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 Technico Aristocrat model 750 dial glass
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 Return to top of page · Post #: 1 · Written at 10:34:07 PM on 11 June 2018.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 508

Hi, does anybody have or know where I might find a dial glass for one of these? I have one minus a dial glass and would like to find one if I can. As I don't have one I have no original to copy.

Another thing, (a technical question) Mine has a 6J8 valve as detector, whereas the schematic says that it should be a 6A8, but it's working fine, but I'm wondering if I should put a 6A8 in it, but looking at the two valves data sheets, they're a bit different so I'm wondering if putting a 6A8 back in might damage it? (Assuming it has been modified perhaps to take a 6J8, although I can't see any evidence)?


 
 Return to top of page · Post #: 2 · Written at 11:03:07 PM on 11 June 2018.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4342

It is never unusual to find 6A8, 6K8, 6J8 & ECH35 where it should not be.

6A8 was superseded by 6J8 in SW sets. They will happily run in the others hole & I often use either, if I think the one in the set is a dud.

Where you may run into strife, & Astor JJ is a prime example, is with the band spread of the dial. In the case of JJ a 6J8 will compress the band & it will encroach into the NDB's on the low end & go way past 1600kHz the other.

6J8 Has a triode exciter for the oscillator directly coupled via its grid, to the Hexode at grid 3

6A8 is a Heptode and grid 1 is actually the oscillator grid with the oscillator anode the next element.

Very different valves. They work as the 6J8 triode plate is on the same pin as the 6A8 oscillator anode.

Sort the set out with it in there at the moment.

Be careful with nomenclature, there are often references to the converter / mixer being the first detector and the one doing the separation of the audio, as the second detector, or just detector eg 6B8


 
 Return to top of page · Post #: 3 · Written at 12:24:55 AM on 12 June 2018.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 508

Aha thank you Marc! Good to know it won't do any harm.


 
 Return to top of page · Post #: 4 · Written at 9:22:20 AM on 12 June 2018.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4342

Also forgot: In a SW 6A8 may not have enough puff. There is a limit as to how high these things can oscillate, Even when there is a separate exciter, I have seen different cathode resistors switched in as the band changes. Pentagrids normally die at high frequency when they die, or are starved of volts due to failed components around them.


 
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