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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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12th May 2019, 10:11 pm | #1 |
Heptode
Join Date: May 2015
Location: Reading, Berkshire, UK.
Posts: 692
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Black box EL42 valve voltage measurements
Hi all
I have a Pye black box MK2 Amp with the ecc83 ez41 and two el42 valves. I have checked the voltages on the two output valves as follows Pin 2 = 291v Pin 3 = 15.7v Pin 5 = 298v Pin 6 = 0v Pin 7 = 15.7v Pin 8 = 0v Other valve Pin 2 = 291v Pin 5 = 297v Pin 6 = 0v Pin 7 = 15.7v Pin 8 = 0v Also the HT is 267v on one tag and 300v on the other Are those measurements what should be expected? Les |
12th May 2019, 10:54 pm | #2 |
Hexode
Join Date: Mar 2018
Location: Bishop Auckland, County Durham, UK.
Posts: 373
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Re: Black box EL42 valve voltage measurements
The EL42 pin connections are as follows:
1 and 8 heaters 2 anode 3 and 4 internal connections 5 g2 6 g1 7 cathode The two EL42 cathodes are connected together in this model of Black Box. The voltages you have seem about right.
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Regards Martin |
12th May 2019, 11:59 pm | #3 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: Black box EL42 valve voltage measurements
The HT is a bit high and the cathode voltage a bit low. However, the voltages don't tell you a great deal as the valves share the same cathode bias resistor so it is impossible to tell if they are well matched and taking roughly the same anode current.
You can roughly check the current of each valve by measuring the voltages from HT to each anode then (with power off) measure the resistance of HT to each anode and use ohms law to calculate the current. It is 'rough' because the resistance of copper wire changes with temperature and part of each winding is also carrying the screen current. |
13th May 2019, 10:35 pm | #4 |
Heptode
Join Date: May 2015
Location: Reading, Berkshire, UK.
Posts: 692
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Re: Black box EL42 valve voltage measurements
Thanks to both of you for your help.
Les |