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Old 19th Jan 2023, 10:08 pm   #1
DonaldStott
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Default Heathkit RF1U Signal Generator

Back in June 2020 with the help of David G4EBT I manage to repair and restore a Heathkit RF1U Signal Generator.

It's worked well for a couple of years and I've used it for the IF and RF alignment of various sets.

Over the past couple of weeks its gone downhill - first I had a detached connection on the RF ATTEN FINE control, then I lost the AF and the RF on one of the Frequency ranges and it's like dominos where more and more sections are failing! Tonight I have AC going into the Heathkit but no AC going into the rectifier and the neon pilot light has failed?

I will of course endeavour to get to the bottom of this but in the meantime there seems no harm in considering a more modern replacement for the Heathkit RF1U Signal Generator. A quick Google search and a search on this Forum has yielded too many options for me to assess! I'd like some advice on possible options please but not sure what I am looking for and what is available? I primarily need the replacement for RF and IF alignment but have seen too many offerings with numerous bells and whistles that I would never use!

In terms of budget I am looking at the bottom end of the price range but nothing too cheap'n'cheerful from exotic locations please!
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Old 19th Jan 2023, 10:25 pm   #2
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Default Re: Heathkit RF1U Signal Generator

There was an Advance P1 on offer on this thread; https://www.vintage-radio.net/forum/...d.php?t=197025.

If you are thinking of any of the Chinese modules, I suspect you may be disappointed with them. Pity your Heathkit seems to be in its death throws; the vintage signal generators can be perfectly adequate for hobbyist use.

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Old 19th Jan 2023, 10:55 pm   #3
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Default Re: Heathkit RF1U Signal Generator

@DonaldStott: I have a spare RF-1U, which I also repaired with the help of David G4BET. I have replaced the old selenium rectifier and some out of spec resistors too. You might not want another RF-1U, but if you do I can offer it for purchase. If this might be of interest, please drop me a private message. Thanks.
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Old 20th Jan 2023, 12:12 am   #4
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Default Re: Heathkit RF1U Signal Generator

Quote:
Originally Posted by DonaldStott View Post
Tonight I have AC going into the Heathkit but no AC going into the rectifier and the neon pilot light has failed?
Seems far more likely that there is no power getting as far as the neon. Have you checked the switch? Start at the basics first! Neons can fail of course but it seems highly unlikely it would fail at the same time as everything else....it is after all only an indicator and wouldn't stop the generator from working even if it did fail.

Most neons dim down over the years mainly because they turn black but they rarely just stop working unless they get broken.

No AC getting to the rectifier and the neon not lighting suggests a fault either just after the switch, the switch itself or possibly a mains filter coil if there is one fitted. There really can't be much left to check.
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Old 20th Jan 2023, 12:39 am   #5
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Default Re: Heathkit RF1U Signal Generator

If the fuse in mains plug, the mains flex, and the switch are all OK, then the cause will almost certainly be a break in one of the RF chokes, L2 and L3.

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Old 20th Jan 2023, 11:20 am   #6
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Default Re: Heathkit RF1U Signal Generator

I checked the 1.1mH chokes using both my DMM and MK-328 tester.

The bottom choke measured 1.19mH (18Ohms) and has continuity while the top choke measured 1.18mH (18Ohms) and also has continuity - so those check out ok.

Some of the solder joints around the switch look a bit tired, dull and grey so I will reflow those and see what happens?
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Old 20th Jan 2023, 11:30 am   #7
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Default Re: Heathkit RF1U Signal Generator

Hello
and good morning.
Go for an Advance E2 signal Generator they were in all the Radio and TV repair shops and loved by the people that used them. Outside they look battered but inside it will be like new, They are so well screened.

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Old 20th Jan 2023, 12:59 pm   #8
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Default Re: Heathkit RF1U Signal Generator

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Originally Posted by DonaldStott View Post
I checked the 1.1mH chokes using both my DMM and MK-328 tester.

The bottom choke measured 1.19mH (18Ohms) and has continuity while the top choke measured 1.18mH (18Ohms) and also has continuity - so those check out ok.

