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Hoffman Amps Forum image Author Topic: Pin 1 on EL34/kt77 Grounded?  (Read 5021 times)

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Offline 67polara

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Pin 1 on EL34/kt77 Grounded?
« on: January 13, 2011, 11:07:23 pm »
I was just reading someone's post on screen and grid resistors and Just realized I did not ground pin one Of my finals.  What will this cause as far as sound issues?  I did not know about the pin 1 and when I built my TOS I did not ground it.  It works ok I think???

Tony

Offline 67polara

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Re: Pin 1 on EL34/kt77 Grounded?
« Reply #1 on: January 13, 2011, 11:10:34 pm »
Wait pin 1 on a KT77 isn't hooked to anything.  Guess I don't have a problem only if I use EL34's right?

Tony

Offline FYL

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Re: Pin 1 on EL34/kt77 Grounded?
« Reply #2 on: January 14, 2011, 05:37:30 am »
KT77: 1 is NC (not connected)
EL34: 1 is G3 (suppressor grid). Should be grounded or cathode-connected in most amps.

Your amp should be fine with KT77s, no issues. Making it EL34 friendly is easy...




Offline Fresh_Start

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Re: Pin 1 on EL34/kt77 Grounded?
« Reply #3 on: January 14, 2011, 01:31:20 pm »
The real fun begins if you use pin #1 as a tie point for either the screen grid resistor or control grid stopper the way Fender did and then try using an EL-34.  NOT a good plan...

Chip
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Offline 67polara

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Re: Pin 1 on EL34/kt77 Grounded?
« Reply #4 on: January 14, 2011, 06:27:29 pm »
OK, clear this up for me since it is cathode biased to connect to cathode or ground?

Tony

Offline FYL

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Re: Pin 1 on EL34/kt77 Grounded?
« Reply #5 on: January 14, 2011, 06:39:45 pm »
Quote
OK, clear this up for me since it is cathode biased to connect to cathode or ground?

Cathode, so G3 will see the same potential.


 


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