Larry Molitor wrote:
>At 09:20 3/31/98 +0100, you wrote:
>>It would be a terrible waste. Using a UHF tube like a 7213 on HF would
>>be like using a high-spirited racehorse to pull a cart.
>
>Well, Ian, I must agree with that statment. However, out here in the middle
>of the desert, there is a real lack of VHF/UHF types. Email me direct and
>I'll tell you all about it. The tube was originally obtained for use in a
>432 amp when I was still doing EME.
Your classic az-el indicator circuit is still working fine here, Larry.
>>Worse than that,
>>in triode-connected grounded grid (TCGG) the poor beast would be dead in
>>six months.
>>
>
>>I don't have the characteristic curves for a 7213, but most of the RF
>>drive in TCGG goes into the control grid, and modern ceramic-metal
>>tetrodes do not have the control-grid dissipation to handle that - and
>>in TCGG you can't even measure the screen and control grid currents
>>independently. If experience with 4CXC250s is anything to go by, TCGG is
>>a quick, sure way to ruin the tube.
>>
>
>I wonder how true that is in this case? My old RCA tube manual only lists
>class C operation but does give 0.2 amps as max grid current. Don't sound
>real delicate to me.
>
Problem is that the total grid current divides heavily in favor of the
control grid, but you can't actually measure the split. Then there is
the totally unknown IMD performance.
>
>>The 7213 is rare and desirable for use at UHF, so why not trade it for
>>an 8877?
>
>I just checked again, not many folks lined up in the driveway wanting to
>trade!
On the Internet, your driveway can extend to the ends of the earth,
although I don't remember seeing you advertise it in the vhf, weak-
signal vhf, vhf-dx-discuss or EME mailing lists, where a "7213 for sale"
posting would surely attract attention.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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