Hi Bill,
A couple of questions to add diagnostic information, if you would...
Did this build ever work normally, or did it deteriorate after having worked correctly?
You mentioned adjusting supply voltage: have you tried a completely different power supply?
Have you measured Rx/Tx current? Is there any voltage droop during Tx?
You said the oscillation is "affected by the position of the volume control; in what way? pitch, volume, tone?". The reason I ask that is to try to determine if either IC9 or IC10 are directly complicit in the oscillation.
What happens if, instead of removing power, you remove and reconnect headphones? By the way, they are high impedance headphones, right? 48 ohms or? above per side?

Instability on a proven design can be caused by high impedance supply (long, thin wires) and a faulty decoupling capacitor (the 10uFd caps before &/or after the regulator. It can also be caused by a badly behaved op-amp in the receiver circuit. Changing op amps is hard, though...

If you have the equipment to do so, could make sure there is no supply voltage being fed to the top end (Q6 end) of L4 during Rx. That point in the circuit is high impedance, so the voltage may appear to wander or a bit until the impedance of the DVM pulls it down, but it won't be anywhere near supply.

Those are some thoughts. I'll give it another shot if you can answer the questions:-)
--
Julian, N4JO.

Top with labels printed fine. Now you have a choice of no-labels and labels, both with vents!

73
Mark
AJ6CU

--

--

Love that $50 paddle! ?Small and solid. I use mine most of the time

Oh, good, PayPal solved it with a 78 cent fee. ?

73, Willie N1JBJ

Bryan,

Can you make the bias adjustment as described in the manual?? That is done with the QCX in practice mode (no RF output) and an amp meter connected in line with the power supply.? If that works, I would think the IRF510s are OK and look to the transformers as the possible issue.

Most of the time, it is poor connections with the leads of the inductors and transformers in these types of kits.? It can be hard to burn or scrape off the enamel insulation.? I scrape the wires and crank up my temperature-controlled iron when soldering them.?

The RF probe would at least tell you if you are getting the signal to the gates of the IRF510s.

If you plan to build more kits, I would suggest that you look into purchasing an oscilloscope, at least 20MHz capable.? I like the Siglent series of scopes.? I have read good reviews of the Hantek and Rigol series as well.? Hantek is the lowest cost of the three, with Rigol offering lower-priced models with lesser specifications than the Siglent that I have.

73
Evan
AC9TU

Evan,
Thank you. I will look into the probe
?I may have a few parts around.?

But for the other comment, I do have the radio connected just as he showed and rf should be present in the amp. If the voltage measurement he makes between d3 and d5 is due to no or little RF then I think the irf510s are blown (most likely since i did hookup backwards) or a winding is shorted or some problem in that row of? diodes arrangement perhaps?

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Rut Roe! ?I’ll have to declare the Obscene Profit on my taxes. ?I’m sure Pat will send me a 10-99. ?8*)

Spot on Andy. V.

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Good to know, and the padded envelope is probably a buck, so $10 sounds about right.

I would be interested in purchasing a pair! De K2SCH?
kd2qlm@...

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I don’t remember what size wires my Knipex tool strips. I bought the extra teeth that were offered with the purchase but have never needed them so far. I have stripped size 30 ga wire up to size 20 without issues. ?Works great. ? They offered teeth for thinner and thicker wire on the site when I bought mine a few years ago.

On Tue, Mar 29, 2022 at 08:57 PM, <bc3910@...> wrote:

Where he measures the voltage from the doubler, between D3 and D5. running the same rail voltage of 12.7v he got about 70VDC between the two diodes. I got about 8VDC. Hopefully, that might be a clue to help someone smarter than I toward the next steps.

Bryan,

The voltage at that point comes from rectifying and doubling the output of the amp.? Since the amp is not amplifying RF, there is not signal to double.? The value you are measuring seems reasonable if there is no RF being supplied to the amp.

In place of the oscilloscope, you can in some cases use an RF Probe.? I have one built from a kit that I tested for our Build Club:

Or if you have parts already:


That would at least let you know if you are getting RF from the QCX through to the IRF510s.?

73
Evan
AC9TU
?

I built a QCX mini for 80 meters. The kit is version 2. ?The receiver works very well and the transmitter puts out about 5 watts. The transceiver seems to function very well except when it breaks into oscillation. The oscillation occurs following transmit. If the unit is in full QSK it happens almost every time the unit is keyed, if in semi QSK it happens after about 10 transmit to receive changeovers. ?The oscillation seems to be effected by the volume control, when turned down most of the way the oscillation is not noticeable, a strong signal can be copied. If the volume is turned up past about 20% the oscillation becomes a problem. The only way to stop the oscillation once it starts is to disconnect the power supply. Once reconnected there is no oscillation until the transmitter is keyed.
I tried to reduce input voltage down to 12 volts with out effect. I redid the alignment without effect. I have actually had quite a few qso’s with this little rig, it works great until the oscillation starts.
any thoughts would be appreciated
thanks; Bill (AA2MX)