REDD47 - R11 getting hot

[Deepdark]

Hi there

I posted it on the upgraded site, but it has dissapear. Anyway, here it is. I've build a Redd47, turret board. Integral to the original schematic exept for the psu, I made a RC filter made of 5 stages.

R11/8k2 is getting hot. First, it was a 5W ww, and it started to smoke once I turn the unit on. weird. I then tested all voltages, all spot on. Then, I measured vdrop everywhere, spot on again. Then, i inspect the layout for anormalities, mistakes, resistors and caps values, everything looks good.  Looks after all caps to be sure there was no dc, and it's ok. So no caps leakage. I changed the tubes, changed nothing. I then measured current, again, spot on everywhere. Then, I changed teh 5w 8k2 for a 10w. It does not smoke, but remains quiet hot. I tested the unit and sounds good.

So here we are. I've been told it was due to the class A output being hot. I know Class A can get quiet hot (just like my octopre here in my studio). I've been told also that the output stage of the redd47 is hot, due to the hight current/power consumed here. Total power 6.6-7.0W, and probably the majority of it comes from the output, so maybe it's just normal and I'm overthinking here.

Attached is the schematic with my readings

 

[emrr]

Backstory on this build

http://realgearonline.com/thread/3952/redd47-8k2-resistor-smoke

 

[Deepdark]

yeah thanks EMRR. Can't upload the schematic now, it seems the server can't access the path.

In another note, maybe that 3.3W IS hot (through R11), in term of heat, and it was too hot for the 5W ww resistor, maybe my 308V B+ is a little too high for the matter, compared to the 290V spec.

Here are my measurement, until I can linked schematic:

B+ current: 21.4ma
R11, before and after: 19.6ma
R7, before and after: 1.7ma

So here, current looks fines. Here are my voltages:

V2 plate: 143v
V2 cathode: 4v
V1 plate: 81v
V1 grid: 90v
V1 cathode: 1.7v

R11 vdrop: 165v
R7 vdrop: 83v
R2 vdrop: 136v
R3 vdrop: 116v
R9 vdrop: 43v
R8 vdrop: 8v

 

[Deepdark]

Concerning the class A, it means that the unit isn't load dependant in term of power consumption, right? Do you have any ideas what can cause R11 to be hot, other than the Class A suggestion?

 

[Deepdark]

I'm reading the E88CC sheet right now, Max anode dissipation is max 2W (section 1 + section 2). Is it possible that there is an excess of power that dissipate through R11?

 

[moamps]

I'm reading the E88CC sheet right now, Max anode dissipation is max 2W (section 1 + section 2). Is it possible that there is an excess of power that dissipate through R11?

Your bigger problem here might be overheating of the output tube, but that's the way how the REDD47 was designed.

 

[Deepdark]

Gracias Mopamp.