Metalwork - Lathe and Mill topics

Thursday, 26 June 2025

Re: [Amateur-repairs] Old test eqpt? Chuck it? Refurbish it?

A few thoughts.
First, there are a lot of people around who could make use of some of that equipment. Think young people with few resources but interest. A fifty dollar/pound piece of "modern" equipment might seem cheap to you or I, but out of reach for some young person learning. So getting it to them could be very beneficial.
Second, there are others who collect various old equipment for various reasons. Probably for most of your equipment there is someone who would like to have it.
In some cases museums may be interested. I had an oddball piece of RCA equipment from around 1960 that ended up going to a museum. It was rare enough they didn't have one.
Getting it to these interested parties is sometimes challenging. Some ideas.
There are various forums in different places that cater to such things as old test equipment. You can look for them. Google groups, facebook, etc. Amateur radio clubs might also be able to help. For things you think might be museum worthy, you could search for museums directly. And of course you could haul it all to a hamfest or two or three... Could be a lot of trouble.
If you would like to keep it available without all the work, you might list it all as a single lot for sale at some nominal price. Sell it to someone else who will then do whatever with it. That would increase the chances of it going someplace it is appreciated and put a bit of change in your pocket without very little effort.

Hope this is helpful,
Will, N4JBD

> On 06/26/2025 10:37 AM EDT Gareth Evans via groups.io <headstone255=yahoo.com@groups.io> wrote:
>
>
> We seem to have been overtaken by the miniaturisation of Anno Domini
> when VNAs and the TinySA give us almost everything we need in a size
> not much bigger than a packet of cigarettes.
>
> What then, to do with shelves full of the test eqpt slowly amassed
> over 50 years but now worth almost nothing, perhaps only 5 or 10
> shekels / dollars / pounds sterling at the various rallies and hamfests,
> hardly worth the hassle of trying to sell it?
>
> I'm thinking of my valve (tube to the Left Pondians :-) ) RF sig genny,
> AF sig genny, RF millivoltmeter, bench DVM, freq counter,
> homebrew capacitance meter; all taking shelf space that is on
> increasing scarcity of shelf space in the shack and all of which has been
> superseded by miniaturisation.
>
> There's even a W95 laptop in there somewhere purely to support
> the ICOM PCR1000 RX, long made redundant by RTL-SDR
>
>
> 73 DE G4SDW (Was G8DXY) GQRP #3339 Gareth
>
>
>
>

You just can't beat the person who never gives up.
Babe Ruth

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Re: [Amateur-repairs] Old test eqpt? Chuck it? Refurbish it?

Gareth,

I sympathize with you. What some of us locally are doing is to use this equipment as training pieces for restoration and use. Simply, repurpose it for training. Also, some of the components are valuable for other restorations. Variable caps, IF cans, oscillator coils, x'tals, tubes/valves, etc... are all valuable to the restorer / homebrewer. You can make an x'tal radio, Low Power AM transmitter, etc... and still have parts left over.

Just some thoughts here. Is there a vintage electronics club you could donate these to?

73.

Joe AB1YO

On Thursday, June 26, 2025 at 10:37:14 AM EDT, Gareth Evans via groups.io <headstone255=yahoo.com@groups.io> wrote:

We seem to have been overtaken by the miniaturisation of Anno Domini

when VNAs and the TinySA give us almost everything we need in a size

not much bigger than a packet of cigarettes.

What then, to do with shelves full of the test eqpt slowly amassed

over 50 years but now worth almost nothing, perhaps only 5 or 10

shekels / dollars / pounds sterling at the various rallies and hamfests,

hardly worth the hassle of trying to sell it?

I'm thinking of my valve (tube to the Left Pondians :-) ) RF sig genny,

AF sig genny, RF millivoltmeter, bench DVM, freq counter,

homebrew capacitance meter; all taking shelf space that is on

increasing scarcity of shelf space in the shack and all of which has been

superseded by miniaturisation.

There's even a W95 laptop in there somewhere purely to support

the ICOM PCR1000 RX, long made redundant by RTL-SDR

73 DE G4SDW (Was G8DXY) GQRP #3339 Gareth

[Amateur-repairs] Old test eqpt? Chuck it? Refurbish it?

