The AM Forum
March 28, 2024, 10:04:31 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: Time Delay  (Read 3530 times)
0 Members and 1 Guest are viewing this topic.
L8RS
Guest
« on: January 11, 2012, 05:54:03 PM »

I am building an AM KW patterned somewhat after the Johnson Desk Kilowatt.  Everything is working fine except for an occasional arcing when releasing the PTT on the D104 on AM phone.  CW is fine.  I need a good circuit for a time delay on the DowKey 115 vac relay.  I've not had much luck with the circuit in the Johnson KW manual.  The "make" voltage is not strong enough to fully close the relay contacts consistently.  Does anyone have a reliable circuit with a complete set of values?  I am using a Ranger II as the exciter and have 2700 volts on the two 4-400 finals and the pair of triode connected 813s. The modulation transformer is a UTC CVM5 set for 20000/6800 impedance.
                                     Roger K8RS
Logged
KE6DF
Member

Offline Offline

Posts: 784


WWW
« Reply #1 on: January 11, 2012, 06:44:22 PM »

It likely has nothing to do with the arching problem, but the 20000 : 6800 ohm ratio seems like too much step down.

It would make it difficult to achieve 100% modulation.

I'm assuming the same voltage on the modulator and the final. If the modulator is running at a higher voltage, I withdraw my comment.

The other question is: Do you know what is arcing and where?
Logged

W2XR
Contributing
Member
*
Offline Offline

Posts: 890



« Reply #2 on: January 11, 2012, 08:14:58 PM »

It likely has nothing to do with the arching problem, but the 20000 : 6800 ohm ratio seems like too much step down.

It would make it difficult to achieve 100% modulation.


I thought much the same thing, especially considering the 813s are triode-connected. That will reduce the plate-to-plate impedance of the tubes significantly.

73,

Bruce
Logged

Real transmitters are homebrewed with a ratchet wrench, and you have to stand up to tune them!

Arthur C. Clarke's Third Law: "Any sufficiently advanced technology is indistinguishable from magic".
WQ9E
Member

Offline Offline

Posts: 3282



« Reply #3 on: January 11, 2012, 09:15:45 PM »

Roger,

I am not a big fan of trying to use that delay circuit with an AC coil relay since you are feeding it DC and it will be (as you have found) difficult to find a value for R3 that doesn't either overheat the relay coil or result in slow make.   R3 needs to be used to limit the coil voltage but if it is very large it is forming an RC timing circuit.

I use a DC coil relay with my Desk KW and have never had a problem with slow make time (or flashover on release).   You can easily feed the switched 120 VAC on transmit to a transformer/rectifier/filter cap supply and use this to control the DC coil relay.   Generally you can choose a filter cap size which is sufficient both for filtering and to provide the slight delay on release.  If you need additional filtering then you may have to use a resistor in parallel with the relay coil to keep the release upon delay time reasonable.   For the Desk KW I use a vacuum relay for antenna switching and a regular cube relay with 120 VAC coil  (where speed isn't critical) to handle muting.
Logged

Rodger WQ9E
KM1H
Contributing
Member
*
Offline Offline

Posts: 3519



« Reply #4 on: January 12, 2012, 12:33:59 PM »

Its simple to make a speed up circuit for a DC relay, I do it for several amps with slow clunky relays.

http://www.ifwtech.co.uk/g3sek/in-prac/best-of.htm#speedup

Ive also used DC on AC relays such as the NCL-2000 12VAC antenna relay. At 3.3VDC it stays right up with the VOX on SSB and CW.

Carl
Logged
WA3ONG
Member

Offline Offline

Posts: 9


« Reply #5 on: October 22, 2012, 12:08:32 PM »

Regarding your e-mail from earlier this year.  How are you doing with your homebrew rig modeled after the desk kilowatt?
I just recently picked up a "500 w" RCA 1:1 modulation transformer and I have an homebrew RF deck that uses a pair of 4-400 (built from a '65 or '63 handbook article) so I've been thinking...
I also am fond of 813's having had a homebrew linear (now gone) that I built using four in grounded grid - grounded screen.
Thanks,
Jay
WA3ONG
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 0.069 seconds with 19 queries.