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Sets, Parts and Service Information Wanted (private buyers only, no swaps) If you need help obtaining components, sets or equipment, post a message here. Private buyers only - no traders. No swaps.

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Old 1st Dec 2019, 11:26 pm   #1
jdavis6809
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Default 12AU7 ECC82 Valve wanted

hello,

wanted 12AU7 ECC82 valve one off

regards

john
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Old 2nd Dec 2019, 8:27 am   #2
Tim
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Default Re: 12AU7 ECC82 Valve wanted

Available from suppliers such as Rapid Electronics, Cricklewood etc.
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Old 2nd Dec 2019, 1:12 pm   #3
jdavis6809
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Default Re: 12AU7 ECC82 Valve wanted

hello,

want used because new means 100hr burn in

regards

john
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Old 2nd Dec 2019, 1:43 pm   #4
mark_in_manc
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Default Re: 12AU7 ECC82 Valve wanted

If you fancy buying two new ones and swapping me for a used one, I'll see what I can do...
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Old 2nd Dec 2019, 7:48 pm   #5
GrimJosef
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Default Re: 12AU7 ECC82 Valve wanted

Quote:
Originally Posted by jdavis6809 View Post
... want used because new means 100hr burn in ...
Are you certain, because this would be news to Mullard ?

Cheers,

GJ
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Old 2nd Dec 2019, 8:15 pm   #6
Craig Sawyers
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Default Re: 12AU7 ECC82 Valve wanted

Quote:
Originally Posted by GrimJosef View Post
Quote:
Originally Posted by jdavis6809 View Post
... want used because new means 100hr burn in ...
Are you certain, because this would be news to Mullard ?

Cheers,

GJ
Tektronix used to burn in all the valves they used in their gear, and had massive racks to do just that http://w140.com/tekwiki/images/0/0a/Tek_tube_aging.pdf

Specific extract for the 12AU7:

SPECIFICATION NO. 154-0041-00
11-23-76
Page 1 of 1
ITEM NAME AND DESCRIPTION. 12AU7/ECC-82 ELECTRON TUBE, 9 pin miniature,
medium-mu twin triode. Manufactures heater rating (series) 12.6 volts,
150 MA.
TEKTRONIX SELECTED PART NUMBER. 157-0049-00.
3 AGING.
3.1 AGING CONDITIONS.
Tubes are aged on 40 socket aging racks with never less
than 32 sockets loaded.
Heater voltage with 40 sockets loaded shall not exceed
13.0 volts nor be less than 12.0 volts. A 25 watt wire
wound resistor may be used in the transformer primary
circuit to obtain the specified heater output voltage.
B-Plus Supply. A bridge rectifier, a 10 to 15 n wire
wound resistor and a capacitor of not less than 80 mfd
are used to recify and filter the 117 volt, 60 cycle line.
Plate voltage, 130 to 155 volts.
Both heater and B-Plus supplies are floating.
Cathode-circuit resistor, 680 n ± 10%.
Grid-circuit resistor, 100 Kn± 10%.
3.2 AGING CYCLING PROCEDURE.
4
The 40 socket aging racks are placed in portable
AGER-CYCLE units which are pre-set to automatically
control cycle-age time.

Power is applied to tubes for 55 minutes of each
hour; power removed for 5 minutes of each hour.
Power on time, not less than 88 hours and not over
120 hours.


Craig
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Old 2nd Dec 2019, 8:19 pm   #7
Craig Sawyers
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Default Re: 12AU7 ECC82 Valve wanted

More on "aging" (AKA burn-in), vibration testing and valve matching at Tektronix here

http://w140.com/tekwiki/images/1/14/..._procedure.pdf

Craig
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Old 2nd Dec 2019, 10:32 pm   #8
GrimJosef
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Default Re: 12AU7 ECC82 Valve wanted

The difference is that Tektronix had a reason for doing it. It might be to weed out infant failures, given the general 'bathtub' shape of the failure rate vs time curve. Or it might be to select for matched pairs, in which case they'd want the valve characteristics to settle which in some (but not all) valves they do.

But the OP wants just one valve. And its characteristics don't matter to him (at least, not sufficiently for him to specify them).

In the absence of any declared reason for 'ageing' the valve all you'd end up with would be, um, an aged valve. The best used valves are described as 'tests like new'. I've yet to see one described as 'tests better than new'. But I've seen plenty of old ones that are worse than new.

