Date
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QCX Plus 50 Watt PA Combo
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George Korper
Hi All,
Hans has published the dimension available and I am looking for designs to incorporate the 50 watt amp inside the case. Can you separate the IRF510 and heatsink from the board with wires? Or would it better to just leave it in case and bolt on, etc. Any suggestions would be helpful. Is the case itself enough heatsink for moderate use? George K3GK |
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It is probably a bad idea to seperate the PA transistors (IRF510) too far from the circuit board. Since they are trying to work together in a push-pull arrangement to drive a few amps of RF current through a transformer at high frequencies you are going to run in to all sorts of problems that will not be easy to predict or replicate for each different installation.
Determining if the heat sink is sufficient requires quite a few data-points; 1. Power level you will be running at 2. Band you will be operating on 3. SWR that the amplifier sees from the antenna system 4. DC supply voltage and current 5. Duty cycle of the transmitter and mode of operation 6. Type of heat sink (aluminum finned, copper, just a steel plate) 7. Acceptable temperature rise of the PA 8. Thermal conductivity of the junction between the PA and heat sink 9. Convection cooled heat sink or forced air .... You can see why many designers will put some margin in heat sink selection or incorporate devices to measure temperature at the PA to fold back the power or put the amplifier in to protection mode to prevent the magic smoke packets from being released. -- Tisha Hayes, AA4HA Sr Engineer, 4RF Inc. |
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George Korper
Tisha, for your intuitive use: Band:20 meters Output: 30 Watts Voltage: 19 V Heatsink: top of QCX + case Longest transmission, 2 ea. 3x3 CQ, followed by QSO basic exchange of OP, QTH and RST, Callsign. normal speed 18 wpm. I have hardly heated up the heatsink so far, so I am thinking, taking your suggestion of leaving on board and drilling a couple of holes in the top of the case and using it as a heatsink. What do you think? George On Fri, May 29, 2020 at 9:28 AM Tisha Hayes <Tisha.Hayes@...> wrote: It is probably a bad idea to seperate the PA transistors (IRF510) too far from the circuit board. Since they are trying to work together in a push-pull arrangement to drive a few amps of RF current through a transformer at high frequencies you are going to run in to all sorts of problems that will not be easy to predict or replicate for each different installation. |
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ajparent1/kb1gmx
>>> Can you separate the IRF510 and heatsink from the board with wires?
No, lead inductance and inter lead capacitance are really bad juju. Its more than bad to separate them by any distance. IRF510s have significant gain to VHF and most of the bad designs out there the poor thing are standing on full legs and working very poorly or bordering on oscillation. Tisha, the 50W PA has no fold back so introducing that confuses the issue. The key is the board and layout is very short leads for RF stability and also managing to mount the devices. If the board is the correct height above the case the transistor mount to it and on the outside mount the heatsink supplied for cooling (to remove the heat). Allison ------------------------------- Please reply on list so we can share. No private email, it goes to a bit bucket due address harvesting |
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ajparent1/kb1gmx
A good reference image from the very detailed manual.
It give the sandwich of the board, IRF510s and the case plus heatsinks. End view. The manual has a lot of pictures so all of this should be clear. Allison ------------------------------- Please reply on list so we can share. No private email, it goes to a bit bucket due address harvesting |
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Hans Summers
Yes. It is as Allison says. If I was gonna install the 50W PA in the QCX+ I'd drill holes in the top for the IRF510s, the same as is done for the 50W PA enclosure, and bolt the 50W PA in the roof of the QCX+ Enclosure. There is room for it (by design). You need to fit it a little left of center so that the 50W PA PCB does not interfere with the 5K gain potentiometer or the LCD mounting bolts. This will be very easy to see when you have it in front of you. Bolt it to the roof of the case using 5mm spacers, these are enough for the body of the IRF510. There are even convenient mounting holes in the corners of the 50W PA PCB (also by design). Be sure to solder the 50W PA IRF510s AFTER having bolted them to the enclosure case and bolting the 50W PA PCB to the enclosure case, so that you aren't putting undue stress on their wires. You will need to think carefully about what to do at the back. And how to power it. You don't want to power both the QCX+ and the 50W PA at 20V; that will be too much for the QCX+. At one extreme: drill holes in the rear of the QCX+ Enclosure for ALL the connectors of the 50W PA, and arrange separate 12V and 20V power supplies for the QCX+ and 50W PAs; have a short coax jumper cable from the output of the QCX+ to the input BNC of the 50W PA; and a 3.5mm jumper cable from the QCX+ PTT output to the 50W PA PTT input. At the other extreme: drill NO extra holes in the rear of the QCX+. Cut a couple of traces and install a 7812 regulator to power the QCX+ from the 20V supply of the 50W PA. Don't install any of the