[ARC5] ARC-5 Issues

Sun Feb 24 10:47:32 EST 2013

Yes you are missing something.  In the original  design, K53 in the transmitter 
is turned on by the transmitter selector switch in the little transmitter 
control box. Each one of the 4 positions turns on K53 in an individual 
transmitter....it stays on, while the K53s in any other transmitter in the 
installed system stay off.  With K53 on , the cathodes of the finals are 
returned to ground, and incoming  externally keyed B plus is lined up to be sent 
to the MO and resonance indicator tube.  The final plates and screens do not get 
their voltage via K53.  DC  power keying to all of the circuits are done by 
relay K52 in the BC-456 modulator/dyno supply, a single contact makes and breaks 
the 550V DC from the dyno that feeds the final  plates, the circuit that 
develops the final screen voltage, and the  circuit that sends B plus to the K53 
contact that sends B plus to the MO and resonance indicator tube. A seperate 
antenna relay is also keyed in parallel with K52 and switches the antenna from 
receiver to the transmitter(s).  All of the transmitters output terminals of an 
installation  are wire in parallel, relay K54 in each transmitter is turned on 
with K53 by the control box channel selector switch to connect the selected 
transmitter's output to the antenna circuit.  Are you also keying K54 in the 
transmitter, or did you just either jam the contacts closed or short around 
them.  In  the original design, K53 and K54 in the transmitters were never 
keyed, they just were turned on to select an individual transmitter from a group 
of up to 4 of them.

Since you are using K53 as a keying relay, you are in fact making and breaking 
the final cathode circuit.  With the contacts open, R75 limits the final plate 
current on key up  so leaving the B plus on them and the screen may be OK on key 
up, but I am not sure.  You should put a milliammmeter in series with the R75 
cathode circuit to check how much current is being pulled, or you could check 
the voltage developed across R75 on key up and do the ohms law math to figure 
the current through it (and by extension the final plates).  But putting the 
power on to the MO without going through K53 will give you that big backwave on 
key up.

If I were you, I would try to keep the keying circuit as close to original as 
possible, you will have no backwave issue and no issue with overheating the 
finals.

You should download the ARC-5 and SCR-274 N tech manuals from the BAMA web site, 
they provide indepth discussion of the two systems.  The Handbook of Maintenance 
Instructions provide the most info.

________________________________
From: Mark K3MSB <mark.k3msb at gmail.com>
To: Christopher Bowne <aj1g at sbcglobal.net>
Sent: Sat, February 23, 2013 1:33:34 PM
Subject: Re: ARC-5 Issues

Hi Chris –

All I’ve (currently) got is a lone transmitter; no rack, no control boxes etc.  

I did recently score an almost mint tray for my receivers, but have not been 
able to locate a tray for the transmitter yet.   I’m keeping my eyes peeled as 
the saying goes.

Thanks for your comments on me wearing out my final with my approach;  I’m going 
to change some things around.

Currently, 550 B+ and 270 Screen are always going to my transmitter.  When I 
want to SPOT, I apply 200 Regulated power to the OSC.   When I want to 
transmit,  I also key down and  closes K-53.

So, if I understand your email,  you have K-53 closed all the time (via a SELECT 
key in an external piece of equipment), which means 200V regulated is applied to 
the OSC and R-75 / C-74 is shorted.   If that is the situation, and B+ and 
Screen are also applied,  then the transmitter is always keyed!  So, how are you 
keying for CW ?   I’m missing something from the manual and your email.

73 Mark K3MSB

On Thu, Feb 21, 2013 at 4:40 AM, Christopher Bowne <aj1g at sbcglobal.net> wrote:

Not surprised you get a strong backwave signal from the MO.   That is very 
common on many transmitters that keep the MO on, if you run that way you will 
have to back off the RF gain on the receiver if you want to listen to your own 
keying. You obviously will have to turn off the MO when you want to listen to 
the other end of a QSO!
>
>My setup is totally original, the MO B plus, the final screen, final B plus, and 
>RF output (via the system's external antenna relay) are all keyed using the 
>original relays in the BC-456 and the external antenna relay box. The two relays 
>in the transmitter itself are NOT keyed, they are locked on my the transmitter 
>selector switch in the external little transmitter control box, which can select 
>from up to four transmitters. On occasion I have  thought there was a problem 
>with my T-19 because it wasn't putting out RF even with the dyno running, 
>problem was merely having the selector switch lined up to another position which 
>did not correspond to an actual transmitter.
>
>Although I don't use it, the original keying circuit on the BC-456 also keys the 
>audio oscillator used for MCW tone modulation in both the TONE and CW modes, and 
>the output is sent out to the headset audio of the  system receivers for a 
>keying sidetone.  I believe in voice mode, the modulating audio is also sent out 
>on the sidetone circuit so the operator knows his microphone is actually 
>working. As built, the system is full PTT on voice and full break-in  on TONE 
>and CW, although there is a lot of loud transient noise in the headset audio 
>when keying.
>
>Don't expect to get perfect chirp free keying, the sets never had it, even when 
>new, and never will.  Consider the chirp as vintage "character"  that sets you 
>apart from the riceboxes!  There are lots of reasons, you can have really bad 
>chirp on keying (poor B plus voltage regulation, bad bypass caps, etc.), but if 
>you run the transmitters with the dynos and key using the original arrangement, 
>they don't sound bad at all.
>
>One thing you said that bothers me, you said you keep your final B plus and 
>screen voltage on all the time.  If you do that with the final cathode also 
>returned to ground without any excitation from the MO, like during receive, you 
>will be drawing excessive final plate current and will quickly destroy the final 
>tubes.  You should at least remove the  screen voltage from the finals to 
>prevent that. There is no internal bias voltage that cuts the finals off without 
>excitation.  That's why the original design keys the final screens and plate 
>voltages along with the MO plate.  
>
>
>So, if you keep the MO running all the time in transmit, and  you always have 
>voltage to the final screens and plates, where are you keying, the final 
>cathodes using the transmitter "select" relay in that circuit (the one that 
>normally locks on when the transmitter is selected as described above)?
>
>
>
>
>
>
________________________________
From: Mark K3MSB <mark.k3msb at gmail.com>
>To: aj1g at sbcglobal.net
>Sent: Wed, February 20, 2013 7:31:36 PM
>Subject: ARC-5 Issues
>
>
>
>Hi Chris –
> 
>I worked you on New Years Eve in the SKN with my T-19 and BC-454-B.   If you 
>don’t mind, I’d like to ask you a question about how you key your transmitter.
> 
>Currently I have the HV and SG (Screen Voltage) always going to the radio.   The 
>regulated OSC voltage is going through a panel mounted SPOT switch (on my PS, 
>not the radio….), and I’m bypassing the OSC contacts on K-53.    So, when I want 
>to spot, I close my panel mounted SPOT switch, and when I’m on frequency, I key 
>as normal.
> 
>I’m running into some issues.  First, when I send CW I obviously hear the OSC 
>tone when key up as the OSC is always running.  I’ve heard that you do not want 
>to key the transmitter and OSC via K-53 as is indicated in the manual due to 
>chirp reasons; one wants to have the OSC always on for stability.   I still get 
>some chirp, but it’s very slight.
> 
>Second, even when I ground the receiver antenna when I transmit, I still get an 
>almost overload signal in the receiver.  I have to physically remove anything 
>connected to the front panel connector; even a short pigtail to an SPST switch 
>won’t work. 
>
> 
>How have encountered these issues?  Any suggestions you might have will be 
>appreciated.
> 
>73 Mark K3MSB