5E3 putting out 19 watts!?!?

[waldner]

Ok, so after getting bias set properly on my 5F6A, I now turned to my favorite amp, the 5E3 and here's what I am getting.

The Compu-Bias readout is showing the following:

Vp= Plate Voltage (voltage between cathode and plate)
IK= Cathode Current -
D= Tube Dissipation in Watts (total as measured at cathode)

Vp= 355/359
IK= 54/52
D= 19.2/18.6 watts

Isn't that way to much output for a 6V6?  The tubes are EH6V6gt's and I've played this amp a ton over the last few years with no problems. 
What if anything can I do to correct and get into a more reasonable range?  Or is it ok that my 5E3 w/ 6V6's is putting out more than my 5F6A with 6L6's?

Thanks,

[eleventeen]

I have never used one of those Compu Bias thingys. I note that under the LCD window, there are those word...1 probe / 2 probes ----common cathode only...........


Somehow I think the particular wiring config of your amp is "fooling" the Bias tester and you are reading double what the reality is. Because yes, >50 mils through a 6V6 would be redplating the tube with gusto.

[sluckey]

I'd like to get a reading using my old fashion method...

Remove your bias probe and plug the tubes in as usual. Now measure voltages WRT chassis ground on pin 3 and 8 of each output tube. Post those voltages. Also post the value of your cathode resistor. If you have separate cathode resistors post the value for each.

[waldner]

I think you found the problem in that fine print about using two probes with only fixed bias or common cathode bias.

I will try to measure according to Sluckey's instruction and also try just one probe.

Thanks

[PRR]

It is not "putting OUT" 19 Watts of sound. The 19 Watts is heat.

And since this meter seems to read total cathode current (plate and screen) the plate dissipation is less (maybe 18 Watts).

That's over-spec. However I think all new-made guitar-market "6V6" will stand it.

[waldner]

Ok, it's not using two probes simultaneously that caused the reading, because I get the same reading with one probe.

Sluckey, I measured as you said at pin 8 and pin 3 for each output tube and got around 27 and 389 respectively. 

The cathode resistor is 5w 250.  I assume that's what you were looking for?

Does this mean my Compu Bias is lying to me or being fooled?

[eleventeen]

Can you run the thing in a darkened room? In case the tubes are just barely redplating.


Do the tubes get super hot? 6V6 (actually *any* output tube) can run pretty hot and it is hard to describe in words what's too hot. They can certainly burn your hand even when running OK.


If you are reading 27 volts, your bias device isn't lying: You have 27 volts through 250 ohms, 27/250 = .108 amps = 108 mils = over 50 mils per tube. Don't know what to say, except, that's really high.

[Willabe]

I'd like to get a reading using my old fashion method...

Remove your bias probe and plug the tubes in as usual. Now measure voltages WRT chassis ground on pin 3 and 8 of each output tube. Post those voltages. Also post the value of your cathode resistor. If you have separate cathode resistors post the value for each.

Please try this!   

[waldner]

I'd like to get a reading using my old fashion method...

Remove your bias probe and plug the tubes in as usual. Now measure voltages WRT chassis ground on pin 3 and 8 of each output tube. Post those voltages. Also post the value of your cathode resistor. If you have separate cathode resistors post the value for each.

Please try this!   

I did and put the readings in a previous post.  Here are the results:

Pin 8= 27
Pin 3= 389
Cathode Resistor= 250 5w

Can you run the thing in a darkened room? In case the tubes are just barely redplating.

Do the tubes get super hot? 6V6 (actually *any* output tube) can run pretty hot and it is hard to describe in words what's too hot. They can certainly burn your hand even when running OK.

If you are reading 27 volts, your bias device isn't lying: You have 27 volts through 250 ohms, 27/250 = .108 amps = 108 mils = over 50 mils per tube. Don't know what to say, except, that's really high.

I will try to check for red plating tomorrow.  So according to the math she's running high.  That's what I was afraid of.  Now I just need a method to bring things to a more reasonable level.  Again, the amp sounds great and has worked fine for a few years of infrequent but sometimes intense use on the same pair of EH6V6 tubes.  To PRR's point, maybe these tubes can handle it, but I'd still like to avoid running this far beyond what's intended.

[sluckey]

Sluckey, I measured as you said at pin 8 and pin 3 for each output tube and got around 27 and 389 respectively. 

The cathode resistor is 5w 250.  I assume that's what you were looking for?

Does this mean my Compu Bias is lying to me or being fooled?

Your compu bias is correct. Using those voltage readings with a 250Ω cathode resistor the amp is idling at 39W total. Assume the tubes are well matched and divide by two shows each tube is idling at 19.5W. Your compu bias does not assume. It actually measures the current through each tube and it's results are more accurate for each tube.

Bottom line, those 6V6s are cookin'!

[VMS]

From the picture it looks like you are using Sovtek 5y3GT rectifier. According to the internets that tube won't give you the same voltage drop as a NOS 5y3GT tube will. Changing that tube could run your power tubes little cooler.

Here is the 5E3 power amp analysed:

http://ampbooks.com/mobile/classic-circuits/fender-deluxe-5e3-power-amp/

[Willabe]

I did and put the readings in a previous post. 

Very sorry, my mistake.

[waldner]

Ok, I put in a NOS 5Y3 rectifier and got the following:

Plate v 323
cathode current 47
Dissipation in watts - 15.3

So that brought it down.  Is that still too high or is it normal for a 5E3?

Also which number is too high, my plate v or cathode current and what can I do to remedy that?  I have read about increasing the cathode resistor value to more than 250.

[John]

The current is what you really need to pay attention to. That plate voltage is fine. I'm a little puzzled as to why the current is a little higher than expected.


You can try raising the K resistor to 300. That will also raise the plate voltage a little, but should ease up the current draw. Also, try putting in a new K bypass cap (maybe someone already suggested that). If it's leaky, I think that will cause some issues too.

[DummyLoad]

i'd run it as is with the NOS 5Y3GT. you're just going to chase your tail, so to speak, by increasing the cathode R; when you do, B+ will rise to compensate.

--pete

[tubeswell]

I've played this amp a ton over the last few years with no problems. 
What if anything can I do to correct and get into a more reasonable range?

You say you've played it a ton with other tubes over the years? What were the voltages like with the previous set of tubes in it? Maybe it's those tubes? (Are they real 6V6s (or are they dressed-up Russian 6P3S? - seen it happen)

[HotBluePlates]

you're just going to chase your tail, so to speak, by increasing the cathode R; when you do, B+ will rise to compensate.

... What if anything can I do to correct and get into a more reasonable range?

... What were the voltages like with the previous set of tubes in it? Maybe it's those tubes? (Are they real 6V6s (or are they dressed-up Russian 6P3S? - seen it happen)

Both these are right. The individual set of tubes could be a far end of the 6V6 spec range, with high Gm and higher-than-normal plate current for a given bias.

You can bring the total dissipation down by raising the cathode resistor value. It will take some experimentation cause as you raise the cathode resistance, the (bias) voltage across it will rise, tube current will go down, but plate voltage will rise due to less drop across OT winding resistance. Which then might not reduce dissipation much (or at all). Keep raising the cathode R, eventually the dissipation will drop to the desired value. If the tubes are abnormally-high Gm, or worse yet gassy, then when you plug in a normal-performing set of 6V6's they will tend to be too cold with the new very-high cathode R.

So do try an old, known set of tubes to evaluate how different these particular ones are.