HP501 and HP502 surface mount devices.

[Station X]

Does anyone have any data for these devices which are mounted on the output amplifier board of my Racal 9087 signal generator? I can't find anything useful on Google.

I assume they're transistors. The left hand device in the picture has 501 written on the underside. They work from about 100 kHz up to 1.2 GHz. Signal path is from left to right.

Applying a 5 MHz signal to the input results in it appearing on what I assume is the base of the 501, but it gets no further.

[Radio Wrangler]

I've no idea about the devices, but it is likely that the DC power to the poweramp stage and possibly its driver are controlled by a feedback loop which provides ALC control of the output power to stabilise it and to give fine steps of level control as well as providing linearised AM.

First check is to see if there's power floating around, then if the devices seem to be biased in class-A.

The other likelihood is some0ne pressed PTT when a transceiver was connected.

There's a reasonable choice of newer bipolars which will do the job, but getting the same package may be a problem. What carrier output level does it go up to?

David

[peter_scott]

Hi Graham,

Unfortunately HP had internal stock numbers of the form nnnn-nnnn and they also had marketing numbers and it wasn't always easy to relate them.

There is a fair amount of HP component info here:
http://www.datasheetarchive.com/1--H...t.html#catalog

although at a cursory glance I didn't spot your devices.

Peter

[Station X]

Thanks David and Peter.

I've attached a sketch showing how the amplifier board is connected within the Racal 9087 and what's on the amplifier board. The bandwidth control is on a daughter board and is documented in this thread:-

https://www.vintage-radio.net/forum/...d.php?t=111091

There is indeed an ALC feedback loop which I believe provides fine level control over a 10dB range, coarse level control being set by the attenuator. I've tested the attenuator and it's fully functional.

The SG won't have had RF shoved up it, as I've never connected it to a transceiver. It may have had HT connected to the O/P though.

I'm testing the amplifier in isolation with a 23V stabilised external supply, another SG and a 'scope.

The next thing I'll do is to measure the transistor voltages and test the junctions using the diode function of my DMM.

[Station X]

Here are the voltages. References to top, bottom, left and right refer to the image of the component on a vertical display. Daughter board was connected.

501
Top and bottom tags 0V.
Left tag 3.0V. This appears to be the signal input.
Right tag 14.91V. This appears to be the signal output.

502
Centre round 0V.
Let tag 9.3V
Right tag 14.36V.

Nothing seems test as a semiconductor junction.

I'm trying to reverse engineer the circuit by visual inspection, but it isn't easy as I can't tell which are chip resistors and which are chip capacitors.

[Station X]

I've identified the HP 502. It's actually an HXTR 5102 and it isn't cheap:-

http://www.amazon.com/Hewlett-Packar.../dp/B00B061R64

[Station X]

Predictably the other device in an HXTR 5101.

I have data sheets for both devices, so I should be able to make a better stab at reverse engineering the circuit and checking whether the test voltages look good or bad.

[Radio Wrangler]

So it looks like your sig gen is designed to do about +23dBm output, which was a value in some of the military contracts. Marconi cleaned up most of those with their 2024 generator with its high power option.

Matching the package is going to be a pain, so I'd look for a modern solder-down packaged part and make a copper flange to solder it onto. Something for the cellphone market before they all went LDMOS?

I've got a big lump of hefty copper if you need some, Graham.

David

[Station X]

Thanks David.

I have shed loads of copper and will have no difficulty in making a new mounting should the need arise.

However I won't be repairing this PCB myself. I lack the manual dexterity and tackling the job would be a sure way of reducing the signal generator to an expensive door stop. The best I'll be able to do is diagnose the fault and get someone with experience of SM soldering to do the repair.

I've reverse engineered the first stage and the circuit is attached. The resistor symbols could be chip resistors or chip capacitors. It's impossible to tell as they're unmarked, but in most cases the component type can be deduced.

[Radio Wrangler]

SMT parts can be lifted off and measured... the little yellow Peak LCR box does a good job,
but I have an HP varactor diode tester at work and it'll measure up to 1000pf with femtofarad resolution. Not calibrated in years, but very probably accurate.

Even the driver will be running a fair amount of power. The circuitry will be designed for low stage gain as a sacrifice to make the gain versus frequency flat, so having three collector resistors paralleled is not surprising, ditto two emitter resistors.

Resistive feedback from collector to base is usual, often with a blocking capacitor, but in this case it looks like the only route for base bias.

Stupid question, i know, but I suppose you've already checked all the power supplies in this area? The output device and probably the driver will have collector supplies which have AM applied to them as well as being controlled to ALC the carrier. Failure of the modulator shuts down the output amplifier. It's worth being very thorough going through all the peripheral stuff before getting stuck int the RFery.

SMT soldering becomes easy once you can see it. I bought myself a stereo microscope (low magnification is ideal) and I wouldn't be without it. It's worth keeping your eyes open incase you come across one.

David

[avocollector]

Originally Posted by Station X

I've identified the HP 502. It's actually an HXTR 5102 and it isn't cheap:-
http://www.amazon.com/Hewlett-Packar.../dp/B00B061R64

$150 for a TRANNY! arrrrrrgh! and I thought valves were bad enough

[Radio Wrangler]

Transistors can get quite expensive once you get into niche markets. Those Hewlett-Packard Associates microwave parts were never cheap. The people who made them were spun out as part of Agilent, then Agilent sold them off to a bunch of venture capitalists, and now they trade as Avago.

It would be tempting to put in an IC amplifier device, but they use feedback to control their gain and so the AM/ALC stuff won't work. This unit is going to need a pair of transistors if they are the fault. It sounds like it's been Graham's sig gen for some time and that it's been used sensibly so that leaves random failure as the only cause. (So many sig gens die from unintentional keying of transceivers)

His output device may live on, in a slightly different package as AT-64000. Still available, but NRND. It may be cheaper to find something from elsewhere, otherwise finding a scrap 9087 that didn't suffer reverse power may be the cheapest way.

David

[Station X]

Here's the listing I originally linked to:-

http://www.amazon.com/Hewlett-Packar.../dp/B00B061R64 ($150)

and here's a couple of cheaper ones:-

http://www.ebay.com/itm/150863931094 ($33.95)

http://www.amazon.com/Set-1-Piece-TR...ords=hxtr+5102 ($29.95)

What concerns me is that two of these listings uses the same picture, so the cheaper ones could be scams. Then of course it's pot luck as to whether you get charged import duty, VAT and Royal Mail collection charges on the items from the USA.

The HXTR 5101 is available here at what looks like a reasonable charge, but there's a 30 Euro minimum order charge.

http://www.rf-microwave.com/en/shop/...HXTR-5101.html

Before buying any new devices I'll need to convince myself that the original is actually faulty.

[Station X]

While I'm here can anyone tell me what the components marked -C4- are?

The component marked 120 is of course a 12 ohm resistor, but it's the only marked resistor on the PCB.

Thanks.

[Dickie]

Probably HSMS-2824 dual schottky diodes that have something to do with the levelling. Although looking at the earlier photos they could be transistors involved in the bias supplies. Consult:

http://www.marsport.org.uk/smd/mainframe.htm

[Radio Wrangler]

Roger's website, posted by Richard is a valuable resource for unravelling surface mount component short codes, so it's worth putting in your bookmarks.

Roger is the UK agent for 'Dubus' magazine so he's especially interested in microwave parts.

David