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Old 9th Jul 2013, 11:09 am   #1
WME_bill
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Default Advance 63 AM/FM Signal Generator.

I have been asked by "Marconi MPT4" for information about this signal generator.
As it may be of more general interest, I here start a thread upon this subject.
The original versions, 63 and 63A covered 5 ranges, from 7.5 to 230 Mhz, with 12AT7 valve.
The later versions (63E & 63F) of 1967 covered 6 ranges, 4.5 to 230Mhz, with the 6BQ7 valve.
It is interesting that the FM is obtained by a couple of point contact germanium diodes, rather than the more sophisticated vari-cap diodes as used now for TV tuners etc. Originally the BTH CG6, comparable to OA81, GEX45.
I attach the circuit for the earlier version to illustrate this point. The manuals for both versions is too large to post. wme_bill
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Old 10th Jul 2013, 9:43 pm   #2
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Default Re: Advance 63 AM/FM Signal Generator.

I have one of these the SG63F in very good condition.
However it has one problem that I have never managed to solve, the setup meter was damaged (O/C coil) and I can not get a replacement, not at a sensible price anyway.
The original meter is 25uA fsd, the only meters available are 50uA fsd.

The original post for this is here:

https://www.vintage-radio.net/forum/...ad.php?t=84761

That posting has a link to an even earlier one. I just tried this earlier link and the earlier post seems no longer to be available.

To bring the story up to date.
A 25uA meter is like asking for the moon. I place that does have it available is Bee Instruments in India but they want £120 for it and say that £40 is shipping cost, another £40 is taxes the remainder is the cost of the meter at £40. All the 40's "Bingo".

I have tried different ways to attempt to drive a 50uA movement but without success. I just cant obtain enough DC voltage to drive anything, including op amps to try to gain DC amplification.
To date it sits on the back of the bench doing nothing.

Dave.
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Old 10th Jul 2013, 11:26 pm   #3
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Default Re: Advance 63 AM/FM Signal Generator.

I have the service manual for the Advance SG63E and F in pdf format. If anyone has need of a copy, pm me with email address, as its too large to post here.
Bill
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Old 10th Jul 2013, 11:29 pm   #4
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Default Re: Advance 63 AM/FM Signal Generator.

A 50uA meter is usually about 1.2K or so internal R so I would guess a 25uA one would be a bit higher. So.... there must be a few mV available to drive a substitute burden resistor. Does the original meter have any useful labelling?

Once you've got those mV across a 1-2k resistor, there's plenty of signal to work with an opamp to drive any meter you like, within reason. 1mA is nice, robust and cheap(ish).
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Old 11th Jul 2013, 10:55 am   #5
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Default Re: Advance 63 AM/FM Signal Generator.

Hi Chris,

The original meter was Sifam, labels give Model, fsd and Fe. Meter is obsolete.
Sifam can not supply a replacement.

This information and all about the problems I found trying to drive a 50uA meter are at an earlier posting the link is at P0st #2 this thread.

What is a burden resistor? I don't know that term.

Dave
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Old 11th Jul 2013, 12:46 pm   #6
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Default Re: Advance 63 AM/FM Signal Generator.

Ahh. A burden resistor is normally the load resistor on a current transformer. 25uA is a current (meter FSD) and to use it you need to convert it to a voltage using a resistor (or burden). Ideally, you need to use the same value of resistor as the original coil resistance of the dead meter. That way you know what the voltage will be for any point on the meter's scale between zero (0uA) and FSD (25ua). If there's no information about what this resistance was, maybe someone with a working unit could measure the voltage across its meterat a known deflection in uA with a DVM or VTM to derive the value?
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Old 11th Jul 2013, 9:31 pm   #7
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Default Re: Advance 63 AM/FM Signal Generator.

Hi Chris,

Thanks for that information, I now know what a burden resistor is.

I have attached a picture of the original Sifam scale plate.

When adjusted to the "SET" mark the output is then set at 100mV. I think that then calibrates the attenuator circuit as the maximum output is 100mV.
I have made a note on the circuit at some time saying that when the output is 100mV RMS then the DC voltage at MR4 cathode is at 150mV.

From that I think we can assume that to drive the original meter to fsd there was say 200mV at MR4 cathode. We can make the assumption that we therefore need some 400mV to drive a 50uA meter to fsd.
That is what I was trying to obtain by using an Op Amp but was unable to get an output.

That is as far as I ever got with it all.

I have noticed that there are some markings on the rear of the scale plate written in pencil, whether they have any bearing or not is another matter.
I will try to write them just as they are on the plate:

150 0
---- /52
-- 3/3
-- TFormer
- C in ------ (not sure of this as difficult to read)
--- 35%
--- X7 ----- (Appears to be X)
- O/C

Dave.
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Old 12th Jul 2013, 4:38 pm   #8
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Default Re: Advance 63 AM/FM Signal Generator.

Hi wme-bill,

Thanks for your PM. My particular signal generator is Type 63A with external FM input and X Sweep input/output? It has a few battle scars, but otherwise is complete. Tuning knob has been damaged and repaired at some time in its history.

Although the calibration and frequency stability is good, have never been able to get external FM to work at all, but is fine with internal AM modulation and CW mode. Even the internal FM modulation is suspect. In the past have used it just as a marker generator in conjunction with a wobbulator when doing sweep alignment.

I think also the switched attenuator might have suffered damage with the previous owner. Some time back I had a look but there are a lot of screws to undo before any real circuitry is accessible and without a circuit was not going to make it worse.

What signal level does Ext FM input need?

Cheers
Rich
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Old 12th Jul 2013, 8:16 pm   #9
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Default Re: Advance 63 AM/FM Signal Generator.

