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admin - Sunday, November 11, 2012 at 14:54:59
HP 1715A 200 MHz dual-channel oscilloscope.
(Refer to the main photo. for item description)
admin - Sunday, November 11, 2012 at 14:52:45
Hewlett-Packard 1715A: 200 MHz oscilloscope, (dual-channel).
Vintage: mid-1970's.
(This is the main photo. of a set of four. The other three are close-ups of the front panel).

HP made several 'scopes in this range, so they all look very similar at a casual glance. This is the 200 MHz version in the 17xx range. It could be viewed as HP's answer to the Tek. 475 (but I am sure that Tek. aficionados would debate that point strongly!)
One unusual and useful feature of this range of 'scopes is that the input sockets for the vertical amplifiers can be configured for an internal 50-ohm load to be switched in. (But be careful that you don't overload it!). Very handy for R.F. work.

Maintenance issues.
By-and-large, this range of 'scopes from HP are quite reliable, but they do have a few short-comings.
1. The feet, mounted at the rear of the item: they are fabricated from some type of hard plastic (they look just like Tektronix feet, but Tek's are made of hard rubber). With time, that plastic becomes very brittle. The first you usually know about this is when you rock the 'scope back onto two feet at the rear - whilst trying to pick it up - and crack!: two feet shear off.
2. The time-base switches. With time, the internal rotary selectors become very stiff. The usual consequence is for the delayed time-base rotary knob to split internally where it meets the brass milled annulus that couples that knob to the shaft. On account of the age of this range of 'scopes, obtaining a replacement knob will be very difficult. So, prevention is better than cure: before trying the controls for rotation, take the top cover off the 'scope and squirt the switch contacts with switch cleaner: you should feel a gradual 'easing-up' of the switch knob rotation as the cleaner takes effect.
3. General construction. The internal construction does not permit for easy maintenance, but it is no worse than the Tek. 455 / 465 / 475 / 485 series (could anything be worse?).

Availability.
They appear on the second-hand market now and again. Typical prices (for a 'declared no-faults' model) is in the range £130 - £170 at time of writing, with the 100 MHz version fetching a bit less.

Submitted by Al. (Skywave) on Nov. 11, 2012.
admin - Saturday, November 10, 2012 at 10:05:24
The wide-range of modulation options can be seen in this photo.
admin - Saturday, November 10, 2012 at 10:04:25
RF O/P level continuously adjustable from 3-v. down to 0.1 µV. That is quite impressive!
admin - Saturday, November 10, 2012 at 09:58:56
Hewlett-Packard 8640B signal generator.
A high-quality sig. gen. aimed at the professional electronics & radio communications market.
Freq. coverage 450 kHz - 1024 MHz. Versatile modulation options: C.W., A.M., F.M. ; int. / ext. mod.; a.c. or d.c. coupled. Internal mod. freq. is continuously variable as is the mod. depth / deviation. Front panel meter enables all variables to be set / monitored; O/P freq. is displayed on red L.E.D. displays, 6 digits. Facility for switching that counter / display to external signal. O/P freq. can be fine-tuned: front panel adjustment.
The heart of the unit is a cavity oscillator running at UHF. There then follows a chain of freq. dividers to produce the final freq. - the manual explains it all.

Maintenance comments, etc.
Build quality internally is of the very high standard that you would expect from HP in a piece of kit like this. Generally speaking, mine has proved to be very reliable, although this product does have a few 'age-related' issues, the most predominant being HP's use of a type of plastic used for the gearing between the front panel controls and the internal mechanics. The plastic (which I believe is called 'Delrin') disintegrates over time. The first you know about this is when the rotary switches go all floppy and won't indent properly. My fix is to carefully dis-assemble the item (not a trivial task), strip down the front panel mechanics (again, quite a challenge) and use Araldite to perform a repair. Ideally, replacement parts would be nice - but on account of the age of this item, such parts are no longer from HP. It should be noted that this problem with the plastic disintegration is remarkably common to ALL HP's products of this vintage.
There other faults that can appear with time; there is quite a lot of repair commentary on the Internet about the 8640B.
The extractor fan is a rather 'over-the-top' affair using a motor with a pair of integrated Hall effect transducers. The voltage from these is fed into a phase-shifting controller to regulate the fan speed. The failure of the fan to rotate is usually caused by semi-conductor failure on the fan's controller board - which, fortunately, is easily removable for repair. I have never had to replace the fan itself in the event of 'the fan doesn't spin anymore' syndrome.

Finally, before even contemplating doing any maintenance on this item, it is essential that you obtain the manual, study it thoroughly first and give yourself plenty of time, space and good lighting to do any diagnostic work and repair.

Availability.
The 8640B does appear infrequently on the second-hand market - but (of course) they are certainly not cheap! At date of writing, you can expect to pay upwards of £500 for one in a reasonable state of functionality, but compared to the cost when new, that is very, very cheap indeed!

If you haven't got one, but can afford one and can find one - buy it! You won't regret it.

