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Old 23rd May 2019, 8:58 pm   #1
davidgem1406
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Default Advance E2 with problems.

I have an Advance E2 that I have used for some time now but recently it has thrown up some problems.
Maybe they have been developing for a while now but I had missed it.

The HT smoothing required replacing as 1 half had gone down.
I also replaced R8, C12, C13, R9, R30. All for good measure. The HT and modulation are OK now other than the HT being high.

HT1 305V actual 360V, HT2 285V actual 355V, HT3 97V actual 110V,
V2 Pin 6 100V with modulation internal, AC to V3 (Pin 3/5) 300V actual 290V.

I had noticed that the generated wave form was changing in value from band to band, so I did a full check on all bands, starting at the low end and then the midpoint followed by the high end for each band. The results follow:

I used the full RF output, so that the attenuation was not in circuit, with a 75 ohm terminator and scope probe set to x 10.

(Sorry the table does not hold it's formatting when submitted to the posting, hence all the dashes)

Band ------------- Low end ---------- Midpoint ------------ High end
F ----------- 100KHz – 160mV ------ 160mV -------- 300KHz – 158mV
E ----------- 300KHz – 180mV ------ 190mV -------- 1000KHz – 210mV
D ---------- 1MHz – 130mV --------- 185mV -------- 3MHz – 210mV
C ---------- 3MHz – 135mV --------- 165mV -------- 10MHz – 165mV
B ---------- 10MHz – 120mV -------- 165mV -------- 30MHz – 150mV
A ---------- 30MHz – 80mV --------- 100mV -------- 100MHz – 75mV

We can see from the table that there us quite a variation in the P to P output dependant on frequency.
That makes a total mess of the attenuator calibration. I need to solve this problem so any pointers would be most helpful and welcome.

Also at the 100MHz it is sometimes difficult to obtain that, and when we do get the 100MHz it is past the 100MHz marker point on the scale.

I would also like to know how to adjust the calibration using the coils only as it will be impossible, or at least very difficult and risky, to try to adjust the capacitors.

The oscillator valve has been tested and check out OK, although I was surprised to find it is a valve that was designed for audio use (From the data sheet). Maybe it is not so uprising that it has a job to reach 100MHz.

Thanks,
Dave.
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Old 23rd May 2019, 9:07 pm   #2
Andrewausfa
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Default Re: Advance E2 with problems.

What is your oscillator valve David, mine has an ECC91 and a 6SN7 for modulation though I'm sure another up in the loft had something other than a ECC91.

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Old 24th May 2019, 7:03 am   #3
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Default Re: Advance E2 with problems.

Getting a scope and probe flat to 100MHz is quite a task in itself.

In a 75 or 50 Ohm system, you can at least avoid the probe by using some matching coax to a Tee adaptor and a load termination right at the scope panel.

Some posh scopes have 50 Ohm terminations which can be switched in.

I'm afraid the valved Advance sig gens are just better quality 'repair bench' grade instruments, and that sort of level variation is what you get.

If you go up to the serious lab grade instruments you gain better level control and metering as the biggest improvement.

The HP606A and 606B are an example of accurate control of output level. It uses a precision detector and a feedback loop to level control the output. And the output is very clean.

http://hpmemoryproject.org/timeline/...g/hp606_01.htm

Art Fong was a legendary R/Microwave designer.

From the Marconi stable there is the TF144H of which there's quite a lot of material on this site regarding the fixing thereof. This one uses a thermocouple detector and a meter.

If you don't object to transistors then there is the Marconi TF2002

These things are now seen as boat anchors and can be picked up quite cheaply if you look around and aren't in a hurry. The Advance sig gens are a lot more familiar to more people and look a lot less intimidating, so they often go fo more money.

The Marconi TF2008 is well worth looking out for and is VERY comprehensive. It's also a sweeper/wobbulator. But prices are lifted out of the junk category. I paid £80 for a dead one back in the 1980s. All that was wrong was the tuning pointer cord jammed down the side of a pulley This was Marconi's competitor to the HP8640 class of generator.

The HP8640B is getting into the expensive region and they are beset with problems of crumbling plastic gears. Output amps are custom microcircuits and irreplaceable once some prat has transmitted into the output. These are exceptionally clean generators.

If the level variation of your E2 is a problem, look out for a 606 or a 2002 and a bit of timber to prop up your bench.

David
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Old 24th May 2019, 11:18 am   #4
davidgem1406
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Default Re: Advance E2 with problems.

Hello Andrew,

The oscillator valve is an ECC82 and the 6SN7GT for modulation.


