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Old 20th Feb 2024, 12:55 am   #1
Philips210
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Default Hacker Autocrat Mk2 (RP73)

Hi.

A radio I've had in my collection for quite some time but haven't yet looked at it until fairly recently. I had opened it up in the last couple of months to assist forum member wireless john with regard to the loudspeaker. Forum member mhennessy identified the loudspeaker is not correct for my set and would normally be fitted to a Hacker Mini Herald. https://www.vintage-radio.net/forum/...d.php?t=206087

Today, I had a quick look at the chassis and immediately noticed a mechanical problem with the 3-way push button waveband switch bank. The central AUTO switch for switching in/out a car radio aerial functions correctly. The main problem is with the MW selector switch, it's extremely stiff and won't return to its normal fully out position due to spring action. The LW switch is also quite stiff but not to the same degree as the MW one. It would appear that the plunger which carries the moving contacts is fouling the inside of the switch body as if the plastic has swollen. I've seen this sort of thing before if someone has applied oil to plastic. It seems that this is not the case however as everything looks clean and dry.

I think the plan will be to desolder it from the PCB and carefully dismantle it to identify the actual cause. A fix may involve slightly filing the plunger so there is a normal working clearance.

This switch bank carries the name Oreor on it and wondered if this problem of stiffness in operation has been experienced by other forum members?

Regards,
Symon
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Old 21st Feb 2024, 11:20 pm   #2
Philips210
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Default Re: Hacker Autocrat Mk2 (RP73)

I managed to remove the push button switch assembly from the PCB. To make this easier, it's often a good idea to apply a little fresh solder to each pin before using the desoldering pump. It then allows the solder to be cleanly removed from each solder pad.

The attached pics show the switch assembly.

Pics 1 and 2 show the removed switch from my radio.

I found a scrap board and also removed its switch assembly but found it to be quite stiff in operation so couldn't use it as is. I also found that the body of the switch was showing considerable cracks very similar to our old favourites, Rifa class X safety capacitors. Perhaps it's a similar composition plastic. Anyway, I thought that I'd first experiment with the cracked switch before tackling my original.

Pics 3 to 5 show the cracked switch assembly from a scrapped radio but now stripped down.

To dismantle the switch, the five retaining plates have to be driven out with a very small punch whilst supporting the main body of the switch. The plungers which carries the contacts can then be withdrawn from the front. The latching lever will have to be held over to one side to allow the plungers to be pulled out. The contacts can then be lifted out of the plunger. The LW and MW plungers each have four contacts whereas the AUTO plunger has two.

Note the latching bar which operates on both LW and MW switches is spring loaded and its torsion spring is centred on the front LW retaining plate pin. One torsion spring end is located against a lug in the plastic housing. The other end hooks over the latching plate.

The central AUTO switch is independently latching and has its own little latching clip together with a small torsion spring. This torsion spring is centred around the pin of the AUTO switch retaining plate. Note the torsion spring is smaller compared to the main latching plate spring.

The individual contact pins can easily be withdrawn with pliers from the body of the switch to make cleaning them easier.

A few other points. The LW and MW switch body is in two sections which easily separate. The LW and MW plungers are also in two pieces which are dovetail jointed. The five retaining plates have a swaged lug and note which way around before fully driving them out of the switch body. The three front mounted retaining plates are located directly behind the plunger compression springs and its important to remove these springs before reassembling the switch. The compression springs can then be carefully refitted.

With everything dismantled, the contacts and contact pins can be cleaned with metal polish.
I found, as suspected, the plungers were a tight fit in the switch body. It seems the switch body has swollen with age making the fit tight. I carefully filed the plungers on all four faces, only taking off the bare minimum and rechecking the fit and clearance. Clean off any plastic dust before retesting to avoid any problems.
A tiny amount of grease can be applied to the latching bar but I'm reluctant to apply any to the plungers due to the deteriorated nature of the plastic. Also not a good idea to use a silicone lubricant where switch contacts are nearby.

Its a good idea to make a few sketches before dismantling the switch.

Hopefully it will all go back together without problems. I will then tackle my original switch.

