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Old 5th Dec 2017, 7:14 pm   #1
thejazzageuk
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Default Advance E2 Signal Generator repair

I purchased an Advance E2 signal generator to try to trim the tuner. However, although advertised as working, the SG does not appear to generate anything when I connect up a scope to the ATTEN RF socket. Any suggestions on fault finding the E2?
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Old 5th Dec 2017, 7:54 pm   #2
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Default Re: Restore a Beau Decca

Good signal generator, I've got one the same.

Should be an easy fix if it's not working.

Make sure you describe clearly what tests you've done so far. State settings including frequency bands and output levels etc. Also state the settings you used on your oscilloscope and the type of scope. Hopefully members should soon be able to advise you.

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Old 8th Dec 2017, 11:19 am   #3
thejazzageuk
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Default Advance E2 Signal Generator repair

Thanks Techman.

Not sure if I am testing it correctly though. I have connected a 75ohm resistor across the 'ATTEN RF' socket and connected a scope across the resistor. With all the settings set to minimum I slowly increased them but see no reading on the scope.The scope I have is a basic PC version (Hantek 6022BE). I've not connected the full RF socket yet- thought it best to go slowly.
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Old 8th Dec 2017, 12:20 pm   #4
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Default Re: Advance E2 Signal Generator repair

Try the "Full RF" socket. This will bypass the attenuator. No need for a terminating resistor when doing a simple functional test.

Also try the AF output socket. What you see here, if anything, will tell you whether the SG has any functionality at all.

The circuit can be found here:-

http://www.thevalvepage.com/servdata/testeq/advance.htm
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Old 8th Dec 2017, 4:51 pm   #5
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Default Re: Advance E2 Signal Generator repair

Hmmm ..... I seem to have acquired two of these over the years - and they are generally 'bullet-proof'. Are you picking-up anything on a broadcast receiver placed in proximity i.e. when you cycle the generator through the ranges?
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Old 9th Dec 2017, 6:52 pm   #6
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Default Re: Advance E2 Signal Generator repair

Quote:
Originally Posted by thejazzageuk View Post
Thanks Techman.

Not sure if I am testing it correctly though. I have connected a 75ohm resistor across the 'ATTEN RF' socket and connected a scope across the resistor. With all the settings set to minimum I slowly increased them but see no reading on the scope.The scope I have is a basic PC version (Hantek 6022BE). I've not connected the full RF socket yet- thought it best to go slowly.
As Graham says, just connect it directly to your scope.

When you say 'you haven't connected the full output yet - thought it best to go slowly', if you look at the manual you'll see that the full output is just 1V p-p. The attenuated output ranges from 1V to 100mV so you won't do any harm with it. Indeed, you'll need to set the scope to less than 1V per division to see a trace. The 400Hz AF output ranges from 0 - 50Volts, so is of much higher in amplitude. With the internal modulation switched off, you should get a nice clean sine wave, then a modulated sine wave with the internal mod switched on, and will see the variation in modulation depth when you turn up that control.

Really well made generators - their outward appearance is often scruffy and pitted with rust, but internally, unless 'got at' will look as good as when it left the factory, as can be seen in the pics below, of Type E Model 1, similar to the E2 but only goes up to 60MHz rather than 100MHz, which is no hardship). Very well screened - can be quite a task to open the case as it's such a snug fit. Easy to work on if any restoration is called for, and all the key voltages are listed in the manual. Because test gear tends to be little used, it's unlikely that the valves will be on their way out.

There are just two tubular paper caps that might benefit from being changed, (.05F 350V - use .047F), and two 16F separate tubular electrolytics (reservoir & smoothing caps). All easy to get at. The two filter caps in the mains input should also be upgraded to modern 'Y' rated caps, but best to check the actual values of the caps - they're stated on the circuit as .0005F, (500pF), which sounds like at least one decimal place too many, but I may be quite wrong on that.

You might actually discover that when you familiarise yourself with the controls and the scope, that it's working fine. I don't have the one in the pics any more, but when I did have it, the calibration was spot on when checked on my frequency counter, with no drift after being left on for several hours. They were built for professional use, which is abundantly evident from the solid construction and screening.

(The output sockets are sometimes modified to BNC to be more compatible with modern test leads).

Best of luck with it.
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Old 9th Dec 2017, 7:45 pm   #7
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Default Re: Advance E2 Signal Generator repair

There's a link on the forum somewhere that leads to a redrawn schematic where the values of some of the capacitors given differ from those given by the manufactures and the heater pin numbers given for the 6SN7GT are wrong and the valve type number given for the RF oscillator is wrong (ECC82 v ECC91)

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Old 10th Dec 2017, 3:29 pm   #8
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Default Re: Advance E2 Signal Generator repair

Thanks all- great information and advice.

I have now connected a scope to the Full RF socket- and ..success, I get a sine wave that agrees with the frequency on the generator.

Doing the same test with the 'ATTEN RF' just gives noise. I don't have a plug for the RF, so am just inserting the scope plug directly into the socket- can anyone advise what type it is?

Will try to resolve the ATTEN RF then perhaps replace the caps recommended by David E4GBT?
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Old 10th Dec 2017, 4:09 pm   #9
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Default Re: Advance E2 Signal Generator repair

Looking at the 2nd photo it looks like you've set the output to approx 100uV, maybe a bit low for the 'scope, try turning the voltage output control to 10 and the multiplier switch to X10mV, if no go then it would suggest a poor connection or that the attenuator might be faulty, sometimes caused by a burn up or overload due to the output being connected to a high voltage/current source without using an isolating capacitor.

