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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 11th Feb 2019, 4:49 pm   #1
PJC58-Hythe
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Default Wanted EAF801 valve

Bit of a long shot but does anybody have a good EAF801 they would like to part with?
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Old 11th Feb 2019, 6:13 pm   #2
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Default Re: Wanted EAF801 valve

There is at least one available on eBay at the moment but the location is Spain.
Failing that you may have to rewire the base for an EF80 or an EF184 and separate diode....

https://www.ebay.co.uk/itm/EAF801-TU...frcectupt=true
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Old 11th Feb 2019, 6:43 pm   #3
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Default Re: Wanted EAF801 valve

Langrex stock list states 6 in stock but I don’t know the price.
https://www.langrex.co.uk/
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Old 11th Feb 2019, 7:50 pm   #4
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Default Re: Wanted EAF801 valve

I did think about using an EF80 with separate diode and different screen grid resistor. I did a search on Langrex before posting here and they didn't have any...
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Old 11th Feb 2019, 8:07 pm   #5
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Default Re: Wanted EAF801 valve

Upto date stock list, they are in there, only 85 pages, perhaps,worth a phone call and pick the best deal between the sellers.
https://www.langrex.co.uk/public_html/valvenov.pdf
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Old 11th Feb 2019, 9:20 pm   #6
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Default Re: Wanted EAF801 valve

You can ask Langrex by email for a price. They told me that they don't put prices on the website because they are constantly changing.....
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Old 11th Feb 2019, 9:53 pm   #7
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Default Re: Wanted EAF801 valve

EBF89 is almost the same valve, with almost the same pinout. Probably easier to obtain. In some cases it may be a straightforward plug-in substitute.
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Old 11th Feb 2019, 10:55 pm   #8
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Default Re: Wanted EAF801 valve

....except that EBF89 is vari-mu and the EAF801 is not. Probably an EF80 or EF184 will be best although a separate diode will be required.
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Old 12th Feb 2019, 8:02 pm   #9
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Default Re: Wanted EAF801 valve

Interesting, depending on different websites the information varies as to whether the EAF801 characteristic is straight or variable-mu.

Although not explicit, the Telefunken data sheet shows two columns of gm for Vg at 0V and -20V and a characteristic curve showing gm (mA/V) over 0 to -40V control grid range. Strongly suggests VM.

Although comparable with EBF89, the internal screen is brought out to a separate pin. Depending on cathode circuit configuration EBF89 operation could be unstable but still perhaps worth a try.

Rich
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Old 12th Feb 2019, 9:59 pm   #10
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Default Re: Wanted EAF801 valve

Thanks for all the input I'm going to give Langrex a call when I next have some spare time (probably later this week).

When I looked up the data I came to the conclusion it isn't a variable-mu valve.

Typical of Grundig to use something not so common!
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Old 13th Feb 2019, 2:12 pm   #11
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Default Re: Wanted EAF801 valve

The Telefunken data sheet I have says explicitly that it is remote cutoff. The curves seem to confirm this.

The EAF801 screen (pin 7?) will almost certainly be grounded or connected to the cathode. Either of these will be fine for the diode in EBF89.

I have read that it was Grundig which asked for the EAF801 to be produced. It is essentially an EBF89 with one diode missing and the screen brought out to its own pin. The reason for this was to avoid instability when an unbypassed cathode resistor was used in order to reduce input capacitance variations with AGC. As your radio is a Grundig there may be a risk of instability of you use an EBF89, but perhaps more likely is a wobble in the IF frequency response. See Kompensation_%20dyn_%20Eingangs-C_%20final.pdf (in German - I used Google to translate).
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Old 13th Feb 2019, 6:52 pm   #12
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Default Re: Wanted EAF801 valve

Dave,

You are right the datasheet explicitly states remote cut-off, not sure why I didn't check the original datasheet first! Anyway given your comments and the text of that paper I agree substituting and EBF89 would be a last resort. For interest I have attached a snip of the circuit showing the connections to the EAF801.

Regards
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Old 13th Feb 2019, 7:13 pm   #13
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Default Re: Wanted EAF801 valve

As the cathode resistor is bypassed and pin 7 is grounded I can see no reason why an EBF89 should not work. In fact I am puzzled why they chose EAF801, when EBF89 would work just as well in that particular circuit. Maybe they had to justify asking Tfk to make the valve, so they had to buy a lot of them.
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