12v trigger for Mark IIIs

Hello, new to the forum but have been enjoying Dynaco equipment for 30 years. I recently picked up a set of Mark IIIs and went through and replaced all the components and tubes. These amps are placed in a very difficult location to access the per switch so I built a 12v trigger with an SSD relay, a 20 amp recepticle, and a 3.5mm plug. The trigger works perfectly with my Parasound P5 preamp. The problem is that it works with everything but the amps. Everytime I try it the fuse pops. I went to the local electronics store and they suggested a mechanical relay and that t too popped the fuse. I then just plugged the amp in with the power switch on and it again blew the fuse. The amps work and sound awesome otherwise. Someone had had to have comer up with this before, any suggestions?? Thanks

Couldn't you just use a couple of these to turn the amps on and off?

https://www.amazon.com/Belkin-Conserve-Power-Switch-F7C016q/dp/B005MYN3OO/ref=sr_1_1?ie=UTF8&qid=1493263437&sr=8-1&keywords=belkin+power+switch

raptor357r wrote:Hello, new to the forum but have been enjoying Dynaco equipment for 30 years. I recently picked up a set of Mark IIIs and went through and replaced all the components and tubes. These amps are placed in a very difficult location to access the per switch so I built a 12v trigger with an SSD relay, a 20 amp recepticle, and a 3.5mm plug. The trigger works perfectly with my Parasound P5 preamp. The problem is that it works with everything but the amps. Everytime I try it the fuse pops. I went to the local electronics store and they suggested a mechanical relay and that t too popped the fuse. I then just plugged the amp in with the power switch on and it again blew the fuse. The amps work and sound awesome otherwise. Someone had had to have comer up with this before, any suggestions?? Thanks

This is what I have used the last 25 years.
I guess that the total load of both MkIII is too much for the 20A fuse, can you start
one amp with the device ? If so, the solution is to sequence the power on, using one
SSR in each MkIII and fire them with a short delay.
You might also add a "thermistor" to reduce peak current surge. See :
https://dynacotubeaudio.forumotion.com/t1826-cl-80-or-90-thermistors-vs-time-delay-circuit
where this is discussed.

Wonder if you could make it work by adding a thermistor to the main power in on each amp? Those ramp up relatively slow (in electron years anyway) and might get around whatever surge is killing the fuse ... cheap fix if it works, and never really a bad idea on tube equipment anyway.

Just wire it in series at the fuse holder. Worth noting, it could be a problem if you've got borderline B+ as any thermistor never opens up fully - you might lose 1-2vac at most though, and that's normally not a concern, especially in this day and age where line voltage tends towards high.

raptor357r wrote:Hello, new to the forum but have been enjoying Dynaco equipment for 30 years. I recently picked up a set of Mark IIIs and went through and replaced all the components and tubes. These amps are placed in a very difficult location to access the per switch so I built a 12v trigger with an SSD relay, a 20 amp recepticle, and a 3.5mm plug. The trigger works perfectly with my Parasound P5 preamp. The problem is that it works with everything but the amps. Everytime I try it the fuse pops. I went to the local electronics store and they suggested a mechanical relay and that t too popped the fuse. I then just plugged the amp in with the power switch on and it again blew the fuse. The amps work and sound awesome otherwise. Someone had had to have comer up with this before, any suggestions?? Thanks

https://www.amazon.com/dp/B001Q9EFUK/ref=asc_df_B001Q9EFUK4958159/?tag=hyprod-20&creative=394997&creativeASIN=B001Q9EFUK&linkCode=df0&hvadid=167140365824&hvpos=1o2&hvnetw=g&hvrand=14740267545262823443&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9007378&hvtargid=pla-273878094210


This. Cheap and effective. And 'remote'. Calculate based on the "Tungsten" load. Receptacle -->remote switch --> surge-protector -- >devices.

