Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Amplifier using multiple radios  (Read 1270 times)
WA1YDH
Member

Posts: 33




Ignore
« on: June 12, 2017, 07:34:58 AM »

All

I currently have an ICOM 7300 and utilize an Ameritron 811H as my amp.I also have some Older Drake gear and would also
like to use the same amplifier--having a switch of some sort to switch the relay.

With my 7300 I just connect directly to the relay on the 811h to trigger the amp, I do not use the ALC on the amp and just keep my power low on my 7300. With the ICOM its very easy to adjust/control the output power.

I have a Drake T4XC transmitter that I would like to also put through the amp--however not sure how to make it happen. The power output on the drake is a little hard to control so I suspect I would need to use the ALC for the Drake.

Ive heard of problems interfacing these old drakes to modern amps.

Would I be better off just buying a Drake L4B amplifier--if there is even the chance of me screwing my new 811 amp up I would rather buy another amp. Getting full power out of the L4B would also be a benefit where the 811 gets me only 600 watts. Id rather not but buy another amp but you can ever have enough  Drake gear (:

Has anyone interfaced a Drake (T4xc)  to an 811--and if so how did you do it?

Thanks
Dave

WA1YDH

 





Logged
N3QE
Member

Posts: 4883




Ignore
« Reply #1 on: June 12, 2017, 07:50:32 AM »

I have a Drake T4XC transmitter that I would like to also put through the amp--however not sure how to make it happen. The power output on the drake is a little hard to control so I suspect I would need to use the ALC for the Drake.

A very common mod to the 811H involves putting a resistor inside the amp, in parallel with the cathode drive, to allow it to be driven with a 100W-class radio that has trouble with power spikes. By tweaking the value of the resistor I'm sure you could make it a good match to your T4XC running full-out. See W8JI's 200-ohm-resistor mod here: https://www.w8ji.com/al811_important_modifications_changes.htm

Another way of dealing with ALC from one amp to multiple radios, is to keep the ALC adjustment on the amp in one place, and use an adjustable resistor divider on the ALC jack of each radio. A one-of-N RCA switch can route ALC to the appropriate radio.
Logged
WA1YDH
Member

Posts: 33




Ignore
« Reply #2 on: June 12, 2017, 08:10:36 AM »

OK thanks--



But what about the triggering of the amplifier? Is the Drake compatible?

thanks
Logged
N3AJB
Member

Posts: 39




Ignore
« Reply #3 on: June 12, 2017, 09:10:01 AM »

HI,

According to the manual, the T4XC requires an external relay, like the Dow Key relay, to operate with a linear amplifier, 811H, L4B or anything else.  See Figure 2-5 on page 2-7:  link to the manual is below)

When loading the 811H, start with low drive from the T4XC (or any other exciter) and continue to load the amp until you reach the desired output power.  This requires an external power meter that reads average and peak power.   Once you have reached desired output (600w or 800w), then switch to SSB (peak output power setting on the meter) and adjust the mic gain to peak to your maximum output.   

I usually adjust the mic gain to peak below the maximum power output to avoid any distortion; i.e. load to 600w and peak to 500-550 w on SSB.    As long as you don't over drive the amp, no distortion will occur and ALC isn't needed.

The procedure is applicable to any amplifier and will insure a clean signal, no ALC is ever required.  The use of ALC is to ensure that the amplifier is not over driven resulting in a distorted audio signal.  The use of ALC is equivalent to the manual choke versus the automatic choke or manual transmission versus automatic transmission.  The technology reduces the likelihood of human error.

http://www.hug-a-bug.com/T4XC_manual.pdf

JON
Logged
WA1YDH
Member

Posts: 33




Ignore
« Reply #4 on: June 12, 2017, 10:29:57 AM »

Do you know of a commercially available
relay i could use--no clue as to what
a dow key relay is or where to get one, or how to hook up?
Thanks
Logged
N3AJB
Member

Posts: 39




Ignore
« Reply #5 on: June 12, 2017, 12:42:22 PM »

Dave,

Below is a link to Ebay and Dow Key relays.  Or just get on Ebay and search for Dow Key relay.  Some are 120VAC, 12VDC or 28VDC so be careful when ordering.  Some have extra external contacts for muting the receiver but the T4XC has that built in.

Check out "completed sales" on Ebay to get an idea of what they cost.

JON


http://www.ebay.com/sch/i.html?_odkw=&_sc=1&_sop=1&_mdo=Consumer-Electronics&_trkparms=65%253A1%257C66%253A2%257C39%253A1&_pcats=1500%2C293&_osacat=4670&_ipg=200&_from=R40&_trksid=p2045573.m570.l1313.TR2.TRC0.A0.H0.Xdow+key+relay.TRS0&_nkw=dow+key+relay&_sacat=4670


Logged
WA4JQS
Member

Posts: 71




Ignore
« Reply #6 on: June 12, 2017, 02:28:30 PM »

Jon:
the Drake T4XC only needs a dowkey relay if the amp does not have one. the AC4 2 pin Vox plug is used to apply power to the relay in the amp.the L4B ect have a built in relay . the MFJ 811A amp should have a relay. just use a 2 wire connection from the vox plug on the AC4 to the relay on the amp.
73 Tony WA4JQS
Logged
WA4JQS
Member

Posts: 71




Ignore
« Reply #7 on: June 12, 2017, 02:42:42 PM »

Dave :
i have 5 c-lines two tr4cw a b- line and two l4b's and never had to use a dowkey relay. also i have a drake unit connected to my Henry 2KD5. and Alpha 89 still no outboard relays.. with that said all you need to do is look at the AC 4 you will see a 2 pin black jack on the side that has the bais control. this is your relay voltage output to key your relay in your amp. connect a two wire cable from it to the relay input on your MFJ amp. which i think is 12 to 18 volts could be wrong. Now if you want to switch between two radio to one amp. then you could use a dow key  or go with a coax switch common post to the amp  post 1 and 2 to the radios. then all you have to do it switch between them this leaves the problem of how to switch the relays controls from the radios you could use a DPDT switch to do this or use a dow key relay with external contacts again the end with one so239 goes to the amp the radios go to the other two. only think you have to make sure of is which is N. Open and N closed contacts on the so239's and the external contacts on the relay. there are many ways to do what you want to do.
73 Tony WA4JQS
Logged
N3AJB
Member

Posts: 39




Ignore
« Reply #8 on: June 12, 2017, 06:08:14 PM »

Tony,

I completely overlooked the fact that the modern amps have built in antenna relays to handle transceivers.  Shows that reading the manual can get you into trouble sometimes.   Thanks for the correction.

JON
Logged
ZS5WC
Member

Posts: 632


WWW

Ignore
« Reply #9 on: June 13, 2017, 03:34:44 AM »

I've been thinking about this myself.. Roll Eyes
Obviously the simplest way to do it would be a box / plate with bulkhead fittings for the coax, rca sockets for the PTT and ALC.
All you do then is use a jumper cable to select the required rig.
However one must be careful not to wire two transcievers together-Hi!..
The other issue is that ALC levels for different rigs differ slightly-so some sort of ALC preset system could be built in.

Or the most elaborate and expensive way:
http://www.w2ihy.com/3-x-4-coax-switch-plus.html

73 de William
ZS4L / ZS5WC
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!