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Old 8th Jun 2019, 6:15 pm   #1
John10b
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Default Voltages on ECC83 in BlackBox

Could someone give me the typical working voltage readings on V1b, of the above valve, as used in the Pye BlackBox. I’m particularly interested in control grid reading!
Just as matter of interest I’ve got a reading of +7volts on g1, C3 has been replaced. All other voltages are as expected as per service sheet.
Cheers
John
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Old 8th Jun 2019, 6:55 pm   #2
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Default Re: Voltages on ECC83 in BlackBox

Might be worth checking the valve base/pin connections are sound. I have had trouble with open circuits between the valve pins and the holders on these before resulting in some weird effects.
Alan.
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Old 8th Jun 2019, 7:56 pm   #3
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Default Re: Voltages on ECC83 in BlackBox

Hi John, sockets on the ECC83 in BB's are notorious for giving btrouble. I've seen a few with bus tickets etc wedged in them to get a contact.
Not too difficult to replace.

Ed
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Old 8th Jun 2019, 7:57 pm   #4
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Default Re: Voltages on ECC83 in BlackBox

Thanks Alan I’ll bear that in mind.
Cheers
John
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Old 8th Jun 2019, 7:58 pm   #5
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Default Re: Voltages on ECC83 in BlackBox

Thanks also Ed.
Cheers
John
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Old 9th Jun 2019, 4:14 pm   #6
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Default Re: Voltages on ECC83 in BlackBox

Well you were right about the valve base, Pin 2 was fractured and being held in place by the components. This is interesting because the Amp was “working” on my first quick test, with no sign of distortion, and I only became suspicious when taking voltage readings. New valve base will be ordered very soon.
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John
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Old 1st Jul 2019, 9:25 am   #7
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Default Re: Voltages on ECC83 in BlackBox

This is most odd, I’ve replaced the valve base and fitted a new ECC83 and I still get a reading of +7 volts on control grid. Could someone with knowledge of this BB please let me know the actual voltages on the ECC83. Many thanks.
Cheers
John
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Old 1st Jul 2019, 10:31 am   #8
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Default Re: Voltages on ECC83 in BlackBox

Does it remain at +7v if V2 and V3 are removed?
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Old 1st Jul 2019, 11:22 am   #9
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Default Re: Voltages on ECC83 in BlackBox

If I'm looking the correct diagram, V1B is the phase splitter. According to the service sheet it should have 33VDC on the cathode. Check it.

The control grid isn't returned to earth via a resistor, but instead goes, via a resistor, to a tap on the cathode resistor. Shouldn't it read positive wrt chassis? Check R6, R7, R8, R9 and C5.

EDIT. What's the control grid voltage wrt the cathode?
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Old 1st Jul 2019, 12:03 pm   #10
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Default Re: Voltages on ECC83 in BlackBox

Thank you for getting back to me.
These are the voltage readings on V1b : wrt chassis,
cathode = + 25v,
control grid = + 7v.
Cathode current 0.5 mA.
I haven’t measured the grid wrt cathode, I presume it will be -18v.
I haven’t tried removing v2,3 Nick.
I should say that all capacitors have been replaced (except c 4,7 ). All resistors are with spec.
Cheers
John
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Old 1st Jul 2019, 12:21 pm   #11
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Default Re: Voltages on ECC83 in BlackBox

What voltages do you see across R7, R8 and R9?

The voltages across R7 and R9 should be similar as they're the same value and have the same currect flowing through them.
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Old 1st Jul 2019, 12:28 pm   #12
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Default Re: Voltages on ECC83 in BlackBox

R7 is anode load of v1a, did you mean R11 load of V1b?
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Old 1st Jul 2019, 12:34 pm   #13
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Default Re: Voltages on ECC83 in BlackBox

We're obviously not singing from the same hymn sheet. What service info are you using? I was using the manufacturer's sheet.

EDIT. It appears you're using Trader Sheet 660. The resistors I quoted should be R8, R9, R10 and R11. What values ar R9 and R11?
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Old 1st Jul 2019, 12:35 pm   #14
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Default Re: Voltages on ECC83 in BlackBox

Voltage across R9 = +12v.
Cheers
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Old 1st Jul 2019, 12:36 pm   #15
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Default Re: Voltages on ECC83 in BlackBox

Trader Service Sheet 1360.
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Old 1st Jul 2019, 12:43 pm   #16
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Default Re: Voltages on ECC83 in BlackBox

The voltages are obviously dependent on the value of the resistors. The Trader Sheet quotes a range of values for R9 and R11. I would expect them to be of the same value and to have the same voltage across them.
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Old 1st Jul 2019, 12:46 pm   #17
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Default Re: Voltages on ECC83 in BlackBox

Quote:
Originally Posted by John10b View Post
Thank you for getting back to me.
These are the voltage readings on V1b : wrt chassis,
cathode = + 25v,
control grid = + 7v.
Cathode current 0.5 mA.
I haven’t measured the grid wrt cathode, I presume it will be -18v.
I haven’t tried removing v2,3 Nick.
I should say that all capacitors have been replaced (except c 4,7 ). All resistors are with spec.
Cheers
John
Quote:
Originally Posted by John10b View Post
I haven’t measured the grid wrt cathode, I presume it will be -18v.
Definitely not, the voltage between the cathode and grid should be the resistance of the cathode bias resistor multiplied by the current flowing through it, eg. (approx.) 4700*0.0005 = 2.35 volts -ve between grid and cathode, what it registers at on your meter will depend on the meters input resistance and the actual value of the grid return resistor.

Lawrence.
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Old 1st Jul 2019, 12:53 pm   #18
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Default Re: Voltages on ECC83 in BlackBox

Lawrence can you take a look at the bb circuit?
Station x, R9,11 are 50k.
Cheers
John
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Old 1st Jul 2019, 12:58 pm   #19
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Default Re: Voltages on ECC83 in BlackBox

Just a further comment, if there is indeed ment to be +ve voltage on control grid why isn’t it shown on service sheet.
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John
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Old 1st Jul 2019, 12:58 pm   #20
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Default Re: Voltages on ECC83 in BlackBox

25V on the cathode is near as damn it the 26V quoted in the Trader sheet for later models.

Just check the control grid voltage wrt the cathode.
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