connectors on the 50W PA, and instead, wire them to the appropriate places... cut a trace near the RF output of the QCX+ and instead wire that to the 50W PA input, then wire the 50W PA output to the QCX+ BNC RF connector. Connect the PTT signal directly to the corresponding place (on the QCX+ and 50W PA kits). There are shades of grey between these extremes, where you do different amounts of internal wiring to replace some connections, and have some but not all of the 50W PA connectors come out the back through holes in the rear panel you drill. Note also that there is space for the QCX+ Dev board http://qrp-labs.com/qcxpdev in the QCX+ enclosure, as well as the 50W PA kit. As long as you don't put any too tall components on the QCX+ Dev board, everything will fit. So that could be a convenient place to site a 7812 regulator and low profile heatsink neatly, and replace a bunch of wiring with the pin header connectors supplied in the dev kit. Lots of possibilities! Which is the fun thing about QCX+... being physically larger there is more scope for customization and experiment. 73 Hans G0UPL http://qrp-labs.com On Fri, May 29, 2020 at 10:02 PM ajparent1/KB1GMX <kb1gmx@...> wrote: >>> Can you separate the IRF510 and heatsink from the board with wires? |
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Hans Summers
P.S. For 50W operation I would keep the heatsinks, and have them bolted on top of the QCX+ enclosure. PPS. Note of course, the other EASIEST option is separate 50W PA unit and QCX+ which also looks very nice, two black enclosures, one sitting on top of the other... starts to look very sophisticated... :-D 73 Hans G0UPL On Fri, May 29, 2020 at 10:21 PM QRP Labs <hans.summers@...> wrote:
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ajparent1/kb1gmx
One last suggestion use the external jumper option because if the PA quits
you cannot use the QCX barefoot, it does not have a straight through powered off option. So the hardwired version means your full power all the time. Also you can run both of 13V, the PA will be at reduced power [20-25W] but for many that is a comfortable increase. Allison ------------------------------- Please reply on list so we can share. No private email, it goes to a bit bucket due address harvesting |
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George Korper
Hans, The link is not working for me. Thanks for the info, I order cases with the AMP so I probably will settle for the elegant (Collins S Line) look. So here is the question. Will separate enclosures be available for purchase? Like for a spectrum scope? Or SWR Meter tuner, etc. 73, George On Fri, May 29, 2020 at 7:55 PM ajparent1/KB1GMX <kb1gmx@...> wrote: One last suggestion use the external jumper option because if the PA quits |
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Hans Summers
Hi George
Sorry should be http://shop.qrp-labs.com/qcxpdev
Ha! In this case, a QRP Labs Q line
Separate QCX+ enclosures are already available. But I know you mean, the enclosure with plain front and back panels that you can make your own stuff in and have it match. So I'd have to buy some extra, blank panels. I suppose that's possible! Let me think about it! 73 Hans G0UPL |
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George Korper
I actually would prefer it as is so I don't need to add a cutout for an LCD. Any other holes I can plug. If I don't use the LCD slot I will put a screen behind it. On Fri, May 29, 2020 at 5:04 PM Hans Summers <hans.summers@...> wrote:
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Hans Summers
On Sat, May 30, 2020, 02:15 George Korper <georgekorper@...> wrote:
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George Korper
Hans, I am not clear on one thing. If you purchase the enclosure what is the best way to use a development board without a QCX+ board? Ideas? Drill the bottom? George On Sat, May 30, 2020 at 1:14 AM Hans Summers <hans.summers@...> wrote:
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Hans Summers
Hello George Yes. Drill the bottom. The QCX+ PCB width is designed to slot into the PCB rails in the enclosure extrusion walls. But the QCX+ Dev board is narrower and is designed to be bolted to the main QCX+ PCB with four 12mm hex spacers, one in each corner. It isn't wide enough to slot into the enclosure or course. These 12mm spacers and the associated 8pcs M3 6mm screw are included in the Dev board kit. If you have no QCX+ PCB but wish to use the dev board then you could drill four corresponding holes in the enclosure floor and use the 12mm spacers and screws supplied. 73 Hans G0UPL On Sat, May 30, 2020, 14:38 George Korper <georgekorper@...> wrote:
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George Korper
Easy enough, using the holes in the board to mark the bottom. Will it save money to consolidate a second enclosure and two boards with a QCX+ and enclosure combo, and will you do that? On Sat, May 30, 2020 at 11:20 AM Hans Summers <hans.summers@...> wrote:
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Hans Summers
Hi George Yes sure. I suggest just order what you want, in a new order. Then email me to make sure I see it. Then I will combine the two orders and if refund any difference between the shipping you paid, and the calculated shipping on the combined order. If that's clear :-/ 73 Hans G0UPL On Sat, May 30, 2020, 18:32 George Korper <georgekorper@...> wrote:
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George Korper
TNX, will do. On Sat, May 30, 2020 at 11:37 AM Hans Summers <hans.summers@...> wrote:
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