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    ST-70 Voltage Help & Introduction

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    Kinski

    Posts : 26
    Join date : 2017-09-20

    Re: ST-70 Voltage Help & Introduction

    Post by Kinski on Fri Sep 29, 2017 10:18 am

    Thanks for the info! My PAS-2 and ST-70 do not have fuses at all. So what do you mean when you say I should use the existing fuse?
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    Peter W.

    Posts : 552
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: ST-70 Voltage Help & Introduction

    Post by Peter W. on Fri Sep 29, 2017 10:53 am

    Kinski wrote:Thanks for the info! My PAS-2 and ST-70 do not have fuses at all. So what do you mean when you say I should use the existing fuse?

    http://img.canuckaudiomart.com/uploads/large/1355837-dynaco-st70-with-vintage-mullard-el34-oo-getter.jpg

    No fuse? Is there a hole for a fuse-holder?

    Kinski

    Posts : 26
    Join date : 2017-09-20

    Re: ST-70 Voltage Help & Introduction

    Post by Kinski on Fri Sep 29, 2017 11:08 am

    Oh yikes. A bit embarrassing. I didn’t notice it. But yes, there IS a fuse for the ST-70. Sorry for the confusion. So I just need to add one to the PAS. I’ll just mount one internally, as I’d prefer to not drill any new holes.

    So based on this image, how would I wire the fuse?
    http://usr.audioasylum.com/images/4/42505/PAS_fil.JPG
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    Peter W.

    Posts : 552
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: ST-70 Voltage Help & Introduction

    Post by Peter W. on Fri Sep 29, 2017 11:43 am

    Neither - the transformer output is not fused.

    On the input side of the power transformer, find the lead from the power-cord that goes to the front switch, insert the fuse between the power-cord and the line running to the front switch.

    Ideally, you will change the power-cord to a polarized cord, making the narrow prong (Hot) the switch-lead and the fat prong (neutral) running directly to the transformer. This way there is no power on the transformer when the switch is off.

    NOTE: Polarized plugs do not fit into most Dynaco rear-receptacles. By code they should not fit into any rear receptacles unless that device also has a polarized plug.

    Kinski

    Posts : 26
    Join date : 2017-09-20

    Re: ST-70 Voltage Help & Introduction

    Post by Kinski on Fri Sep 29, 2017 11:53 am

    Thank you!
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    Peter W.

    Posts : 552
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: ST-70 Voltage Help & Introduction

    Post by Peter W. on Fri Sep 29, 2017 12:09 pm

    These sorts of very basic, but critical, useful and apt questions are what pushed me towards offering a clinic. I will post to that thread shortly as I have at least one date that has become open in October.

    GP49

    Posts : 786
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: ST-70 Voltage Help & Introduction

    Post by GP49 on Sat Sep 30, 2017 2:14 am

    I like to mount the PAS power transformer OUTSIDE the case on the back panel. I believe it is necessary to drill one hole, the other attachment points can be bolted to the existing vent slots but it's been a while since I did one of these. The wiring can be routed through those existing vent slots.

    The external mounting of the transformer provides better heat dissipation and gives you more room inside to install a fuseholder, or bigger power supply capacitors.

    This isn't my idea, by the way; it is Frank Van Alstine's.

    Kinski

    Posts : 26
    Join date : 2017-09-20

    Re: ST-70 Voltage Help & Introduction

    Post by Kinski on Fri Nov 17, 2017 1:51 pm

    Hi there, so remember that red plating el34? Its been happening again. Tried to mess with the sockets and offers no help. I'm pretty sure its the tube at this point. But wondering if there is anyway to salvage it.

    I noticed the faulty tube as one difference. They are all the exact same Sylvania brand. But the one that is red plating seems to have a different piece than the other three.

    The good tubes have a tiny funnel piece. The bad tube has a little loop that lights up red when powered on.

    Sorry, I dont know the name for all of these parts, so its the best I can do.

    I've attached two photos. Hopefully these will clarify it all a bit. I labeled which one is the bad tube and highlighted the detail I'm talking about.



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    Tubes4ever

    Posts : 107
    Join date : 2015-07-14
    Location : Star, Idaho

    Re: ST-70 Voltage Help & Introduction

    Post by Tubes4ever on Sat Nov 18, 2017 12:48 am

    The element you are referring to is the heater. This heats the cathode to orange heat so it emits electrons. The placement of the heater will not effect the operation of your tube. This difference isn't causing the tube to red plate or fail. If the tube red plates in another socket then it is the tube.

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