Some of the solder joints around the switch look a bit tired, dull and grey so I will reflow those and see what happens?

On the RF1U, Why don't you just use your DMM to trace the AC mains voltage through all its connections? It doesn't seem to be getting as far as the neon indicator (unless that's faulty), so it shouldn't take long to find out where the continuity is broken.

Mike
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Old 20th Jan 2023, 2:01 pm   #9
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Default Re: Heathkit RF1U Signal Generator

Thanks Mike

I did just that and found some dodgy connections at the switch. All tags were reflowed with some fresh solder and AC has been restored - hurrah!

I also changed some over tolerance resistors around V2A (ECF80) and this seems to have somehow restored the AF output?

Now getting a nice sine wave on my 'scope when connected to AF OUT and switched to INT.MOD.AF.OUT so some progress.
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Old 28th Jan 2023, 7:58 pm   #10
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Default Re: Heathkit RF1U Signal Generator

It would appear you are back up and running, but if you want something cheap but usable, I can recommend the quintessentially English Nombrex battery-powered units.

They are cheap and reasonably cheerful - I restored one and used it for my first ever RF and IF alignment.

The signal purity is very average but after a little twiddling the scale is acceptably accurate (see attachment) and 100% usable for basic stuff.

I did 'upgrade' to an RF-1U, which I restored. And eventually succumbed to an IFR 2025.

Where the Nombrex is useful is that being battery powered (and cheap!) I can take it up the garden and couple it to the extreme ends of things like my long wire aerial.
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Old 28th Jan 2023, 9:03 pm   #11
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Default Re: Heathkit RF1U Signal Generator

I suppose that there is always a reliability risk with Heathkit equipment. They were largely available in kit form, so long term reliability is largely down to the technical abilities of the original constructor.
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Old 1st Feb 2023, 11:53 am   #12
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Default Re: Heathkit RF1U Signal Generator

Quote:
Originally Posted by 6SN7WGTB View Post
It would appear you are back up and running
Thanks Richard but not quite as I have nothing, no signal on RF OUT when viewed on my 'scope?

Quote:
Originally Posted by 6SN7WGTB View Post
I did 'upgrade' to an RF-1U, which I restored. And eventually succumbed to an IFR 2025.
Of course I'd love to be in a position to 'succumb' to an IFR 2025 but can't really justify it given that this is just a hobby for me with only the very occasional need to tackle IF or RF alignment.
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Old 1st Feb 2023, 12:15 pm   #13
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Default Re: Heathkit RF1U Signal Generator

Quote:
Originally Posted by DonaldStott View Post
Quote:
Originally Posted by 6SN7WGTB View Post
It would appear you are back up and running
Thanks Richard but not quite as I have nothing, no signal on RF OUT when viewed on my 'scope?
Ah, not so good.

Have you checked whether RF is present upstream of the attenuator, notably at the plate of V2B? (with the output of C25 lifted and taken to GND via a suitable resistor).

I would check all valves are connecting with their bases - I have had three awkward-to-trace faults caused by intermittent connections.

If still not OK, it's probably back to basics - checking all voltages throughout before delving in any further.
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Old 1st Feb 2023, 12:17 pm   #14
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Default Re: Heathkit RF1U Signal Generator

Adding for completeness, although not an issue hopefully as your RF-1U has worked in the past, but there is a really clumsy error on some HeathKit schematics - showing dead shorts on input and output of the attenuator!!!
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Old 7th Feb 2023, 12:32 pm   #15
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Default Re: Heathkit RF1U Signal Generator

I've initiated a temporary Truce with this Heathkit RF-1U as it was winning, but not in a good way for my mental health!

All pin voltages on V2 were good and a nice sine wave was being displayed on my 'scope from the AF OUT socket. Voltages on pin 1 of V1 were all good on Ranges A-E and voltage on Pin 6 of V1 was good for Range F.

On Pin 2 of V1 all voltages were OK apart from Band B? The display on my DMM for Range B seemed to be cycling up and down, but only on that range? Did everything I could to check and clean the switch wafer and contacts but nothing fixed this problem. Similarly all chassis tags were checked but if this was an issue I would assume that all Bands would be affected?