peterh wrote:

raptor357r wrote:Hello, new to the forum but have been enjoying Dynaco equipment for 30 years. I recently picked up a set of Mark IIIs and went through and replaced all the components and tubes. These amps are placed in a very difficult location to access the per switch so I built a 12v trigger with an SSD relay, a 20 amp recepticle, and a 3.5mm plug. The trigger works perfectly with my Parasound P5 preamp. The problem is that it works with everything but the amps. Everytime I try it the fuse pops. I went to the local electronics store and they suggested a mechanical relay and that t too popped the fuse. I then just plugged the amp in with the power switch on and it again blew the fuse. The amps work and sound awesome otherwise. Someone had had to have comer up with this before, any suggestions?? Thanks

This is what I have used the last 25 years.
I guess that the total load of both MkIII is too much for the 20A fuse, can you start
one amp with the device ? If so, the solution is to sequence the power on, using one
SSR in each MkIII and fire them with a short delay.
You might also add a "thermistor" to reduce peak current surge. See :
https://dynacotubeaudio.forumotion.com/t1826-cl-80-or-90-thermistors-vs-time-delay-circuit
where this is discussed.

The issue is not in the trigger but in the amp/start up. If I just plug a single amp into a receptacle with the switch on it'll blow the fuse which is essentially what the trigger is doing.

How would you wire the thermistor to the amp?

Dave_in_Va wrote:Couldn't you just use a couple of these to turn the amps on and off?

https://www.amazon.com/Belkin-Conserve-Power-Switch-F7C016q/dp/B005MYN3OO/ref=sr_1_1?ie=UTF8&qid=1493263437&sr=8-1&keywords=belkin+power+switch

I have a z-wave switch that I was using, but controlling everything with my I-pad is ideal. I'll go back to it if I cant get this to work out.

Bob Latino wrote:Are you using a SLO-BLO fuse in your Mark III's and not a normal fast blow fuse ? A Mark III should use a 3 amp SLO-BLO fuse.

Bob

Yes. And they blow in about a nanosecond with this trigger or just by plugging it in with the switch in the on position.

sKiZo wrote:Wonder if you could make it work by adding a thermistor to the main power in on each amp? Those ramp up relatively slow (in electron years anyway) and might get around whatever surge is killing the fuse ... cheap fix if it works, and never really a bad idea on tube equipment anyway.

Just wire it in series at the fuse holder. Worth noting, it could be a problem if you've got borderline B+ as any thermistor never opens up fully - you might lose 1-2vac at most though, and that's normally not a concern, especially in this day and age where line voltage tends towards high.

I will make a run to the electronics store this afternoon and try this out. Thanks

raptor357r wrote:

peterh wrote:

raptor357r wrote:Hello, new to the forum but have been enjoying Dynaco equipment for 30 years. I recently picked up a set of Mark IIIs and went through and replaced all the components and tubes. These amps are placed in a very difficult location to access the per switch so I built a 12v trigger with an SSD relay, a 20 amp recepticle, and a 3.5mm plug. The trigger works perfectly with my Parasound P5 preamp. The problem is that it works with everything but the amps. Everytime I try it the fuse pops. I went to the local electronics store and they suggested a mechanical relay and that t too popped the fuse. I then just plugged the amp in with the power switch on and it again blew the fuse. The amps work and sound awesome otherwise. Someone had had to have comer up with this before, any suggestions?? Thanks

This is what I have used the last 25 years.
I guess that the total load of both MkIII is too much for the 20A fuse, can you start
one amp with the device ? If so, the solution is to sequence the power on, using one
SSR in each MkIII and fire them with a short delay.
You might also add a "thermistor" to reduce peak current surge. See :
https://dynacotubeaudio.forumotion.com/t1826-cl-80-or-90-thermistors-vs-time-delay-circuit
where this is discussed.

The issue is not in the trigger but in the amp/start up. If I just plug a single amp into a receptacle with the switch on it'll blow the fuse which is essentially what the trigger is doing.

How would you wire the thermistor to the amp?

Which fuse are you discussing ? My impression was that it is the 20A mains fuse
that blows. That why i ask.

A thermistor should be connected between the internal fuse in the MkIII and the transformer. It's sole purpose is to reduce the current surge at power on.

