|
Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
|
Thread Tools |
14th Jul 2019, 9:30 pm | #61 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
|
Re: Voltages on ECC83 in BlackBox
I would agree with Lawrence, you probably measured the screen grid current (Ig2) which is typically around 10% of the anode current.
We can get the combined cathode current from Ik=V/R = 15/470 (31mA). The anode current based on the 25V across the output transformer = 25/680 (37mA) or 25/915 (27mA) as you don't say which is the good valve. The most likely is the 915 ohm winding. To see if you are over-running the good EL42 we will roughly calculate the combined anode and screen grid dissipation as follows D = (Va-Vk) * Ik = (288-15) * 0.031 = 8.4W. This is a bit high as the max is 7W according to the datasheet but not as bad as I expected. Again looking at the datasheet, the anode current of say 29mA seems about right with 273V on the anode and screen grid so that valve is still good. The anode and screen grid should be less than 250V but it will be high due to the lower current being drawn from the HT supply due to only one valve working. |
15th Jul 2019, 10:12 am | #62 |
Nonode
Join Date: Nov 2016
Location: Aberaeron, Ceredigion, Wales, UK.
Posts: 2,887
|
Re: Voltages on ECC83 in BlackBox
I have just ordered two EL42’s from Langrex, so I’ll wait till they arrive and then carry out some further measurements.
Cheers John |
15th Jul 2019, 4:00 pm | #63 |
Nonode
Join Date: Nov 2016
Location: Aberaeron, Ceredigion, Wales, UK.
Posts: 2,887
|
Re: Voltages on ECC83 in BlackBox
Quick update pending new valves.
Heater o/c on “cold” valve. Measurements on “hot” valve, Iκ = 28.8mA:Ia = 24.8mA. I presume Ig2 = 4mA. Cheers John |
16th Jul 2019, 4:09 pm | #64 |
Nonode
Join Date: Nov 2016
Location: Aberaeron, Ceredigion, Wales, UK.
Posts: 2,887
|
Re: Voltages on ECC83 in BlackBox
Two EL42 fitted. All seems well. Voltages across o/p Tran. 12v and 14v each, Vκ 15V, all other voltage reading as expected.
Thanks for all the feedback it’s been most helpful. Cheers John |