2. amps-preamps
  3. 151214-2744

Tube amp forethought

Hello, im researching my retirement two ch audio system and tube amps are in the forefront of my “wants” my plan will be a pair of QUAD ESL’s not sure which just yet

What do i need to know about maintaining a tube amp, like a AudioResearch 120 for starters or other tube amps. Biasing is totally new to me. Tube life and modes (triode, Pentode, UltraLinear) all foreign to me.

im a 40 year hobbiest so im pretty versed, this is just an unknown territory for me, thanx guys !

kgveteran
jperry
2,448 posts
 
Look for a used Bedini 25/25 for your Quad ESL 57 speakers. One of the best matches.
monoogan
55 posts
 
Check out the Audio Research Documents page. They have biasing instructions for most all their classic amps. Usually, although there are exceptions, all you need is a small insulated screwdriver, a meter that can read millivolts and the restraint to keep one hand in your pocket when the amp is live. For the most part biasing is setting the standing current for the output tubes by measuring the voltage across two points while adjusting a pot with the screwdriver.

Usually you bias after the initial tube install and then after an hour or so of warmup. The manufacturer will have recommended bias values. Run it for a week or two and repeat. After that you should be good checking it every few months. You see a deviation your not comfortable with its time to look into new tubes.

Self biasing is for people who'd buy a self driving sports car. I get the convenience and all but why even bother when you can get a mini van.

Nothing against people who like mini vans or have to have one. You're just looking to get from A to B with minimum fuss. I guess like self biasing. Just not as involving to me.




quantumphysics
6 posts
 

Tubes amps are crude - they like silver wire.

Near field listening (in a treated room) will give you the best results.

For me - tubes behave well with jazz and classical.

Low watt amps (40 wpc) sound sweet at 85 db (nearfield)

Bias the amp yourself - it’s easy and boosts self esteem.

The amp will appear to sound different every time you turn it on.

Have a solid state rig for rock - loud listening.

Tubes are seasonal - they keep you warm on a cold night.

Tubes look sexy in a dark room.

roberjerman
4,319 posts
 
@jperry +1 - I used a Bedini 25/25 with my Quad 57's for years. The only tube amps I found comparable were the Futterman OTL's (I still have 3). An alternative choice would be a nicely restored Quad 303. The 57's are voltage-limited. They will be damaged with more than 20 volts (50 watts). 
roberjerman
4,319 posts
 
If you are still insistent on a tube amp, the Dynaco ST 70 (either vintage or new) is a good match for the 57's.
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