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Old 6th Sep 2021, 7:12 pm   #1
vintage_8bit
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Default Marconi TF1066B/1

Hi all.
I'm working on this genny and due to low r.f. output I'm thinking the disc sealed triode may be low, it's a TD03-10. A few more checks to do yet, but anyway I would like to know how to remove it. I'm guessing the black grooved heat sink / shield unscrews, and releases the triode. It looks like someone has allready had pliers on it. Colin
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Old 6th Sep 2021, 7:50 pm   #2
Draker4c
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Default Re: Marconi TF1066B/1

If no answer forthcoming here you could try the Marconi Test Gear Forum on Groups IO.
Hugh G1AUR
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Old 7th Sep 2021, 6:44 am   #3
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Default Re: Marconi TF1066B/1

It’s many years since I owned one of these but my recollection is that yes, the black heat sink unscrews. The reason I know that is that my TF1066 also had low output and the cure was indeed to replace that valve.

Hugh
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Old 7th Sep 2021, 8:59 am   #4
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Default Re: Marconi TF1066B/1

Thanks Hugh. I tried with a bit more confidence and it came undone. I don''t know whats gone on before but if you look at the attached image. Colin
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Old 8th Sep 2021, 6:49 am   #5
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Default Re: Marconi TF1066B/1

Ooh, that doesn’t look good,
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Old 16th Sep 2021, 8:38 pm   #6
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Default Re: Marconi TF1066B/1

Update
I found that an old fault had come back to haunt me, I had this in a previous Marconi genny, and it was conductive sleeving in the turret! I’ve now corrected that and also 3 of the plastic contact pin holders that had split.

I tried again. With the original valve. I now only have trouble with reduced amplitude on the 1st and 3rd ranges at the low end of the ranges.

Fitting in a new valve, a DET22 / CV273 I found the output amplitude increased slightly on the 1st two ranges up to 48MHz, but it refused to oscillate in places on the last two ranges between 110 to 470MHz.

As the original valve works reasonably well, I’m wondering if the valves as listed in the parts list are not suitable. Looking at the beginning of the manual it lists a TD03-10E / CV5458, not a TDO3-10 / CV273 as listed in the parts list, schematic & valve replacement data.? To confuse further the valve originally fitted was a CV354 So I’m now looking for a TD03-10E / CV5458 or CV354 as originally fitted to try.

I can fix the low output on the 3rd range by adjusting an s.o.t. resistor but on the 1st range this s.o.t. is shorted out. The s.o.t. resisters increase the H.T. to the output valve. The regulated H.T. is set to 280V, the regulated L.T. is set at 6.3V at the output valve heater contacts. There is a potential divider from the H.T. feeding the “set carrier” pot and these resistors are in tolerance.
As suggested above by Hugh, maybe the Marconi user group could help here. Colin.
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Old 16th Sep 2021, 8:44 pm   #7
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Default Re: Marconi TF1066B/1

I don't know that sig gen, but just one silly thought.... Is there supposed to be a shorting ring killing the unused inductors? These things if needed and not working can cause mayhem in pats of bands.

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Old 16th Sep 2021, 9:39 pm   #8
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Default Re: Marconi TF1066B/1

David. Thanks for that suggestion. I know theres a killer, I think its on the lowest range when the highest is selected. It physically works, but havent checked for continuity. Will look tomorrow. Colin.
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Old 17th Sep 2021, 10:22 pm   #9
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Default Re: Marconi TF1066B/1

Ive looked at the "killer" switches &, they are all working fine.

I was investigating why one of the turret coils was touching a coil on the piston attenuater, which is just a straight piece of wire and found a dry joint to the detector. This ia CS2A, see pic.

I've not seen these diodes before. Are there any precautiom to take when soldering these? I assume I will have to check the calibration of the set amplitude mark, as this coil has moved. Colin
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Old 25th Sep 2021, 2:14 pm   #10
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Default Re: Marconi TF1066B/1

Im still not sure how to proceed here. Ive asked on the Marconi user group but no replies. So I'm still not sure how the CS2A diode anode (MR6) should be terminated. I did try and solder it but it fell apart☹. Luckily I have a spare. When this is sorted I can get back to the reduced output amplitude problem. Colin
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Old 25th Sep 2021, 6:23 pm   #11
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Default Re: Marconi TF1066B/1

Cannot remember what gear, but I have seen those diodes fitted within a spring clip assembly at either end. I don't recall seeing one that was soldered into circuit.
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Old 25th Sep 2021, 8:30 pm   #12
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Default Re: Marconi TF1066B/1

I think your right Rob, & the fact that my spare diode came from a similar piece of equipment in which it was just plugged in. The socket looked like a fuse holder.

