[ICOM] IC 735 Amplifier Keying circuit ?

[Larry Young]

There is no substitute for fore knowledge of an old amlifier's keying spec's before connecting it to a modern transceiver designed to interface to a modern amplifier. Here is one source of amplifier keying specs. http://www.qsl.net/icom/keyspecs.html 
Larry K4LXV

--- On Sat, 3/31/12, Roger (K8RI) <k8ri at rogerhalstead.com> wrote:

From: Roger (K8RI) <k8ri at rogerhalstead.com>
Subject: Re: [ICOM] IC 735 Amplifier Keying circuit ?
To: icom at mailman.qth.net
Date: Saturday, March 31, 2012, 5:53 PM

On 3/27/2012 8:47 AM, Taylor Jim-CJT001 wrote:
> Good morning to the group.
>
> I just noticed that the relay that is used to key an external amplifier has become intermittent at least this is my suspicions. I can key the microphone several times and eventually the amplifier will key. At this point I'm not sure if the contacts are pitted, or some other issue is making the relay intermittent. With an ohm meter, sometimes the relay makes a high resistance contact, other times it appears not to close at all, and sometimes it seems to work correctly.

I used my 756 Pro to key a Henry 2K4 directly for quite some time with 
no problems.  I did the same with a 745 and 751. Then I picked up an 
Alpha 76A. First time I used it I welded the relay contacts together in 
the 756 Pro. That was when I went out and picked up a relay interface.  
A good hard whack with the flat of my hand on the cabinet broke the 
contacts loose.  It's still working, many years later.  I would 
recommend a relay interface with any of these older rigs used to key an 
amp...unless you get really a really old rig.<:-)) I think one of those 
would key the contactor for my milling machine.

>
> The schematic calls it rly1, but on the board it is labeled as rly2. The relay is a small cylindrical probably reed type relay. The relay is my suspicion, but I guess it could be the transistor that drives the relay as well. Haven't checked that far yet.

Transistors are rarely intermittent unless the voltage is right on the 
ragged edge.

> Has anyone noted this problem and or replaced the keying relay ? is the relay available from Icom ? is there a substitute out there ?

I don't remember the current rating of that relay, but it's not much.   
It's doubtful you will still be able to get one from Icom, but I'd 
certainly give it a try.  If they don't have them ask if they know where 
you might get one, or the nomenclature of the actual relay, not just 
rly1 or what ever.   Some one some where likely has at least a few. OTOH 
if you can't find the exact relay, just find one that will fit in the 
space, even if you have to hang it on leads. (I just did that with the 
caps for a computer monitor)  Just make sure it has the proper coil 
impedance and contact ratings...and will operate fast enough.

Good Luck es 73

Roger (K8RI)

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