#124 completed ! But ... to much heat from PT ?

[jmrckr]

I just fihished my ODS100 #124 build, and I have to say thank you to you all.I couldn't have been able to do this without all that information on this forum. I took the CE chassis, jborder boards (I have them since 6 years ... and hammond transformers). That being said, I have a question ... what is a normal temperature rise up on the power transformer ? When I play my amp, everything is normal, clean, OD, no feedback no noise nothing. Super quiet ... But after an hour of playing or so (not really loud volume), the transformer start to get hot. After nearly 2 hours, its really hot, and power tubes as well. I mean, it is a tube amp so it is normal to have temp rise up but, how much is normal ? Maybe There is something with the bias circuit ? But the biasing seem to work well, power tubes plates are not red or there is nothing visual that could let me think that they draw too much current ... test points indicates 40 mA for the bias current (wich is more on the cold side then hot side for 6L6GC tubes).

I will recheck all voltages and the bias wiring to be sure but, do you guys have any clues with this ?

[martin manning]

What is the part number of the PT? Is it too hot to touch, or can you hold your fingers on it for a few seconds or more?

[jmrckr]

P/N for PT is 290FX. I can hold my fingers on it a maybe 6-7 seconds. The base (plastic part) of power tubes it is another story tough ... 1 or 2 seconds. My references may not be really good for this because my other amp has same transformer sizes but 50W power output (THD flexi 50) ... so nothing really heats up thaaaat much.

[martin manning]

Doesn’t sound out of line to me.

[Guy77]

Yes I agree too, that sounds right. I used the same 290FX in a 100 watt John Mayer build and mine got that hot as well. The owner gigs with it several times a month and there have been no problems with it for the 6 months it has been in service.



Guy

[Charlie Wilson]

Hello, I have been working on a couple Twin Reverbs lately and I had forgotten how hot those things get. The ODS chassis puts the power tubes even closer to the power transformer so there is quite a bit of heat transfer. You did tape off the filament center tap and not ground it, Right?
CW

[jmrckr]

Thanks for your replies guys. I guess I just don't have much experience with these types of design. There is no filament center tap on 290fx from what I see on the spec sheet ... the only thing that could look like it is the two 120R that goes to ground from the 124 schem. But those have to be grounded ... right ?

[martin manning]

Those two resistors are a faux center tap for ground-referencing the filament string. It's common practice in tube amps.

[jmrckr]

That's I was thinking. Thanks for the confirmation. I spent the last day playing with it and adjusting all the trimmers inside. Damn it sounds and feels great. I was craving ODS type of amp for almost 10 years, collecting information, listening to clips, analysing schematics. Now I can say that it is a dream come true.

[telentubes]

Sure is tidy inside. Nice job.