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Old 12th Nov 2023, 10:08 am   #1
JanWra1
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Default American vs British in AVO's Valve Data Manual

Hi guys

My AVO Mk3 is now working and when studying the AVO Valve Data Manual I notice something odd when comparing with the valve data supplied with the American TV-7 tube tester:
Taking the valve 12BR7 as an example:
- AVO states that Vf is 6 V
- TV-7 states Vf is 12.6V, (TV-7 states 12.6 V for all 12xxx valves).

Another example is 12BZ6: Both AVO and TV-7 states that Vf is 12.6 V

Can anyone explain the difference ?

Jan
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Old 12th Nov 2023, 10:52 am   #2
Cobaltblue
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Default Re: American vs British in AVO's Valve Data Manual

12BR7 like Many other valves in that series 12AX7 for instance has a centre taped filament.
The AVO would be putting the two halves of the filament in parallel.

This is how this valve would often be used in service.

If you look at the 12AX7 equivalent ECC83 the first letter E stands for 6.3V filament.

The advantage of this arrangement when used in TV service or Radio where no mains transformer is used the filaments run a more convenient 150mA.

However when used in transformer powered equipment it was common practice to use the filaments in parallel so that they could run from a common 6.3V winding used by the rest of the valves.

Cheers

Mike T
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Last edited by Cobaltblue; 12th Nov 2023 at 11:09 am. Reason: added reason for series operation
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Old 12th Nov 2023, 11:07 am   #3
ms660
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Default Re: American vs British in AVO's Valve Data Manual

The thumbwheel settings for the 12BR7 heaters (2, 2 and 3) connect pins 4 and 5 of the valve together to one side of the heater supply and connects pin 9 to the other side of the heater supply which will power up the two internal heaters if they have continuity to the relevant pins.

Lawrence.
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Old 12th Nov 2023, 11:38 am   #4
Cobaltblue
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Default Re: American vs British in AVO's Valve Data Manual

Incidentally don't rely completely on the AVO data manuals there quite a few errors.

A good tip is to check the setting against a resource such as http://www.r-type.org/

Cheers

Mike T
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Old 13th Nov 2023, 1:13 am   #5
JanWra1
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Default Re: American vs British in AVO's Valve Data Manual

Thanks guys for the explanations Now I understand ,

73 Jan
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