[ARC5] Army/Navy transmitters from a NON COLLECTOR viewpoint, the ham version...

[Brian Clarke]

The ARC-5 transmitter stall power plug, in terms of pin spacing and
arrangement, is the same as the receiver IFT plug, except you need to drill
a hole in the centre to fit a mini-banana plug.

Voltage doublers have several problems:
1. if half-wave, DC is fed back into the mains; yes, I know it's done in
computer SMPSUs, but sending DC into the mains is against the law in
Australia and New Zealand, and if enough hornswogglers do it, the
distribution transformer (pole pig in USA) gets unhappy
2. at start-up, increasing the capacitance of the filter increases the load
on the diodes, the power transformer and the mains fuse
3. increasing the size of the mains fuse increases the risk of taking out
the power transformer, and no longer protects the power supply from excess
load.

73 de Brian, VK2GCE

On Tuesday, 11 February 2020 2:57 PM, Ken replied:

On 10 Feb 2020 at 22:14, Rich Post wrote:

>     1: Can either variant be either screen or plate modulated?

Yes....or cathode modulated....or controlled-carrier modulated...or...

>     2: Any suggestions on how a beat-up FT-226-A tray might accommodate
either style 
>     transmitter? 

Put one of each type of socket at the rear.

> I am thinking having each
>     rear connector wired for a particular transmitter pin out, but how to
avoid accidentally 
>     putting the wrong version in the wrong
>     slot? One side Army, one side Navy...

You would have to have two different "sockets" mounted, one Army, one Navy.
The (later) 
Navy one is a bit larger and has different pin spacing. So there wouldn't be
much danger of 
plugging them in wrong.
     
>     3: For power... a modified Heathkit PS-23 junker... get rid of the
voltage doubler nonsense 

What is your main dislike of the voltage-doubler? If you replace the 150 MFD
caps with 
those with MUCH greater capacitance, there are several real advantages to
using 
voltage-doublers. For one thing, the output voltage ramps up a bit slower,
so, often, 
step-start isn't needed.

There is nothing, really, non-sensical about them. I like them.

As an old handbook I found many years ago proved, if your total filter
capacitance is at least 
30 MFD, droop will only be limited by the power transformer internal
resistance.

Higher values of capacitance (easy, these days) results in much better
dynamic 
regulation...as proven in an old GE Ham Notes by test.

I replaced the 150 MFD caps in my Heathkit SB-200s with 560 MFD caps in one
of them 
and 620 MFD caps in the other , for instance. 

In my case, the only "ARC-5" transmitters I own were, literally, hacked to
ribbons long 
before I ever got them, so I am not a bit averse to doing whatever is
necessary to get them 
in operation.

Also voltage-reguating the 200 volt supply for the 1626 is an excellent
thing to do. And 
voltage regulating the final amp screens is, IMHO, about the best thing you
could do for CW 
work. I heartily approve of Rich's suggestions.

Do remember to remove the screen voltage whenever you remove plate voltage,
or the 
screens may "disappear", usually in a flash of light.

DC on the filaments, at least for the oscillator is also pretty much
necessary.

Ken W7EKB
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