How hot is too hot for the chassis?

[mbratch]

OK, so my Mojo 5E3 build works great. It has the stock mojo parts. The only thing I did differently was to change the ground switch to standby (using the CT), and add two 11V (@5W each) zeners to the CT to bring the voltage down a bit (it's stock at 384-0-384), so I am happy with the bias I'm getting.

The wiring for this is simple: the PT HV CT connects to one lug of the standby switch. The other lug of the standby switch connects to the two zener diodes in series, and the other end is bolted to the nearby PT lug on the chassis.

Now to my question. When I'm using the amp, it gets rather warm emanating from the power transformer area. It's not nearly hot enough to burn your hand, it is uncomfortable to touch for more than a couple of seconds or so.

I might go in and remove the zeners and see where it goes, but I wasn't sure the zeners were generating that much heat.

Can someone relate their experiences with this or shed some light? Thanks.

[PremiumPlus]

Hi mbratch, I've got a 5E3 with a Heyboer transformer, and right now mine is running a 5U4 rectifier with a pair of 6L6GC's, a 275 ohm cathode resistor. The voltage at pin 3 of the output tubes is, if I remember, right around 375vdc. Sounds really nice, and it runs very warm, hot enough to not hold the power transformer for more than 5 seconds or so. But so does my '68 Super Reverb...it is right around the same temperature. The chassis on the 5E3 gets nice and toasty but it won't scorch the tweed
I've run it for several hours at a time without issues. I guess one thing to check would be to make sure the low voltage heater windings are holding their respective voltage levels up, and not sagging. If they are, you should be okay. I remember when I started in electronics that I was astonished how hot transformers would run in those old tube tv sets...

[JoeM]

I dont feel the heat is too much concern on your amp. My tube amps all get quite hot after being left on. My BF Princeton for example gets real hot (the PT too) and it's worked fine for 40 years or so.

[mbratch]

Thanks for checking guys. I know stuff usually runs a little hot in tube amps, but the 5E3 has things a bit 'closer to the user' so you can more easily feel the heat. And I had read somewhere on the internet (gotta watch that) that it shouldn't run that hot unless there's something wrong with the PT or its specs. I guess whatever I read was nice but incorrect.

Mine is uncomfortably hot, not to want to hold/touch more than just a few seconds, but it won't scortch anything.