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  #1  
Old 05-19-2017, 10:26 AM
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dtvmcdonald dtvmcdonald is offline
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Wanted: MHD4 British tube

I need a British very old tube, an MHD4. This is essentially a 4AV6 ( a 4 volt 6AV6)
in a large "G" bulb (with the tiered top) and a 7 pin base not like any American tube.
I have not yet found one in Britain.

Alternatively ... does anybody have one of those standard British 7 pin bases,
a broken tube will do. I could use a 4AV6 but don't want to smash the bad tube.

Yes, its a radio tube used in a (1936) TV, since its AM sound.
The sound is just like the 4 signal tubes of a BCB radio except for the
1.5 MHz IF frequency and the oscillator tunes 49.5 to 40.5 MHz.

Doug McDonald
Champaign IL 61822
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Old 05-19-2017, 03:47 PM
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N2IXK N2IXK is offline
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Is $18 too much to spend on one?

http://www.vivatubes.com/marconi-eng...g-vacuum-tube/

Have bought a few tubes from that vendor in the past, with no issues, FWIW.
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Old 05-19-2017, 06:15 PM
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dtvmcdonald dtvmcdonald is offline
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Quote:
Originally Posted by N2IXK View Post
Is $18 too much to spend on one?

http://www.vivatubes.com/marconi-eng...g-vacuum-tube/

Have bought a few tubes from that vendor in the past, with no issues, FWIW.
For that price I expect some test. I had no difficulty testing mine,
which tested good but a heater-cathode short.
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  #4  
Old 05-21-2017, 06:07 PM
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miniman82 miniman82 is offline
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Put a brightener on it
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Old 05-21-2017, 06:30 PM
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benman94 benman94 is offline
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Quote:
Originally Posted by miniman82 View Post
Put a brightener on it
MHD4? Probably series string. Less effort to just find a good tube.
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Old 05-22-2017, 12:09 AM
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Penthode Penthode is offline
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4 volt ac was the British standard pre-war filament voltage for AC sets and a parallel filament string.
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  #7  
Old 05-22-2017, 11:28 AM
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baursam baursam is offline
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Ask seller if they can test/ship

http://www.ebay.co.uk/itm/THE-marcon...-/262983829774


Or tested unsold probably due to the category it was placed in!!

http://www.ebay.ca/itm/MARCONI-MHD4-...8AAOSwrhBZA0bt

Last edited by baursam; 05-22-2017 at 11:40 AM.
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Old 05-22-2017, 10:36 PM
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baursam baursam is offline
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Also, here's a cross reference chart, Mullard is the only other match.

http://www.6v6.co.uk/vcomp/valve_xref/british_1930s.htm

And here's a match

http://www.mullardmagic.co.uk/mhd4met-osram-nib

Last edited by baursam; 05-22-2017 at 10:41 PM.
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  #9  
Old 05-23-2017, 09:47 PM
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dtvmcdonald dtvmcdonald is offline
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I'm getting one, pig in a poke.

A brightener won't help. The tube works but has an
intermittent heater-cathode short.
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  #10  
Old 05-24-2017, 07:42 AM
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miniman82 miniman82 is offline
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Some brighteners are also isolators, so it would work to cure the H/K short. Unless it's directly heated of course, in which case H/K shorts are a given.
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