Hacker Sovereign Mk. I - RP18

[SteveCG]

I have one of these AF11* populated radios which is fine on VHF/FM but no trace on LW/MW.

I've got the circuit diagram of the Mk. II version - the one with the 'silicon' VHF/FM IF strip.

My question is This: Is the AM side of the Mk. I the same as the Mk. II?

It looks to me like the AM LO is not working, however I think the +ve supply on the IF strip is low (decouplers gone leaky/short circuit?). Also I suspect the final IF stage AF117 of being tin-wiskered.

So on a set that worked fully a year ago I may now have a triple fault with decoupling electrolytics, and possibly two AF117s now dead.

BTW, extracting the AM IF strip printed circuit board looks like it will be non-trivial. And I've yet to find the LO !

[Nickthedentist]

For what it's worth, the decoupling electrolytics are always suspect on Hackers nowadays.

Good luck with it.

[AC/HL]

Two posts deleted, please be aware of the Forum rules (particularly B12)

[mhennessy]

In the AM sections of this set (shared with the RP30/31/32 Herald), I've never come across anything other than whiskery transistors and dead electrolytics. Usually both at the same time

If your set uses light blue Mullard/Philips jobs, they are probably OK. Anything else is automatically suspect. The audio amp is usually killed by dead electrolytics too. Fortunately, you can still buy the Philips axial caps these days, so a modern repair doesn't have to look too incongruous.

You're no-doubt aware of the various ways to revive AF11x transistors - obviously there is plenty of info on this forum.

The carbon comp resistors can go high - I don't recall an instance of problems with an RP18 specifically, but it's something else to bear in mind if the HT doesn't come back after you've looked at caps and transistors...

With this set, the first AF117 is a combined mixer/oscillator. The newer sets used a separate oscillator, but this vintage didn't. And you don't need to remove the PCB from the chassis - these sets were designed with future servicing in mind, and the whole chassis comes out really easily. Getting at the first AF117 is a bit of a fiddle, but it's quite doable.

Oh, I've just remembered another cause of AM failure - damaged/bent vanes in the tuning capacitor. I've seen a few of those. Could obviously happen to any set with an air-spaced capacitor, but I've seen more RP18s with this than anything else. Honestly no idea why.

Good luck,

Mark

[SteveCG]

An update:

Whilst at first VHF worked but LW/MW did not - the situation has now reversed (without me doing anything) !

Having been kindly give a tip on what I should be expecting with this receiver I find that the voltages around the circuits are broadly what should be expected.

I tried using a second receiver to detect the VHF Local oscillator and did not find anything. As the tuner uses AF11* devices I assume that the LO device has tin whiskers.

Extracting the tuner looks to be a pig! so the receiver will have to be a 'cosmetic' entity now as far a VHF is concerned.

[samoca58]

The FM tuner in an RP18 uses one AF121 and one AF125 which dont suffer from whisker problems.
The FM IF strip however uses 4 AF114 types that in my example were suffering from said whiskers.
I replaced them all and the AF11x transistors on the AM side and that sorted the problem out.

[Nuvistor]

Hi Steve,
Be aware that the LO could be low or high of the wanted frequency, unless you know which it is it needs both checking.
Frank

[mhennessy]

There are no AF11x transistors in the tuner module - that won't be the problem. I've never had a fault in the FM mdule.

Funnily enough, I repaired an RP18 at the weekend, and that was dead on FM. I zapped all the transistors in the IF strip and all came good. Funnily enough, when I checked the transistors before zapping, there was no obvious short-circuits, but there was obviously something going on.

To get to the first IF transistor, it's worth undoing the 3 bolts that secure the PCB to the side panel. Otherwise, it's dead simple. I use long-nose pliers to pull out the "outer" leads (collector and emitter), then heat the base and screen pads alternatively. Cleaning out the insides of those metal posts before reinserting the leads is a pain, but a good solder-sucker should do the job.

For a first-generation set, the FM performance isn't at all bad on these. Definitely worth the effort

[SteveCG]

Frank,

I believe I covered both situations - however I may have one last go just to be sure.
BTW I did notice a Hunts capacitor lurking...

[SteveCG]

I double checked for the presence of the VHF LO - both above and below - it was not present.

[SteveCG]

A further bit of info:

The VHF tuner has 'Gorler', 'made in Germany' on the case.

So, can somebody help here please: Is this an AF11* populated tuner or is a siliconised one? To get at it is non-trivial.

[mhennessy]

We've already told you about the transistors in the tuner. They aren't AF11x types, and are likely to be fine. Have you "treated" all the transistors on the IF board yet?

[SteveCG]

mhennessy, yes I've checked all the VHF strip IF transistors - there are no collector to shield shorts. As I mentioned earlier since I'm not getting any tuner LO I think that is where the problem may lie. My earlier question about the type (Ge or Si) of transistor used in the tuner was more to confirm the type that I have to deal with.

[ronbryan]

Have you cleaned the band switches and ensured that there is HT getting to the FM tuner? I note that the you have said the fault has switched from AM to FM, so switches are in the frame.

Ron

[SteveCG]

Ron,

Yes, unfortunately (for me for fault finding) HT at the correct voltage is getting to the tuner. I hope to be able to spend some time on the set in the next few days, when I'll check the switch work as you suggest.

[mhennessy]

As I suggested earlier, you might still need to "treat" them, even if they seem Ok. Mild leakage can be a problem. Seen it countless times, and not just in RP18s

[SteveCG]

Thank you mhennessy for the suggestion about zapping even apparently non-leaky AF 11* transistors. I've already got the First IF stage one out - I'll try that first.

[SteveCG]

I've had a little workshop time, so here is an update:

First, I disconnected the shield of the 1st VHF IF transistor - no difference.

Second, with a sensitive receiver set to 10.7 Mc/s and its aerial in very close proximity to the IF out wire from the VHF tuner, I did not pick up anything whilst going up and down the Hacker's tuning scale.

Third, I can confirm the voltage on the VHF tuner's power pin is correct.

To my mind, this all points to a dead VHF tuner LO.

However, it's work in progress, as next I'll completely remove the IF transistor and check again for tuner LO / IF output just in case the IF output was being loaded by a faulty IF transistor and so had caused the LO to stall.

[mhennessy]

Have you checked the bias voltage going into the tuner. It comes (via R24) from the emitter of the first IF transistor. There is a pre-set (R28) that needs to be adjusted to get it correct - details are in the manual.

[SteveCG]

Yes, I had checked it. It was the -1.5 Volts wrt the + HT rail that the manual specified.