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Old 1st Aug 2023, 11:32 pm   #1
Jez1234
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Default Advance H1B signal generator.

I got this recently from ebay at a decent price of £25 (for once! I'm outbid on prob 90% of the stuff I want as I can't afford and won't pay the silly prices some people seem to think anything old is worth).

It was a little tired looking and had issues which were not apparent from the pictures or description such as the tuning control had seized and the dial "glass" glue had given way and it had pushed in and turned about 10 degrees before managing to lock itself into place like that.

After a couple of hours building up on the variac it basically all worked apart from being stuck at one frequency.

Around 20 hours work later and it's as A1 as an honest used H1B is likely to get. Better than new in many ways in fact.

Attenuator is rebuilt with 1% resistors, slow motion drive repaired, corroded Belling Lee socket replaced with BNC, all out of tolerance parts replaced, switch cleaner on all switches (had to take the Colvern level control to bits to do this!) and it's been re-calibrated. All control knobs were removed for cleaning and all casework cleaned. I added an output capacitor of 1000uF 25V as there was an offset of 9V present at full output! Yes it's supposed to be like that and it mentions it in the manual! It beggars belief that they considered this OK!

Frequency accuracy is good, stability excellent and output level stability good across the ranges, Distortion is claimed to be "below 1%" and actually measures 0.4% @ 1KHz, half of which is due to the output amplifier section.
It covers 15Hz to 50KHz and max output is 22V RMS into a high impedance.

Unlike the J1 which I also have (and recently gave a proper sorting out, freshening up and calibration after owning it for about 30 years) it lacks any sort of well defined output impedance. It changes wildly depending on attenuator setting and output level control setting.

Like the J1 the output level according to the Colvern level control is out by a mile and is obviously supposed to like this as both are identical. Their generators give an accurate and very stable max output but using the level control gives only a very rough approximation to the dial calibration! "0v" = 2V, "6V" = 7.5V, "15V" = 17V etc until you reach maximum of 22V. It then gives 22V. The J1 is exactly the same.

The square wave output is pretty crap and only really any good up to 1KHz... although the manual claims a good square wave up to 10KHz. It seems their idea of a good square wave is very different to mine!

Valve line up is 2 X ECC88 and an EZ80 rectifier. They are not original as they are all Mullard (one badged as Cossor!) and Brimar is original fitment.

These must surely have the last instance of "coloured body with a dot" WW2 era type resistors being used! This is late 60's and yet 4 x 22k ones are present (I changed the one most likely to effect calibration) as anode loads. The J1 also has 22K's of exactly the same type as its anode loads so they must have bought loads of them and hence still using them in maybe 1970! It's probably a fairly late one as about half the resistors are more modern looking carbon films and are certainly original (could possibly be Japanese), these are used in all the more critical places that don't need 1% precision resistors and all measure spot on. The remaining ones are ye olde Sir Driftalot Erie's.

Electrolytics are all Hunts and all were fine. All other caps are Wima Tropifol and all A1 despite rumours that these are now becoming dodgy. The Visconol's in my J1 were all replaced as they were as leaky as all Visconols are.

I did take loads of photos of the rebuild at different stages but it seems that at 2.5M each they are too big to post.

Breaking news! It's been on soak test for hours and on my way to the loo a few minutes ago I found a flat line on the scope screen and no heaters lit in the Mullard ECC88. The dodgy valve was still hot so it must either have just happened or an internal heater to something else short circuit heating it.
I've put a NOS Mullard in and normal service is resumed. "Luckily" it was the amplifier valve so no calibration of frequency to check. Case still off so I'll check output level cal (one wirewound pot, dead easy) when I'm next passing... First valve failure I've had in a long while is that.

Last edited by Jez1234; 2nd Aug 2023 at 12:02 am.
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Old 2nd Aug 2023, 6:09 pm   #2
Jez1234
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Default Re: Advance H1B signal generator.

Well its had several hours further soak testing since changing that valve and all seems well.
The faulty valve looked OK when it went but on examining it today it has gone soft and there is a hairline crack in the glass around the base.

It can be set to 1000Hz and will maintain that on the frequency counter for hours so frequency stability is pretty good. Output level with no attenuation stays within about 0.3V of the specified 22V over hours. Output level Vs frequency is quite good and if the very lowest and highest frequencies are not required then considerably better still.
Over the full range of 15Hz - 50KHz it's flat to within 1.5dB. If this is limited to 50Hz - 30KHz then it is very much better at around +/-0.25dB and if using just the middle range of 300Hz - 4KHz then it's within 0.1dB across this range.

A usable classic I would say.
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Old 2nd Aug 2023, 6:35 pm   #3
barrymagrec
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Default Re: Advance H1B signal generator.