Regards,
Symon
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Last edited by Philips210; 21st Feb 2024 at 11:46 pm. Reason: typo
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Old 22nd Feb 2024, 10:57 pm   #3
mark_in_manc
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Default Re: Hacker Autocrat Mk2 (RP73)

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Old 3rd Mar 2024, 1:40 am   #4
Philips210
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Default Re: Hacker Autocrat Mk2 (RP73)

I am pleased to say that the switch assembly went back together without too much problem. The sticking switch plungers were cleaned up with a flat needle file and now operate normally. With the switch assembly soldered back to the PCB, I then removed all ten electrolytic caps for testing/reforming. All except one were very good with low leakage. The only suspect cap was C14, 6.4uF 25V, its leakage was a little higher than expected and seemed to be creeping up rather than down during reforming. It was replaced with a 6.8uF 50V radial lead cap made by Rubycon. This too was reformed before fitting it to the board.

With everything reassembled, I connected the radio to my current limited bench power supply set for 9V output and the current limit set near minimum. The radio worked straight away and the switch operation was found to be good with no crackling. The set is quite sensitive and functions very well. I will make a point of checking the power amplifier quiescent current so that there's minimal distortion and optimum battery life. A check on the RF/IF alignment will be done but I doubt it will be far off normal.

The only other minor points to mention. One of the ferrite rod aerial's 'P' clips was fractured. I managed to find an identical one in my spares. The carrying handle would not stay in place when moved to its top position. This was due to damage to the rubber washers on the side of the cabinet. Also one of the handle metal end cap trim pieces was wrong. Luckily, I found two that matched from a scrapped Hunter model. I also located a couple of rubber washers to complete the repair to the handle. Something that is more serious however is the base of the cabinet. It's of a chipboard type construction and since the radio has previously been in a damp environment it has swollen up slightly. As a result it fouls the fitment of the back cover. The only workable solution is to carefully file a little amount away from the battery support plates so that the pins on the back cover clear the plates and then engage in the horseshoe shaped spring clips. The back cover now fits well without any rubbing/friction to the base of the cabinet. Something I have found though, there seems to be a slight mouldy aroma coming from inside the cabinet despite thoroughly cleaning it and leaving out in the sun (when we get any!) It's as if the mould has impregnated the chipboard base and it seems that it's going to be hard to remove.

All in all a satisfying repair that hasn't really cost much but just a little effort.

Regards,
Symon
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Old 3rd Mar 2024, 9:49 am   #5
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Default Re: Hacker Autocrat Mk2 (RP73)

That is a very dedicated restoration, well done. The switches should last many more years.
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Old 3rd Mar 2024, 2:15 pm   #6
mhennessy
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Default Re: Hacker Autocrat Mk2 (RP73)

Yes, I agree - well done

I must admit that I'd forgotten that the switches were of that type, rather than the more common type with the brown plastic body. Admittedly, I haven't looked inside one of these for at least a decade. The last one I worked on was the FM version (the Harrier), which of course doesn't have any push-button switches.

They are nice sounding sets, especially for their size, but the Harrier uses the same speaker as the Autocrat, and is seriously lacking in high frequencies. I added a cap to the audio amplifier to help, but it needs more work really. But for AM, the Autocrat is a fine performer.

Quite nice to look at, too. The grille can pick up dents easily, but is easy to flatten out in most cases. There's a choice of teak or rosewood for the end cheeks. Some of mine need re-finishing, but if I rub off the existing finish to get the dents and scratches out of the wood, I'm not sure how best to re-stain the rosewood version - some experimentation is needed. The only minor aesthetic grumble is those screws on the dial. It's a shame about the chipboard, but I guess that's a result of needing to hit the price point. But even the posher sets suffered from this - at some point in the run, the cabinet of the Sovereign 2 changed from birch ply to some kind of particle board. Back to birch for the 3rd generation though.
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Old 4th Mar 2024, 12:46 am   #7
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Default Re: Hacker Autocrat Mk2 (RP73)

Thanks Stephen and Mark for you nice comments.