Cheers,

GJ
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Old 3rd Dec 2019, 12:53 am   #9
turretslug
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Default Re: 12AU7 ECC82 Valve wanted

I expect that, for Tektronix, a major incentive was to thoroughly "settle" valves that were to be used in complex multi-stage DC-coupled amplifiers and timebase circuits. It wouldn't look good to have to say, "this shiny and very expensive new 'scope was calibrated before it left the works- but, um, you may have to twiddle quite a few internal presets to keep the trace centred on the screen for a few months yet". For a straightforward, fully (OK, Mullard applications, partly...) AC-coupled AF amplifier-type use, I'd be very surprised if ageing was necessary or useful.
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Old 3rd Dec 2019, 2:13 am   #10
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Default Re: 12AU7 ECC82 Valve wanted

I don't think Tek cared at all about the smoothness of the anodes or the shape of getters and the colour of lettering. They cared a lot about reliability. Burn-in was partially to let things settle, but mostly to weed out short lived individuals. They designed circuits around the specifications of available valve types. Any part in spec would work properly. Properly toleranced design made it so. Same at HP. Good quality instruments still renowned today. Places where Ohm's (and Kirchoff's and Faraday's, and...) law ruled.

David
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Old 3rd Dec 2019, 5:34 am   #11
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Default Re: 12AU7 ECC82 Valve wanted

Quote:
Originally Posted by Radio Wrangler View Post
I don't think Tek cared at all about the smoothness of the anodes or the shape of getters and the colour of lettering. They cared a lot about reliability. Burn-in was partially to let things settle, but mostly to weed out short lived individuals. They designed circuits around the specifications of available valve types. Any part in spec would work properly. Properly toleranced design made it so. Same at HP. Good quality instruments still renowned today. Places where Ohm's (and Kirchoff's and Faraday's, and...) law ruled.

David
I agree with that and the Engineers at those companies were masters of circuit design and excelled in it, leaving examples behind today, of the equipment that they designed and built, that are inspirational in my view. And much of it still working, due to the high quality components used and the fact they were determined to screen out any defective parts. This M/O is rarely seen anymore in a throw away world.
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Old 3rd Dec 2019, 7:39 am   #12
Bazz4CQJ
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Default Re: 12AU7 ECC82 Valve wanted

I use a 12AT7 as a standard valve for my AVO VCM. I recal taking a brand new Mazda valve and observed it during a period of ~24 hours of burn in. One triode barely changed but the other changed quite a lot. I just regard this as yet another indication, if one was needed, that even the modern valves were very variable commodities.

B
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Old 3rd Dec 2019, 11:08 am   #13
simpsons
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Default Re: 12AU7 ECC82 Valve wanted

John

Fully respect your point of view.

I have recently tested a number of ECC83's and ECC82's both NOS and used and will PM you.

Chris
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Old 3rd Dec 2019, 11:42 am   #14
jdavis6809
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Default Re: 12AU7 ECC82 Valve wanted

Hello,

The ECC82 is for the Marconi TF1245

The manual states if valves are changed that a 100hr burn-in required before calibration.

I have sourced one NOS Philips ECC82 for now because the old one has gone to air.
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Old 3rd Dec 2019, 12:34 pm   #15
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Default Re: 12AU7 ECC82 Valve wanted

Ah, I understand!

That valve is used in a DC-coupled bridge amplifier, a VTVM, where good balance and stability are needed. Marconi's recommendation for burn in to get DC conditions settled is quite sensible.

Sorry for the misunderstanding, we've just got a little battle-weary on here regarding audio cultists looking for valves containing their preferred sort of invisible fairy dust, for bargain prices.

Those are rather nice instruments, especially if you manage to find the box of standard inductors and various fixtures to go with them.

Glad you've got things sorted.

David
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Old 3rd Dec 2019, 2:30 pm   #16
Paul JD
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Default Re: 12AU7 ECC82 Valve wanted

Quote:
Originally Posted by jdavis6809 View Post
The manual states if valves are changed that a 100hr burn-in required before calibration.

I have sourced one NOS Philips ECC82 for now because the old one has gone to air.
If the replacement valve is NOS then by definition it is no different to a new one and will presumably still require burn in before calibration.
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Old 3rd Dec 2019, 3:05 pm   #17
turretslug
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Default Re: 12AU7 ECC82 Valve wanted

Quote:
Originally Posted by Paul JD View Post
If the replacement valve is NOS then by definition it is no different to a new one and will presumably still require burn in before calibration.
It may well contain a little more helium than a new one....

I'm assuming that the OP is content to burn-in the valve- after all, 100 hours is only 4 days plus a bit of housework, and a simple jig could be set up to run heater and bias it for a few mA of anode current. All set for next weekend!
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Old 3rd Dec 2019, 3:25 pm   #18
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Default Re: 12AU7 ECC82 Valve wanted

I wouldn't worry. that instruction will have been for the benefit of repair centres. The application requires balancing the valve up better than the manufacturing match, so Marconi wanted to check that the valve's match was stable to a better extent than the data sheet guaranteed. Doing a burn in before adjustment would save on repaired instruments coming back.

For your own instrument, if it drifts a little, you wait until it's settled, open it up and give the right pots a twiddle to zero the VTVM and cal the FSD. It's less of a deal than having to send something away.

David
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