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Hi,
I usually turn all my tube amps on for some hours every few month and today it was the turn of my Sherwood S-5000 (7189).
After a couple of hours I touched the power transformer and I noticed it is very hot (you can keep your hand on it for 10-20 seconds but it's very hot anyway), while the output transformers are cool. Is it normal? I know that the S-5000 has a very hot HT at 415V. Can be this the reason?
Any advice is welcome.
Raul
P.S. the amp work fine, nice sound with no noticeable hum. The only thing I replaced was the only one small electrolitic that is under the chassis.
Follow Ups:
I have several sherwood s5500 and s5000 and the PT all run hot after 2 or more hours of use.The way to rectify the situation is to go to radio shack and or soemwhere on ebay and buy yourself a 3 amp 6.3volt transformer and use it on the filaments of the output tubes..I did this on 2 of my sherwoods and even one i converted to use 6l6 output tubes as opposed to the 7868s..Most of your heat in your power tranny is from the filaments being the fact they draw the most current.Disconnect the filaments on the outputs and use your new separate tranny for just the outputs..You can mount it on top of the chasis as i did and run the wires thru a hole to the filaments.. You can still use your big PT filament tap to run the 12ax7s. The reason transformers get hot as they do is really the innefficiency of the power trans..When ac voltage enters the transformer it hits the iron core which produces a current from the resistance of the core.The current is then dissapated as heat..These currents we call eddy currents..Thats a general idea of why power trannys get do hot.But do as i said with a separate filment tranny and guaranteed it will solve your problem.Any further assistance email me at mikeLs2@hotmail.com.
mike
I think you may need some TLC. I have a later 5000 with the 7864 tubes and experienced the hot transformer after several hours of use. I had it in for service with the tuner and the tech replaced some caps. Since then I have been able to leave the unit on for more than 8 hour sessions and the transformer is cool to the touch; can leave my hand on it for as long as I want, similar to my McIntosh. Admittedly, the tuner transformer runs hot.
Too hot to touch for more than a brief moment (like ~2 sec) is about 60*C (140*F). The lowest grade of insulation used in transformers is rated 105*C (220*F). Put a thermometer on it if you are worried, but if you can hold your fingers on it that long I'd say it is running normally. Search the archives here and at Tubes for *hot* for lots of soothing replies to your concern.
In a search @ Tubes, it was mentioned that many commercial transformers are designed with a temperature rise over ambient of between 40 and 60 deg C (104 to 140 F rise) when in operation.
Hi Raul - How's everything it Italy? If you can keep your hand on a power transformer that long it really isn't that hot - not a problem.
Thank you Charlie and thank you Ron for your reassuring answers.
After more than three hours of use I still was able to keep my fingers on it for 8-10 seconds, so it's all ok.
Charlie: here is cold and foggy today, I wish I was in Florida (is it there that you live, right?)
Raul
The skies are clear here but it's cold too - at least for Florida. In fact it was below freezing for several hours last night and this morning and it didn't warm up much today. Currently about 52 F (~12 C) since we're talking temperatures today. Time to fire up the tube amps!
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