We seem to have been overtaken by the miniaturisation of Anno Domini
when VNAs and the TinySA give us almost everything we need in a size
not much bigger than a packet of cigarettes.

What then, to do with shelves full of the test eqpt slowly amassed
over 50 years but now worth almost nothing, perhaps only 5 or 10
shekels / dollars / pounds sterling at the various rallies and hamfests,
hardly worth the hassle of trying to sell it?

I'm thinking of my valve (tube to the Left Pondians :-) ) RF sig genny,
AF sig genny, RF millivoltmeter, bench DVM, freq counter,
homebrew capacitance meter; all taking shelf space that is on
increasing scarcity of shelf space in the shack and all of which has been
superseded by miniaturisation.

There's even a W95 laptop in there somewhere purely to support
the ICOM PCR1000 RX, long made redundant by RTL-SDR

73 DE G4SDW (Was G8DXY) GQRP #3339 Gareth

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Monday, 2 June 2025

Re: [Amateur-repairs] Test leads and other things needed ?

Dave,

I appreciate the detailed response. Thank you for taking the time to make this post.

Juha

NI2M

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Sunday, 1 June 2025

Re: [Amateur-repairs] Test leads and other things needed ?

Dave I think the top statement you made that is the first thing to remember all the time is:

"inserting a long wire at a test point is like attaching an antenna"

so ask yourself what happens in here, and over there, if I insert this "wire" into that gadget!

And just hope that your instrument was notleft on "amps" or "ohms"

Re: [Amateur-repairs] Test leads and other things needed ?

Juha

Well, this can be a very lengthy discussion since it is more about technique than it is about tools. Test probes do not have to be exotic or expensive, but they do need to be selected with consideration of the circuit you are using them in.

There are two cardinal rules I reccommend you adopt.

Study the circuit first, then probe. - determine what the signal and DC voltage levels are at the intended test point.
Don't insert problems while looking for problems. - don't use a probe the induces resistive load at the test point or induces resonance.

For most general circuit analysis, my probe of choice is most often a common 1:1 O-Scope probe. Handy, easy to use, minimal in-circuit loading. However, keep in mind that they have series impedance, typically 1MΩ or 10MΩ, so will impart attenuation in the signal level displayed. Typically, when performing alignments, the goal will be to obtain maximum level of the desired signal, and the true acurate level measurement is seldom critical. When accurate level measurements are required, the gold standard is an Active Probe (e.g. Fet Probe), but a simple wire probe is usually sufficient. However, always remember you are observing low level RF signals, and inserting a long wire at a test point is like attaching an antenna, it can become part of the resonant circuit and potentially de-tune the target circuit. I seldom encounter this problem in most IF circuits, but when directly sampling tuned circuits like oscillators, beware. Probe lead resonance can be a significant problem when attempting to observe very low level HF signals. This is why commercial probes like those from Pasternak are expensive, they are designed to limit in-circuit loading. Keep in mind that in radio receivers, most RF paths are either 50Ω impedance.

Always keep in mind that your TinySA is a very sensitive instrument designed to detect and display RF signals are very low levels. Remember, at signal that will ultimately result in an S-9 reading on a the meter of a calibrated receiver is actually a very low level signal on the antenna wire, -73dBm (50 uVolts). In most IF circuits, signal levels will seldom be higher than @ -25 dBm (@35mV). The TinySA specifications state "Suggested maximum input power of +0dBm with internal attenuation in automatic mode", so it is important to always ensure you protect it from potential damage. Always study the circuit you are going to probe to determine what the potential signal level may be. It is also a good idea to always use "Automatic Attenuation" to ensure the instrument can at least attempt to protect itself from overload.

The entire purpose of a Spectrum Analyzer is to observe signals in the frequency domain. Obviously, this assumes the most important observation is the level of the signal at a specific frequency. In the IF circuits of radios, the RF signals may or may not be isolated from DC bias voltages depending on the circuit design. Some signals will be gated, e.g. "Switched" via DC levels. When working with most solid state circuits, the levels of DC present are seldom significant and not a threat to your TinySA, but in Tube radios, bias voltages can be very high and it is necessary to protect the instrument from a high level input.

