[Drake] Electrolytic Caps inside TR-4C?

[Glen Zook]

"Modern" capacitors don't follow the "olde tyme" values.  They now follow the "tolerance" values just like resistors.  For example, a 20 mfd capacitor is now a 22 mfd capacitor, a 30 mfd capacitor is now 33 mfd, a 40 mfd or 50 mfd capacitor is now 47 mfd, and so forth.  However, the "modern" capacitors are going to be a lot closer to value than the "olde tyme" capacitors.  The old capacitors generally had a tolerance of -50/+80 percent whereas the "modern" capacitors are generally either +/- 20 percent or +/- 10 percent.

For example, the original 20 mfd capacitor could range from 10 mfd to 36 mfd and still be in tolerance.  A "new" 22 mfd capacitor (at 20 percent tolerance) can be between 17.6 mfd and 26.4 mfd which are MUCH closer to the design values than the "olde tyme" capacitors.

Glen, K9STH

Website:  http://k9sth.com


--- On Sat, 1/9/10, David Walker <vk2na at bigpond.com> wrote:

> From: David Walker <vk2na at bigpond.com>
> Subject: [Drake] Electrolytic Caps inside TR-4C?
> To: drake at mailman.qth.net
> Date: Saturday, January 9, 2010, 2:42 PM
> Many many thanks to all that have
> responded.  It has been extremely 
> helpful and confidence building. 
> 
> I replaced the caps by reposting new ones to the various
> wires.  
> Needless to say I used plenty of heath shrink over exposed
> cap legs and 
> connections to ensure nothing shorted to earth. 
> 
> However, I was not happy about the appearance no matter how
> neat I tried 
> to be about it, and when I did the smoke test the hum in
> the audio was 
> still present.  But the audio quality was a little
> improved and more 
> full bodied than before.
> 
> So I ripped it all out and returned it to orginal for
> now.  I have the 
> AC4R from the heathkitshop arriving soon and I will install
> that and 
> then work back from there.  I notice 4 section cap
> cans for sale ie 
> hayseed, and I will do that. 
> 
> I can't rebuild it myself as the caps from my supplier -
> for instance 
> they are large and I had to paired 2x10uF to get the 20uF
> value etc.. so 
> I am a bit compromised at this stage. 
> 
> I figure a few bucks for a new 4 section cap would be worth
> it.
> 
> Regards,
> 
> Dave.
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