UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

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.

Reply
 
Thread Tools
Old 14th Jul 2019, 9:30 pm   #61
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 4,157
Default 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.
PJL is offline   Reply With Quote
Old 15th Jul 2019, 10:12 am   #62
John10b
Octode
 
Join Date: Nov 2016
Location: Aberaeron, Ceredigion, Wales, UK.
Posts: 1,161
Default 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
John10b is offline   Reply With Quote
Old 15th Jul 2019, 4:00 pm   #63
John10b
Octode
 
Join Date: Nov 2016
Location: Aberaeron, Ceredigion, Wales, UK.
Posts: 1,161
Default 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
John10b is offline   Reply With Quote
Old 16th Jul 2019, 4:09 pm   #64
John10b
Octode
 
Join Date: Nov 2016
Location: Aberaeron, Ceredigion, Wales, UK.
Posts: 1,161
Default 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
John10b is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 3:25 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.