[Hallicrafters] Re: [Boatanchors] Replacing recttubeswithdiodesquestion

[Bob Macklin]

Transmitters have separate B+ controls from the main power controls. Good
ones are interlocked so as not to allow B+ until after a warm-up cycle is
complete.

It's the classic BA receiver this discussion really applies to.

Bob Macklin
K5MYJ
Seattle, Wa,
"Real Radios Glow in the Dark"
----- Original Message -----
From: "David C. Hallam" <dhallam at rapidsys.com>
To: "Bill Kirkland" <kirklandb at sympatico.ca>; <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 11:36 AM
Subject: RE: [Hallicrafters] Re: [Boatanchors] Replacing
recttubeswithdiodesquestion


> The situation of applying plate voltage to a tube at the same time as
> filament voltage is applied belongs to the realm of transmitting tubes not
> small receiving tubes.  If by chance some cathode stripping does occur it
is
> so slight as to be insignificant.  Given the hours of life vs. the price
of
> a small receiving tube, why worry about it even if it should occur?  If we
> were talking about a multi thousand dollar indirectly heated transmitting
> tube it might have some validity.  How many times a day will the radio be
> turned off and on?
>
> This discussion is in the same vein as the theological one of "How many
> angels can dance on the head of a pin?".
>
> David
> KC2JD/4
>
> > -----Original Message-----
> > From: hallicrafters-bounces at mailman.qth.net
> > [mailto:hallicrafters-bounces at mailman.qth.net]On Behalf Of Bill Kirkland
> > Sent: Wednesday, February 13, 2008 1:48 PM
> > 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
> > 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 will
> > >>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
> >
> >
> > ______________________________________________________________
> >
> >
> >
> >
>
>
> ______________________________________________________________
>