Are the MkIII in origina shape ? A Si rectifier for B+ ( i know some people
uses this) will make the amp draw significantly more power at startup.

Again, power on via the build-in switch or an external switch is equivalent as far
as the amp is concerned.

raptor357r wrote:Hello, new to the forum but have been enjoying Dynaco equipment for 30 years. I recently picked up a set of Mark IIIs and went through and replaced all the components and tubes. These amps are placed in a very difficult location to access the per switch so I built a 12v trigger with an SSD relay, a 20 amp recepticle, and a 3.5mm plug. The trigger works perfectly with my Parasound P5 preamp. The problem is that it works with everything but the amps. Everytime I try it the fuse pops. I went to the local electronics store and they suggested a mechanical relay and that t too popped the fuse. I then just plugged the amp in with the power switch on and it again blew the fuse. The amps work and sound awesome otherwise. Someone had had to have comer up with this before, any suggestions?? Thanks

https://www.onlinecomponents.com/bussmann-eaton-mdl3.html?p=10812327&utm_source=google&utm_medium=cpc&utm_campaign=Shopping%20Suppliers&utm_term=&utm_content=4MV8ESSb&ref=GoogleAd:Shopping%20Suppliers-TE%20Connectivity%20/%20Elcon%20Brand&gclid=Cj0KEQjwrYbIBRCgnY-OluOk89EBEiQAZER58kRa6TPPpzcefmztiW7DJuYWsiyoJ2jKnOvOjfXmTQwaAh-g8P8HAQ&cshift_ck=624A2299-4AE1-4BB6-AFF1-06332A987376cs4MV8ESSb

Conversely, go to this fuse and your problems will be over, with no additional risk to the amp. It acts as a slow-blow fuse on start-up, but as a conventional fuse during operation. NOTE: They DO NOT like short-cycling.

Thank you for all of the fast responses. I'm gonna try the CL80 thermistors and see if that does it. It sounds like that's the issue.

I'll keep you posted.

raptor357r wrote:Thank you for all of the fast responses. I'm gonna try the CL80 thermistors and see if that does it. It sounds like that's the issue.

I'll keep you posted.

Minor Snark Warning

Back in the day, Dynaco products were supplied with dual-element fuses to prevent 'blow-on-start' - which seems to be the issue here. Hafler was a cheap SOB, squeezing every nickel until Jefferson howled. He would not have spent 4X as much for a fuse had it not been a *really* good idea.
William of Occam suggested that we eschew needless complexity back in the 1300s.

Thermistors, while they have their place and are generally good things - are not meant to be installed to protect fuses. They serve to provide a soft start to some degree, and where necessary.
Fuses are installed to protect equipment.
It is entirely possible to protect equipment similarly to a standard fuse *AND* have the general benefits of a slo-blo (wire-wound) fuse.

A true dual-element fuse is designed to accept a hard start, but behave as a standard fuse during normal operation. It is a simple, reasonably priced solution that does not require modification of the equipment. Thereby eschewing needless complexity.

http://www.navsea.navy.mil/Portals/103/Documents/NSWC_Crane/SD-18/PDFs/Products/Archive/Thermistors/Thermistors.pdf  

Together with a 15% chance of failing-short.

One more note: If one establishes the normal operating current for a device, and uses a dual-element fuse, it is entirely possible to lower the fuse amperage to very near the operating level. For instance, I fuse my ST70 at 1.75A. Never had a problem, so far.

OK, I am done now.

Peter W. wrote:

raptor357r wrote:Hello, new to the forum but have been enjoying Dynaco equipment for 30 years. I recently picked up a set of Mark IIIs and went through and replaced all the components and tubes. These amps are placed in a very difficult location to access the per switch so I built a 12v trigger with an SSD relay, a 20 amp recepticle, and a 3.5mm plug. The trigger works perfectly with my Parasound P5 preamp. The problem is that it works with everything but the amps. Everytime I try it the fuse pops. I went to the local electronics store and they suggested a mechanical relay and that t too popped the fuse. I then just plugged the amp in with the power switch on and it again blew the fuse. The amps work and sound awesome otherwise. Someone had had to have comer up with this before, any suggestions?? Thanks

