Load resistor on OPT

Tyimo · 3rd April 2011, 04:52 AM

Hi!
I read somewhere that even Power tube amplifiers likes to have load resistor on the secondary.
Does anybody have experience in this theme?

Tyimo

thanhtruc03 · 3rd April 2011, 06:58 AM

Quote:

Originally Posted by Tyimo

Hi!
I read somewhere that even Power tube amplifiers likes to have load resistor on the secondary.
Does anybody have experience in this theme?

Tyimo

Yes, in case of your amplifers have no feedback circle, special with pentode tube

thanhtruc03 · 3rd April 2011, 07:01 AM

Yes, special with pentode tube, in case your amplifier have no feetback circle

webdanong · 3rd April 2011, 08:52 AM

Quote:

Originally Posted by thanhtruc03

Yes, special with pentode tube, in case your amplifier have no feetback circle

How about "MK1 Very Easy Speaker", Mr Talkactive?

DF96 · 3rd April 2011, 02:30 PM

Valve amplifiers like to have some load. If not, clipping can induce big voltages in the output transformer which cause insulation breakdown. Every few weeks, someone pops up on here and says that he thinks he may have blown his amp (often a guitar amp) by accidentally running it with no speaker connected.

The presence of feedback won't help, it could make it worse because when the output stage clips the feedback loop will try to drive it even harder.

M Gregg · 3rd April 2011, 05:32 PM

Quote:

Originally Posted by DF96

Valve amplifiers like to have some load. If not, clipping can induce big voltages in the output transformer which cause insulation breakdown. Every few weeks, someone pops up on here and says that he thinks he may have blown his amp (often a guitar amp) by accidentally running it with no speaker connected.

The presence of feedback won't help, it could make it worse because when the output stage clips the feedback loop will try to drive it even harder.

DF96,

There have been a lot of discussions on how to protect the Tx. It seems to be easier on a PP amp you can go across the two plate connections with MOV. However on SE the situation is different, a MOV trip would cause B+ short. Was there ever a definitive answer regards SE?

Regards
M. Gregg

ryuji · 06:26 PM

I used 1/4 inch jacks that have internal switch for when nothing is plugged in. I wired the switch so when no speakers are plugged in it feeds the output into 25 watt 8 ohm(in my case) resistors in my single ended pentode amp. Of course this does nothing if both ends of your wire are disconnectable and you unplug the speaker side

M Gregg · 3rd April 2011, 06:27 PM

Quote:

Originally Posted by ryuji

I used 1/4 inch jacks that have internal switch for when nothing is plugged in. I wired the switch so when no speakers are plugged in it feeds the output into 25 watt 8 ohm(in my case) resistors in my single ended pentode amp.

Interesting,

It's another way around the problem!

Regards
M. Gregg

woody · 3rd April 2011, 06:36 PM

Would a 100 ohm resistor be enough load to damp the big voltage spikes that
dammage the transformer insulation?

M Gregg · 3rd April 2011, 06:51 PM

Quote:

Originally Posted by woody

Would a 100 ohm resistor be enough load to damp the big voltage spikes that
dammage the transformer insulation?

What you have to remember is how much of the output you are loosing as wasted heat. OK with this you are only dropping resistance by a small amount. It would probably work however you would not know until you get a speaker disconnected.

Regards
M. Gregg

3rd April 2011, 04:52 AM	#1
Tyimo diyAudio Member Join Date: Nov 2002 Location: Hungary	Load resistor on OPT Hi! I read somewhere that even Power tube amplifiers likes to have load resistor on the secondary. Does anybody have experience in this theme? Tyimo

3rd April 2011, 06:23 PM	#7
ryuji diyAudio Member Join Date: Feb 2011 Location: massachusetts	I used 1/4 inch jacks that have internal switch for when nothing is plugged in. I wired the switch so when no speakers are plugged in it feeds the output into 25 watt 8 ohm(in my case) resistors in my single ended pentode amp. Of course this does nothing if both ends of your wire are disconnectable and you unplug the speaker side Last edited by ryuji; 3rd April 2011 at 06:26 PM.

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3rd April 2011, 07:01 AM	#3
thanhtruc03 diyAudio Member Join Date: Apr 2011	Yes, special with pentode tube, in case your amplifier have no feetback circle

3rd April 2011, 02:30 PM	#5
DF96 diyAudio Member Join Date: May 2007	Valve amplifiers like to have some load. If not, clipping can induce big voltages in the output transformer which cause insulation breakdown. Every few weeks, someone pops up on here and says that he thinks he may have blown his amp (often a guitar amp) by accidentally running it with no speaker connected. The presence of feedback won't help, it could make it worse because when the output stage clips the feedback loop will try to drive it even harder.

3rd April 2011, 06:36 PM	#9
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	Would a 100 ohm resistor be enough load to damp the big voltage spikes that dammage the transformer insulation?

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