"Magnetic hardware" in PA for HF Amp?

[N8ETQ]

Yo'

    I got a Hammarlund HXL-One Amplifier in a trade, (Will work
for Gear). Anyway this thing is full of "Steel"  in the RF area.
Hardware and everything. Of course the Chassis and cab are steel.

    I know this is a "No-No" for VHF/UHF Amps. Same logic apply
on HF? I love the look of Copper, silver and Brass so no issues
there. (Wouldn't want it in the living room, but love in a PA compartment!)

BTW: HXL-One = SB-200  +/- 3db

/Dan

[Rob K2CU]

The only concerns with regard to magnetics would be losses, if the fields from the output inductors could induce magnetic fields in the chassis. Otherwise, the concern is resistance and corrosion. The resistance issue comes into play if the circulating currents in the low impedance output circuit involve the chassis, or currents induced from the coils being too close to the steel. Corrosion will be problematic at every mechanical connection point that is also an electrical connection point. The benefit of copper plating has often been more along the lines of reducing corrosion as well as being a better conductive surface. We have all seen restoration projects that get really involved and strip the chassis and have it chemically etched and copper or copper/nickle plated. But, you will want to at least recycle the mechanical connections throughout the chassis. If there are the tube sockets with the ground ring with connection lugs, consider drilling out the rivets and replacing with screws and "star" type lock washers.

It would be interesting to talk to someone who was in equipment manufacturing forty to sixty years ago and see if anyone ever imagined their equipment being used more than ten years later.

[N8ETQ]

Hey Rob,

  Thanks for your response.  I guess I just need to pay more
attention to stuff like this.  I know on HF a couple extra watts
doesn't mean nuthin', but on VHF/UHF where it may be going
to a 22 dbd gain array it's a big deal.

   I was just surprised to find "Purpose Made" parts in there
that were steel. And your right, there all "Munged" up with
corrosion/electraliysis (?).  I never had an HF amp till this thing
"Fell out of the sky".  I've talked to guy's that never knew
Hammarlund even made an Amplifire. They were pretty "pickey"
about thier RX RF stages and it paid off.  As usual, My limited
experience with these things always leads to a question or 2.

   Anyway, Thanks Rob,

73

/Dan

It would be interesting to talk to someone who was in equipment manufacturing forty to sixty years ago and see if anyone ever imagined their equipment being used more than ten years later.

[KA2QFX]

I'd have little concern with steel (ferromagnetic) materials in an HF amp.  Look at most of the exciter cages of the early hybrid transceivers (Kenwood, Yaesu), they're all steel cages with steel hardware all over. 

The effects of magnetic materials depends greatly on where and how much.  For example: A chassis wall perpendicular to the axis of a coil is going to produce a shorted turn effect whether it's aluminum or steel. But a steel wall parallel to the coil's axis will increase it's inductance and reduce it's Q.  But the capacitive coupling of the aluminum wall could be equally distressing when trying to resonate the tank at a specific impedance or Q. 

Small parts (screws, spacers, etc) should not be a concern below vhf.

Corrosion is another issue of course. I don't think it's a big deal in a dry environment but a damp basement or garage will deteriorate any material. I particularly dislike aluminum because a poor ground connection cannot be cleaned and soldered easily (if at all) like on a steel chassis.

I don't think you should have any concerns with your amp made of "real" metal.

Mark

[KM1H]

I certainly wouldnt use plain steel hardware for ANY RF connections and know of very few that do so and those are bottom feeders such as Heathkit. And I always replace those with SS or use all brass and solder for 6M conversions. Its easy to look at the Heath hardware and tell if the amp has been used extensively on 15M and up.

Steel cabinets and lids can raise havoc with tuning when too close to the tank circuit, just ask any Dentron owner.

In the Amp Supply No Tune amps its a PITA chore to align the output since the steel cover is a major detuner.

The National NCL-2000 cabinet and cover has enough seperation to have just a very small effect on 10M or 6M for that matter. All hardware is brass or SS and output is 1200W on any band, even 6M conversions.

Carl

[W1RKW]

I wonder what effect if any would occur if one placed magnets near a vacuum tube in such a way to contain any escaping electrons and redirecting them into the plate area.

[KM1H]

If they reflect the wrong way you might go sterile.....or worse

[k4kyv]

Don't use ferrous (steel) hardware for ANY application that carries substantial current, particularly RF, and avoid using it in close proximity to rf coils, even if it wouldn't be carrying any current.

I once had low filament voltage on a pair of 866As,  causing them to flash over even when handling only about 1200v.  Turned out to be excessive voltage drop at the transformer terminals. Somehow, a steel nut had inadvertently made its way onto the screw terminals.  It got hot enough to raise a blister on my finger when I touched it.  I  replaced it with a brass one, the filament voltage measured normal, and never again had the flash-over problem.

I keep  the magnet from a defunct speaker handy, just for checking hardware before using it on any electrical connection, or any application in the vicinity of rf components.

[Steve - K4HX]

Then you'd have a magnetron.

I wonder what effect if any would occur if one placed magnets near a vacuum tube in such a way to contain any escaping electrons and redirecting them into the plate area.

[N8ETQ]

Yes, Thanks.

   Looks like another trip to ACE Hardware for Brass.

/Dan

Don't use ferrous (steel) hardware for ANY application that carries substantial current, particularly RF, and avoid using it in close proximity to rf coils, even if it wouldn't be carrying any current.

I keep  the magnet from a defunct speaker handy, just for checking hardware before using it on any electrical connection, or any application in the vicinity of rf components.

[KA2QFX]

I should have clarified, if you must use steel hardware, for strength, it must be plated (xinc, cadmium, brass) but never plain steel.  Brass is better, stainless can be iffy depending. I've seen a lot of chinese "stainless" (and brass) lately that doesn't pass the smell test at all.