for the other tips. I will look them up.
Dennis
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Old 21st December 2009, 01:19 AM   #8
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The DH-200 was out of production no later than the 3rd quarter of 1982.
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Old 21st December 2009, 03:11 AM   #9
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Sounds like your main power supply caps are still usable; determining the quality of the smaller decoupling caps is a little harder. In my experience, these fail at least as often as the big caps, depending on the temperatures they were exposed to. At this point, I'd buy up a supply of suitable caps (including bipolar caps for the feedback network and any input coupling) and replace them at your leisure, saving the big caps for last and follow some of the upgrading procedures recommended here.

After that, if you're still motivated, the resistors are probably good candidates for replacement; they were probably carbon film and maybe some composition. Quality metal films might be installed in the feedback network and that's what I'd recommend for the rest of the amplifier, starting with the input section.
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