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  #1  
Old 06-16-2017, 11:59 PM
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Klein & Hummel FS-4-A circuit wanted.

Hello all.

I have a Klein & Hummel Teletest TV pattern generator model FS-4-A dating from about 1956. I have worked on it, every resistor has been replaced, as they had all gone high or O.C., and all of those Wima capacitors replaced, as they were all very leaky, as well as all electrolytic capacitors. However, it does not work! Tracing out the circuit as best I can revealed that at least one component is missing.
I don't have any service information on this instrument at all, not even a circuit diagram. Radiomuseum.org has a circuit for a FS-4, but that is different. Can anyone out there help me with one please?

Cheers, Stuart

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File Type: jpg D_Klein & Hummel_FS-4-A.jpg (62.4 KB, 42 views)

Last edited by Celt; 06-21-2017 at 10:17 AM.
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  #2  
Old 06-18-2017, 07:33 AM
kf4rca kf4rca is offline
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Never seen one here in the States probably because its 625. But its probably a clone of an American design of the time. What tubes does it use?
Can you show us an internal picture?
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Old 06-21-2017, 01:16 AM
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Hello kf4rca. I've added it to Radiomuseum.org here:
http://www.radiomuseum.org/r/klein_t...or_fs_4_a.html

The valve line up is; ECC85 ECC85 ECF80 ECC81 ECC82 ECH81 ECC81 ECH81 ECC82 ECC81 EZ81 0A2.

I'll post some internal pictures shortly.
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Old 06-21-2017, 07:20 AM
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Twelve tubes!!??

Most American generators of that period were probably 6 tubes.
What does it use for a timebase? Does it have a crystal? It could be bad shutting the whole thing down. I'd check for oscillations in the master oscillator circuit first (assuming you have B+).
Remember, that if it worked before, it can work again.
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Old 06-21-2017, 06:41 PM
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Thanks kf4rca. I've found that the circuit given on Radiomuseum.org for the FS5B is similar in many respects. I'll try to use the value shown on this diagram for the missing component. I'm not getting any RF output either, so I'll have to dismantle the channel selector turret section. I've already done this, to replace all the resistors and an electrolytic. It is a big job! Looking at the circuit there is no master oscillator as such, the bar pattern generators and horizontal synch pulse generator being free-running. The vertical synch pulse generator appears to be locked to the mains frequency. There are also four more generators; R.F., I.F., 5.5 MHz audio subcarrier and audio tone.
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Old 06-22-2017, 12:42 AM
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Interior picture.

Here is the interior of the instrument.
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File Type: jpg D_Klein & Hummel_FS-4-A_inside.jpg (102.6 KB, 14 views)
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  #7  
Old 06-23-2017, 06:45 AM
kf4rca kf4rca is offline
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That's great. I think if you get the RF working that will solve some other problems too. Most likely it's a power supply problem. Very common.
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Old 06-24-2017, 10:20 PM
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Update: I've got the video generating section of it going! It turns out this thing has been well and truly butchered, but I managed to find that the video section is similar to that given for the FS5B on Radiomuseum.org, although I'm sure that circuit is not actually for that model. See http://www.radiomuseum.org/r/klein_f...nder_fs_2.html
I ended up just stripping out the components around V1, the horizontal oscillator, and building it according to that circuit; and it works! I had to fiddle with the values somewhat, to get it on frequency. There were other errors too, but I do have a video signal. One thing puzzles me, the video waveform seems to indicate that the bars are black on a white background, not what I expected.
Continuing with the R.F. section...
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Old 06-25-2017, 06:37 AM
kf4rca kf4rca is offline
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Assuming your transmission system is like ours...

it uses negative modulation. Sync is peak power. So the waveform is inverted from what you think. The idea was that in weak signal conditions the picture would lock up first before you would see picture content.
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Old 06-27-2017, 07:13 PM
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Working at last!

I've got it going! The lack of R.F. turned out to be due to two faults. One was the output coupling capacitor inside the turret tuner section had broken loose from the valve pin. The other was that the attenuator control was burned out, probably due to the output being accidentally connected to the B+ of a TV. I had to use an ordinary carbon potentiometer, which is of course less than ideal at R.F. As I figured, the picture is black bars on a white background, so not much good for convergence!
I still have a slight problem though, some slight vertical jitter, caused by some instability in the vertical synch generator which is a blocking oscillator synched to the mains. I've replaced all the capacitors again, and the valve, but no difference. Interestingly, I replaced a capacitor and the problem vanished, - for 15 minutes, but then returned. I think I'll call it a day. It is still quite usable. Thanks for your replies.

Cheers, Stuart
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File Type: jpg FS-4-A working.jpg (75.5 KB, 8 views)
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  #11  
Old 06-28-2017, 06:09 AM
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That's wonderful!

Perseverence pays.
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Old 06-28-2017, 08:29 AM
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If you know where the video is mixed with the sync before it is injected into the modulator, then perhaps you could build a simple unity gain signal inverter stage to get white bars on a black background for convergence.....If you do it with a dual triode you could use the other triode section as an amp for video output.
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Old 06-28-2017, 07:09 PM
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Hi Tom. Not much room on the chassis to add extra stages. I might just leave it as it is, after all, it is what it is. I've plenty of other means of generating other patterns, including an old digital camera with a composite video output. I have downloaded a number of suitable test patterns onto it.

Cheers, Stuart
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