Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jeff on March 23, 2023, 07:04:26 am

Title: Trouble understanding Hoffman's relay schematic.
Post by: jeff on March 23, 2023, 07:04:26 am

I'm looking at https://el34world.com/projects/relay_switch.htm (https://el34world.com/projects/relay_switch.htm)
There is a bridge rectifier but the - is connected to the artificial center tap
The - of the cap is not connected to anything.
Two questions.
Should the cap's - be connected to the - of the bridge rectifier?
And if so, should that be disconnected from the two 100K artificial c.t.?


The - diodes are in parallel and 100k's.


Imagine no reference to ground for a sec
You have your 6.3V going to your heaters
You use a bridge rectifier to power the relays with D.C.
Now, you want to use the 100k's to reference to ground.... But do you connect the rectifier to ground too?
Or does it float?
The instructions say use an isolated jack, which would make sense IF the rect wasn't connected to ground.
Maybe split the cap into two caps, twice the uF in series, then connect the midpoint to the artificial c.t.???


Not sure I understand, I must be missing something.
Any help would be appreciated.
Thanks

Title: Re: Trouble understanding Hoffman's relay schematic.
Post by: sluckey on March 23, 2023, 08:19:50 am

This has come up before. That old schematic has errors! I wish Doug would fix it or remove it. The FWB negative side must connect to the cap negative lead and not to chassis ground. This is the negative side of the relay power supply. IT MUST NOT BE CONNECTED TO CHASSIS GROUND. IT MUST FLOAT.

Quote

Two questions.
There is a bridge rectifier but the - is connected to the artificial center tap   That's wrong
The - of the cap is not connected to anything.   That's wrong too
Two questions.
Should the cap's - be connected to the - of the bridge rectifier?   YES
And if so, should that be disconnected from the two 100K artificial c.t.?   YES

BTW, the resistors are 100 ohm, not 100K.

Title: Re: Trouble understanding Hoffman's relay schematic.
Post by: EL34 on March 23, 2023, 08:31:07 am

No one has told me about this
Give me a link to the exact thing that needs removed?

Title: Re: Trouble understanding Hoffman's relay schematic.
Post by: sluckey on March 23, 2023, 08:38:19 am

These three schematics all have the errors stated above and have caused this kind of confusion several times. 

(https://el34world.com/projects/images/relay3.png)

(https://el34world.com/projects/images/Relay1a.png)

(https://el34world.com/projects/images/Relay1b.png)

Title: Re: Trouble understanding Hoffman's relay schematic.
Post by: EL34 on March 23, 2023, 09:03:10 am

I don't really need those on the web site any more since getting the relay boards shown at the top of that page

I deleted that whole lower section on that page and left the upper are with the relay boards

Title: Re: Trouble understanding Hoffman's relay schematic.
Post by: JPK on March 23, 2023, 09:37:09 am

Just for my educational purposes, is the attached a correct redline typical of all three?


I realize Doug will be removing it.

Title: Re: Trouble understanding Hoffman's relay schematic.
Post by: sluckey on March 23, 2023, 09:49:50 am

Quote from: JPK on March 23, 2023, 09:37:09 am

Just for my educational purposes, is the attached a correct redline typical of all three?

yes

Title: Re: Trouble understanding Hoffman's relay schematic.
Post by: tubenit on March 23, 2023, 03:51:34 pm

There is an abundance of information on the relays in ARCHIVES:  Relay circuit & layout board & ft switch (el34world.com) (https://el34world.com/Forum/index.php?topic=14348.0)

Title: Re: Trouble understanding Hoffman's relay schematic.
Post by: JPK on March 23, 2023, 11:16:17 pm

Quote from: sluckey on March 23, 2023, 09:49:50 am

Quote from: JPK on March 23, 2023, 09:37:09 am

Just for my educational purposes, is the attached a correct redline typical of all three?

yes

Thanks.

Title: Re: Trouble understanding Hoffman's relay schematic.
Post by: AmberB on March 25, 2023, 07:28:26 pm

I recently spent several hours trying to figure out how to wire the LED indicator to turn on when the relay is engaged.  It seems simple enough on the schematic, but the wiring in my project amp was another story.  I finally got it figured out...

Title: Re: Trouble understanding Hoffman's relay schematic.
Post by: jeff on March 29, 2023, 06:41:38 am

Thanks for the help, guys
Traces on board look correct, seems like a schematic error.