Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Modulator filaments off on CW mode




 
The AM Forum
January 23, 2021, 05:28:51 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Modulator filaments off on CW mode  (Read 196 times)
0 Members and 1 Guest are viewing this topic.
n4joy
Member

Offline Offline

Posts: 202



« on: January 13, 2021, 08:42:42 AM »

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


* 20200315_162725.jpg (4112.53 KB, 4032x3024 - viewed 29 times.)

* 20200320_224036.jpg (3158.75 KB, 4032x3024 - viewed 47 times.)
Logged
WQ9E
Member

Offline Offline

Posts: 3238



« Reply #1 on: January 13, 2021, 10:48:56 AM »

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
Logged

Rodger WQ9E
n4joy
Member

Offline Offline

Posts: 202



« Reply #2 on: January 13, 2021, 12:13:35 PM »

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! 
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.056 seconds with 19 queries.