2. amps-preamps
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Tube upgrades for Jolida 502B?

I realize this is something that has come up before, though in searching the archives I didn't come away with a clear path forward. My amp is completely stock and came equipped with Sovtek 6550s. Using it to drive Totem Forest speakers. I contacted Jolida. They recommend KT88s. Their reply is a bit unclear but they might be suggesting Electro Harmonix. They also indicate reliability issues with Chinese KT88s. Response Audio (Jolida dealer and modder) recommends Shuguang KT88s (Chinese). The Tube Store recommended JJ Tesla KT88s on the strength of their great imaging and deep bass (more bass being something I was looking for). I was initially leaning towards SED Winged "C" 6550s. Now I am a bit more confused. I'm curious about KT88 vs 6550 sonics and reliability differences. Thanks in advance to any one willing to take the time to share their experience and preferences.
128x128ghosthouse
wolf_garcia
6,633 posts
 
I have to wonder what difference better 12at7s would make as I have been told that particular tube purpose (driver/phase inverter) is somehow less important. I welcome any opinions about that, as long as they aren't meant to intentionally upset me.
wolf_garcia
6,633 posts
 
Based on an entertaining conversation with a really cool and tube savvy woman at thetubestore, I ordered a pair of matched section JAN Philips 12at7s...they may or may not be the best option but she was so much fun to talk to (maybe I need to get out more) it's worth the relatively small cost to find out.
tbromgard
814 posts
 
interesting-thanks
tbromgard
814 posts
 
Thanks for the responses. Now can anyone explain how to bias tubes in the 502brc? I dont have the owners manal
wolf_garcia
6,633 posts
 
If it's like the 502p you turn the little bias screws down (a lot) before installing tubes, disconnect any signal to the amp, put the tubes in and turn the amp on and wait 10 minutes or so...then turn the bias up on each tube just until the LED lights...do all of 'em and check 'em in an hour or so and you're done. I bought a Radio Shack meter just to fine tune the bias (and out of curiosity) and found that the LEDs are surprisingly accurate. Note that due to house current fluxuation throughtout the day the LEDs change a little from time to time, but unless your tubes are failing this isn't a worry.
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