Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on March 18, 2017, 11:16:45 am

Title: How to fix power switch popping
Post by: Leevi on March 18, 2017, 11:16:45 am

The power switch pops when turned off.
I found a fix by adding a capacitor across the switch but I don't like the solution.
Are there any other ways to fix it?


The amp is 5F2-A based amp with reverb. For more information see
the power supply below.

Title: Re: How to fix power switch popping
Post by: sluckey on March 18, 2017, 11:51:57 am

Use a high quality switch that doesn't arc so much when you turn it off. Locate the switch as far away as possible from the preamp circuit and input jacks.

Sometimes you can never quite get rid of the pop. I don't like putting a cap or a resistor across a power switch. Doing so will leave a small AC voltage on the PT primary. This small voltage will bite you.

Title: Re: How to fix power switch popping
Post by: Leevi on March 18, 2017, 12:03:50 pm

I use a high quality switch I have even tried with DPDT switch.
The switch is located in other end as the preamp tube and input jack.

Quote

Doing so will leave a small AC voltage on the PT primary. This small voltage will bite you.

That's why I don't like this solution.


/Leevi

Title: Re: How to fix power switch popping
Post by: Leevi on March 18, 2017, 12:10:24 pm

Could the reason be the Hammond PT (290 CAX) use?
There are two 120V primaries connected together in order to get primary for 230V.


http://www.hammondmfg.com/pdf/EDB290CAX.pdf (http://www.hammondmfg.com/pdf/EDB290CAX.pdf)


I have met this kind of popping problem very seldom especially when the power supply is wired as in the picture.


Leevi

Title: Re: How to fix power switch popping
Post by: kagliostro on March 18, 2017, 12:17:02 pm

Or a special unit with cap + resistor in series

(http://el34world.com/Forum/index.php?action=dlattach;topic=14021.0;attach=30628;image)

http://it.rs-online.com/web/p/reti-capacitive-rc/0209213/ (http://it.rs-online.com/web/p/reti-capacitive-rc/0209213/)

http://docs-europe.electrocomponents.com/webdocs/1528/0900766b81528fd8.pdf (http://docs-europe.electrocomponents.com/webdocs/1528/0900766b81528fd8.pdf)

http://docs-europe.electrocomponents.com/webdocs/1515/0900766b81515447.pdf (http://docs-europe.electrocomponents.com/webdocs/1515/0900766b81515447.pdf)

or a "temporary mute" as in the Cornford MH50II

(note triac circuit + fet 2N5462 + C26 & R33 == the mute time is established by the value of C26 & R33)

(http://i.imgur.com/HAziEP5.jpg)

(http://i.imgur.com/wr7a8O7.jpg)

Franco

Title: Re: How to fix power switch popping
Post by: Leevi on March 18, 2017, 12:30:09 pm

Quote

Or a special unit with cap + resistor in series

This is definitely a better solution than a single cap.


Thanks Franco


/Leevi

Title: Re: How to fix power switch popping
Post by: kagliostro on March 18, 2017, 12:39:58 pm

(http://www.diyitalia.eu/images/smilies/salutations-489.gif)

I forgot this link (how to select the RC unit and other info)

http://www.kemet.com/Lists/ProductCatalog/Attachments/146/F9000_GenInfo_RCUnits.pdf (http://www.kemet.com/Lists/ProductCatalog/Attachments/146/F9000_GenInfo_RCUnits.pdf)

Franco

Title: Re: How to fix power switch popping
Post by: Leevi on March 22, 2017, 05:30:20 am

I installed the following unit across the power switch.


http://uk.farnell.com/productimages/standard/en_GB/2332448-40.jpg (http://uk.farnell.com/productimages/standard/en_GB/2332448-40.jpg)



It works fine, I measured the idle current which is 7.3mA i.e. the power consumption is about 1.7W (230VAC).


/Leevi

Title: Re: How to fix power switch popping
Post by: drgonzonm on March 22, 2017, 07:12:21 pm

Where is the standby switch?  Is it on the B rail or on the PT centertap?.   Because of the lower voltages involved, I would expect a standby switch on the CT, to be less noisy.  (I do not have experience). 

If you are replacing a switch on the B rail, I would strongly recommend that the switch be rated as the B-rail voltage.

Title: Re: How to fix power switch popping
Post by: sluckey on March 22, 2017, 07:24:37 pm

Quote from: drgonzonm on March 22, 2017, 07:12:21 pm

Where is the standby switch?  Is it on the B rail or on the PT centertap?.   Because of the lower voltages involved, I would expect a standby switch on the CT, to be less noisy.  (I do not have experience). 

If you are replacing a switch on the B rail, I would strongly recommend that the switch be rated as the B-rail voltage.

Did you even read the thread? Or the subject line???