[Happy Camper]

Should we ask Mr Gilmore?

 

[PhaedrusX]

Quote:

Should we ask Mr Gilmore?

nah, you only need ask George Ohm, or failing that, Mr. Google.
 
these two links should answer most of the questions concerning impedance load mismatching with tube amps:
 
http://www.prestonelectronics.com/audio/Impedance.htm
http://www.geofex.com/tubeampfaq/taffram.htm
 
the first is a good primer for understanding Ohm's Laws; the second link delves into all things tube amp-related. it is exhaustive and comprehensive. highly recommended reading for those who are interested in the technical aspects of their gear.
 
for those averse to technical treatises, here's a brief summary of the issue:
 
a general rule of thumb for tube amps is the allowance of impedance loads up to twice the amount of the output impedance of the amp. a lot depends on the quality of the output transformers though, so while this may be safe for some amps, it may pose a danger to others. if in doubt, you should probably consult with the designer of your specific amp.
 
however, presenting a high impedance load that exceeds the tolerance of a tube amp can damage the output transformers and output tubes.
 
using the "garden hose" analogy from the first article, where the water pressure from the tap represents the voltage, the nozzle on the other end of the hose represents the impedance, and the actual flow of water out of the nozzle represents the current, problems can arise if the nozzle only allows a trickle over an extended time, which is the case when a too high impedance load is presented. the water pressure can build up inside the hose and it could spring leaks.
 
similarly, with an excessively high impedance load, energy can get stored inside tube amps, high voltages can build up with nowhere to go, and voltage spikes can occur that can penetrate the insulation of the transformer, and short the windings. in the same way, voltage spikes can penetrate the insulation of tube sockets or flash over them, and a permanent short can occur.
 
just to be open and clear, i am no "hard-core tube techno-expert," just a messenger.
 
 
 

 

[grokit]

Why isn't this an issue with solid-state amps, they have transformers as well right?

 

[PhaedrusX]

solid state amps do not use output transformers.

 

[Skylab]

Well, I shall restrict my use of the pigtail to my SS speaker amps, then, although those are all high-powered vintage receivers and have no trouble driving the HE-6 even from their headphone outs, where many dozens of watts are available even with the resistors they use to pad them down. But I don't want to damage my Leben. Sadly, that means no HE-6 on the Leben, because it doesn't have enough power on it's headphone out to do a really great job with them.

 

[sillysally]

Quote:

Well, I shall restrict my use of the pigtail to my SS speaker amps, then, although those are all high-powered vintage receivers and have no trouble driving the HE-6 even from their headphone outs, where many dozens of watts are available even with the resistors they use to pad them down. But I don't want to damage my Leben. Sadly, that means no HE-6 on the Leben, because it doesn't have enough power on it's headphone out to do a really great job with them.

Because of your earlier post about headphone Jack in a speaker amp I ran my complete system though my Onkyo 7.1 120W per Ch speaker amp using the direct audio function for headphones (source direct) 2Ch interconnect inputs of my Onkyo and the 1/4" headphone Jack with my HE6's. The good news was there was more than enough volume to blow my ear drums, the bad news was the audio compared to my WA5LE and tubes sucked, not even close. If I had no WA5LE and tubes to plug in my HE6 and only my Onkyo I would go back to my WA6SE and my HD-800's.
 
Sorry to hear no Leben with your HE6's.
 

 

[kwkarth]

Quote:

Well, I shall restrict my use of the pigtail to my SS speaker amps, then, although those are all high-powered vintage receivers and have no trouble driving the HE-6 even from their headphone outs, where many dozens of watts are available even with the resistors they use to pad them down. But I don't want to damage my Leben. Sadly, that means no HE-6 on the Leben, because it doesn't have enough power on it's headphone out to do a really great job with them.

Putting a 10 ohm resistor in parallel with each headphone channel and then using the 8 ohm tap or, preferably, putting a 24 ohm resistor in parallel with each headphone channel and using the 16 ohm tap will give your Leben the perfect load so both it, and you, will be happy.  One should use a non inductive load power resistor rated at 10W or more for this task.  Happy listening!
 
 

 

[wuwhere]

That's what I did on my tube amp before I used it solely for my HE-6. I actually soldered the resistor at the back of the speaker posts inside the amp. This is the resistor I used. Its 10 Ohm 10W 5% wirewound resistor, you can buy them from RadioShack, $1.99/pair.
 
 
 

 

[kwkarth]

Quote:

That's what I did on my tube amp before I used it solely for my HE-6. I actually soldered the resistor at the back of the speaker posts inside the amp. This is the resistor I used. Its 10 Ohm 10W 5% wirewound resistor, you can buy them from RadioShack, $1.99/pair.
 
 
 

Wirewound resistors are inductive, so they're not so good sonically, nor are they completely non reactive as an audio load as such.  
 
Here's what you want:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=004-10

Or for a 16 ohms transformer tap:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=004-30

 
 

 

[wuwhere]

Thanks! I'll try those.

 

[kwkarth]

If you want to go for the better solution, it will cost you a little more:
 
For 8 ohm tap:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=005-12.5
 
For 16 ohm tap:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=005-30
 
 

 

[Happy Camper]

Wirewound resistors are inductive, so they're not so good sonically, nor are they completely non reactive as an audio load as such.  
 
Here's what you want:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=004-10

Or for a 16 ohms transformer tap:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=004-30

 
 

Thank you very much.

 

[wuwhere]

Quote:

If you want to go for the better solution, it will cost you a little more:
 
For 8 ohm tap:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=005-12.5
 
For 16 ohm tap:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=005-30
 
 

Those Mills resistors are expensive, but I've paid a lot more for capacitors   I'll try those then. Thanks!
 

 

[Happy Camper]

So are the resistors recommended for the SS amps and what about OTL tube amps?

 

[wuwhere]

Quote:

So are the resistors recommended for the SS amps and what about OTL tube amps?

Its probably not a bad idea as well for SS amps. Not sure about OTL since they don't have output transformers.