Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Rubrburnr on September 21, 2015, 08:43:41 pm

Title: 5E3 Pilot Lamp Grounding Q
Post by: Rubrburnr on September 21, 2015, 08:43:41 pm
Hey, just a quick question regarding the pilot lamp grounding.  Both the schematic and the layout say to ground the pilot lamp with two 100ohm resistors.  The hookup sheet says to connect them to the turret board.  My problem is that I don't see the 100 resistors on the board anywhere, I have 100k but not 100, nor did the kit come with it nor is it on the order form.  I looked elsewhere online and some of them don't get grounded at all.  Would this be the case here?

Thanks!
Title: Re: 5E3 Pilot Lamp Grounding Q
Post by: sluckey on September 21, 2015, 09:11:02 pm
Did your 5E3 board come from Hoffman? If so, those 100Ω resistors are not on the board. There are several common ways to install those 100Ω resistors. You may find them on the pilot lamp assembly, or on the board, or on the tube sockets. They are all electrically connected between the filament windings and ground. This gives the filaments a ground reference which reduces filament hum.

But you may not need them at all. If your PT filament winding has a center tap lead (usually, but not always, a green/yellow wire) just connect that lead to chassis. If your PT does not have a center tapped filament winding, then you need to procure two 100Ω resistors and install them.
Title: Re: 5E3 Pilot Lamp Grounding Q
Post by: Rubrburnr on September 21, 2015, 09:41:01 pm
Quote from: sluckey on September 21, 2015, 09:11:02 pm
Did your 5E3 board come from Hoffman? If so, those 100Ω resistors are not on the board. There are several common ways to install those 100Ω resistors. You may find them on the pilot lamp assembly, or on the board, or on the tube sockets. They are all electrically connected between the filament windings and ground. This gives the filaments a ground reference which reduces filament hum.

But you may not need them at all. If your PT filament winding has a center tap lead (usually, but not always, a green/yellow wire) just connect that lead to chassis. If your PT does not have a center tapped filament winding, then you need to procure two 100Ω resistors and install them.

Sure did.  Everything came from Hoffman, no upgrades or changes just straight off the website.  I just checked to PT, no green/yellow wire, both filament wires were solid green. 

Procuring 1/2 watt 100Ω resistors now... 

Thanks for the response!  Can't wait to get this this up and running!!
Title: Re: 5E3 Pilot Lamp Grounding Q
Post by: EL34 on September 22, 2015, 07:22:17 am
I updated the instructions page to show some pics of the different ways to run the 100 ohm center tap resistors

http://el34world.com/Hoffman/instructions.htm (http://el34world.com/Hoffman/instructions.htm)
Title: Re: 5E3 Pilot Lamp Grounding Q
Post by: Rubrburnr on September 22, 2015, 07:58:33 pm
Quote from: EL34 on September 22, 2015, 07:22:17 am
I updated the instructions page to show some pics of the different ways to run the 100 ohm center tap resistors

http://el34world.com/Hoffman/instructions.htm (http://el34world.com/Hoffman/instructions.htm)

Bingo!  Exactly how I was going to do it!  Thanks EL34!!
Title: Re: 5E3 Pilot Lamp Grounding Q
Post by: HotBluePlates on September 29, 2015, 01:16:04 pm
Quote from: drgonzonm on September 25, 2015, 02:11:11 pm
Is the ohmage on the resistors hard and fast?

Not really. It should be reasonably low.