The AM Forum

The AM/CW switch on my Lettine 130 turns off the filaments and voltage to the modulator section when in CW mode.  The modulator section is a pair of 807s driven by an 807.  Wiring appears to be original, but I am tempted to keep the modulator tube filaments on all the time to prevent the extended delay waiting for the filaments to warn up.  I'm not sure why it was originally designed/wired this way--perhaps to minimize heat?  There is a plate switch on the front, but I can't imagine one was supposed to switch the plate transformer on/off to transmit on AM mode.

Thanks,

Chris

Chris,

It is very likely that Lettine intended for the plate transformer to be turned off in AM mode when NOT transmitting.  Most medium and higher power classic AM rigs turn off HV in AM during standby and this is why a PTT mod is popular with a lot of the older rigs. 

Typically turning on the plate supply on these older rigs also activates a 120 VAC feed to terminals on the rear to control an antenna switching/muting relay.

I have a Lettine 240 (lower power) along with a Lettine VHF transmitter but never have been inside a 130.

Rodger WQ9E

Thanks, Rodger.  This makes sense now! 

Chris- I have a Lettine 130 that was my first plate modulated AM rig. I chopped it up a bit with mods when I was a teenager and new ham in 1970. I want to put it back to stock and restore it. Need a schematice. Do you have or know where I can find one? Have tried to email you several times and have reached out to you on this forum in the past but no response. Hope you can help.

73
Chris W2JBL

Chris. 

Unfortunately, I have not been able to locate a manual and/or schematic.  I thought about making a schematic but it comes down to time.  I would be happy to send you tons of high quality photos.  Let me know if that would help   The 130 must be very rare.  I haven't found ANY information on the net other than some old advertisements.

Chris

   I need the wiring for the PA tank circuit. I changed it and can't remember how the B&W coil was connected to the plate tune cap and 807 plates also where the modulated B+ was applied to it. The rest is mostly intact. Besides being my first plate modulated rig, it was also my first on 160 and later on I had it on 200 meters (1610) driving a big amplifier. Pictures or a hand drawn schematic would be a big help. Thanks Chris.

73
DE W2JBL
radioguy28@aol.com

Presuming the secondary of the mod transformer is shorted or disconnected in CW mode, turning off the 807 mod filament may have been their easy way to avoid accidentally passing modulator-807 current through the modulation transformer without a proper load on it.

There should be a way to keep the heaters on, and also make sure the 807s are completely cut off, like removing screen volts and adding lots of bias. YMMV