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Adding a dummy load to prevent amp from being damaged by having no load?
Adding a dummy load to prevent amp from being damaged by having no load?
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Old 11th May 2015, 07:43 PM   #1
Joku is offline Joku  Finland
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Default Adding a dummy load to prevent amp from being damaged by having no load?

Just wondering if it would be a good idea to add some sort of a dummy load to the output terminals of a tube amp to prevent damage in case speaker is disconnected for some reason? Also, how big of an load would you need, would a 100-200 ohm resistor be fine for 8 ohm output?
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Old 11th May 2015, 07:51 PM   #2
DF96 is offline DF96  England
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No, you need a load which is a bit nearer to the correct value. A series CR might help (like a Zobel network). Best to simply ensure that you don't run without a load.
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Old 11th May 2015, 08:13 PM   #3
Joku is offline Joku  Finland
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Quote:
Originally Posted by DF96 View Post
No, you need a load which is a bit nearer to the correct value. A series CR might help (like a Zobel network). Best to simply ensure that you don't run without a load.
Yes, plan A is definitively going to be running it with speakers attached at all times. However, accidents can happen, such as a cable coming loose or something. I'd like to a have plan B other than buying a new output transformer.
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Old 11th May 2015, 10:25 PM   #4
Palustris is offline Palustris  United States
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I built some dummy loads that I use when warming up an amp or changing from one amp to another.
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File Type: jpg dummy load 1.jpg (163.0 KB, 174 views)
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Old 12th May 2015, 03:45 AM   #5
e_fortier is offline e_fortier  Canada
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Adding a dummy load to prevent amp from being damaged by having no load?
If I build a tube amp for a friend who is more used to SS or doesn't know much about tubes I normally add some 100 ohm, 5W in parrallel to each outputs. This way the output transformers won't get damaged, there is always a load. So far no OPT got damaged.
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Old 12th May 2015, 03:55 AM   #6
ballpencil is offline ballpencil  Indonesia
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Is wiring the output as triode safer for the OPT compared to pentode? I would imagine it is if i draw a horizontal loadline (no load condition) on both curves but i maybe missing something. If so, with the expense of some power loss, i think the best foolproof way would be this, no?
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Old 12th May 2015, 07:27 AM   #7
Merlinb is offline Merlinb  United Kingdom
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Quote:
Originally Posted by Joku View Post
how big of an load would you need, would a 100-200 ohm resistor be fine for 8 ohm output?
Yes, that's certainly better than nothing. Guitar amps commonly use such a resistor nowadays (up to 470 ohm, 5 watt), and it is seems to be enough to damp the secondary and save the OT from dire flashover.
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