From: liz@poppyrecords.invalid.invalid   
      
   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.   
      
   >   
   > >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.   
      
   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!   
      
      
   > >> >> 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.   
      
   > >   
   > >At higher speeds the flywheel effect of the rotating components is much   
   > >greater and any given actual speed variation is a smaller percentage of   
   > >the faster running speed - so both effect improve the overall speed   
   > >stability.   
   >   
   > Right, so the increased inertia helps to stabilize the speed? That   
   > makes sense. I assume those flywheels are so heavy for the same reason   
   > (tape deck flywheels, I mean).   
      
   The slower the flywheel, the heavier it needs to be - with the mass   
   concentrated as near to the rim as possible.  In the Uher, the capstan   
   shaft has only a very lightweight driving wheel that rotates slowly, so   
   the inertia of that is negligible.  The speed,stabilising inertia is in   
   a heavy brass flywheel on the cross-shaft, which rotates much faster and   
   friction-drives the lightweight wheel through a rubber tyre on the   
   latter.  It is vital that this rubber tyre is in good condition, because   
   any notches or lumps will tend to deflect the speed of the lightweight   
   driving wheel (and the capstan) rather than being absorbed in the speed   
   of the brass flywheel.   
      
   That is why disengaging the drive when the machine is being stored is   
   very important.   
      
      
   > >Hiccups due to dirt on the capstan will be the same magnitude at all   
   > >speeds but will occur at a faster rate at higher capstan and tape   
   > >speeds..   
   > [...]   
      
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