Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tdvt on April 10, 2024, 09:09:33 am

Title: LRC filter node?
Post by: tdvt on April 10, 2024, 09:09:33 am

I had bookmarked this thread specifically for pdf64's suggestion to the OP (reply#18) about adding a resistor inline with a choke, & I was able to actually find it, much less remember reading it.

https://el34world.com/Forum/index.php?topic=30681.msg338303#msg338303


I would like to add a choke to a small SE harp amp I rebuilt for a friend earlier this year to try to further reduce some hum. (https://el34world.com/Forum/index.php?topic=31267.msg344475#msg344475)

I could add a new node at the front end of the power rail, but as it has a fairly small first dropping resistor (50R on the drawing, 500R installed), I am wondering if simply adding the choke in series on the same node will do the trick?

Title: Re: LRC filter node?
Post by: Dave on April 10, 2024, 09:24:22 am

I would think, in-place-of, but you could try it both ways and see which one you like better.


Dave

Title: Re: LRC filter node?
Post by: shooter on April 10, 2024, 10:27:04 am

have you verified the PS volts?  going from 680v to 350v over a 50 ohm 5W R seems dubious

Title: Re: LRC filter node?
Post by: Dave on April 10, 2024, 11:07:32 am

Quote from: shooter on April 10, 2024, 10:27:04 am

have you verified the PS volts?  going from 680v to 350v over a 50 ohm 5W R seems dubious

It says VAC, so I was assuming 340-0-340 secondary on the xformer.


Dave


Edit - But, there are other secondary voltages present, so I don't know.


Yeah... I just looked at the xformer specs. It has 540 and 680 secondaries.

Title: Re: LRC filter node?
Post by: sluckey on April 10, 2024, 11:17:13 am

The schematic shows the 540VAC (270-0-270) taps being used. That makes the 350V B+ very believable.

Title: Re: LRC filter node?
Post by: shooter on April 10, 2024, 11:53:52 am

i believe the 350vdc, just not the 680vac above the 1st filter cap

Title: Re: LRC filter node?
Post by: tubeswell on April 10, 2024, 06:32:23 pm

Quote from: sluckey on April 10, 2024, 11:17:13 am

The schematic shows the 540VAC (270-0-270) taps being used. That makes the 350V B+ very believable.

Yep

Title: Re: LRC filter node?
Post by: tdvt on April 10, 2024, 09:01:50 pm

Quote from: shooter on April 10, 2024, 10:27:04 am

have you verified the PS volts?  going from 680v to 350v over a 50 ohm 5W R seems dubious

Those are some wacky numbers that are part of the original schematic, not mine.


The B+ 1st node is right at 355-ish.

By the time I moved some terminal strips around to make room for the choke (inside), it ended up being pretty straight forward to add another node on the front end.

It is now almost dead silent at idle, not bad for an SE amp, I would say.