It has been suggested (Thanks now to the Marconi user group) that the wrap might be to give an air gap around the terminal forming a capacitor. I'm not sure of this as the wrap is to tight and the diode can move around when just held by the other terminal. It's also not shown on the circuit diagram. All I can think of now is to put a slight twist in the wire (L19) so it grips the terminal more. The wire is of a heavy gauge. Colin
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Old 30th Sep 2021, 11:39 am   #13
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Default Re: Marconi TF1066B/1

Im happy now with the connection on MR6. I have also changed V9 for a new DET 23. This has now fixed the amplitude as best as I can tell.

Im now wondering how to calibrate the carrier level meter. I can only use my scope to monitor the gennerator output on the lower ranges before it runs out of steam.

The Marconi manual shows a Diode volt meter circuit for amplitude calibration, see image. It also has a CS2A diode in it, which I don't currently have.

If I built that circuit I assume it should it be able to give a constant D.C. output over 10MHz to 470MHz, range of the generator, providing the output amplitude is held constant. This would be only 100mV into 50 Ohm. Am I right thinking that? Colin
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Old 7th Oct 2021, 12:42 pm   #14
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Default Re: Marconi TF1066B/1

Just to finish off this thread. In the end I used a scope with more bandwidth to calibrate the first 3 lower ranges for amplitude.

Although out of the scopes range I found it could still display the higher frequencies of the generator, with reduced & uncalibrated amplitude. I then compared and transferred measurements between the last 3 ranges to obtain a crude amplitude calibration on the last 2 ranges.

I normally don't have a requirement for greater than 30 MHz so this generator is not of much practical use to me anyway, but it's at least saved from the scrap man now. Colin
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Old 7th Oct 2021, 11:25 pm   #15
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Default Re: Marconi TF1066B/1

Marconi TF1066B

“Am I right thinking that?”.

If your SG has the “two cal lines” on the attenuator dial, one for EMF and one for Volts in 50 ohms load, then if the output is set for 100mV EMF, this is so called 50mV PD (Potential Difference) in Marconi speak.

This is RMS.

These diode detectors don’t work well for small signals, as the detection efficiency falls off with input amplitude, as well as frequency.

They are useful as relative meters, but dont expect too much at higher freqs.

Only use your CRO at the very lowest freqs in this type of test, and only if the CRO bandwidth with probe, is at least twice the SG operating freq, or you will have to derate the measurement, which is possible but troublesome.

An indicated SG level of 100mV EMF into 50 ohms load will be (50x2.828) 141 mV P-P on a suitable CRO.

Apologies if I am preaching.

Good work with your restoration.
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Old 8th Oct 2021, 4:52 am   #16
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Default Re: Marconi TF1066B/1

I think that you may struggle with that detector circuit suggested by Marconi?

I wonder what the context is, and how they suggest you use it?

I just did some tests with a number of detector diodes including a number of 1N21 type (similar to CS2A) into a 50uA 3000 ohm meter, and the voltage level is just too low at 100mV PD 50, (-13 dBm50), for the diodes to work.

This type of detector circuit is OK at levels above about 200 mV RMS, and about the best type diode is a BAT45 as it is cheap and readily available.
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Old 8th Oct 2021, 12:02 pm   #17
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Default Re: Marconi TF1066B/1

Thanks for your reply and time. I also tried a similar experiment and found the same. There is just not enough output for the diodes to work properly. (On my TF144H/4S you have up to 2.0V to play with instead of 0.1V.) The TF1066B/1 carrier level meter uses a CS2A diode but this has more volts to play with, being connected closer to the main oscillator.

Apologies for preaching not needed, as it gives me reassurance on my own thoughts. Colin
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Old 9th Oct 2021, 5:20 am   #18
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Default Re: Marconi TF1066B/1

I was in your position a few years ago, trying to fault-find and "calibrate" Sig Gens, and measure low RF levels generally
In the end, I got so fed up that I built up an RF Milliwattmeter, with three sensors, two LCD and one panel meter indicators.
Uses three AD8307s, and measures -80 to +20 dBm50.
Use it all the time now.
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Old 9th Oct 2021, 9:40 am   #19
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Default Re: Marconi TF1066B/1

If anyone has these sorts of problems near me, I have precision RF power meters from 10MHz to 18 or 26GHz which also go down to -70dBm.

I can also measure AM & FM modulation and frequency fairly well.

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Old 9th Oct 2021, 2:31 pm   #20
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Default Re: Marconi TF1066B/1

Thanks for the replies. My R.F. knowledge is not that good specially when you get over 30MHz. I normally stick to domestic radios. I've enjoyed looking at this beast of a signal generator and now happy it is working as best as I can do here, with my knowledge and equipment. Scotland is unfortunately a long way from here.....
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