[Amps] Alpha 86 PIN Diode Fuse

[mike kendall]

Hello,
  I didnt' see my post make it the first time (maybe I deleted it by accident).  I had a QSK switch from MFJ (PIN diode T/R switch).  It had a bulb fuse in it and it blew eventually.  The guy at Ameritron told me to replace it with a bulb from a christmas tree.  Sure enough it worked like gangbusters and when the VSWR climbed the bulb began to glow.  I have a huge inventory of spares that can be replenished off christmas season at garage sales or in christmas season at K-mart or wallmart.  
Regards,
ETC(SW/AW) Mike Kendall USN.....IT9/KE6CVH
 


"Joe Subich, W4TV" <k4ik at subich.com> wrote:

As one who helped Doc Sheller design and build the DEO-1500 
back in the early 80's ... 

> I own a DEO QSK-1500 and a previous owner wired a bulb in 
> series with the fuse. When the QSK-1500 is presented with 
> a SWR higher than what it wants to see the bulb begins to 
> glow. 

The DEO-1500 "fuse" is a standard light bulb - Chicago Miniature 
#12. Other than lightning or operator error the only reason 
it should blow is if the transceiver is generating RF before 
the unit is switched into transmit. The QSK-1500 was designed 
to be connected between the keyer and the transceiver "Key In" 
jack so that it could switch the amplifier at the same time the 
key was closed. This generally allowed even the slowest amplifier 
relays to get settled before the QSK transceivers of the day 
produced any RF. 

If you are relying on the PTT output from a transceiver (even 
the solid state output from the modern transceivers) to drive 
the QSK-1500 (or QSK amplifier), you will blow fuse lamps. 

If the fuse lamp glows with high SWR, one of three things is 
happening: 1) the feedline impedance is greater than 150 Ohms 
(3:1 SWR), 2) at least one of the pin diodes D3, D4, D5 are 
shorted, or 3) the 500 volt supply is not right. Of course, 
the 3:1 SWR must be derated if you are running "smoke" . 

> The bulb is mounted on top of the unit so it is easy to see. 
> I believe the bulb is a #47.

This is unnecessary. I have not refreshed my memory as to the 
characteristics of the #12 and similar lamps and can't say how 
much additional loss the #47 is creating on receive. 

> Can these guys be popping fuses because the QSK switch 
> doesn't see a match?

Fuse popping is almost always due to failure to run the keyer 
through the switch (I believe the Alpha also has loop through 
for a key/keyer) or lightning. Years ago the info we had put 
the unknown fuse lamp failures in the 2 to 3% area. The other 
failures were about half and half operator error (improper hook 
up or running the amp into the wrong antenna) and lightning. 

73, 

... Joe, W4TV (ex K4IK) 

PS. I still have one copy of the QSK-1500 service manual and 
my design notes for a version that was intended to be used
with the R4C/T4XC. Unfortunately, transceivers replaced 
the C-lines far too soon. 

> 
> At 01:49 PM 07/14/2005, you wrote:
> >ke6cvh at yahoo.com wrote:
> >
> > > I blew the PIN diode fuse.
> >
> >This is strange. I had an 86 for a couple of years, used it a lot --
> >always full QSK at at least 1300 watts output on all bands, and NEVER
> >blew the fuse. Yet some guys have continual problems with this.
> >Something is going on that isn't clear to me.
> >
> >--
> >73,
> >Vic, K2VCO
> >Fresno CA
> >http://www.qsl.net/k2vco
> 
> John and Susan Bohnovic
> (954) 432-1467 voice
> (954) 431-7751 fax/data
> curlhead at bellsouth.net (she)
> bohnovic at bellsouth.net (he)
> 
> 
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