With respect to a "DC Blocker", yes, this is always a good idea, especially when working with Vacuum Tube radios due to the exceptionally high DC voltages present. But all you need is a method of blocking that DC voltage from entering your delicate instrument. That is what capacitors do. When probing RF signals, a simple solution is to insert a small capacitor, e.g. 25-50 pF, in series with the probe tip. Be sure the capacitor has a DC rating high enough for the target cirtuit. This will effectively block the DC while allowing the RF (AC) signal to pass with minimal attenuation. A simple 1:1 Sope Probe is ideal for this, you can clip on lead of the capacitor in the probe tip, and use the other lead to probe the test point.

For your Lafayette Receiver, again, I recommend you study the circuit first. The method they use for alignment could be performed with a reasonably accurate signal generator and a RF level meter, e.g. AC Volt Meter (True RMS DVM) or an O-Scope. They introduce a fixed RF frequency to a tuned circuit (455 KHz or 2.608MHz) and optimize the circuit for maximum output level. So, the input level is not critical, it just needs to be sufficient to excite the circuit but not too strong to avoid saturation. I would start out with a relatively low level e.g. -60dBm and then increase the level until you can observe response at the test point.

For the remainder of the alignment, they simply introduce an RF signal at the antenna port. No modulation is necessary but won't matter much anyway. Each band is tuned again for maximum signal strength, and again, they do not specify the level. I suggest using -72dBm as the input level since that normally represents and S-9 level signal. However, examining the HA-800B manual, I noted that the S-Meter alignment uses 100uV (-67dBm) as the calibration value.

WRT the 1st IF Trap, understand what the circuit is for. Since the 1st IF frequency is 2.608 MHz, the receiver front end needs to reject an outside signal at the same frequency to prevent IMD and overload of the receiver. They use a relatively strong signal modulated at 1Khz to emulate an AM signal. This adjustment ensures that that frequency is sufficiently attenuated when it is applied to the Antenna terminal.

Good Luck, this is where the fun begins. BTW, when you get to the Kenwood, don't forget the DC blocking cap to protect the TinySA, and keep your fingers out of the spitzin sparken circuits.

________________
73's
Dave - KB7JS

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Saturday, 31 May 2025

[Amateur-repairs] Test leads and other things needed ?

Hi all!

Completely new to this group, but I have owned a TinySA Ultra for a few months now (mainly using it for calibration of S meters) and I am really impressed at the functions and features of this device. When it comes to conducting any sort of "Alignment", I am a complete novice. Hence, the questions below are pretty elementary to many of you.

I wanted to ask for any recommendations for test leads and other things I need, to carry out the following type measurements/alignment. I don't care if the leads cost serious money (like those from Pasternak). Erik who has designed this device also has suggested a "DC blocker" and obviously I need a mechanical "adaptor" to convert from SMA to BCN for instance. What else do I need? I will check out any YouTube videos that are out there for carrying out alignments such as these.

Alignment of a 100% solid-state ham radio receiver which goes back more than 50 years. In my case, I need to do an "alignment" of a Lafayette HA-800B receiver. The Installation and Operating Manual provides fairly detailed instructions on this. Next up for alignment is a 100% tube Receiver by TRIO-Kenwood (9R-59DS).

In more detail:

* IF (1st at 2.608MHz and 2nd at 455 kHz)

** 2nd IF at 455kHz at 30% AM modulation depth at 1,000Hz) and 1st IF, injecting an unmodulated (I believe) signal at 2.608MHz connecting the test leads between the chassis and the Gate of a FET ("FET-2")

* 1st oscillator (different ham radio bands, not including WARC) - It doesn't say which level the signal needs to be though and I believe that an unmodulated sinusoidal wave is sufficient?

* ANT and RF coils (here, too, no information is provided about the signal that I need to inject so, I am assuming a sinusoidal wave would suffice?)

* S meter (100uV level unmodulated signal at 14.0MHz)

* 1st IF Trap Coil (at 2.608MHz, AM modulated at 1,000Hz at 30% depth)

Any guidance/suggestion or recommendations would be highly appreciated on all of the above!!

73!

Juha

NI2M

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