Hi Rich,

You may find this thread useful, there is also a manual that may help.

https://www.vintage-radio.net/forum/...ad.php?t=90132

Dave.
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Old 12th Jul 2013, 10:46 pm   #10
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Arrow Re: Advance 63 AM/FM Signal Generator.

Quote:
Originally Posted by Marconi_MPT4 View Post
What signal level does Ext FM input need?
Cheers
Rich
Advance sig. gen. model 63: this might help - extract from the model 63 manual. It may - or it may not - be applicable to the model 63A.

Al. / July 12, 2013 //
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Old 13th Jul 2013, 11:41 am   #11
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Default Re: Advance 63 AM/FM Signal Generator.

Supporting the advice from "skywave". The SG63 (the 5 range model) gives 3 khz per volt for the External FM, max to 150/200khz. The SG63E (6 range model) with a slightly different circuit, gives 6 khz per volt, for 200khz EXT FM. You don't say whether your 63A is the 5 range or 6 range version. wme_bill.
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Old 13th Jul 2013, 2:36 pm   #12
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Default Re: Advance 63 AM/FM Signal Generator.

Quote:
Originally Posted by WME_bill View Post
You don't say whether your 63A is the 5 range or 6 range version. wme_bill.
This 63A is the 5 range version:
1: 13~7.5 MHz
2: 25~13 MHz
3: 50~25 MHz
4: 100~50 MHz
5: 230 ~100 MHz

Skywave & davidgem1406, thanks for info regarding input signal and circuit description. It does indeed appear that even driving input with up to 30 Volts rms from a Radford LDO4 audio gen still no FM.

Inside are many Hunts capacitors and I suspect these should be replaced with a great deal of care to avoid upsetting alignment. Just hoping the FM diodes are not faulty.

Cheers
Rich
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Old 14th Jul 2013, 8:51 pm   #13
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Default Re: Advance 63 AM/FM Signal Generator.

for"MarconiMTP4". I don't think you need worry about replacements for the FM diodes. Almost any germanium point contact should be good enough to get the FM working. Once working, it is much easier to select alternative types to get better performance. wme_bill
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Old 19th Jul 2013, 10:55 pm   #14
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Default Re: Advance 63 AM/FM Signal Generator.

Finally managed to get some time for a bit more investigation into this problem.

Undid four very tight screws in each front corner and prised the front away from the case. Internals as shown of the PSU area in photo 1 . The mains power neon appears to be an RS part! Found many Hunts

Next removed twenty outer screen screws in photo 2. Not much to be seen except another screen, feed through capacitors and chokes. Removed another fourteen screws to detach inner screen, photo 3, and gain access to the circuitry, photo 4.

Valve is a Brimar 6BQ7. A check on HT supply shows after half an hour starts at 154.7V and drops to 146.8V. At this point it had not stabilised and continued to drop, so looks as if the rectifier and electrolytic capacitors will need replacing.

With the generator switched off, a quick check on resistor values show many have gone high, two 56k resistors reading 69k and 64.9k, 10k reading 12.6k and so on. Also there are quite a few Hunts capacitors to replace and many are located amongst the tuned circuits. Replacing them will disturb the layout potentially requiring a complete realignment.

As for lack of FM, a measurement of the diodes, physically located between tuning capacitor and wave change switch, show one may be weak with a high forward voltage. However, the reason why there is no FM is an open circuit HF choke in the modulation signal path, seen in photo 3 attached to the yellow wire.

@wme_bill: Is there a manual available for the 63A detailing alignment procedure?

Cheers
Rich
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Old 30th Jul 2013, 7:33 pm   #15
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Default Re: Advance 63 AM/FM Signal Generator.

Found all resistors > 10k to be out of tolerance and Welwyn MFR4/5 appear to be suitable replacements for non-critical circuits such as power supply, filtering and audio modulation.

However, does any one have experience of how these perform in VHF circuits up to 230 MHz? According to the data sheet although metal film there is no mention of laser trimming, such as cutting a spiral resulting unfortunately in increased inductance. Strictly speaking carbon composition should be used as replacement but these will also change value in time. Hoping find something that will be a fit and forget solution.

Rich
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Old 30th Jul 2013, 7:59 pm   #16
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Default Re: Advance 63 AM/FM Signal Generator.

Are there any high resistances in the actual VHF signal path? I would have thought that stray capacitance would make anything over about 1K meaningless above 100MHz.
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Old 5th Aug 2013, 9:04 am   #17
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Default Re: Advance 63 AM/FM Signal Generator.

Hi,

I attach HF data covering Welwyn MFR4 but the short answer is I'd not recommend this at high frequencies > 100mHz as it is indeed spiralled to value.
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Old 18th Aug 2013, 9:22 pm   #18
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Default Re: Advance 63 AM/FM Signal Generator.

Hi, Sorry for not getting back quickly, have had a two bereavements within five weeks of each other to deal with and nearly forgot to re-check this thread.
Quote:
Originally Posted by Herald1360 View Post
Are there any high resistances in the actual VHF signal path? I would have thought that stray capacitance would make anything over about 1K meaningless above 100MHz.
Checking resistor values around the oscillator section these range from 10k to 27k and one at 270k. Generally most are positioned either across the tuning coil or in series with a pre-set capacitor, presumably for damping circuit and increasing bandwidth. Also includes the 10k grid leak resistor.

Quote:
Originally Posted by Omega-W View Post
Hi,

I attach HF data covering Welwyn MFR4 but the short answer is I'd not recommend this at high frequencies > 100mHz as it is indeed spiralled to value.
Many thanks for HF data on this range of resistors. Although MFR4 is not suitable for this application still a very useful reference when designing in for other applications.

Cheers
Rich
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