Hacker RP38A Hunter with poor FM sensitivity

[mhennessy]

Yes, that's right

[canonman75]

Time for another update.....

I'd put the Hunter to one side for the time being as I wasn't keen on the idea of doing alignments without the proper equipment, and grabbed an RP77MB Sovereign IV off the pile to look at instead.

The RP77MB turned out to be completely silent on MW and LW, and working on VHF but with poor sensitivity. The first thing that stuck me was how poor a lot of the soldering was, certainly nowhere near as good as earlier Hackers. After giving both boards a good going over with a soldering iron, it was still no better. I decided to take out all the BF194 transistors on the IF board, one at a time, and test them on my Peak Atlas. Every single one of them tested fine on there but, having read about the curse of the Lockfits, I replaced them all with MPSH10's. Bingo! MW and LW now work fine and the sensitivity on VHF is right where it should be! I'm not in the clear with it yet though, as all three control pots are noisy as hell and it doesn't look like there's any openings in them to spray some Super 10 inside

Anyway, I think I'll replace all those nasty Lockfits in the Hunter with MPSH10's and see what happens. Who knows, it might even cure the poor VHF reception

I'll have a crack at it later and report back with my findings!

[paulsherwin]

Told you so

[canonman75]

To be fair, yes, you did

[paulsherwin]

It's good to know that you've found MPSH10s to be a good replacement. The more evidence about this we can get the better. The Lockfit problem is definitely getting worse as time passes, so it's important to identify trouble free substitutes.

[canonman75]

Well, they certainly improved things in the Sovereign IV.

I'm not so sure about the Hunter yet, it only seems slightly more sensitive. Mind you, I only replaced the four on the IF board. I forgot to change the two on the FM tuner....

[paulsherwin]

We don't know that bad Lockfits are responsible for the Hunter fault yet, it's only a possibility (though a strong one).

[mhennessy]

And if they are, my money is on the ones in the FM front end. Partly because of Murphy (them being the hardest to get at )

[Hybrid tellies]

I think I should have aligned the pointer to the datam point on the right of the scale but the alignment is good enough for me as I can pick up the weak BBC R2 signal from North Hessary Tor on 88.10Mhz just to the left of 88 on the dial. But I suspect it will not go down to 87.70Mhz and the only way I can prove this is to wait for a nearby RSL station or perhaps a good Sporadic E opening to bring in some decent signals below 88MHz.

[canonman75]

I finally got round to changing the two Lockfits in the FM front end for MPSH10's. It took about 45 minutes which wasn't too bad....

...it doesn't seem to have improved the sensitivity though

[mhennessy]

But hasn't made it worse? If so, that's a good result in terms of validating the MPSH10 as a good substitute in the FM front end

[paulsherwin]

And, you know you won't have to deal with Lockfit problems in the future, so it's not been time and money wasted.

[canonman75]

Originally Posted by mhennessy

But hasn't made it worse? If so, that's a good result in terms of validating the MPSH10 as a good substitute in the FM front end

It's no worse, but no better either. It just means I've still got work to do on it! I will have a go at doing a proper alignment but it can wait until I've got an RF generator and frequency counter. I'd rather be tooled up than not

Originally Posted by paulsherwin

And, you know you won't have to deal with Lockfit problems in the future, so it's not been time and money wasted.

True! It was an interesting experience, and if I have to do another one I'm sure it'll be a lot simpler next time