DL-1000 Dummy Load ID, please

[Damo666]

I've been on the lookout for a rugged & large Dummy Load, & I see these around now & again at reasonably cheap prices.

Does anyone know who the manufacturer is, & are these dry or oil filled, please?

Many thanks.

[G6Tanuki]

R.L. Drake made a dummy-load sold as the DL-1000

See http://www.wb4hfn.com/DRAKE/DrakeArt...Deratiingl.htm

Though the original Drake one looked a bit different

https://www.universal-radio.com/used/sold287.html

[Radio Wrangler]

There are also dodgy ones that have been marketed since the eighties where there is a resistor inside and no definite thermal coupling to the extruded case and all those fins. You can put a fair amount of power in, but only for a matter of less than a minute, set by the thermal mass of the resistor.

There's no sealing tokeep oil in, so none is put in. There are no fixings to make positive contact with the dissipating element.

I'm afraid if it is one of these, it is rather limited and very easy to burn out. You have no way of knowing for sure without opening it up.

You normally see plenty of them on stalls at amateur radio rallies.

David

And not a very good heatsink design (even if it works) as the airflow is orthogonal to the convection current. If it where a couple of quid it may be worth getting one, and find a way of filling with oil.

[Damo666]

Many thanks for the replies, guys.

As a result of the responses, I will avoid this specific one if I see any in future.

If anybody can recommend anything with similar specifications or thereabouts with a maximum budget of around ~£150 that's half decent, I'm all ears.

[Damo666]

Originally Posted by G6Tanuki

R.L. Drake made a dummy-load sold as the DL-1000

See http://www.wb4hfn.com/DRAKE/DrakeArt...Deratiingl.htm

Though the original Drake one looked a bit different

https://www.universal-radio.com/used/sold287.html

Yes, when I did a little online research I immediately thought it might have been a Drake model but it wasn't.

A good few Dummy loads use the "DL" prefix including Zetagi & Diamond, so I'm still unsure as to who makes this thing.

[HamishBoxer]

Diamond do make aerials though.

[Restoration73]

I've had one of the finned type for 40 years, Toyocom, but the rating is a bit optimistic
for carrier modes unless you limit the duration of use.
One of the best loads is the Bird Termaline which was made in a range of powers and
matched the Thru-line power meters.

[Damo666]

Looking around, I see a good few use the resistive elements - including a Zetagi DL61 & the MFJ-264 & all other MFJ products in the range.

The MFJ paint can (like the old Heathkit Cantenna) get reasonable reviews, but there's a few stories about oil seeping out & lids blowing off. That wouldn't go down too well if my better half witnessed it.

I've looked around & tried to find a Bird model, but I've not found anything yet.

[Sparky67]

There's always the option of building your own dummy load using one or more high power thin-film resistors suitably mounted. I used a similar 20dB thin-film 150W attenuator recently and it has proved to be very good.

Martin
G4NCE

[Peter F4VSA]

I have a Bird Termaline dummy load type 8431 rated at 500 watts, a mighty beast. The bad news is that it reads 58 ohms but I've aimed a few hundred watts at it with no problems. The resistive element is on a berylium oxide substrate and there is a chippd edge, probably by the unit being dropped. I have opened it up but I have worked with the evil substance professionally over the years. Not recommended.

[Damo666]

Many thanks for the replies.

I ended up getting a good deal on a Zetagi DL61 1KW dummy load - https://www.radiomuseum.org/r/zetagi...load_dl61.html

Zetagi are renowned for exaggerating specifications, that said, I have a small Zetagi dummy load here that's served me well over the years & I've exceeded input power on a few occasions without any failure.

[SiriusHardware]

I have one of those DL1000s which a local amateur kindly passed on to me some years ago. I've never run more than 100W into it (from a TS-50 amateur HF radio) and not for long. It says on the label on the load that the load is rated 300W for 3 minutes, 1KW peak.

I've never tried to take it apart. I agree with the observation that if it is meant to be used horizontally (as suggested by the positioning of the 'feet') then the vanes of the heatsink should run in vertical rings around the outside rather than horizontally along it.

If I pick it up and shake it I don't hear anything sloshing around inside.

[Damo666]

Originally Posted by SiriusHardware

I have one of those DL1000s which a local amateur kindly passed on to me some years ago. I've never run more than 100W into it (from a TS-50 amateur HF radio) and not for long. It says on the label on the load that the load is rated 300W for 3 minutes, 1KW peak.