https://www.onlinecomponents.com/bussmann-eaton-mdl3.html?p=10812327&utm_source=google&utm_medium=cpc&utm_campaign=Shopping%20Suppliers&utm_term=&utm_content=4MV8ESSb&ref=GoogleAd:Shopping%20Suppliers-TE%20Connectivity%20/%20Elcon%20Brand&gclid=Cj0KEQjwrYbIBRCgnY-OluOk89EBEiQAZER58kRa6TPPpzcefmztiW7DJuYWsiyoJ2jKnOvOjfXmTQwaAh-g8P8HAQ&cshift_ck=624A2299-4AE1-4BB6-AFF1-06332A987376cs4MV8ESSb  

Conversely, go to this fuse and your problems will be over, with no additional risk to the amp. It acts as a slow-blow fuse on start-up, but as a conventional fuse during operation. NOTE: They DO NOT like short-cycling.

That's what I was using until they all got popped. I just ordered some more.

peterh wrote:

raptor357r wrote:

peterh wrote:

raptor357r wrote:Hello, new to the forum but have been enjoying Dynaco equipment for 30 years. I recently picked up a set of Mark IIIs and went through and replaced all the components and tubes. These amps are placed in a very difficult location to access the per switch so I built a 12v trigger with an SSD relay, a 20 amp recepticle, and a 3.5mm plug. The trigger works perfectly with my Parasound P5 preamp. The problem is that it works with everything but the amps. Everytime I try it the fuse pops. I went to the local electronics store and they suggested a mechanical relay and that t too popped the fuse. I then just plugged the amp in with the power switch on and it again blew the fuse. The amps work and sound awesome otherwise. Someone had had to have comer up with this before, any suggestions?? Thanks

This is what I have used the last 25 years.
I guess that the total load of both MkIII is too much for the 20A fuse, can you start
one amp with the device ? If so, the solution is to sequence the power on, using one
SSR in each MkIII and fire them with a short delay.
You might also add a "thermistor" to reduce peak current surge. See :
https://dynacotubeaudio.forumotion.com/t1826-cl-80-or-90-thermistors-vs-time-delay-circuit
where this is discussed.

The issue is not in the trigger but in the amp/start up. If I just plug a single amp into a receptacle with the switch on it'll blow the fuse which is essentially what the trigger is doing.

How would you wire the thermistor to the amp?

Which fuse are you discussing ? My impression was that it is the 20A mains fuse
that blows. That why i ask.

A thermistor should be connected between the internal fuse in the MkIII and the transformer. It's sole purpose is to reduce the current surge at power on.

Are the MkIII in origina shape ? A Si rectifier for B+ ( i know some people
uses this) will make the amp draw significantly more power at startup.

Again, power on via the build-in switch or an external switch is equivalent as far
as the amp is concerned.

It is the main fuse on the amp but it's only a 3 amp slo-blo.

No Si rectifier, it's been upgraded to the diode.

And lastly that's what I'd think but it's still blowing the fuse on both amps, together or individually. It's also doing it by just plugging it in with the switch on not using the trigger.

If you are blowing 3A Dual-Element fuses on Switch-On, something is definitely going on entirely apart from the normal turn-on surge. You need to find out what that is.

Do you have the means to determine the actual load drawn b by the amp?

It's not doing it under normal start up, so I'd think the amp is fine.

raptor357r wrote:It's not doing it under normal start up, so I'd think the amp is fine.

What is "normal startup" ? Is it mains cable connected and the amp's
power breaker used to start the amp ?

This leads me to believe that the relay device you use is bouncing i.e. not
closing once but closes, bounces closes etc , like a simple mechanical relay.
But in the first post you say it's an SSR, then i must ask, is the control
signal weak and makes the SSR to close-open-close , this will give the same
effect as a bouncing relay. Or is the SSR a "dimmer type" ? If so replace!

I have used SSR's many years across several amps, all controlled by a 12V DC
usually taken from the preamps filament supply and never seen any trouble
with this.