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In Reply to: RE: GE 6L6GC Heat Issue posted by cabelok on March 21, 2016 at 21:45:29
the tubes are drawing more current, working harder, thus causing the extra heat. Whether the filament is brighter is unlikely. It is very hard to quantify that. I would guess that the pair are more used up and thus drawing more current to satisfy the amp's demands. cheers, Dak
Follow Ups:
You can then tell how used up a tube is by how much heat it causes the OPT to generate? I've switched the tubes (left/right) and it seems to run cooler - Now I'm really confused.
With the information at hand we are just educated guessing about the problem. You should try to find out how much current your tubes are using at operating conditions. The best way to do that is measure the current at the bias resistor. You would need a bias resistor for each tube. I have an amp that has individual bias resistors for each power tube where I can measure with a voltmeter and using ohms law the current consumption of each tube V=IR or I=V/R. If you can not do that you should probably get a matched quad of power tubes. regards, dak
Thanks DAK, I've found someone in the Valley who will test them. Any idea what happens when you don't have a speaker connected to a channel or more precisely a poor/intermittent connection?
Good, but the test needs to measure the current. Tube testers mostly measure voltage output not current consumption.
About your intermittent load. Most amps made now, have circuitry to prevent or reduce oscillation. But, some amps were made without it, so not knowing your amp it is hard to say. A subsonic or high frequency oscillation in the particular channel could make the power tubes work harder and those would be running "hotter".
I really appreciate your info, I will ask if the can test the current consumption. Pity you don't live nearby I could offer you a glass of wine.
I am glad to be of some help. Be sure to have all your tubes tested just to make sure. The small signal tubes don't have to be tested for current just a standard emissions test is fine. I hope your amp is ok and that it is just a tube problem. tc&br, Dak
Edits: 03/22/16
I'll check tonite with tubes I know to be okay. Thanks for advice re pre tubes. Do you think the connectors need to be tweaked regularly so they contact the pins with a consistent force? I will check that also. When I switched the tubes this afternoon(L to R)they run much cooler but warmer than I like (after an hour). At least both sides (feel by hand above the OPT) are the same now.
Yes! Making sure the socket contacts are clean/tight and the tube pins clean is important. The temperature improvement may indeed be due to inserting/reinsert in and switching sockets as a cleaning motion in itself.
Cheers!
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
There was a socket that was a little too open on the side I was have trouble with, tweaked it and cleaned with pipe cleaner dipped in De Oxit. All is well. I have to get into the habit of checking them. When one considers how much some of us spend on tubes and the archaic design of the contact socket I wonder... High end connectors for other applications usually have a stainless collar which acts as a spring to ensure the socket parameters stay the same.
...some old time transmitter grade sockets did indeed have "helper" springs around pin contacts to assure a tight grip at all times. Pic is closeup of contact of an old Johnson 7 pin ceramic socket intended for tubes like 829 or 6C33. Spring wraps around the outside of actual contact.
I'll order myself a socket and check if it feasible to make up something. I was thinking more along the lines of a key ring type of spring (easy to put on)- not too tight and not too soft, just right... I'm sure many have chased problems without thinking of this.
I try cleaning and tightening everything once a year. Including controls, cables, pretty much anthing that makes contact. Even wall outlets. Admittedly it takes a long time and I am getting lazier. Still haven't completed my latest annual clean which I started months ago.
Yes it would be nice if things could be more stable. Sometimes I feel like just soldering everything together and be done with it!!!!
Cheers!
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
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