Uher 24 Hi-Fi Special Check Out

[DMcMahon]

This link covers some investigation into its mains connector.

type.https://www.vintage-radio.net/forum/...d.php?t=180712

I brought this a few months back and this is the first time have had a proper look at it.

It is a mid 1960's, 4 track 2 speed, single motor solid state R2R recorder for tape spools up to 7". Not an overly common model or its 2 track sibling the Uher 22 Hi-Fi Special. In the USA Martel marketed these 2 recorders as the Uher 9000L.

I think it looks quite nice, albeit a little plastic. Overall condition for its age is pretty good.

It was sold as "for spares/not working" with the seller additionally saying that it was functional but he could not get any sound out of it. Maybe he did not know that it does not have internal speakers and/or did not know how to connect the DIN outputs to an external amplifier. It does have a driver output stage via 2 pin DINs for 470 Ohms headphones.

A good chance the heads will be Bogen so if so then hopefully they all will be good.

It has 2 large motor capacitors 22uF & 38uF connected in parallel to give 60uF for 50Hz operation. Capacitance wise they are larger than typical recorder motor run capacitors, so wonder if they may be Start capacitors which are switched out (by motor centrifugal switch) when the motor is up to speed. The motor (Papst I think) is marked 60mF 50Hz, the mF here being an older designation for uF (micro Farad) as opposed to milli Farad.

All 3 drive belts are intact, the counter belt is quite slack but looks functional, all rubber drive/idler wheels look OK.

It has a knurled metal roller for tape cleaning, the knurled roller is a tight push fit onto a shaft and is extremely stiff to rotate, not sure if it is supposed to rotate. It has a 3 position switch for Playback equalisation which also is very stiff to rotate and does not sound/feel like it is actually switching.

David

[Ted Kendall]

I think Uher generally used Miniflux/Woelke, which seem to be lasting well.

[DMcMahon]

Originally Posted by DMcMahon

The motor (Papst I think) is marked 60mF 50Hz, the mF here being an older designation for uF (micro Farad) as opposed to milli Farad.

David

Update and correction - The motor is actually marked 60MF, still being old designation for micro Farad.

A 60Mega Farad capacitor would be a seriously large Supercapacitor.

David

[DMcMahon]

Originally Posted by DMcMahon

A good chance the heads will be Bogen so if so then hopefully they all will be good.

David

I said this because I thought many of the heads in some of my other Uhers are Bogen, I will have to double check that thought.

David

[DMcMahon]

Old Martel info for the 9000L.

[DMcMahon]

After replacing a badly corroded 1.2A 20mm glass fuse on the mains transformer secondary output powered up all OK, had to use a 1A fuse as closent value I had.

Motor runs and all tape transport functions work, not yet tested with tape.

Checked the DC voltage supplies:-
Main output (voltage value not shown on the schematic ) = -50.7V
30V output = -33.9V
10V output = -11.49V

All DC supply rails have negligible AC mains ripple.

With chassis out of its case and upside down for voltage measurements, unfortunately 2 plastic pieces got broke, the control knob for the PB head azimuth adjustment and the tape counter reset button, both should be repairable with glue, looks like the azimuth knob has previously been broken and glue repaired. Also found a small length of angled black plastic, no idea where it belongs, does not look important.

The heads do not look like Bogen heads but definitely Bogen heads on my various Uher Royal de Luxe recorders. The Erase head has very distinctive lettering that someone may recognize.

There is some remnants of a hard black rubber type material on a metal plate that is moved towards the PB head when Play is selected. Assume this may be what is left of some sort of pressure pad. The metal plate also has a thin metal rod across the plate no idea what function the rod may provide.

Checked out the PB Equalisation switch, found that its control knob was just slipping round the switch shaft when knob turned due to the switch shaft being very solidly seized. After WP40 soak and mini moles grips on the switch shaft eventually git the shaft freed up nicely. Now the switch is switching audibly and electrically.

David

[DMcMahon]

The W type symbol with a triangle below it on the Erase head does look to be a Miniflux/Woelke as Ted suggests.

David

[Ted Kendall]

All those heads are Woelke/Miniflux.

[DMcMahon]

Forgot to mention that when powered up it was very noisy somewhere from the mechanical drive, noise did not get worse when Play or Fast Wind selected.

Traced problem to the rubber tyred friction wheel that is driven from the motor pulley and then it drives the flywheel when a tape speed is selected (tape speed selection also switches power on).

Found that when the friction wheel was manually pulled back so not contacting the motor pulley and flywheel, the noise then went away and the motor and upper idler wheels that were still rotating were pretty quiet. The flywheel was smooth and quiet when manually rotated, but the friction wheel when manually rotated was stiff and graunchy. Lifting the copper sprung arm that holds down the friction wheel, enabled the friction wheel to manually easily spin, then realised that the sprung copper arm was in the incorrect position over to the right side, in first photo can see where it has worn a mark on the top of the friction wheel.

