The AM Forum

I am in the final stages of rebuilding a Lettine 240 to clean up both the original messy work and some questionable repairs but one part of the schematic (I am working from the redrawn schematic in the manual from edebris) has me curious.  The coupling between the 6V6 oscillator and the 807 final is a .001 capacitor to a tuned circuit consisting of a coil and variable cap in parallel and then through another .001 capacitor paralleled by a 15K 10 watt resistor to the 807 control grid.

I understand the grid leak resistor bias but doesn't a 10 watt rating seem a bit excessive?  And for this vintage a 10 watt rating would likely have been wire wound.  Anyone have an original manual to confirm this rating and/or a reason why such a large power rating?

Portion of schematic from edebris manual attached.

10 watt does seem a bit much.  Figure drive current 5ma x 5ma x 15000 only = .375 watts.  May be a error.  Anyway you can use a number of carbon resistors to make the 15K 10 watt.

Fred

Maybe it was being used, if it was a wirewound resistor, as a parasitic suppressor.

I also thought the same thing, especially when you look at the strange grid circuit.  Usually the grid leak resistor is at the cold end of the grid coil to ground.

Fred

There is a lot of strange stuff about the Lettine design and layout.  I normally stay away from modifications but the Lettine 240 may be an exception to the norm for me. 

The outside looks nice, the inside not so much.  Both layout and construction are poor. 

It will be interesting to see what the 262 (two band 6 and 2 meter) looks like inside, it may be a shelf queen. 

I have a 240 as well Rodger and your right about the inside.  Heck, they did not even use ground lugs but just soldered right to the steel chassis!!   Have not worked on mine yet but I am sure I will do some amount of redesign without defacing the rig though. 

Joe, GMS     

Roger,

Thanks to you, I've been able to almost complete my 262; there are certainly many strange decision features that I've questioned.  My restoration has largely been keeping it "original" (to include some circuit oddities) but I am cleaning up the poor workmanship.  I am following your photos and the crude schematics as close as possible--we'll see what surprises await!

Chris 

I just checked and the manual for mine is not where its supposed to be.  So either I never had a manual or its in my lab.  If I don't have one, I will place an order with the Manual Man. 

Joe, GMS 

Joe,

Jim Hanlon just sent me photos of his Lettine 240 and he confirmed it is a 1 watt resistor.  I expect the wattage rating mistake on the edebris schematic occurred when it was edited for clarity.  I will forward his email to you later after Cheyenne (the dog) and I get back from errands including picking up her new registration tag.

A W.W.grid leak resistor is an effective method for snubbing parasitic oscillations.   

Darrell

Interesting oscillator coil.