artto Posted November 25, 2002 Share Posted November 25, 2002 A number of years ago I had my Luxman MB3045's in storage for a couple of years. Upon firing them up, one by one, the power tubes (Luxman 8045G) began to fail. One went out very quicker. Others took up to several hours. A recording engineer at a mastering studio told me (also years ago) that tube (power) amps needed to "re-form" the power supply/caps after not being used for a long time. Any truth to this? & if so, whats the safest way to fire them up & not blow a s***load of tubes again? These amps have been in storage again. They are currently tubed with Gold Aero 8045G. One thought I had was to prepare the amps as if I had just put in new tubes. IE: Perform the re-biasing/DC balance procedure from scratch (set the bias pot at the extreme counter clockwise position & set the DC balance pot at center of rotation) & just let them idle for 24 hours with a power resistor for the load before continuing the rest of the biasing procedure. Quote Link to comment Share on other sites More sharing options...
artto Posted November 25, 2002 Author Share Posted November 25, 2002 OK guys. Is this a "first" or what? I'm going to reply to my own post! I have found the answer. Twice. Both from reliable sources. And they both told me basically the same thing. If tube amps have not been for a considerable length of time (1 year?....definetly 2-3 years or more) The power supply caps need to be "re-formed". If they are not, they may draw excessive current & then POOF! There goes your power tubes. You need to use a Variac to slowly bring up the voltage from the power outlet. By slowly, they said maybe 30 minutes. One guy recommended removing the tubes & monitoring the current/voltage at the biasing point to make sure its not "running away" towards a meltdown (my term not his). When you are up to about 75% of the normal line voltage of 110-120 volts, turn the amps off, re-install the tubes, & continue until you reach 100% line voltage. The other guy also said to keep the speaker connected. (I sure hope this doesn't take out my speakers if one of the caps blows). Both said to use the Variac to slowly bring up the line voltage going into the amp. Now I'm having trouble finding a Variac. GRRRRRRRR Quote Link to comment Share on other sites More sharing options...
Malcolm Posted November 25, 2002 Share Posted November 25, 2002 There are a lot of them on eBay, probably the best place to get one at a decent price. Real electronic stores usually have them, too, but not places like RadioShack. Quote Link to comment Share on other sites More sharing options...
artto Posted November 26, 2002 Author Share Posted November 26, 2002 Yes, I saw a lot of Variacs on ebay. Only trouble is I'm not sure what I'm looking at or buying. Big range of prices too. I've checked with a number of local electronics stores/distributers here (Chicago area) & surprisingly, so far, no one has any. I'm thinking that one of the smaller single phase 5 amp self-contained (non-panel mount) ones might be ok. Like a Staco 3PN501. Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted November 26, 2002 Share Posted November 26, 2002 Do a search of this forum, I recently posted a couple of sources, which reminds me, how do you do a search on the forum? -c7s Quote Link to comment Share on other sites More sharing options...
artto Posted November 26, 2002 Author Share Posted November 26, 2002 LOL. As far as I can tell, the search function on here doesn't work very well. Its never retrieved anything for me. Also, an update on re-forming the power supply caps of vacuum tube amps: I finally got hold of an old friend of mine who is a somewhat gifted electronics engineer. Here's what he told me to do. No need for a variac. Take some regular lamp cord & a regular incandescent light bulb socket & wire the lamp socket in series in the lamp cord. Install a 15-25 watt light bulb in the lamp socket. Remove all the tubes from the amp. The amps do not have to be connected to the speakers. Turn on the power to the amp. The light bulb should be glowing normally. As the power supply caps become formed, the light bulb will grow dimmer, almost to the point of going out. When the dimming stablizes, the power supply caps are formed. You should monitor the bias voltage & make sure it doesn't get too high or low during the re-forming process from where its supposed to be. He also said that some of the custom high-end manufacturers even use this technique to form power supply caps the first time the amp is fired up. Quote Link to comment Share on other sites More sharing options...
boa12 Posted November 26, 2002 Share Posted November 26, 2002 the only way i've gotten search to work is by choosing a specific forum. doesn't work if you leave that blank, though sounds like the master is working on getting the search across all forums up & running again. Quote Link to comment Share on other sites More sharing options...
John Warren Posted November 27, 2002 Share Posted November 27, 2002 . Quote Link to comment Share on other sites More sharing options...
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