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Old 23rd Jan 2018, 4:39 pm   #1
brightsparkey
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Default Saba Freudenstadt 8 repair and restoration

Having acquired my SABA Freudenstat 8 table top radio for a very modest sum, I have found that it is in need of considerable attention. This is a good result as a large part of the aim of buying it was for the fun or repairing it and restore it to its former glory.

The case work is immaculate - the veneers are in perfect condition and the cloth is clean. There are a few water spots on one side, but I suspect these will polish out easily enough.

Mechanically the set is in modest order. The FM tuning cord had snapped. The tone pots are both stiff and the antenna rotator doesn't work - slipping. So I started with these mechanical issues first.

Tuning Knob Clutch assembly:

The clutch seems to have been defeated by drilling holes in either side and passing a wire through each bobbin and the shaft. This locks both sides of the clutch together so that both dials tune together.

I'm inclined to leave it alone, at least for the time being - looks like the bakelite was damaged during the process, and I can live with it as I'll use FM mostly.
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Old 23rd Jan 2018, 4:57 pm   #2
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Default Re: Saba Freudenstadt repair and restoration

Next step - the pots for the tone control:

the grease on the sliding indicators was hard, so first released these and cleaned them up and then applied a very small amount of grease to allow them to slide quietly. Move easy-peasy now.

This cured the bass pot, but the treble is still stiff. Removed the pot and cleaned with IPA. Some verdigris on the contact. A bit more working with cleaner and then a touch of light oil on the circlip on the shaft has helped but still a bit stiff. May need further dismantling...

Restringing FM tuning:

Discovered that the set was previously restrung - slightly incorrectly. There are four pegs on the tuning pulley, two low and two high. The front cord for the pointer should be on both high ones, but is strung from one low to one high.

Unwilling to restring the pointer (much trickier route) so restrung the FM tuning cap using the other two pegs as before. Used a nylon cord for necklaces - black, non stretchy and grippy - looks like I got lucky! Tuning cord now works well. There are two holes in the pulley wheel in just the right place for tensioning the spring - you can put a screwdriver through the spring eye and lever it across using the hole so the spring is under tension whilst you wrestle the other end onto its peg - worked a treat..

My thanks to assistance from this thread with photos for restringing.

FM tuning now works OK. I should upload a pic of the result..

Antenna rotator:

Cord is in good nick and its not slipping, but the knobs are loose. Dismantled and cleaned the knobs of filth. The shaft was scored, making it hard for the knobs to grip. A little scrub smooth with fine emery paper has given a sound surface. Tighten the grub screw and the knob no longer slips. Still stiif - the small pulleys were stiff with dust and needed cleaning with IPA. No lubricant as they seem to run fine once cleaned. Now operating correctly. Cleaned and lubricated the shaft of the rotator too for good measure.
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Old 23rd Jan 2018, 5:19 pm   #3
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Default Re: Saba Freudenstadt repair and restoration

Now the mechanics are at least functioning (apart from the treble pot..) I then started on the electronics.

Firstly the double electrolytic cap has popped its lid and there was a telltale ring of corrosion around it. (the rest of the chassis has no corrosion at all). So clearly a new pair of caps required.

In addition there are two wirewound resistors nude of enamel and the EL84 cathode resistor is dark. All 3 measure correct values, but there is clearly some stress in the output circuit. The two bigger resistors form a negative supply from the bridge of -14V, but also take all the current of the rest of the set, so if the output tube is overrun then they suffer too.

My first assumption is that the paper caps are leaky. Replace three of them that are at DC stress between the triode and the pentode (very complex tone control has about 10 caps, but very few of them have HT across them) The Anode capacitor is polystyrene, so probably OK.

Three new yellow LCR 1kV caps in place, so ready to apply power (via a variac kindly lent by a colleague)

Some funny scruffing noises but no reception.. Heaters all alight and lamps lit, but HT is low. EL84 control grid is initially +0.5V, then some crackles and raises to +9-14V. Measure the voltage across the 1k grid stopper - initially not much then once warmed up 25mV, flowing out of the tube, so EL84 is leaky

Power down, and order a tube, then.. In the meantime I have fitted a snazzy cloth covered mains lead 3 core and earthed the chassis. Replaced the paper caps across the rectifier with a pair of Y2 caps. The set now passes a modern PAT test which is great
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Old 24th Jan 2018, 10:10 pm   #4
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Default Re: Saba Freudenstadt repair and restoration

I'd change all those ERO buff coloured caps while you're at it - they are as bad as the Hunts rubbish our set makers used.
The tin caps with the crimped ends aren't much better either.
Though the resistors in these German sets tend to hold their value OK, you'll probably find the odd one a bit off
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Old 29th Jan 2018, 1:06 pm   #5
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Default Re: Saba Freudenstadt repair and restoration

Thanks for the suggestion. I may well replace more of them, but the remaining ones are largely in the tone controls where a small leakage is not too serious, so for now I'll concentrate on basic function.

