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    Dyna ST 70 resistor wattage

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    chefothefuture

    Posts : 26
    Join date : 2018-03-28

    Dyna ST 70 resistor wattage

    Post by chefothefuture on Wed Apr 25, 2018 1:55 am

    Anyone know the wattage of the 15.6ohm ceramic resistors on the output valve sockets in the original circuit?

    Got some big caps in a guitar amp I need to discharge and am wondering if these are beefy enough...

    Cheers.
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    Peter W.

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    Re: Dyna ST 70 resistor wattage

    Post by Peter W. on Wed Apr 25, 2018 7:19 am

    chefothefuture wrote:Anyone know the wattage of the 15.6ohm ceramic resistors on the output valve sockets in the original circuit?

    Got some big caps in a guitar amp I need to discharge and am wondering if these are beefy enough...

    Cheers.

    As I remember, these are two (2) watt precision resistors.
    That being written, DO NOT use them to discharge caps - they are not designed for that, and those that are, are so cheap as to a better idea in any case.
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    corndog71

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    Re: Dyna ST 70 resistor wattage

    Post by corndog71 on Wed Apr 25, 2018 10:06 am

    chefothefuture wrote:Anyone know the wattage of the 15.6ohm ceramic resistors on the output valve sockets in the original circuit?

    Got some big caps in a guitar amp I need to discharge and am wondering if these are beefy enough...

    Cheers.

    I used to use 475K 1/2W resistors for discharging caps.

    chefothefuture

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    Join date : 2018-03-28

    Re: Dyna ST 70 resistor wattage

    Post by chefothefuture on Wed Apr 25, 2018 10:29 am

    Thanks for the answers. I’m just trying to use what I have in the parts box. Sounds like I’ll need to order something and temporarily shelve my project...
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    tubes4hifi
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    Re: Dyna ST 70 resistor wattage

    Post by tubes4hifi on Wed Apr 25, 2018 12:31 pm

    discharging resistors . . . .depends on the voltage.
    Discharging 500vdc thru a 1K resistor gives you 0.5 amps, so 250 watts !! Better use a 100K resistor on 500v (5ma x 500v = 2.5 watts).
    It's all ohms law !!!!! Discharging 100v thru a 10K resistor gives you 10ma x 100v = 1 watt

    chefothefuture

    Posts : 26
    Join date : 2018-03-28

    Re: Dyna ST 70 resistor wattage

    Post by chefothefuture on Wed Apr 25, 2018 12:53 pm

    tubes4hifi wrote:discharging resistors . . . .depends on the voltage.
    Discharging 500vdc thru a 1K resistor gives you 0.5 amps, so 250 watts !!   Better use a 100K resistor on 500v (5ma x 500v = 2.5 watts).
    It's all ohms law !!!!!     Discharging 100v thru a 10K resistor gives you 10ma x 100v = 1 watt

    Still means I won't be able to use stuff in my parts box. I'm needing to discharge @ 400v and I have an old 2w resistor from the Dyna quad cap, (and some extras from the VTA boards I didn't use because they went in ST120s) or some 10K 1Ws which might be too small...
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    j beede

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    Re: Dyna ST 70 resistor wattage

    Post by j beede on Wed Apr 25, 2018 9:15 pm

    CA glue the body of a 330K 1/2W to the end of a bamboo chop stick and bend the leads so they will conveniently, slowly, and safely discharge your caps. This is a tool that I keep on my bench for discharging power supply caps (350-650VDC) and electrostatic speaker diaphragms (3K-6KVDC)

    P=E^2/R=400^2/330K=1/2W and even that is crazy overkill as much of the voltage drops well before the resistor heats. As others have pointed out, using a 15.6 Ohm resistor is not a good idea--not much different than shorting the cap with a screwdriver.

    chefothefuture

    Posts : 26
    Join date : 2018-03-28

    Re: Dyna ST 70 resistor wattage

    Post by chefothefuture on Wed Apr 25, 2018 11:01 pm

    j beede wrote:CA glue the body of a 330K 1/2W to the end of a bamboo chop stick and bend the leads so they will conveniently, slowly, and safely discharge your caps. This is a tool that I keep on my bench for discharging power supply caps (350-650VDC) and electrostatic speaker diaphragms (3K-6KVDC)

    P=E^2/R=400^2/330K=1/2W and even that is crazy overkill as much of the voltage drops well before the resistor heats. As others have pointed out, using a 15.6 Ohm resistor is not a good idea--not much different than shorting the cap with a screwdriver.

    That’s what I thought, though there was some website where a 20ohm/5watt resistor was recommended.
    Still, I’ll have to order something as I don’t have anything in that range.
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    j beede

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    Re: Dyna ST 70 resistor wattage

    Post by j beede on Thu Apr 26, 2018 1:08 am

    Where is Radio Shack when you need them? The days of being able to pick up a pack of 330KOhm resistors or a 10µF, 25V cap, or a ten pack of 1N4007 late on a Sunday afternoon in order to finish a project... are gone. Regrettable. I hope all you guys that regularly referred to the neighborhood electronics store as "Rat Shack" are pleased!

    You probably know that HTML versions of all RS catalogs going to back to the 1940s are available on-line. Seeing those catalog covers from the 1960s and 70s brings back memories from my youth. Be sure to check the difference in price between a Mk III kit and a factory assembled unit.

    http://www.radioshackcatalogs.com/catalog_directory.html


    Last edited by j beede on Thu Apr 26, 2018 11:40 am; edited 1 time in total

    chefothefuture

    Posts : 26
    Join date : 2018-03-28

    Re: Dyna ST 70 resistor wattage

    Post by chefothefuture on Thu Apr 26, 2018 1:42 am

    j beede wrote:Where is Radio Shack when you need them? The days of being able to pick up a pack of 330KOhm resistors or a 10µF, 25V cap, or a ten pack of 1N4007 late on a Sunday afternoon in order to finish a project... are gone. Regrettable. I hope all you guys that regularly referred to the neighborhood electronics store as "Rat Shack" are pleased!

    You probably know that HTML versions of all RS catalogs going to back to the 1940s are available on-line. Seeing those covers from the 1960s and 70s bring back memories from my youth. Be sure to check the difference in price between a Mk III kit and a factory assembled unit.

    http://www.radioshackcatalogs.com/catalog_directory.html

    Yes, I do miss the Shack quite keenly. Never had an issue with them other than towards the end, the sales help were fairly unhelpful. After having lived in Hawaii for 16 years, where many things are unobtainable locally, I learned to put the project down and do something else. So, today (I'm in Washington now) I went to the mountains and foraged. Came home with a bag full of young nettles and had a fantastic dinner. The amp will be there when a resistor is sourced...

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