The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    Dynaco PAS fuse and three prong conversion

    Share

    pakru

    Posts : 10
    Join date : 2015-12-22

    Dynaco PAS fuse and three prong conversion

    Post by pakru on Tue Dec 29, 2015 4:24 pm

    Hi,

    Newbie and first time poster here. I have a Dynaco PAS 3 that does not seem to have a fuse or a chassis ground connection. I am not very comfortable with this and was thinking of adding them to make it safer.

    Is it possible to add a fuse and a chassis ground connection? If so, would greatly appreciate any help on how to accomplish this.

    1. What should be the fuse rating? Would a 1/4 Amp, 250V slow blow fuse do?
    2. I assume the fuse should be inline with the hot wire coming in from the power cord
    3. To convert it into a grounded IEC plug type, should I just connect the chassis to the ground terminal of the plug?
    4. Is there an easy way to cut a receptacle on the back? Any examples would be great.

    Are there any other things I should be aware of?

    Thank you.

    peterh

    Posts : 642
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Dynaco PAS fuse and three prong conversion

    Post by peterh on Tue Dec 29, 2015 6:04 pm

    pakru wrote:Hi,

    Newbie and first time poster here. I have a Dynaco PAS 3 that does not seem to have a fuse or a chassis ground connection. I am not very comfortable with this and was thinking of adding them to make it safer.

    Is it possible to add a fuse and a chassis ground connection? If so, would greatly appreciate any help on how to accomplish this.

    1. What should be the fuse rating? Would a 1/4 Amp, 250V slow blow fuse do?
    2. I assume the fuse should be inline with the hot wire coming in from the power cord
    3. To convert it into a grounded IEC plug type, should I just connect the chassis to the ground terminal of the plug?
    4. Is there an easy way to cut a receptacle on the back? Any examples would be great.

    Are there any other things I should be aware of?

    Thank you.
    Unfortently there is no place where one can cut out a IEC outlet on PAS. One could
    however mount the outlet in a small alu-box, and screw that box at the back. In the same
    box one could install a fuse , or even better use an IEC with built-in fuse(es).

    I thing 100mA would di just fine.

    Ground could be connected at the chassies as you suggested.

    BTW, if you want to replace the SE rectifiers, several of the power-supply boards
    has fuse for the mains.

    google PAS powersupply for sources.

    pakru

    Posts : 10
    Join date : 2015-12-22

    Re: Dynaco PAS fuse and three prong conversion

    Post by pakru on Tue Dec 29, 2015 6:16 pm

    peterh, I will look for the IEC with the built in fuse holder. Thanks for the suggestion.

    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    Re: Dynaco PAS fuse and three prong conversion

    Post by PeterCapo on Tue Dec 29, 2015 8:59 pm

    I used something very much like this in my PAS. Fits under the deck http://www.amazon.com/1st-Source-In-line-Fuse-Holder/dp/B0002KR8EE

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: Dynaco PAS fuse and three prong conversion

    Post by tubes4hifi on Tue Dec 29, 2015 10:12 pm

    if you don't mind cutting the rear panel sheet metal (and thus tremendously reducing the value of the preamp)
    it should be quite easy to cut a hole for a square combo IEC/fuse holder using a standard sheet metal "knibbling" tool,
    which is pretty commonly available, or for more effort use a drill and do alot of filing.
    http://www.amazon.com/Parts-Express-Nickel-Plated-Nibbling/dp/B0002KRACO
    The hole would need to be made about 3" from the far left side of the rear so the IEC connector would clear the power transformer,
    and up high so it be above the power supply parts.

    peterh

    Posts : 642
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Dynaco PAS fuse and three prong conversion

    Post by peterh on Wed Dec 30, 2015 5:14 am

    tubes4hifi wrote:if you don't mind cutting the rear panel sheet metal (and thus tremendously reducing the value of the preamp)
    it should be quite easy to cut a hole for a square combo IEC/fuse holder using a standard sheet metal "knibbling" tool,
    which is pretty commonly available, or for more effort use a drill and do alot of filing.
    http://www.amazon.com/Parts-Express-Nickel-Plated-Nibbling/dp/B0002KRACO
    The hole would need to be made about 3" from the far left side of the rear so the IEC connector would clear the power transformer,
    and up high so it be above the power supply parts.

