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Tube stereo sounds -smaller- after being on

Ok here is a weird one. I’ve been into tube audio for the last 20 years or so and I have one system I leave as is and one system I mess around with and change things out. For the most part, these days, I’m happy with both. Except I’ve been noticing something I thought I was imagining. Which is my experimental system starts out sounding great and after being on for a couple of hours sounds worse. Small soundstage, compressed highs and lows. Just over all enh. I have two turntables -

Gates and an EMT 930. The mixer is a great sounding one hand built in Austrailia called a Condesa Lucia. The amp is a Line Magnetics 2a3 amp LM 217. The cartridges are an EMT and a Denon 102. The tt preamps are by sun valley and auditorium 23. The one thing I can think of is the amp is a 220 version and goes through a power converter. Perhaps this is a sonic wrecker when it gets hot. Any other ideas? Thank you. 

yaluaka

Showing 3 responses by dekay

dekay's avatar
dekay
5,706 posts
 

The only time I've experienced what you describe is when I was using my vintage Pilot 232 (1959/1960 PP EL84 power amp) 15+ years ago.

After 3-4 hours of play the soundstage would gradually shrink/compress and the power transformer would become extremely hot by then.

The amp was all original (lytic caps reformed to spec) with only the ceramic resistor feeding the 5ar4 rectifier being replaced with a like unit.

When I powered it off a variac set to 110 volts the problem did not reoccur and the PT did not become overly hot.

Didn't check the A/C line voltage @ the time, but assume that it must have been fairly high.

 

DeKay

 

dekay's avatar
dekay
5,706 posts
 

If you are "adding" EQ with your preamp/mixer it's possible that doing so is overtaxing the 3 watt amplifier and/or the step-up TF you are using.

What speakers are you using, or are you using headphones (I know ZIP about headphones)?

Just throwing this out there for thought/discussion.

Interesting LM amp which I was not aware of (like the tube compliment and the soft start feature).

 

DeKay

 

dekay's avatar
dekay
5,706 posts
 

Have you tried testing and/or replacing the rectifier tube with one tested to new spec?

The 2 hour time period/demise in sound is what should be telling you/us something, but what is that?

 

DeKay

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