Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joesatch on December 12, 2021, 07:35:55 pm
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I have seen two different variations of this and don't know which one to implement (using EL34 or KT77). What are the differences here?
(https://i.ibb.co/SKb6CzH/1-ohm.png)
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I can’t see where pin 1 goes to in the 2nd image, but I will assume to ground. In which case these are functionally the same. Tying pins 8 and 1 together, and to ground. I imagine someone would do #2 scenario if they had a long run to a power amp ground further away. Allows you to neatly tuck the 1 ohm resistor on the socket and do a long wire run to a different ground point.
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yes the black runs to ground. so i guess there is no difference in running the resistor between pin 1 and 8 vs running it off one of the pins with pin 1 and 8 tied together?
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Joe
Can be done either way depends on the circumstances.
Have a look at Hoffman AB763_2 (https://el34world.com/Hoffman/files/Hoffman_AB763_2.pdf)
With the Long (turret) board, the 1R are placed "onboard" and wired as indicated
However with the Short board, the option is a suitable earth point, eg fit 1R from pin 8 to lug on Octal socket.
Regards
Mirek
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i've gone with the second option. seems like a more solid ground than depending on the resistor lead
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The best way to do it
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The best way to do it
That kinda implies using the chassis as a conductor for circuit 0V, so not really, but each to their own :icon_biggrin:
However, in the case of EL34, it’s inappropriate; note that pin1 is assigned to g3.
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The best way to do it
That kinda implies using the chassis as a conductor for circuit 0V, so not really, but each to their own
Chassis or ground or common......name it .
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The best way to do it
Chassis or ground or common......name it .
You're ignoring the only point of the original question was the connection from Pin 8 (cathode) to Pin 1 (Suppressor Grid) for EL34.
Your diagram shows Pin 1 being used as a mounting point for the screen resistor, which then runs to Pin 4 and has high positive voltage present on Pin 1. That's a complete non-starter for EL34.
There are also times where the amp manufacturer does not use the chassis for ground connection/circuit common, and adding circuit common connections to the chassis will create a ground loop and hum (old Ampeg amps are notorious for this).
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All of these are easy to mods.
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‘Easy to’ mods are still easy to feck up :icon_biggrin:
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Still confusion about this. Normally the ground pin is Pin 8. Running this 1 ohm resistor like this is bypassing that ground how should this be wired?
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#1 is correct. #2 does nothing.
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fabulous. i dont have to unsolder anything. :l2:
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fabulous. i dont have to unsolder anything. :l2:
Of course my reply depends on my assumption that the black wire on pin 1 is connected to ground.
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indeed :icon_biggrin:
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The idea is to put the 1 ohm resistor between the cathode and ground (in a fixed bias amp). The other pin is just being used as a support for the resistor. I just run a wire off pin 8 to some banana plugs and hang the resistor between them, see the photo.