Moving the copper arm to the correct position in the middle of the friction wheel as per photo 2 (it sits on a nylon dimple) completely eliminated the noise.

[DMcMahon]

Loaded a 7" tape, Play, Pause, FFD and RWD all work well, EOT sensor works OK.

Did a quick test recording, good record signals on the VU meters but no sound on Playback. More tests required to establish if actually recording and if Playback amp is good etc

David

[Ted Kendall]

Monitor switch?

[DMcMahon]

Good call Ted.

Pressing the Monitor switch a couple of times got Playback working normally, recorded quality sounds good.

The Monitor switch is a 2 position non latching push switch with the Normal position (not pushed down) being for off tape monitoring (designated B) and the pushed down (and held) position being for straight real time monitoring comparison of the original and recorded signals (designated A), in the pushed down position there are no signals to the DIN outputs.

For good measure have sprayed the Monitor switch with contact cleaner and well exercised. Both positions of the switch now appear to operate normally but yet to fully test the A position as do not yet have suitable high impedance headphones connected to 2 pin DIN connectors.

Things still to do:-

1. PB head azimuth adjustment, because the control knob broke off can not set it to its default setting, from a few quick adjustments not hearing a huge difference, may need to find some music with more HF content or record some HF signals from signal generator and check playback signal on scope.
2. The mains on/off control (part of the tape speed switch) is stiff, need to investigate.
3. Replace decomposing brown foam on PCB clamp down bar.

David

[DMcMahon]

Originally Posted by DMcMahon

The metal plate also has a thin metal rod across the plate no idea what function the rod may provide.



David

Think the vertical sections of the rod are just tape lifters.

[DMcMahon]

Another thing to check out is if the metal fluted (previously called it knurled) tape cleaner roller should rotate or not, currently it is too stiff to rotate.

Interestingly the manual has this information on it wrt tapes having sufficient lubrication for its tape cleaning function.

David

[DMcMahon]

Checked out the stiff mains on/off switch. The switch itself is good but the stiffness was somewhere in in the cam assembly/spring loaded actuator plates that do the speed changes and also operate the friction wheel assembly parts. Without a major strip down very difficult to determine root cause of the stiffness.

Considered stripping it all down but decided the risk outweighed the small gain so cleaned it all and re-lubed in-situ, now a lot better.

While doing this this saw that 2 of the delicate transformer primary wires had broken off the mains voltage selection switch, while trying to work out where they connect to on the switch another 2 transformer wires have broken off !!!

Quite difficult to work out where they connect to, the schematic unhelpfully does not identify the colours of the transformer wires.

David

[DMcMahon]

After working out where the broken off transformer wires connect, reconnected them to the mains voltage selector.

Checked the PB head azimuth adjustment. On the schematic there is a Playback sensitivity adjustment procedure where 10kHz signal is injected in and PB head azimuth adjusted for max output. I found that 10kHz was not ideal test signal, it was somewhat jittery on the scope and my hearing could not easily detect small changes of amplitude at this frequency. So I settled on 5kHz which gave good results both on scope and hearing tests

Optimum azimuth adjustment with test signal correlated well with music with HF content azimuth adjustment. Now need to glue the broken PB head azimuth adjustment control knob to make sure that its azimuth alignment indication mark lines up correctly after head adjusted.

David

[Ted Kendall]

On a stereo machine, it is far easier to work on phase difference between channels with a final cross check for peak output to make sure you aren't on the wrong peak, that is one whole cycle out. Using the scope in x-y to generate a Lissajous figure, you adjust for the nearest approach to a straight line on the display.

[DMcMahon]

Thank you Ted.

I adjusted left and right channels individually and as far as I could see both aligned at same adjustment and there was only one max peak at the available range of adjustment.

I was thinking of doing an X-Y Lissajous phase check, for confirmation and interest sake (have not done Lissajous checks for so long have almost forgot how to) I will do this some time later.

David

[DMcMahon]

Been trying to figure out a mystery control. When the right channel record level control (potentiometer) is turned fully counter clockwise a switch can be heard to actuate. The control has a double pole changeover switch on the end of the potentiometer, this does not appear to clearly referenced in the User manual.

Can see it on the schematic but find it difficult to fully understand its function. Depending upon the setting of the main function switch, gives different results, for example when the function switch is switched to "Stereo" and the right channel record level control is turned fully CCW then the left and right channels are both recorded with their recording level both controlled by the left channel control.

Have now found it referenced under the Multiplay Trick Recordings section, but difficult to fully understand without actually doing the various recording options.

David

[Uncle Bulgaria]

Could this be like the 'channel link' switch on the CR 240? Slide it one way, both left and right levels move together on rotating one control; slide it the other and they can be adjusted individually?

I like following these threads - it's always interesting 'reading your working', as it were, during your investigations!