Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 67polara on January 13, 2011, 11:07:23 pm

Title: Pin 1 on EL34/kt77 Grounded?
Post by: 67polara 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

Title: Re: Pin 1 on EL34/kt77 Grounded?
Post by: 67polara 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

Title: Re: Pin 1 on EL34/kt77 Grounded?
Post by: FYL 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...

Title: Re: Pin 1 on EL34/kt77 Grounded?
Post by: Fresh_Start 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

Title: Re: Pin 1 on EL34/kt77 Grounded?
Post by: 67polara 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

Title: Re: Pin 1 on EL34/kt77 Grounded?
Post by: FYL 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.