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Post by mark4 on May 30, 2017 19:29:21 GMT -5
Since these capacitors are now very expensive to replace. And the 40uf X 3 @ 450V had 2 sections tied together. So you have one circuit operating @ 80uf and the other @ 40uf. Is it ok to use a 2 section 100uf @450v, or does inrush become a issue hurting the transformer.
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Sandbagger
Administrator/The Boss
Posts: 6,245
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Post by Sandbagger on May 30, 2017 20:06:58 GMT -5
Since these capacitors are now very expensive to replace. And the 40uf X 3 @ 450V had 2 sections tied together. So you have one circuit operating @ 80uf and the other @ 40uf. Is it ok to use a 2 section 100uf @450v, or does inrush become a issue hurting the transformer. I have never had an issue using capacitors with a higher uF rating. It provides even more filtering. Just make sure the voltage rating is adequate.
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Post by mark4 on May 30, 2017 21:13:08 GMT -5
I know Greg doesn't recommend it because of inrush when turning on the radio. It may be hard on the transformer. But in this case you already have 80uf. The other section more than doubles.
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Post by 2600 on May 30, 2017 22:52:39 GMT -5
We use a two-section part marketed for guitar amplifiers, 100uf per section at 500 Volts. They have been marketed under the names "LCR", "F&T" and "JJ". New Sensor Corp, Parts Express and CE Distributing sell them. Antique Electronics used to, as well. I get them from CE Distributing. We never have trouble making their minimum-order amount by the time we place an order. The 500-Volt rating is desirable because the 'cold' B+ voltage rises to 470 or more while the tubes are warming up. Once they come to life and draw current, it falls back to the normal 405-Volt range. 400 Volts is perfectly safe for a 450-Volt rated part, but 470 Volts not so much. Doesn't blow them up right away, since it lasts only 15 or 20 seconds at cold power-on. Haven't had anyone wear out one of the 500-Volt parts since we adopted them around 20 years ago. That 470-Volt 'surge' tends to reduce the life of a 450-Volt part. It comes in a cylindrical package, and requires a belly clamp to mount to the chassis. Good news is that the clamp's mounting-hole centers match the rivets that hold the original metal saddle that holds the twist-lock lugs. Drill out the two rivets, and the belly clamp takes two 6-32 screws and nuts. Lines up with the existing two holes just fine. A ground lug goes under the nut on one side to take the place of the twist-lock lug where the ground wires went on the original part. You need a wire from the cap's negative lug to this ground point. As for the 4-section cap, we place three 10 uf radial caps at the far end of the wire on each of those lugs from the original part. The fourth lug of the 4-section cap supports two wirewound resistors, so we solder the foot of a one-lug tie strip to the 4-section cap's saddle. It supports the fourth 10uf radial cap and the two resistors. Surge current is a proper thing to consider, but the original cap has two sections in parallel, so it's functionally a 80uf cap. 100uf is not a big jump up from there. The remaining section of the cap has 100 ohms between it and the rectifiers. This effectively reduces the ripple-current hazard for that section, even when boosted to 100uf. But that's how we have been doing it since the 4-section cap went past 40 bucks. While we're on the subject, this is our cure for the 'rare' 3-prong power cord. Every office supply sells this cord. The Greenlee hole punch for that socket wasn't cheap. But the labor it saves has paid for it. 73
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Post by BBB on May 31, 2017 9:25:48 GMT -5
Nice mods! I've used the 500V JJ brand Multi-caps for some time now without any failures. The price is right. As mentioned above, make sure you order the matching sized capacitor holder clamp along with the cap. They normally do not come with. Simply look at the capacitor diameter specs and get a matching diameter clamp. Thank you Guitar and Bass player dudes...
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Post by mark4 on May 31, 2017 19:44:41 GMT -5
I ordered the JJ brand and Richey Gold caps and clamps. You can also just mount the 3rd section underneath the chassis. I'm really picky about how a radio is restored. I just picked up this mint D201. The only problem is when they replaced the 40ufX3 they used a 40,40uf but forgot the third cap😳
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Post by mark4 on May 31, 2017 19:52:15 GMT -5
If I run out of power cords I planned on using the modern socket also. Speaking on this matter Tram seemed to have made a poor choice where to install the ground terminal on the chassis. I have found multiple loose ground terminals because the a plastic strain relief was installed on top of it. Then a nut. Not a good ground at all! I install another nut directly on top of the star terminal. And install safety bypass caps to ground on both sides and X2 across the line per a very respected tech.
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Post by 2600 on Jun 1, 2017 0:01:43 GMT -5
Using safety-rated capacitors on the power-line entry point is a big deal. The rules were a bit looser when Tram used this three-legged cap for that purpose. It does serve as a sort of demented surge limiter when lightning hits the pole behind your house. But it's a real shock hazard, especially in the older radio with the 2-wire cord. This is what's behind the IEC socket in the previous picture. Has all the approved parts inside it and does a more-effective job of RF-filtering to and from the power cord. They're pretty cheap if you watch for a deal on them. Oh, and yeah. The green chassis-ground wire on this filter is under a different power-transformer stud, not the one with the plastic clamp. 73
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Post by BBB on Jun 5, 2017 19:51:42 GMT -5
The EMI Filter is a very nice touch.
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Post by mark4 on Jun 6, 2017 21:24:03 GMT -5
i I used the Richey Gold Capacitors. Higher temp rating
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Post by brockdorf on Oct 5, 2018 13:59:34 GMT -5
We faced the same issue in our guitar. 400 Volts is perfectly safe for a 450-Volt rated part, but 470 Volts not so much. Doesn't blow them up right away, since it lasts only 15 or 20 seconds at cold power-on. Haven't had anyone wear out one of the 500-Volt parts since we adopted them around 20 years ago. That 470-Volt 'surge' tends to reduce the life of a 450-Volt part. assemblage PCB
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