I hauled the similar J1 (didn't need the square wave) all round the country for a year back in 1969, always worked, never gave a problem. The high level output could be handy but the somewhat crude output control made it difficult to set at low levels, luckily I was normally dealing with 600 ohm line levels.
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Old 2nd Aug 2023, 7:24 pm   #4
Jez1234
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Default Re: Advance H1B signal generator.

I have a J1 as well and it's a real classic IMHO, surely the most ubiquitous and best selling of 50's and 60's AF generators! (?)

I bought mine about 30 odd years ago (and an SE Labs SM111 oscilloscope) from a small electronics shop on a corner in Wimbledon (IIRC called Halcyon Electronics but could be mistaken) and took both home on the back of my motorbike. I was working in that London at the time so no not 300 miles oop north!

Both have provided sterling service for all these years without any servicing whatsoever and remain on my bench.

Whilst never failing, the J1 had long had enough distortion for a sine wave to be visibly not quite as it should be (2nd harmonic distortion) for years but as I have suitably low distortion sig gen for when it matters I'd not bothered to take a look at it till about a month ago. Visconol paper in oil caps (the usual suspects, amongst others) going leaky was the problem and for a reasonably correct for the period repair I sorted it with Mullard mustards and checked the calibration etc. Back to good as new!

I've found the J1 really useful for all sorts of tasks over the years and often for its ability to deliver some actual power (0.5 to 1W ish IIRC) into a load from a truly floating/isolated transformer output (5R output is grounded) with a reasonably well defined impedance of 600R. Great for checking transformer turns ratios and for shorted turns and also been used to drive audio transformers to check response into different loads and at maybe 10mW or more level. It has stable enough output over the full frequency range to do this well and in fact IIRC measured a little better still than the H1 on this at about +/-1dB from 15Hz to 50KHz and something like +/-0.2dB over 30Hz - 30KHz.

If you don't need the (not very good) square wave output then the J1 is by far the more useful out of the two.
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Old 3rd Aug 2023, 3:38 pm   #5
Chrispy57
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Default Re: Advance H1B signal generator.

Hi Jez - I enjoyed your write-up, and thought it worth mentioning that re-sizing photos is a quick and easy job, in comparison to all that work on your sig gen. I use Paint.net to re-size and save jpeg web copies of similarly large original photos, free and very intuitive software, and visually the difference is hardly noticable unless you really zoom in.

Cheers
Chris
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Old 3rd Aug 2023, 3:55 pm   #6
Jez1234
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Default Re: Advance H1B signal generator.

There was a previous thread here on this sig generator by "Swen" in Germany https://www.vintage-radio.net/forum/...ad.php?t=65205 and I see he too added a capacitor at the output to get round the DC offset, 3u3 in his case rather than the 1000uF I used to maintain LF response into lower impedance loads.

He also reports that he thought there was a fault in the square wave output as there was an overshoot on negative going half cycles. I can confirm that mine does exactly the same and so I think we can be confident that it is a design fault/compromise.

It doesn't look like any sort of "normal overshoot" due to amp compensation, stray LC ringing or anything like that. More likely some sort of biasing issue, overdrive issue etc and I reckon due to the square wave generation being done by dual purposing the amplifier double triode as a Schmitt trigger with a DPCO switch. My theory is that this glitch and the comparatively poor square wave shape at higher frequencies is the best compromise they could get between half decent Schmitt trigger action and being able to turn the trigger back into a decent feedback amplifier for the sine waves with only a DPCO switch.
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Old 16th Aug 2023, 8:06 pm   #7
Jez1234
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Default Re: Advance H1B signal generator.

First try at adding pics after finding that there is an auto file compressing widget.

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last use of these resistors maybe?

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various bits and pieces, BNC now fitted

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The recalcitrant slo-mo drive

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New 1% resistors fitted to attenuator
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Old 16th Aug 2023, 8:13 pm   #8
Jez1234
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Default Re: Advance H1B signal generator.

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Completed unit. Scratched ali looks loads worse in photo than in real life!

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Output looking good

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Advance nixie tube frequency counter used in checking frequency cal etc
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Old 16th Aug 2023, 8:13 pm   #9
Jez1234
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Default Re: Advance H1B signal generator.

Quote:
Originally Posted by Chrispy57 View Post
Hi Jez - I enjoyed your write-up, and thought it worth mentioning that re-sizing photos is a quick and easy job, in comparison to all that work on your sig gen. I use Paint.net to re-size and save jpeg web copies of similarly large original photos, free and very intuitive software, and visually the difference is hardly noticable unless you really zoom in.

Cheers
Chris
Thanks Chris. Sorted.
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