From: cd@notformail.com   
      
   On Thu, 15 Jan 2026 11:54:45 +0000, liz@poppyrecords.invalid.invalid   
   (Liz Tuddenham) wrote:   
      
   >Cursitor Doom  wrote:   
   >   
   >> On Wed, 14 Jan 2026 11:30:29 +0000, liz@poppyrecords.invalid.invalid   
   >> (Liz Tuddenham) wrote:   
   >   
   >[...]   
   >   
   >> >If you want an ergonomic probe, put the components into a ball-point pen   
   >> >case (if you can find a small enough capacitor).  ...or just put the   
   >> >resistor in the pen case and have the capacitor in the plug at the   
   >> >amplifier end of the cable.   
   >>   
   >> I'll get the probe I improvised re-jigged, but won't have time to do   
   >> any more to the Uher til Sunday, unfortunately.   
   >   
   >Just a minor point:   
   >It doesn't look as though there will be room for the capacitor inside   
   >the plug where it will be screened, so the capacitor needs to be at the   
   >tip of the probe with the resistor between it and the cable end.  This   
   >is so that the resistor attenuates any stray signals picked up by the   
   >capacitor.  If the capacitor were on the amplifier side of the resistor,   
   >anything it picked up from the mains or the proximity of your hand,   
   >acting like an aerial, would be fully amplified.   
      
   A fine but important point there! We often think 'stuff in series' can   
   go in any order, but so often there are exceptions due to unexpected   
   effects which must be allowed for. I do have some more suitable   
   sub-min 10n caps which would be much easier to shield. I'll use those   
   on the Mk II version. :-)   
      
   >   
   >>   
   >> >I have a home-built test amplifier screwed to the underside of the shelf   
   >> >above the workshop bench, with a veriety of input connectors and probes.   
   >> >It has two attenuators calibrated in 10 and 1 dB steps, with a meter   
   >> >that reads directly in dB or can be switched with an electronic zero to   
   >> >read variations of 0.1 dB.   There is an output at 0dBm level for   
   >> >feeding external equipment, such as high-quality headphones or an   
   >> >oscilloscope, and it has a small loudspeaker, which is often more use   
   >> >than the oscilloscope for identifying the cause of fault.   
   >>   
   >> Yes, I'm sure you're right and it sounds like you have everything   
   >> organized so well at your workshop. You do this kind of thing for a   
   >> living? I'm just a hobbyist and not exactly outstanding at this if I'm   
   >> honest about it. My workbench is an absolute disgrace. I just use up   
   >> all horizontal space that's free in next to no time; always been the   
   >> same.   
   >   
   >My workshop is a 6ft x 10ft wooden shed containing dreadful mixture of   
   >amateur, semi-professional and fully professional work in several   
   >different fields.  The welding and blacksmithing can only take place   
   >outside in good weather and the Harrison L5 lathe is in a spare   
   >downstairs room in the house.   
   >   
   >The workbench is a matted tangle of wire clippings and bits; I have to   
   >clear a space to bring in things I need to work on.  Anything too big   
   >has to be dismantled on the kitchen table, then taken to the shed and   
   >worked on in sections - or the oscilloscope and soldering iron have to   
   >be taken to the kitchen.  That means a very thorough clean-up in the   
   >kitchen before I can do any pastry-making.   
      
   Same here, except with me it's DiY spiced tea. :)   
      
   >   
   >The equipment comprises a large Solartron (valve) audio signal   
   >generator, a Marconi (valve) RF -VHF signal generator.  The   
   >aforementioned measuring amplifier, a Philips twin-trace oscilloscope   
   >and several Farnell power supplies: 0-30v, 50-0-50v and 0-350v.  I have   
   >a few resistance boxes and capacitance boxes for experimental work.  For   
   >the bench mains supply there is a variac-controlled isolation   
   >transformer with 240v and 120v tappings.  Other equipment is scattered   
   >around the house in odd corners and can be brought into the shed when it   
   >is needed.   
   >   
   >One long wall is covered with nests of drawers containing resistors and   
   >capacitors, laid out on a grid pattern with preferred values aligned   
   >horizontally and the decades in vertical columns.   Drums of wire are   
   >stored on broom handles hung in strops from the ceiling.  The end of the   
   >shed nearest the doorhas a cabinet and a bench with the welding,   
   >metalworking and car repair tools.  Small shelves along the tops of the   
   >walls house everything from transformers to household nails and spare   
   >rivets with a rivetting set for the Allen Scythe cutterbar!   
      
   Well, it's damn nice to know I'm not the only one who works in   
   something approaching complete chaos. I was beginning to think I was   
   unique in that respect! I had a theory that having a workshop like a   
   minefield where if you fell or tripped, you'd impale yourself on   
   something would force you to take great care and in doing so,   
   hopefully ward off dementia, but since I got diagnosed with   
   age-related osteoporosis, I've been forced to tidy up the more obvious   
   and lethal hazards at least.   
   >   
   >> >> >> I did notice that for some reason on the slowest speed (the 15/16"ips)   
   >> >> >> there's considerable variation in the tonal reproduction with music   
   >> >> >> off the radio, as if the speed is wandering during transport. Not   
   >> >> >> noticed any such effect at the higher speeds so not sure what that's   
   >> >> >> all about. Fortunately, it's only music where it's noticeable; speech   
   >> >> >> just sounds normal and at that speed, it's really only speech that one   
   >> >> >> would use it for anyway.   
   >> >> >   
   >> >> >Speed variations are much more obvious at slower tape speeds, 15/16 ips   
   >> >> >wouldn't normally be used for music.  3+3/4 ips is the bare minimum for   
   >> >> >domestic music and 7+1/2 ips is the minimum for professional recording.   
   >> >> >I recorded a few folk music items at 7+1/2 ips for local radio and they   
   >> >> >were happy enough with that - but for orchestral music nothing less than   
   >> >> >15 ips was considered good enough for mainstream radio.   
   >> >>   
   >> >> So you're saying the speed's varying at all the higher speeds as well,   
   >> >> then? I guess that would make sense given the relatively agricultural   
   >> >> mechanics of these old decks, but I still can't hear such a wobble at   
   >> >> any of the 3 higher speeds. I suppose a frequency counter and test   
   >> >> tape would be the answer to finding out more about that.   
   >   
   >A counter may not show up the problem because it averages the frequency   
   >over a period of time.  A "wow-and-flutter meter" is the right thing to   
   >use but, being specialised, they are not very common.  Ferrograph made a   
   >test set with all the necessary instruments built-in but they tend to be   
   >collectors' items and will probably need repair themselves before they   
   >can be used.  Human ears work quite well on suitable recorded material.   
      
   Yes, as you say, such a meter is a bit exotic and beyond my needs for   
      
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