Johnson engineering was re:[Johnson] Johnson T-R Switch

Sun, 2 Mar 2003 14:15:33 -0800 (PST)

For the record, I have seen several questionable items come up as a result of oddball EFJ engineering. That heat rating of the 6BL7 is one of them. Another is running 2kv on the 811A's that are inside of the 500. Additionally, the use of VTVM type plastic pin connectors to power the 500, the Viking Invader 2000, and possibly some others is really unsettling. However, they seem to get away with it since apparently, it works o.k. A means to cut costs, perhaps? FWIW, Cal, N6KYR. 
 Jerry Kincade <[email protected]> wrote:I was lucky, mine worked and has ever since I got it. But I did build in a
tiny 12V 1-1/2" muffin fan inside to blow some air around the tube, makes it
run a LOT cooler. Can't even hear the little fan unless you stick your ear
right on the cabinet. I used a diode and small electrolytic to tap some
roughly-rectified DC off the tube's filament voltage. Has worked fine for
about 5 years now, fan runs about half speed so it should last nearly
forever, I hope. FWIW, the Johnson literature says don't worry, these things
are built to run hot. I think they were engaged in some wishful thinking at
the time. With the fan running, I can actually put my hand on the top of the
cabinet without blistering it.
73, Jerry W5KP

----- Original Message -----
From: "Charles Ring, W3NU" 
To: 
Sent: Sunday, March 02, 2003 12:08 PM
Subject: [Johnson] Johnson T-R Switch

> I have three of these, with one good transformer and one good 6BL7 tube
> between them. While replacing the power cord on the one I got running
> again after many years, I also installed an internal fuse holder. I see
> no sign that they ever had a fuse, not even the infamous fused AC plug.
> Is this correct? What was Johnson thinking of to omit a fuse? Was the
> transformer intended to burn out like two of mine did, hopefully with
> the excess heat contained in the metal case? The normal working heat
> around the 6BL7 is already enough to worry about even though the manual
> says that is normal.
>
> I'd like to get one more of these in working order. Any suggestions on
> finding a transformer? The good one measures 425 VCT under load plus 6.3
> filament winding, but i'd like the HV winding a little lower in order to
> use silicon rectifiers instead of the 6X4. Also lower plate voltage
> should reduce the operating temperature - losing some of the unit's 6dB
> gain is acceptable, but i wonder if it's basic function would be
> degraded too.
>
> 73 de W3NU
>
> _______________________________________________
> Johnson mailing list
> [email protected]
> http://mailman.qth.net/mailman/listinfo/johnson
>

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