Photos. and comments submitted by Al. - Nov. 10, 2012.
admin - Friday, November 9, 2012 at 19:36:30
Heathkit signal generator model RF-1U.
Vintage: 1960 - 1970

Heathkit were the U.K. arm of Daystrom, U.S.A.; Heathkit had their manufacturing base at Gloucester. When the Gloucester factory was closed down in the mid-70's, I found myself working with many ex-Heathkit staff: and many were the tales that were told!

Almost everyone who has - or is - 'involved' with repairing radios will own, have owned, seen or heard about the RF-1U. It is a very basic signal generator: to the electronics professional, it is a 'test oscillator'. Nevertheless, it is quite adequate for the job it was designed to do: a controllable R.F. signal source for the radio hobbyist, experimenter and Radio Amateur. The RF-1U can still be found for sale in the 'usual places' and if a repair is needed, they are not difficult to repair. On account of their relative simplicity, it is not unusual to find one that has been modified: a stabilised PSU is one common modification, as is an improvement to the modulation circuitry.

Submitted by Al. (Skywave), Nov. 10, 2012
admin - Friday, November 9, 2012 at 19:23:49
Dymar VHF signal generator, type 1525.
Vintage: 1970's (estimate).

Dymar were based in Watford, North London. The company was formed by three engineers who manufactured R.F. products primarily for the then rapidly expanding mobile telephone market: hence the freq. coverage of this signal generator. Dymar ceased trading in the mid-80s (estimate).

A close inspection of the front panel gives you some indication of its versatility: this is reflected in the clever circuitry that is enclosed within. Not only that, but great consideration towards maintenance has been taken in the internal design - and without degrading the signal leakage performance (not an easy matter to arrange). It contains its own NiCad battery pack, can run from an external d.c. source or (of course) conventional a.c. mains - when the NiCad gets re-charged, if necessary. All-transistor, of course. The handle on the top gives you some idea of its weight: not a lot: easy to carry around.

Submitted by Al. (Skywave), Nov. 10, 2012
admin - Friday, November 9, 2012 at 19:11:20
Airmec H.F. signal generator type 201.
Vintage: mid 1960's (this is an estimate.)

Airmec produced many R.F. products for the electronics industry: they were based in High Wycombe. Sadly, like many U.K. instrument firms, they have long since gone.

What you see in the photo. is as it arrived in my workshop (once out of its outer case) before I began testing it and doing the necessary repairs, etc. The signal level meter is not the correct one: a replacement, suitably re-scaled, was subsequently fitted.
As regards "what will it do?", a close exam. of the controls on the front panel tells you most things. What is not evident from that photo. is the amount of technical sophistication that exists inside this all-valve unit - and it is very well mechanically arranged, too.
Needless to say, it is heavy!

Submitted by Al. (Skywave), Nov. 10. 2012.
admin - Wednesday, November 7, 2012 at 18:47:27
Marconi TF144G signal generator - affectionately known as "The Coffin".
Vintage: mid-1930's, but these were in regular use during WW2 and in the early '50's.
Freq. range: 85 kHz to 25 MHz in 8 bands; O/P level: 1 µV to 1 V; modulation: 400 Hz. (internal) or ext. mod.; A.C. mains or ext. d.c. operation.
Valves: ML4 (oscillator), ML4 (modulator), MU12 (rectifier).
Weight: 68 lbs. (Yes, you read that right: 68 lbs.!)

The Jones plug on the left is for the A.C. mains connection or the external d.c. PSU connection.
The pictures in this collection show empty sockets where the two ML4 valves belong: these were missing when I received this item and the photo was taken soon after. I went shopping for those valves but at the prices I had to pay for them unfortunately made any further restoration work uneconomic.
The front panel is painted brass - about one-quarter on an inch thick! The chassis is silver plated brass and the case is heavy gauge sheet steel. That's why this generator is so heavy! The main tuning capacitor is a delight to behold: a real example of fine craftsmanship; it's a twin-gang affair, each section is about 8 - 25 pF.
Having said all that, it is my opinion that this item doesn't really qualify for any serious use as a signal generator these days: there are many, many other sig. gens. 'out there' that are lighter, smaller, and with far superior spec. Hence, I regard the TF144G as a museum item - but the quality of the workmanship reflects the standards that such items were built to all those years ago.

Photos. and write-up submitted by Al. (Skywave), Nov. 8, 2012.
admin - Tuesday, November 6, 2012 at 09:02:14
Trio JR-310; vintage: late '60's - early '70's.

Summary. Amateur bands only double-conversion s.het.; hybrid: valves (6) & transistors (4). Freq. coverage: AmRad bands 80, 40, 20, 15 & 10 m.
1st. I.F.: tunable 5355 - 5955 kHz; 2nd. I.F. 455 kHz. AM / CW / SSB.
Weight 20 lbs.

Overall, a standard design double-conv. AmRad bands only s/het.; typical of its type emanating from Japan during the decade late '60's to late '70's.

-------------- Submitted by Skywave, Nov. 5, 2012. ---------------------