    This is correct. However, this interferes with future power supply upgrade AND
    introduces AC power close to input signals. That's why i suggested to build a
    "wart" containing the IEC adapter and mount it on the back behind the transformer.

    FM-1/3 has space for a IEC connector, so does sca35 ( and ST-70) PAS has not.

    pakru

    Posts : 10
    Join date : 2015-12-22

    Re: Dynaco PAS fuse and three prong conversion

    Post by pakru on Fri Jan 01, 2016 11:43 pm

    @PeterCapo, I will look into the fuse holder option on amazon.

    Since it looks like cutting sheet metal is detrimental to the value, I will look into the external IEC adapter/mount option.

    Thanks for your responses. Appreciate it.

    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    Re: Dynaco PAS fuse and three prong conversion

    Post by PeterCapo on Fri Jan 01, 2016 11:47 pm

    Radio Shack used to carry one that looks a lot like the one on Amazon.  If it is the same one that Radio Shack used to have, then it will fit fine without having to cut or build anything.  It was a convenient solution for me.

    pakru

    Posts : 10
    Join date : 2015-12-22

    Re: Dynaco PAS fuse and three prong conversion

    Post by pakru on Sat Jan 02, 2016 5:59 pm

    Thanks. I found a similar 18AWG fuse holder at a local store here.

    I was reading the forums about the fuse rating for PAS 3. Will a 250V, 0.25A slow blow fuse work?

    Based on Dynaco PA211 transformer calculation (~ 330VCT, 15mA & 12V 0.8A secondary), the primary current comes out to be around 122mA. Does this make sense in reality or will a 0.25A fuse blow?

    Thanks.

    peterh

    Posts : 642
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Dynaco PAS fuse and three prong conversion

    Post by peterh on Sat Jan 02, 2016 6:17 pm

    pakru wrote:Thanks. I found a similar 18AWG fuse holder at a local store here.

    I was reading the forums about the fuse rating for PAS 3. Will a 250V, 0.25A slow blow fuse work?

    Based on Dynaco PA211 transformer calculation (~ 330VCT, 15mA & 12V 0.8A secondary), the primary current comes out to be around 122mA. Does this make sense in reality or will a 0.25A fuse blow?

    Thanks.
    250mA fuse seems a good choice.
    If it blows one can easily use next step ( 315 )

    pakru

    Posts : 10
    Join date : 2015-12-22

    Re: Dynaco PAS fuse and three prong conversion

    Post by pakru on Sat Jan 02, 2016 6:23 pm

    OK. Thanks. I will try that.

    pakru

    Posts : 10
    Join date : 2015-12-22

    Re: Dynaco PAS fuse and three prong conversion

    Post by pakru on Sat Jan 02, 2016 6:26 pm

    @PeterCapo, how did you install the fuse holder? Did you stick it to the underside using glue or was it a tied using holes?

    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    Re: Dynaco PAS fuse and three prong conversion

    Post by PeterCapo on Sat Jan 02, 2016 7:10 pm

    No glue or anything needed. It fits snugly between the deck and the bottom plate, so once the wires are attached, it just sits in there securely.

    pakru

    Posts : 10
    Join date : 2015-12-22

    Re: Dynaco PAS fuse and three prong conversion

    Post by pakru on Sat Jan 02, 2016 10:29 pm

    OK. Thanks.

    pakru

    Posts : 10
    Join date : 2015-12-22

    Re: Dynaco PAS fuse and three prong conversion

    Post by pakru on Sun Jan 17, 2016 7:19 pm

    Hi,

    If anyone is looking for similar conversion, thought I will give an update, here is what I did:

    1. Used the fuse holder mentioned by PeterCapo earlier and installed a 250mA, 250V slow-blo fuse on the hot side incoming wire from the AC outlet. Fuse fits perfectly underneath the chassis.

    2. For three prong AC outlet conversion, used a garbage disposal cord Amazon Link  (or cut a regular AC cord) that has three prongs. Used a 16AWG 6 ft cord rated for 13A so I guess it should be fine. Wired the neutral and hot as in the schematic, but tied the ground to the chassis

    So far no hum issues.

    Thanks for the help.

    Sponsored content

    Re: Dynaco PAS fuse and three prong conversion

    Post by Sponsored content Today at 11:17 pm


      Current date/time is Wed Sep 28, 2016 11:17 pm