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Post subject: Re: red plating issue
Posted: Fri Oct 16, 2015 1:38 pm
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Quick update, just got another RCA 6V6GTA in the mail, ran over half hour, just fine, no sign of red plating what so ever, looks like it was the bad resistor, bad cap and a bad 6v6, amp is good to go, case closed.Image


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Post subject: Re: red plating issue
Posted: Fri Oct 16, 2015 1:45 pm
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Oct 13 you write ;
"ok, got the Champ back from the tech today, he said a bad resistor and a bad cap. caused by a faulty power tube, I'm guessing the gray glass RCA I took out, here is pic of bad parts "

That are the part you are talking today ?


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Post subject: Re: red plating issue
Posted: Fri Oct 16, 2015 2:06 pm
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stratele52 wrote:
Oct 13 you write ;
"ok, got the Champ back from the tech today, he said a bad resistor and a bad cap. caused by a faulty power tube, I'm guessing the gray glass RCA I took out, here is pic of bad parts "

That are the part you are talking today ?

Not sure I'm following you? but the tech replaced the bad resistor and cap last week, after I got home the RCA 6V6GTA started to redplate, I switched in the brand new Groovetube 6v6, no red plating, I purchased another RCA 6V6GTA, it arrived today, and works fine, no red plating.....So, the tech fixed the amp, by replacing a bad resistor and bad cap, but the 2 RCA'S were also bad, now replaced with a good RCA, amp is fixed, problem solved.


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Post subject: Re: red plating issue
Posted: Fri Oct 16, 2015 2:18 pm
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Ok I follow you , bad resistor and cap was replace oct the 13 , not today or yesterday .

I write few days ago that a red plating tube do not mean the tube is bad it could be the bias resistor with the wrong value.

Each time we put another tube we must check bias and adjust if needed . With same bias ( cathode resistor for your amp ) some tube can work " fine" some not .

IMO all yours tubes are good it is only a matter of bias .
No red plating do not mean bias is the good one , it is only mean tube do not work too hot to redplate. Your amp may not play at it best . You don't know if you do not check bias .

You play lotto with your news tubes


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Post subject: Re: red plating issue
Posted: Fri Oct 16, 2015 3:23 pm
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The Champ has a cathode-biased output tube, single-ended. No separate bias circuit , no need to adjust for new tubes.


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Post subject: Re: red plating issue
Posted: Fri Oct 16, 2015 3:57 pm
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my56strat wrote:
The Champ has a cathode-biased output tube, single-ended. No separate bias circuit , no need to adjust for new tubes.



Sorry you are wrong , proof your need to try few tubes . With the right cathode resistor no more red plating

Cathode bias are less sensitive to new tube but need bias check


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Post subject: Re: red plating issue
Posted: Mon Oct 19, 2015 12:16 pm
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Don't forget outlet voltage can come into play with vintage amps too. Voltage way back was anywhere from 110 to 117 volts. Now it can be around 120-125 or so. My wall voltage is around 122v. That's why checking voltages is so important in a cathode biased amp. Scared me a little when I was reading voltages in my Marshall 18 watt clone. They were a little high but under 10%.

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