Hi David,

Thanks very much for all that information it was rather interesting.
I am not really in the market for buying another generator as it is not something I can afford to do.
However I do have an Advance SG-63F that I use, but it is not usable for AM band radios as it starts at 4MHz.

Many thanks
Dave.
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Old 26th May 2019, 9:18 am   #5
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Default Re: Advance E2 with problems.

For basic alignment work the E2 is probably the simplest generator you can buy.

I had one for years, and only upgraded to better gear as and when it appeared at "sensible" prices.

I am a little surprised that the RF oscillator in yours is an ECC82, most I have seen use the ECC91.

In the case of the one I owned, there was a lot of trouble witht he oscillator, and replacement of the osc valve with a new part cured 90 % of the inaccuracy, the other 10% was cured by replacing out of spec components and realignment.

The RF output isn't flat from LF to 100 Mhz - the nature of construction of the generator really means that VHF is more a happy coincidence than a useful feature, but it's intended use wasn't in a calibration facility, or somewhere where accurate measurement of signal levels were a daily thing.

May be worth swapping the ECC82 for something new, typically these would have been left switched on for at least 8 hours a day 6 days a week, this may be part of the problem.

Cheers
Sean
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Old 26th May 2019, 6:38 pm   #6
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Default Re: Advance E2 with problems.

Advance E2.
I have only ever seen E2 signal generators with the ECC91 / 6J6.
But other Advance models use ECC81 / 12AT7, so perhaps yours was a later modification and fitted with a B9A base instead of B7G. I suspect you would get an improvement in performance by substituting an ECC81 as a direct plug-in replacement for the ECC82, as suggested by SeanWilliams.
My version uses ECC91/ 6J6. It had difficulty in oscillating below 40Mhz on the highest frequency range from 30Mhz. This I suspect is because of the very low Q of the tuned circuit, all capacitance and virtually no inductance.
I solved it by selecting a 6J6 with high Gm, but the output level does alter quite a bit over the range.

If you want a constant output level, fit a monitoring meter and a variable HT supply, so that you can check and set the level. As done in the Avo CT378. But it is a bit laborious in use.
Or use a modern unit with automatic level control.
Most transistor ones like Marconi TF2016 or Philips or others mentioned by RadioWrangler have this. In quite a different price league.

A figure of merit for an oscillator valve is uGm, or Gm2Ra. (See Langford Smith 4Edn para24.2).
For the valves often used: (with higher the better)
ECC91 /6J6 = 200, used in Advance E2, B4, D1D.
ECC81=385, used Avo HF135, Advance P1, SG62, SG63 and lots of others.
6BQ7 = 240, used in your SG63F
EC71 / 5718 = 160, used in CT378.
EC91 = 870, used in Taylor 67 and 68. (amazing performance this valve, but rare, expensive and only by Mullard)
By comparison ECC82 / 12AU7=60.
The original Advance E1 of immediately post war used an EF50 transitron oscillator circuit.
The Taylor 65 used a 6J5, similar to half a ECC82 on octal base, to 80Mhz.
These figures of merit suggests why the 12AT7 was used almost universally.
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Old 26th May 2019, 11:47 pm   #7
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Default Re: Advance E2 with problems.

Quote:
Originally Posted by davidgem1406 View Post

Also at the 100MHz it is sometimes difficult to obtain that, and when we do get the 100MHz it is past the 100MHz marker point on the scale.
I think you are being over-expectant of what is (as has been said) a better quality 'repair bench' grade instrument. Most of these were used for aligning domestic AM radio's and TV's..... don't need much higher than about 45Mhz at the most. You'll find that from around 150Khz through to about 50Mhz, they are fine. The only real problem I found was getting frequencies of 38.15Mhz accurately....I fitted mine with an external frequency counter so that I can...the actual scale reading is superfluous other than as a rough guide. However it is surprisingly accurate until you get higher up the scale. I used a cheap Chinese counter around £10 from eBay. Only lashed up at the moment so I need to find a box and build it properly.
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Old 29th May 2019, 7:39 am   #8
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Default Re: Advance E2 with problems.

I have an early E2 and I'm pretty sure it has an EC52 as an oscillator. The modulation transformer became O/C and the generator was replaced by a later E2 that I'm certain employs the ECC91. I still have my original E2 but it's skin wrapped in plastic..
Very good units and used with a frequency counter guarantee very accurate alignment of 405 TV receivers.
This is my alignment 'rack'. The old Advance is still 100% accurate to the scale showing 45mc/s on the frequency counter. Well made gear. J.
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Old 29th May 2019, 9:24 am   #9
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Default Re: Advance E2 with problems.