So I've replaced the EL84 and now the audio is much happier and the current drawn back to sensible.

When I received the set, there was a wire attached to the output of the FM strip and glued into the base of the case in a loop. I removed this wire, as it was obviously an addition - I figured it was an aerial wire for the FM - the set lived in central London, so plenty of signal available..

Now when I return to that area, I've noticed that the switch is bridged out with wire links and set to defeat the AM parts - I've removed the links and returned the wires as the schematic. Now the AM section works and MW can receive several channels using the ferrite anenna (amazed that in our RF noisy labs it can get anything) . Hoorah! first audio!

FM is completely silent however, not even any hiss. Next stage..
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Old 29th Jan 2018, 1:23 pm   #6
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Default Re: Saba Freudenstadt repair and restoration

Having looked at the FM stages, the voltages are not as the service sheet. All the resistors look good and the caps are all tubular types, so nothing awry there. So I replaced both EC92 in case they were tired. Unfortunately no noticeable improvement.

The second stage seems to oscillate OK - Pick up on the scope with a loop shows plenty of signal at Freceive+Fif (high side oscillator). Looks to be on tune.

Probing around, the grid of the input stage is at -2.9V. I can't see where it gets its negative bias from.. most puzzling - maybe someone can illuminate who know valve circuits better than I...
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Old 29th Jan 2018, 1:58 pm   #7
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Default Re: Saba Freudenstadt repair and restoration

My guess that it gets it from rectifying the grid of V3 and used for AGC.
Try shorting C113 to see if the gain rises.
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Old 29th Jan 2018, 3:39 pm   #8
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Default Re: Saba Freudenstadt repair and restoration

The detector/discriminator stage looks like diode city....

Lawrence
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Old 29th Jan 2018, 5:26 pm   #9
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Default Re: Saba Freudenstadt repair and restoration

Yes there are two diodes for the FM Ratio detector, one for AM demod and Two for AGC for the AM.. as far as I worked out so far..

At least the triode of the EABC80 looks alright - correct bias and audio OK in AM. Have swapped the EBF89 for a loaned old one and no difference, so suspect that's OK too.

Found that the set will demodulate FM, but only if you yell at it - 10mV required at the antenna. Haven't tried shorting the cap yet.. Too much real work to do
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Old 30th Jan 2018, 5:29 pm   #10
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Default Re: Saba Freudenstadt repair and restoration

Got a chance to tinker with the grid bias on the input. There is a small increase in sensitivity when shorted to ground, but still very deaf. Having now gone through the whole FM-can checking everything, I exchanged the ECH81 heptode-triode valve and the FM sprang into life. Now the grid bias on the first tube is ~ -0.7V and sensitivity is much better. Audible output down to 4-5uV from my signal generator. Result!

FM alignment looks OK for a starters, but our lab has no receivable signals at all - the window covering must be conductive! Nothing but interference, but the noise level is correct now, instead of deadly silence.

AM sesnsitivitty also seems to be improved with more stations on MW - not much on LW or SW - may still be issues with band switches here.

So I might put it back together and take it out of the lab to somewhere where it can hear Radio 3 and see how it sounds. Quite hopeful now

Thanks for the AGC steer - seems likely as otherwise there is no reason for the complicated arrangement. Might try to check if it varies on signal level.

Kevin.
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Old 2nd Feb 2018, 5:05 pm   #11
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Default Re: Saba Freudenstadt repair and restoration

So I took the radio home, and found it had good reception on a number of channels on FM, picked up a few MW channels, and not much on LW.

I'm suspecting the external antenna switch contacts need a good clean - evidence of corrosion on the blades, and MW is sometime a bit deaf until you operate the switch a couple of times (by turning the rotator)

I'd like to know if its worth going through the tuning procedure for the FM stages? With a sig gen, the 1kHz tone is audible at 3uV into 300R. However I haven't measured the 20dB quieting yet, which is likely more like 10-20uV.

Max SNR on broadcast stations does seem to line up with the magic eye, but the distortion in audio is not small. Of course I have no mental reference of what to expect from this set, either in audio quality or sensitivity.

I have the equipment available to do the alignment apart from trimming tools (is there a recommended source?), but I'm wary of damaging a core or tunable capacitor..

Kevin.
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Old 6th Feb 2018, 3:49 pm   #12
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Default Re: Saba Freudenstadt repair and restoration

Well I needn't have worried about the tuning procedure. All the adjustments seem quite straight forward and turn easily. I've run the FM alignment through now, but had problems with the neutralisation adjustment. Following the procedure led to too much feedback and when restore to full working state there was an oscillation, so I put the trimmer back and adjusted for maximum signal instead.

After all the effort, performance not much different. -20dB Quieting now 27uV rms in 300R (signal generator is 50R source with '16uV' level in 50R). Is this a good enough figure?

Please find attached my rough translation of the tuning instructions..

