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previous: Bruce I find that hard to believe unless ... -- 7/30/2000 7:25 PM

Re: 448VDC on the plate of a 6V6 (using a 6X5 rectifier tube)

7/30/2000 9:06 PM
DanF	Re: 448VDC on the plate of a 6V6 (using a 6X5 rectifier tube) GW / Bruce – The voltages were surprisingly high - but here’s what I did since I posted the question: I replaced the 6V6 with a NOS, borrowed a Variac to cautiously start up at lower voltages, and now think that the really-high plate voltage on the 6V6 was caused by a bad 6V6. But the voltages still seem somewhat high. Here are the values I’m now getting: 6V6 plate 6v6 cathode Between plate Variac to ground to ground and cathode -------------------------------------------------------- 110 VAC 349 VDC 14 VDC 342 VDC 115 VAC 367 VDC 15 VDC 358 VDC 121 VAC 370 VDC 16 VDC 359 VDC I’m assuming these voltages are still a little high at 121VAC, my typical wall outlet voltage – here are two basic questions: 1) When discussing plate voltages (in discussions on this board, or in the RCA tube manual, for example) are the "max" and "typical" plate voltages, or recommended voltages referring to plate-to-ground, or plate-to-cathode? 2) The cathode resistor on the 6V6 drifted from it’s nominal value of 270 ohms to 312 ohms. Will this drift increase or decrease the voltage "seen" by the plate (plate voltage minus cathode voltage)? Is there a way to calculate by how much? Maybe I should replace this resistor. Thanks, as usual – DanF (excuse any cross-postings)

7/30/2000 9:06 PM

DanF

Re: 448VDC on the plate of a 6V6 (using a 6X5 rectifier tube)

GW / Bruce – The voltages were surprisingly high - but here’s what I did since I posted the question:

I replaced the 6V6 with a NOS, borrowed a Variac to cautiously start up at lower voltages, and now think that the really-high plate voltage on the 6V6 was caused by a bad 6V6. But the voltages still seem somewhat high. Here are the values I’m now getting:

 
             6V6 plate      6v6 cathode    Between plate
 
Variac      to ground      to ground      and cathode
 
--------------------------------------------------------
 
110 VAC      349 VDC        14 VDC          342 VDC
 

 
115 VAC      367 VDC        15 VDC          358 VDC
 

 
121 VAC      370 VDC        16 VDC          359 VDC

I’m assuming these voltages are still a little high at 121VAC, my typical wall outlet voltage – here are two basic questions:

1) When discussing plate voltages (in discussions on this board, or in the RCA tube manual, for example) are the "max" and "typical" plate voltages, or recommended voltages referring to plate-to-ground, or plate-to-cathode?

2) The cathode resistor on the 6V6 drifted from it’s nominal value of 270 ohms to 312 ohms. Will this drift increase or decrease the voltage "seen" by the plate (plate voltage minus cathode voltage)? Is there a way to calculate by how much? Maybe I should replace this resistor.

Thanks, as usual – DanF

(excuse any cross-postings)

Replies:

Cole The voltages seem kind of high - wi... -- 7/30/2000 10:07 PM
Bruce Assuming that you also just don't h... -- 8/2/2000 4:55 AM