If you like Advance (for stability and good attenuator) the later SG62 and SG63(with fm)
can also be recommended.
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Old 29th May 2019, 10:44 am   #10
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Default Re: Advance E2 with problems.

I would say those figures look good for a basic generator whose only amplitude control is the valve characteristics.
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Old 30th May 2019, 8:35 am   #11
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Default Re: Advance E2 with problems.

It is certainly not up to professional standards but is still capable of giving very satisfactory results with domestic equipment.

Still obtainable very cheaply and with a few cap replacements makes a very good basic generator for tracing faults and aligning our old beasts. John.
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Old 1st Jun 2019, 5:16 pm   #12
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Default Re: Advance E2 with problems.

Thanks to everybody for the input and such useful information.

I have to correct the valve used for the oscillator. I said it was an ECC82, having looked at the circuit. In fact the valve in my unit is an ECC91 this being intended for VHF .

I have 5 copies of the service information 2 stating ECC82, whilst the other 3 are not readable well enough to be sure what they say.

The ECC91 I have just tested again the result being Ma/v 5.4 and 5.7. Data sheet gives 5.3.

I do have a spare ECC91 but it is much the same at Ma/v of 5.1 and 5.2, little point in changing it.

I will run another set of tests, this time using the attenuator in circuit and see what happens.

Also I am thinking of making an adaptor to be able to plug into the 7 pin base an ECC81, maybe.

Best regards,
Dave.
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Old 1st Jun 2019, 7:52 pm   #13
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Default Re: Advance E2 with problems.

Two posts moved to a new thread here:-

https://www.vintage-radio.net/forum/...d.php?t=156979
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Old 7th Jun 2019, 1:21 pm   #14
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Default Re: Advance E2 with problems.

These are the further checks I have now made.

With the attenuator set to 100mV, output un-terminated, frequency set to band F at 200KHz, and connected to the scope by a 50 Ohm BNC cable, the output voltage is 1V.

I then connected the generator output to an Advance TP1B pad and the pad output to the scope, using 50 Ohm BNC cables.
With the pad set to 37 Ohm the output is 400mV, when set to 10 Ohm or DA the output is 40mV.
The pad is working correctly. (The TP1B is one I built myself)

The output of the generator is giving an output that is high by a factor of x 4. This is a problem as it makes the attenuator calibration meaningless.

I then continued as follows:

Leaving the generator set to band F at 200KHz (the midpoint) and switching through the bands in order of F to A we get the results that band F is 400mV whilst bands E to A rise to 500mv.

Changing band F to 100KHz (Low end) we get the following:
Band F 400mV
Band E rises to 500mV
Band D falls to 350mV as do bands C & B
Band A falls to 130mV

Diversion:
The Tek 465B scope suddenly had a very bright and large spot dancing on the screen that then vanished, smoke was issued from the L. H. side, I switched off.
I left it off for a while, then chanced turning it back on fully expecting more smoke, but no, it worked quite normally?!! Needs to be investigated.

To continue:
Repeating the same process but with band F at 300KHz (High end) we had the following results:
Band F 400mV
Band E increasing to 500mV
Band D increasing to 540mV
Band C increasing to 500mV
Band B remaining at 400mV
Band A falling to 260mV at 90MHz

The Tek 464B scope is still working fine.

I then stripped out the attenuator and checked the resistor values that all seemed to be OK.
However this switch was nothing like the circuit that I have as it consists of a 2 pole 5 way device.
3 poles on each wafer are bridged out by wire links.
The circuit shows this switch as a single pole 5 position device, why a 2 pole with poles bridged out?
Also resistor values are in some cases different to the circuit I have.

I canít imagine this came out of the factory as it is now, with the output voltage being 4 x that as indicated.

Regards,
Dave
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Old 7th Jun 2019, 1:51 pm   #15
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Default Re: Advance E2 with problems.

Are those output voltage figures peak, peak to peak or RMS?

Lawrence.
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Old 7th Jun 2019, 1:56 pm   #16
davidgem1406
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Default Re: Advance E2 with problems.

Hi Lawrence,

All P to P measured on a Tek scope.
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Old 7th Jun 2019, 2:01 pm   #17
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Default Re: Advance E2 with problems.

So far as I know the specified output voltages are RMS and they can swing + or - 3dB.

Lawrence.
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Old 7th Jun 2019, 9:45 pm   #18
davidgem1406
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Default Re: Advance E2 with problems.

Hi Lawrence,

I really don't know, it says nothing in the Advance manual about that.
I have an HP 3400A true RMS meter I could try with that, but I will have to look up the frequency range it can handle, I think I have the manual for the meter. Just the lower ranges would do for a check.

Dave
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