[Hallicrafters] Re: [Boatanchors] Replacing rect tubeswithdiodesquestion

[Bob Macklin]

AC/DC radios apply the full B+ to the tubes before they warm up. They don't
have a problem. And these tubes are the same as other receiving tubes except
for their filament voltage.

Bob Macklin
K5MYJ
Seattle, Wa,
"Real Radios Glow in the Dark"
----- Original Message -----
From: "Bill Kirkland" <kirklandb at sympatico.ca>
To: <km1h at jeremy.mv.com>; <wq9e at dtnspeed.net>; <erastber at tampabay.rr.com>
Cc: <boatanchors at mailman.qth.net>; <hallicrafters at mailman.qth.net>
Sent: Wednesday, February 13, 2008 10:48 AM
Subject: Re: [Hallicrafters] Re: [Boatanchors] Replacing rect
tubeswithdiodesquestion


> forgot one other item. With solid state rectifiers you will be applying
the
> B+ almost
> instantaneously to the tube plates, well before they have had a chance to
> heat up.
>
> I am not a tube expert but I can buy into arguments that this is not good
> for the
> tube.
>
> In essence if you just replace the tube with solid state rectifiers, you
are
> not
> replacing the rectifier tube with an equivalent system.
> - rectifier tube has to heat up before it applies B+ to the rest of the
> tubes
>     start up surge will put more stress on the transformer and filtering
> circuit
> - rectifier tube has a huge voltage drop compared to a silicon diode, e.g.
> 40V.
>    at 250V plate voltage, this is > a 15% increase in the operating point
of
> the circuit.
>
>
> Will the system work, quite possibly/probably.
> Is it working within its intended  parameter range, probably not.
> Is it fatal - don't know, but I would expect it to shorten the life of the
> tube - which will get harder to find
>
> bill
>
>
> >From: "jeremy-ca" <km1h at jeremy.mv.com>
> >To: "Rodger" <wq9e at dtnspeed.net>,WØQFC <erastber at tampabay.rr.com>
> >CC: boatanchors at mailman.qth.net,HALLICRAFTERS
> ><hallicrafters at mailman.qth.net>
> >Subject: Re: [Hallicrafters] Re: [Boatanchors] Replacing rect tubes
> >withdiodesquestion
> >Date: Wed, 13 Feb 2008 11:15:42 -0500
> >
> >A dropping resistor simply generates more heat and provides no useful
> >function. The tubes are all rated at a higher voltage than is used,
> >recapping takes care of that area and the output transformer has
sufficient
> >insulation. The extra B+ current drain is well under 10W.
> >
> >Benefit of a resistor in a rebuilt radio =  Zero.
> >
> >Benefit of a SS surge protector =  Zero also since they function at the
> >zero crossing of the sine wave.
> >
> >Carl
> >KM1H
> >
> >----- Original Message ----- From: "Rodger" <wq9e at dtnspeed.net>
> >To: "WØQFC" <erastber at tampabay.rr.com>
> >Cc: <boatanchors at mailman.qth.net>; "HALLICRAFTERS"
> ><hallicrafters at mailman.qth.net>
> >Sent: Wednesday, February 13, 2008 9:36 AM
> >Subject: [Hallicrafters] Re: [Boatanchors] Replacing rect tubes with
> >diodesquestion
> >
> >
> >>Hi Gene,
> >>
> >>You also need a dropping resistor to reduce the voltage to close to what
> >>would normally be supplied by the tube rectifier.  You can get a decent
> >>idea of what the resistor should be by looking at what the typical tube
> >>voltage drop is in normal operation, this information is available in
the
> >>tube data books or the NJ7P online data base is handy:
> >>http://www.nj7p.org/Tube.php  I would imagine a 270 ohm 20 watt resistor
> >>connected in series with the common cathode connection would get you
close
> >>enough.  Of course you could also use separate resistors for each
> >>replacement diode, in this case the resistor value would be doubled and
> >>the power rating would be halved.  I do replace a fair number of my tube
> >>rectifiers with SS rectifiers and some of the Halli power transformers
> >>definitely benefit from this replacement.  I always build the SS as a
plug
> >>in and disconnect the 5 volt heater leads from the socket to remove the
B+
> >>from the 5 volt winding of the transformer since this is a fairly common
> >>failure mechanism in these older transformers.
> >>
> >>A couple of other considerations:  The B+ will come up instantly and wil
l
> >>be higher than usual until the remaining tubes warm up and begin drawing
> >>current so if the filter caps are marginal this extra voltage will
> >>probably cause their rapid demise.  So replace any doubtful caps first.
By
> >>the way, even with a tube rectifier the voltage is much higher just
after
> >>turn on as the directly heated rectifier cathode heats up almost
instantly
> >>in the existing tube type rectifier.  I would also consider adding an
> >>inrush current limiter to your set to further reduce the stress on the
> >>transformer and tube filaments, suitable ones are available from Mouser
or
> >>Digikey for around a couple of bucks and they are installed after the
fuse
> >>and in series with the transformer primary.
> >>
> >>73, Rodger WQ9E
> >>
> >>WØQFC wrote:
> >>>I want to replace the # 80 in my S-40A with diodes so I can reduce heat
> >>>by less draw on the tranny.
> >>>
> >>>Can I just use two diodes that will handle the current, or is there
> >>>something else I should do ~ additional parts, etc?
> >>>
> >>>Also, I would like to replace the 6H6 for the same reason, but what
> >>>diodes should I use?
> >>>
> >>>I know that these items are available but in the interest of saving
> >>>money, I would like to do it myself. . . .
> >>>
> >>>Comments?
> >>>
> >>>73
> >>>
> >>>Gene, WØQFC
> >>>
> >>>www.w0qfc.com
> >>>
> >>>_______________________________________________
> >>>
> >>>
> >>
> >>______________________________________________________________
> >>
> >
> >______________________________________________________________
> f
>
>
> ______________________________________________________________
>