I've cleaned the pot -it was the bass pot and its very odd! It's track is in two segments, each 3Mohms, with a gap at the centre. I thought it was broken at first after dismantling it. Meant to be that way! Cleaned up the wiper and replaced the grease. Now its free enough to operate correctly.

Also replaced the lamps that had failed. One was OK and it was the holder that needed a clean.

Need to clean the ext antenna switch and then I might have a go at setting up the AM parts. I suspect that L and SW may still need attention.

Kevin.
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Old 6th Feb 2018, 3:56 pm   #13
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Default Re: Saba Freudenstadt repair and restoration

Tuning instructions in pdf as well for those who don't or wont have MS word.

Of course both documents provided in good faith without warranty or claim of perfect translation Fell free to amend/correct/chastise as appropriate!

K.
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Old 13th Feb 2018, 3:50 pm   #14
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Default Re: Saba Freudenstadt repair and restoration

Decided to have a go at removing the water marks on the cabinet. The cabinet work looks like its has walnut veneer. The finish looks like a shellac polish, so my usual treatment for water marks is a little oil worked into the surface.

One end looked a lot drier than the other, having largely lost its shine. This end is pictured in the the first image below. After working a small amount of oil in with a cloth it looked much better, and less dry looking. Colour is darker too and more consistent with the other end.

A bit of wax polish and a buff up then to follow and the case looks quite handsome now. Final picture also shows the new plug and mains cable.

More or less done for now. There are a couple of marks here and there - the brass trim has a few marks in the lacquer and the disc on the knobs are dull. I'm in two minds whether to polish them or leave them with their natural patina. There is a small chip in the veneer on the back edge on one side which I might try to wax repair when I'm feeling brave.

Kevin.
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Old 13th Feb 2018, 7:12 pm   #15
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Default Re: Saba Freudenstadt 8 repair and restoration

That’s looking really good Kevin, good work!
BTW when you say “oil” for the cabinet do you mean teak oil?
I also have a water damaged cabinet and wondered what was a good cure.

Peter
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Old 13th Feb 2018, 8:23 pm   #16
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Default Re: Saba Freudenstadt 8 repair and restoration

The lacquer is very unlikely to be shellac based - more likely nitro-cellulose.

You can test it in an inconspicuous place. A few spots of methylated spirits (known as 'denatured alcohol' outside the UK) on a cloth applied to the surface will dissolve it if it's shellac. (Shellac flakes are dissolved into meths to make French polish). If meths doesn't dissolve the finish, but a dab of cellulose thinners does, then it's nitro-cellulose lacquer.

In recent years, for safety and other reasons, nitro cellulose lacquer and paint finishes (car bodywork) have been abandoned in favour of water based acrylic finishes.

Great restoration Kevin - I don't think there was anything in the UK from that era to come close to the large Saba, Grundig and Telefunken sets.
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Old 14th Feb 2018, 8:48 am   #17
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Default Re: Saba Freudenstadt 8 repair and restoration

Quote:
Originally Posted by Reelman View Post
That’s looking really good Kevin, good work!
BTW when you say “oil” for the cabinet do you mean teak oil?
I also have a water damaged cabinet and wondered what was a good cure.
Topp's scratch cover 'polish' is the best stuff for this. It comes in light, medium and dark variants and comprises an oily dye that you apply then buff up later. It's not called 'Topp's' any more though. But just google it. Go for a lighter colour than what you think you will need as it has an inherent darkening effect.
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Old 14th Feb 2018, 9:40 am   #18
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Default Re: Saba Freudenstadt 8 repair and restoration

Servisol also make a product called 'Refurb 40' which is quite good for these sorts of jobs. AFAIK it only comes as an aerosol.
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Old 14th Feb 2018, 3:06 pm   #19
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Default Re: Saba Freudenstadt 8 repair and restoration

David,

looks like you are right. Meths has little impact, so not shellac.

The oil I used was in fact from brazil nuts, although linseed oil or other oil based finishes should work. Most nuts contain a drying oil of some sort and Brazil nuts are easy to apply, just snap and wipe over the surface where the blemish is. This means the barest minimum is applied, so the surface can't get sticky. Leave for 24hrs then finish off with a wax based polish to put back the shine.

Danish oil is actually a varnish as it contains solvents and resins. Some teak oils are also varnishes, and some are not. For removing watermarks a pure oil is better as you just want it to fill the damaged areas rather than re-finish the whole area.

Kevin.
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Old 22nd Feb 2018, 9:36 pm   #20
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Default Re: Saba Freudenstadt 8 repair and restoration

Quote:
Originally Posted by stevehertz View Post
Topp's scratch cover 'polish' is the best stuff for this. It comes in light, medium and dark variants and comprises an oily dye that you apply then buff up later. It's not called 'Topp's' any more though. But just google it. Go for a lighter colour than what you think you will need as it has an inherent darkening effect.
Thanks for that Steve, Believe it or not have had a bottle of Topp’s in the garage for 40 years! About time I bought some more then.....

Peter
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