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    Triode/Ultralinear mode switch specs?

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    JunkyJan

    Posts: 100
    Join date: 2008-12-09
    Location: BC, Canada

    Triode/Ultralinear mode switch specs?

    Post by JunkyJan on Mon Aug 30, 2010 12:36 am

    Hello Bob and all,

    I have started work on a set of Mark 3 monoblock amps, and I am planning to add a Triode/Ultralinear mode switch to both.

    What should the specs be for the actual toggle switch? I have sourced a DPDT toggle switch from a local electronics store that physically looks identical to the ones supplied in your ST-70 kit and is spec'ed as follows:
    "125 VAC 6 Amp
    250 VAC 3 Amp"

    (and I guess that it should be able to handle 1.5A @ 500 Volts)

    Is that acceptable?

    -- JunkyJan
    BC, Canada

    Bob Latino
    Admin

    Posts: 1975
    Join date: 2008-11-26
    Location: Massachusetts

    Re: Triode/Ultralinear mode switch specs?

    Post by Bob Latino on Mon Aug 30, 2010 7:31 am

    JunkyJan wrote:Hello Bob and all,

    I have started work on a set of Mark 3 monoblock amps, and I am planning to add a Triode/Ultralinear mode switch to both.

    What should the specs be for the actual toggle switch? I have sourced a DPDT toggle switch from a local electronics store that physically looks identical to the ones supplied in your ST-70 kit and is spec'ed as follows:
    "125 VAC 6 Amp
    250 VAC 3 Amp"

    (and I guess that it should be able to handle 1.5A @ 500 Volts)

    Is that acceptable?

    -- JunkyJan
    BC, Canada

    Hi Jan,

    That switch will work fine as a triode/pentode switch.

    Bob


    JunkyJan

    Posts: 100
    Join date: 2008-12-09
    Location: BC, Canada

    Re: Triode/Ultralinear mode switch specs?

    Post by JunkyJan on Tue Aug 31, 2010 12:55 am

    Bob Latino wrote:That switch will work fine as a triode/pentode switch.

    Thanks a ton for the information, Bob - much appreciated!

    -- 'Jan

    JunkyJan

    Posts: 100
    Join date: 2008-12-09
    Location: BC, Canada

    Re: Triode/Ultralinear mode switch specs?

    Post by JunkyJan on Thu Sep 09, 2010 1:48 pm

    Hi Bob and all

    More questions: You recommend a 100 Ohm / 1 Watt resistor to be used to "tie the plates together" when running in Triode mode.

    1) Would a Carbon Film resistor (1 watt) work?
    2) I have a whole bunch of 100 Ohm 2 Watt Metal Oxide power resistors, will that work too?
    3) Same spec whether you use it in a ST-70 or a Mark III?

    Thank you for your time & advice :-)
    -- 'Jan in BC, Canada

    Bob Latino
    Admin

    Posts: 1975
    Join date: 2008-11-26
    Location: Massachusetts

    Re: Triode/Ultralinear mode switch specs?

    Post by Bob Latino on Thu Sep 09, 2010 2:08 pm

    JunkyJan wrote:Hi Bob and all

    More questions: You recommend a 100 Ohm / 1 Watt resistor to be used to "tie the plates together" when running in Triode mode.

    1) Would a Carbon Film resistor (1 watt) work?
    2) I have a whole bunch of 100 Ohm 2 Watt Metal Oxide power resistors, will that work too?
    3) Same spec whether you use it in a ST-70 or a Mark III?

    Thank you for your time & advice :-)
    -- 'Jan in BC, Canada

    Hi Jan,

    What you do is disconnect the GREEN or GREEN/WHITE wire at pin #4 of each output tube and insulate the end so that it can't short out to the chassis. You then tie the plate (pin #3) of each output tube through a 100 ohm resistor to the SCREEN (pin # 4).

    1) Yes
    2) Yes
    3) Yes

    Some "Dynaco Dudes" even suggest a 100 ohm 1/2 watt resistor but there is a lot of heat under that chassis and IMHO you are better off with a 1 watt (or higher) resistor to make the triode connection.

    Bob

    JunkyJan

    Posts: 100
    Join date: 2008-12-09
    Location: BC, Canada

    Thanks a ton, Bob!!

    Post by JunkyJan on Thu Sep 09, 2010 4:48 pm

    Thanks Bob - very much appreciated! I'll be running it through a switch so that I can still switch back to the ultra-linear tap, same as your ST-70 kit works.

    Again, thanks a ton!
    -- 'Jan

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