The first switch bank from the scrap panel was dealt with first to see if it was going to be possible to repair before delving into the one in my radio. That cracked switch bank was successful but I've noticed its latching isn't 100% positive. It would seem the torsion spring controlling the latch plate is fairly weak. I'll try to locate a suitable replacement. It's strange why the housing to the switch is affected with all those cracks just like the old Rifa safety caps.

Mark, yes those two screws securing the tuning scale to the chassis were also corroded on my set. They seem to be a round Phillips head with a 6BA thread. I have a good selection of BA and Metric machine screws with various head types. The only ones I had to hand were some chrome plated brass ones with a slotted round head. Although not original they look very good so will settle for those until I can source the correct ones.
The hardwood side panels on my set were generally in good condition without any bad dents but the finish was fairly dull. I used some Rustins scratch cover applied with a soft cloth and then buffed it up which has greatly improved the finish.

Re the TAD100 IF IC. I've been trying to find the Mullard data sheet for it without much luck. Does anyone have a copy by any chance? I believe the TAD100 first appeared around 1968 and wondered what other radios used them.

I like Hacker sets more so than Roberts due to the overall construction and they're easier to repair. I have quite a few Hacker sets to repair and service, the problem being the available time. Too many jobs not enough time.

Regards,
Symon
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Old 4th Mar 2024, 1:12 am   #8
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Default Re: Hacker Autocrat Mk2 (RP73)

How's your German?
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Old 4th Mar 2024, 1:37 am   #9
mhennessy
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Default Re: Hacker Autocrat Mk2 (RP73)

Hi Symon,

Just in case I wasn't clear, my comment about the screws on the dial was aimed at Hacker's design - I couldn't actually see from the photo that you'd replaced them

The other sets that I'm aware of that use the TAD100 are the Roberts RIC1 and RIC2, plus the Hacker Harrier. But you can find other sets from Radiomuseum.org from this page: https://www.radiomuseum.org/tubes/tube_tad100.html

I don't think I've seen a Mullard datasheet. Will have a look at some old databooks tomorrow if I get a chance...
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Old 4th Mar 2024, 1:34 pm   #10
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Default Re: Hacker Autocrat Mk2 (RP73)

Not a brilliant copy, but English.....
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Old 4th Mar 2024, 2:56 pm   #11
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Default Re: Hacker Autocrat Mk2 (RP73)

The TAD100 was developed and produced by Valvo, the german branch of Philips Semiconductors. I would be surprised if the data sheet did not exist in English under the Philips logo in the early 70s, I remember it existed in French under the RTC logo when I arrived there in 1974. However I cannot find it ...
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Old 4th Mar 2024, 3:37 pm   #12
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Default Re: Hacker Autocrat Mk2 (RP73)

Please find below the TAD 100 datasheet which I translated into English:
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Old 5th Mar 2024, 5:22 pm   #13
Philips210
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Default Re: Hacker Autocrat Mk2 (RP73)

Thanks very much to Nanozeugma, Herald1360 and marceljack for the data on the TAD100 it's much appreciated.

I had wondered if the TAD100 was listed in Mullard's little data books. I have quite a few including the period the IC was first used. I'll have a look sometime.

Regarding the Philips/Mullard blue axial lead electrolytics. I always used to trust these as good reliable components but lately I have had a several that weren't so good. In my repairs to a Gould J3B audio signal generator, I found that most had highish leakage current even after reforming, so couldn't be trusted. I have quite a few new old stock as well and often the leakage current is worse than comparable caps from a different manufacturer. In some cases, including NOS, they won't reform well.
Conversely though, when I checked and reformed the same type of caps in the Autocrat Mk2, I was surprised to find that 9 out of the 10 were excellent, better infact than some of my new old stock. Only one as mentioned before needed replacing. Some of the very low value ones seem to be more prone to problems. Re Philips electrolytics. There's a more modern blue radial version and I've had a number of these fail, either very leaky or in a couple of cases going s/c. I like Rubycon, Panasonic and Nichicon caps for replacements where you need to have low leakage current.

Regards,
Symon
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