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  #31  
Old 06-22-2018, 11:18 AM
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Man, that looks like factory condition to me. Good!
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  #32  
Old 06-29-2018, 07:35 PM
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Ok, so why did the 6GH8 suck so much, and how come if they sucked so much, did RCA and everyone keep using them?
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  #33  
Old 06-29-2018, 11:08 PM
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I don't know, but comparing schematic voltages and calculated plate dissipations to the GE spec sheet, It seems like the pentode section was pushed rather hard in some of the sockets.
The burst amp in the CTC-20 shows a plate voltage of 385 v, but the GE spec sheet says the max rating is 350.

In the CTC-12, the pentode section in the chroma oscillator appears to have a plate dissipation of 2 watts (spec max = 2.5w). In the few sockets I checked in the CTC-20 6GH8 "forest", it appears the plate dissipation was about 1.5w.

Not sure why the plate voltage and dissipation was designed to be so high, because, unlike a triode, a pentode's AC gain is mainly affected by plate current, not voltage.

I guess these tubes were just used too close to their design limits, but by using multitudes of them, the cost to the factory was probably reduced.
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  #34  
Old 07-08-2018, 09:55 AM
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On the 6GH8 subject, Last time I went to my local surplus store they had a bunch of em, mostly RCA. I noticed some of them were marked "Brazil" as the country of origin. I wonder if that is one of the factors in the reliability of this tube? Thankfully this set (CTC-21) only uses one 6GH8.
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