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H/K 430 Twin Receiver refurb

post #1 of 4
Thread Starter 

Ive had a 1975 Harmon/Kardon 430 Twin receiver that was handed down from my dad for about 5 years now. I plan on keeping it, as Its got alot of sentimental value,  and being an extremely solid and good quality receiver. A few problems I need help with though:

 

* As its 40+ Years old, alot of the components, Im sure are worn.

 

- Ive managed to find the properly rated Fuse Lamps for the 5-6 dead Lamps on the front tuning/indicator panel(250mv 6V), so thats all set

- Ive also managed to find the properly rated LED to replace the dying on inside the tuning needle, I can simply solder a new one on.

 

What I really need help with is:

 

- Im not sure where to take it to have it looked at to see if any of the Internal components could use replacing/repairing, I don't want to spend a fortune right now. But If I could make it last another 10+ Years, I might.

 

If anyones experienced with Old school A/V or Audio equipment could give some advice, or anyone for that matter, it'd be great.

post #2 of 4
If everything functions properly you can probably just leave it alone. The first thing you replace on something like this is ALL of the electrolytic capacitors. They dry out and become basically absent from the circuit, causing AC line hum at the least and transistor damage at the worst.

Most of the time if the equipment wasn't mistreated and it's just old, that will be all that's wrong. The next most common thing is output transistors.

Don't know where you could take it and trust the technician, everybody thinks they're an expert but rarely do they actually know what they're doing.




source: I mess with a lot of HI-FI stuff and I'm an electrical engineer by trade
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post #3 of 4
Thread Starter 
Quote:
Originally Posted by Dieselbird View Post

If everything functions properly you can probably just leave it alone. The first thing you replace on something like this is ALL of the electrolytic capacitors. They dry out and become basically absent from the circuit, causing AC line hum at the least and transistor damage at the worst.

Most of the time if the equipment wasn't mistreated and it's just old, that will be all that's wrong. The next most common thing is output transistors.

Don't know where you could take it and trust the technician, everybody thinks they're an expert but rarely do they actually know what they're doing.




source: I mess with a lot of HI-FI stuff and I'm an electrical engineer by trade

Yea, its got some obvious Ground Loop hum. I Know somebody with alot of experience soldering Through-hole components and Desolder SMD IC's/Components, do you think If I checked all the ratings on the caps and bought replacements, it would be a good idea to get him to desolder the old ones and replace them?

post #4 of 4
It's a good place to start.

The hum is normally caused by dried out power supply caps not filling in the gaps between the 60Hz peaks created by the transformer and rectifier section. Super common.

Remember, You can get caps with a higher voltage rating if necessary, but no lower. Same goes with capacitance, A bit higher ain't gonna hurt but you can get exact if you think the engineers were perfect haha.

I'd recommend digikey for buying them as their search is really good for entering multiple criteria.

Another important thing is that since technology has come a looooong way, capacitors with the same ratings are much smaller these days, so you don't care how tall they are but the lead spacing needs to match so they go into the holes properly and the thing sits nice where it belongs.

There was a wicked good article on what you're doing in a magazine called "nuts and volts" in the july 2015 edition where a guy fixed up an H-K A-401. I can't find it free online maybe you can
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