Tode issues

[xcortes]

I finally finished my son's tode. The  resistance measurements are good but the voltages are not. I carefully went over the manual ti make sure things are as supposed. Also reheated all solder joints with no luck.

I can infer that the EL84 tube is drawing too much current. The 1.6kW at the ps gets very hot so I need to turn the amp off very quickly.

Voltages are:

T3 215 vs 215 specd.
T4 207 vs 215
T5 412 vs 430
T9 204 vs 215
T10 408 vs 430
T11 181 vs 325!!!

Front chassis:
T2 70 vs 35!!!
T5 75 vs 37!!!
T10 70 vs 36!!!
T11 137 vs 293!!!
T14 130 vs 215!!!
T22 134 vs 295!!!
T24 129 vs 30!!!
T24 4 vs 4

Any thoughts?

Thanks

 

[Paul Birkeland]

If it's not too much trouble, could you post the voltages you see at the sockets? 

-PB

 

[xcortes]

Will do

 

[xcortes]

Here they are:

EF 86

T1 72v
T2 2 v
T3 .3 v
76 82v
T7 0v
T8 0v
T9 0v

EL84

T1 54v
T2 83v
T3 79v
T6 1v
T7 132v
T8 1.4v
T9 120v

Thanks

 

[xcortes]

Back home from the vacation where we vuilt the amp. Tested another EL84. Bingo!

Now to rock

Thanks Paul!!!

 

[xcortes]

Woooow, she does rock 😄😃😀

 

[Paul Birkeland]

EF 86
T9 0v

That's where I would start.  The circuit has a little polystyrene capacitor and a 10M resistor at the grid of the EF86.  The 10M resistor is so high that the grid leakage of the EF86 forms bias voltage across it.  You should actually see negative voltage here (I'm remembering something like -2 to -3V).

Causes for this voltage to be 0V might be -
1.  Elimination of the input cap.
2.  Swapping the 10M and 150 Ohm resistors on the EF86 socket (they are tiny, but measurable in circuit).

Also, pins 3 and 8 on the EF86 socket should be wired together (you indicated 3V on one and 0V on the other).

I hope this helps! 

-PB

 

[xcortes]

It was a bad tube Paul. Thanks

 

[Paul Birkeland]

It was a bad tube Paul. Thanks

I suppose that should have been item #3.  So the EF86 wasn't behaving?

 

[xcortes]

The el84