Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Curranm on April 11, 2022, 09:03:19 am

Title: hoffman switching and DC board grounding question (AGAIN)
Post by: Curranm on April 11, 2022, 09:03:19 am

I want to use up the last of my Hoffman boards which take the AC heaters and rectify them to 5vDC for relay switching. I had great success with adding a transistor an RAC03-05SK 120vAC to 5vDC converter in another amp for foot-switching between channels. SO the Hoffman board use a "floating" ground. me heaters are CT to ground. can I implement this transistor setup with the "floating" ground system of the Hoffman board?

Title: Re: hoffman switching and DC board grounding question (AGAIN)
Post by: sluckey on April 11, 2022, 09:26:29 am

Sure. But do not connect any part of your circuit to chassis ground.

Title: Re: hoffman switching and DC board grounding question (AGAIN)
Post by: acheld on April 11, 2022, 09:55:51 am

Sorry if this is off topic, but I'm curious what transistor does for you in this circuit? 

I've been looking at the Dumble switching circuits recently, and they are bone simple, with a switch turning power "on" or "off" at the relay -- ie, no transistor in switching circuit.

Title: Re: hoffman switching and DC board grounding question (AGAIN)
Post by: Curranm on April 11, 2022, 10:23:36 am

thank you got the info! and yes NOTHING goes to chassis with this part of the circuit! I did that on my 1st hoffman board! the smoke was MAJIK and MAJESTIK............

as far as the transistor it SHOULD be a 2N3906 NPN. I have it marked as a 2N3904 which is wrong

Title: Re: hoffman switching and DC board grounding question (AGAIN)
Post by: sluckey on April 11, 2022, 11:03:11 am

Quote from: acheld on April 11, 2022, 09:55:51 am

Sorry if this is off topic, but I'm curious what transistor does for you in this circuit? 

It's a switch. With SW1 open the transistor is turned on and the relay is energized. With SW1 closed the transistor is turned off and the relay is de-energized.

Title: Re: hoffman switching and DC board grounding question (AGAIN)
Post by: PRR on April 11, 2022, 12:16:17 pm

>> Sorry if this is off topic, but I'm curious what transistor does for you in this circuit?
> It's a switch. With SW1 open the transistor is turned on and the relay is energized.

I think he wonders: what is the advantage over a no-transistor connection?

Title: Re: hoffman switching and DC board grounding question (AGAIN)
Post by: thetragichero on April 11, 2022, 08:35:53 pm

Quote from: Curranm on April 11, 2022, 10:23:36 am

as far as the transistor it SHOULD be a 2N3906 NPN. I have it marked as a 2N3904 which is wrong

2n3906 is silicon pnp (the complementary pnp to 2n3904). not meaning to stir up an argument, just making sure whoever finds this on google isn't led astray (also want to add to my knowledge since i have yet to make a channel switcher): what transistor are you using? if it is pnp the schematic isn't quite right