Remember that turning the voltage output control and the multiplier switch clockwise increases the output not the amount of attenuation.

From memory I think the RF plug is a standard 75 Ohm TV coax plug.

Lawrence.
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Old 10th Dec 2017, 5:14 pm   #10
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Default Re: Advance E2 Signal Generator repair

Quote:
From memory I think the RF plug is a standard 75 Ohm TV coax plug.
Actually I think you'll find it's like a car radio aerial plug. Many have been modified to take an alternative plug....mine has been changed to a standard Belling Lee coaxial type.
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Old 10th Dec 2017, 5:45 pm   #11
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Default Re: Advance E2 Signal Generator repair

Could well be, the middle of the socket looks a bit empty in the 1st photo.

Brings back memories of a soldering iron hooked on the handle and a cig perched on the top...

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Old 10th Dec 2017, 6:23 pm   #12
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Default Re: Advance E2 Signal Generator repair

Quote:
Originally Posted by thejazzageuk View Post
Thanks all- great information and advice.

I have now connected a scope to the Full RF socket- and ..success, I get a sine wave that agrees with the frequency on the generator.

Doing the same test with the 'ATTEN RF' just gives noise. I don't have a plug for the RF, so am just inserting the scope plug directly into the socket- can anyone advise what type it is?

Will try to resolve the ATTEN RF then perhaps replace the caps recommended by David G4EBT?
Remember that the attenuated output ranges from just 1,000th of a Volt, to 0.1Volt so your scope input settings need to be adjusted to take account of that. The attenuator circuitry is only a network of resistors and a wire-wound pot. If - when you've checked your scope settings - you don't have a sine wave just like that from the 'Full' output but of much smaller amplitude, you can use your scope probe to follow through the attenuator circuitry to discover what's happening to the signal, starting at the slider of the wire-wound pot, R24.

As to replacing the caps, whether or not they're causing any deterioration of the generator's performance, given its age, it would be wise to replace them. Probably cost well under a tenner for the bits, and an hour to do. As has been said, the output sockets are like car radio aerial input sockets, and given that most test gear for some years - scope probe leads, frequency counters etc, have used BNC plugs and sockets, for the little expense and effort involved, it would be well worth upgrading the sockets to BNC.

As I said earlier, these generators were made for professional use in busy workshops and are robustly built to that standard - not for light 'hobbyist' purposes such as the Heathkit RF1U or Tech TE20D, so it's well worth spending a little time and expense on it. The only things against the E2 is its size, weight and often rather tatty external appearance.

Have you looked at the modulated RF output or the 400Hz AF output yet? (very handy for signal injecting when fault finding, along with a signal tracer).

Hope that helps a bit.
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Old 10th Dec 2017, 6:28 pm   #13
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Default Re: Advance E2 Signal Generator repair

The car radio socket I believe takes what is known as a "banana" plug.I have now 2 of these generators, tough as an old boot.
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Old 10th Dec 2017, 7:49 pm   #14
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Default Re: Advance E2 Signal Generator repair

I got one of these generators that worked OK on the full RF socket but didn't on the attenuated socket. When I removed the cover over the attenuator switch there were o/c resistors and black burn marks everywhere.

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Old 21st Dec 2017, 11:52 pm   #15
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Default Re: Advance E2 Signal Generator repair

Thanks all.
I've done some further checking- the connector does appear to be a generic TV aerial connector and it appears that a poor connection was responsible for the early errors. I've re-checked across all bands, and it looks like C to F are good for both full and ATTEN connections- see summary table for full results. B is lower amplitude and A is not working (unless the scope it not capable of operating for these freqs).
The main issue now is modulation. Flicking the Mod switch to INT does not appear to have any AF modulation effect that I can see- just reduces the amplitude slightly. I've attached some images that I hope will help to show what is happening.
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Old 22nd Dec 2017, 9:44 am   #16
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Default Re: Advance E2 Signal Generator repair

Good to read it's working again. Your scope has 20mHz bandwidth, correct?

Andrew
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Old 22nd Dec 2017, 9:59 am   #17
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Default Re: Advance E2 Signal Generator repair

With luck the RF generator should be ok on all ranges, best to check the VHF range with a radio as your 'scopes response will have dropped off like a stone much above 20MHz, at VHF frequencies it will be non existant.

For no modulation I would first check the AF output, if no go then check the mod switch and valve contacts and the tuning capacitor across the AF inductor, that capacitor is known to have failed in the past so I would replace it and the other one (C12 & C13) and take it from there.

EDIT: To see any AF modulation on the scope properly its best to reduce the 'scopes timebase speed so that one or two cycles of the modulation frequency can be displayed.

Lawrence.

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Old 22nd Dec 2017, 10:00 am   #18
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Default Re: Advance E2 Signal Generator repair

The modulator is quite simple. Mine failed and it was just a question of changing the leaky caps. Mine uses a 6SN7GT
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Old 22nd Dec 2017, 10:40 am   #19
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Default Re: Advance E2 Signal Generator repair

The modulation transformer failed in my very early version E2 given to me by a television shop that was shutting down. I still have it stowed away but now use a slightly later one. I think the oscillator valve in my original version was an EC52 on the EF50 type base.

Very reliable and if used with a frequency counter is capable of outstanding accuracy with negligible drift. John.
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Old 5th Jan 2018, 12:49 am   #20
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Default Re: Advance E2 Signal Generator repair

I hope to get some time to investigate the modulation this week, so will follow the suggestion of ms660 and check C12 and 13, replacing if necessary. I've take a picture of the internals of my SG, and indicated the 2 caps indicated.
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