Amp swings lower power?

[Handy Andy]

Looking back...

I have 2 amps, a Palomar TX250 and a Shooting Star 225 plus, 10G power cables.

Radio is a Galaxy DX939, lowest output is 2W -> 3W, high is 6W -> 8W using Dosy Test Center.

When key up, DK approx 60W, but audio drops it to 40ish?

Radio is a DX 939, unknown mods but puts out well. Variable power all the way down is around 2W.

I could understand if the DVOM dropped, as ok, meter is 20 years old. But the meter drop AND output drops, that tells me something is wrong.

What am I missing??

Ok, the 939 has a wonderful little circuit used in the AM section to force more carrier regulation than the earlier models, like the 88 or 33 did.

The AM Regulation section...

There were several problems incurred by the earlier versions (READ: Galaxy DX series with Variable Power) that caused rather bizzare interference as well as wildly swinging radios making them one of the hottest and most desired radios to have - even though they bled like crazy...which their swing generated part of that problem to begin with...

All due to how you LOWER Carrier Power, the radio responded in kind by providing more asymmetric forward power swing when you modulated. Dynamite for special effects, but lousy for interference and even harder on the parts due to the dynamic range and linear function the Bi-polar design had to deal with. (Power Dissipation being one main culprit)


So, your choice, either keep that part in or remove it ...

Not responsible for errors, omissions - lost wages - lost income - any offspring or any other offensive materials deemed Offensive by any that may deem it Offensive for any Offensive Reason

--- There I Said It - Neet...

There's always a Bigger Fish - In this mod, if you try it, that 10K WIPER arm that goes to COLLECTOR of Q56 - USE 1N4148 Diode IN SERIES - BANDED end goes IN TO HOLE of JP8 that is RED that goes to COLLECTOR of Q56... GREEN ARROW shows where LIVE SUBSTRATE of 10K pot goes FROM Q55 into pot - OTHER SIDE OF POT SUBSTRATE to FOIL GROUND. This will make Envelope adjustable for effect...



The Above mod affects Q56s' ability to control envelope...

 

[Cutlass327]

Well, I now have a SuperStar 400 Hi Drive. It shows the drop too, but only in the RMS side of the RMS/Peak switch, just like the others.

I'll look at that diagram later, in the middle of homework but figured I'd check here real quick and update.

 

[loosecannon]

cutlass327,

i have a couple of questions that might have already been asked, but if you would indulge me please...

which meters are showing the drop?
the radio's meter? the external wattmeter? both?

what model of wattmeter are you using?

does it act the same when going into a dummy load as it does when going to an antenna?
LC

 

[Cutlass327]

cutlass327,

i have a couple of questions that might have already been asked, but if you would indulge me please...

which meters are showing the drop?
the radio's meter? the external wattmeter? both?

what model of wattmeter are you using?

does it act the same when going into a dummy load as it does when going to an antenna?
LC

Dosy Test Center, about 20 years old.
The radio's power meter swings up like it should.
Does the same whether into the 300W dummy or into the A99 antenna.
I'm starting to think it is all the Dosy...

Just hooked up the DX44, low power is 2.5W, turned up it is 10W. Dosy does not drop on either setting (RMS or Peak) no matter how high I turn radio output. OK, if only this one had sidebands, the others would be in storage...

 

[338_MtRushmore]

The dosy shows the radios swinging, but not the amp, correct?

 

[nomadradio]

The "falls back" problem was something our "balls-to-the-wall-audio" customers complained about.

One simple low-cost trick to try: Pull R362, a 33k resistor. Install a 1k part in its place.

See if the problem goes away.

I would argue with Andy about Q56 and what it does in this circuit, but there's no point. He may be right. I may be.

And there's nothing to gain by disputing your explanation without a proper rebuttal Andy. I respect your opinion, even when I think you may be wrong.

Doesn't matter. Too late in the day to construct a proper argument with explanatory illustrations.

Maybe another day.

See if changing R262 makes the symptom go away. Just one warning. You'll need to set the mike gain a bit lower in AM mode set up this way.

And maybe I'll summon the motivation to discuss the circuit function of Q56 in some coherent detail.

Another day.

73