I've never tried to take it apart. I agree with the observation that if it is meant to be used horizontally (as suggested by the positioning of the 'feet') then the vanes of the heatsink should run in vertical rings around the outside rather than horizontally along it.

If I pick it up and shake it I don't hear anything sloshing around inside.

I was doing a bit of testing with the Zetagi DL61 last night with a B550P amplifier, and with 220W for about 4 minutes it just ran slightly warm.

There is more than adequate ventilation on this dummy load, so if I was to use more power I'd use fan cooling.

The dummy load has a resistance of 48.2R, so isn't quite 50R so shows just below 1.1:1 on a SWR meter.

I'm very happy with this, and at around 8" x 4" x 5" it's nice & compact.

[dodgy-dxer]

Originally Posted by Damo666

I was doing a bit of testing with the Zetagi DL61 last night with a B550P amplifier, and with 220W for about 4 minutes it just ran slightly warm.

There is more than adequate ventilation on this dummy load, so if I was to use more power I'd use fan cooling.

The dummy load has a resistance of 48.2R, so isn't quite 50R so shows just below 1.1:1 on a SWR meter.

I'm very happy with this, and at around 8" x 4" x 5" it's nice & compact.

I have used one >500w for short periods

Handy for testing at the end of cables outside too

Not peeled the paint yet

Use the 1.5kW Bird for real jobs

Fred

[m0cemdave]

Originally Posted by Damo666

I've been on the lookout for a rugged & large Dummy Load, & I see these around now & again at reasonably cheap prices.

Does anyone know who the manufacturer is, & are these dry or oil filled, please?

Many thanks.

They are dry, and often sold under the brand name "Welz". Several different sizes were available. Made for the amateur market.

I had a smaller one (300, I think?). It worked fine, although I only used it for HF, not VHF/UHF. I only disposed of it after acquiring a commercial / professional load that made it redundant.

[Damo666]

Thank you for shedding some light on the manufacturer of the dummy load in the original post, M0cemdave. I have seen a few Welz products in the years gone by, but don't see very much by them nowadays.

One final question regarding my latest purchase if anybody knows, please; My Zetagi DL61 dummy load shows 48 ohms when checked cold/unused with an ohmeter, but when it heats up after use, checking it again with an ohmeter, the resistance can go as low as ~35 ohm.

Is this normal?

Even though the resistance of the dummy load varies so much, the SWR stays under 1.1:1 at HF, and under 1.3:1 at VHF (2M band).

Surely an impedance/resistance of ~35 ohms would exhibit a SWR of around 1.6:1 or thereabouts, so am I missing something?

I say this because a 100 ohm or 25 ohm impedance would be a mismatch of 2:1.

This is what's inside my dummy load.

[Terry_VK5TM]

Impedance and resistance are two different things, especially in the RF realm.

Highly simplified explanation:-

Resistance is (notionally) what you measure across a resistor.

Impedance involves reactance in resistive, inductive and capacitive forms.

It is the combination of these that gives you the SWR figure of ~1:1 at 50 ohms impedance.

[Radio Wrangler]

It's one of those areas where you have to be careful with nomenclature:

Resistors on their own give pure resistance
Inductors on their own give pure reactance (positive signed)
Capacitors on their own give pure reactance (negative signed)

Impedance is the catch-all. It encompasses not only all the combinations, but you mustn't overlook that it also covers pure resistances and pure reactances.

So a perfect 50 Ohm resistor has an impedance of 50 Ohms. You don't HAVE to have a mixture of components to make an impedance.... everything is an impedance. We could write everything as an impedance, but for brevity's sake we don't bother. A pure resistor would be written as an impedance of 50 Ohms, and a statement of impedance would need to have both resistive and reactive terms, but the reactance term would be zero.

Once you get up to RF, then pure resistors are harder to find. You get inductance by virtue of their length, or if someone made them with a spiral cut track. Stray capacitance gets in on the act as well. Once you have reactive elements, their reactances vary with frequency, so you have to start getting picky about specifying what frequency measurements or specs apply at.

It's handle-able but you have to do double book keeping to keep track of resistive and reactive parts separately.

David

[Damo666]

Thank you so much for the in depth replies, guys.

They say you learn something new every day, and today has been one of those days for me.

I will do some more research on this subject.