Moving on, I checked for a signal at the plate of V2B, upstream on both sides of C25 and the input/output of R13. I was getting a 'signal of sorts' as far as the input of R13 but nothing after that - what I mean is that when I toggled between EXT.MOD and INT.MOD.AF.OUT the display on my 'scope did not change. Still getting a sine wave though at the AF OUT socket.

Next move was to by-pass R13 by bridging a wire from C25 directly to the Step Attenuator assembly but still nothing at the RF OUT socket!

So multiple problems in several sections but I don't have the time or energy (or expertise? ) to resolve these so the Heathkit is back in its case, unplugged and underneath the desk for the foreseeable future!

Eagerly anticipating the BVWS Online Auction this Friday 3rd February 2023 where hopefully some suitable test equipment may appear? A Leader SG17A would seem to be a suitable successor to the Heathkit RF-1U?
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Old 7th Feb 2023, 6:48 pm   #16
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Default Re: Heathkit RF1U Signal Generator

Heathkit RF1U signal generator.
You have done so well, it seems a pity to give up now, when you have identified the fault areas.
1. Mains input. Solved - bad soldering.
2. B range not oscillating. As you have checked the switch contacts, it only leaves the coil to check. Disconnect two of the three ends and measure the resistance. The tapping should be between one third and one half of the total.
3. No RF output. Set the RF range to lowest frequency, say 200khz, and get your oscilloscope out.
3A. Check input to g1 (pin 2) of Output/Modulation pentode, V2B ECF80, with MOD off. Scope timebase set for high frequency (same as when checking the oscillator output, V1 12AT7).
3B. AF input to Modulator valve. Set timebase for AF low frequency. Check at junction R9/R10 for about one third AF output, and at top of R9/g1 (pin2) for more attenuated version. With MOD on.
This will be fuzzy and if you speed up the oscilloscope timebase to settings in 3A you will see the RF as well.

4. Output to attenuator. It is not unknown! for the resistors to be burnt out, due to being connected to the anode of an IF stage without using a 100pf series capacitor.
So check with your DMM the resistance of the variable output pot, R13 3k or 5k. It should be smooth and linear. And inspect the resistors at the attenuator switch - look for signs of scorching will be quickest.
5. Then look for RF output with the scope,set for hig frequency, at 200 khz, no MOD. Work from anode of ECF80 (pin6); output side of C25-R13 variable output; R13 slider into attenuator switching. These voltages will all be small 50/100mv.
6. Check the modulation if above all resolved. MOD on, and look at the anode of the ECF80 (pin6) with scope timebase set for low frequency,AF. You should see the AF envelope all filled in and fuzzy with the RF.

Note: The DMM on AC ranges will be fine for 50hz, doubtful for AF 1000 hz, useless for RF 200khz. Same for an Avo.
You don't say what your scope is. Almost any will be suitable for this. Ignore the siren voices who say you need a 100Mhz digital costing hundreds of pounds. Impossible to "drive" for this sort of job. A good old fashioned Cossor 1039, Telequipment S32 or S51, Metrovick CT52 or Heathkit OS2 or IO12 will be ideal, as designed for this sort of job in testing radio and B&W TV. and very straightforward to repair if necessary. Often turn up on ebay. Manuals on the web or here on the Forum.
And buying another signal generator may get you into the same sort of faults, while all your work to date will be wasted.

wme_bill

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Old 7th Feb 2023, 7:55 pm   #17
DonaldStott
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Default Re: Heathkit RF1U Signal Generator

Thanks WME_bill - I do need some time away from my Heathkit as it was in danger of ending up in the nearest skip!

I have a number of ongoing projects that take priority at present and will get back round to the Heathkit in due course.

When I do get the chance I will of course go through the detailed steps in your helpful email and report back.
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Old 8th Feb 2023, 1:47 pm   #18
Kevin Hoyland
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Default Re: Heathkit RF1U Signal Generator

Hello
WMB Bill, People like you make this Forum Outstanding.

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