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Triode/Ultralinear mode switch specs?

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JunkyJan

Posts: 100
Join date: 2008-12-08
Location: BC, Canada

Triode/Ultralinear mode switch specs?

Post by JunkyJan on Sun Aug 29, 2010 11:36 pm

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: 1954
Join date: 2008-11-26
Location: Massachusetts

Re: Triode/Ultralinear mode switch specs?

Post by Bob Latino on Mon Aug 30, 2010 6:31 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: 2008-12-08
Location: BC, Canada

Re: Triode/Ultralinear mode switch specs?

Post by JunkyJan on Mon Aug 30, 2010 11:55 pm

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: 2008-12-08
Location: BC, Canada

Re: Triode/Ultralinear mode switch specs?

Post by JunkyJan on Thu Sep 09, 2010 12:48 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: 1954
Join date: 2008-11-26
Location: Massachusetts

Re: Triode/Ultralinear mode switch specs?

Post by Bob Latino on Thu Sep 09, 2010 1:08 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: 2008-12-08
Location: BC, Canada

Thanks a ton, Bob!!

Post by JunkyJan on Thu Sep 09, 2010 3:48 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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