Hacker RP31SW, IF problems. - UK Vintage Radio Repair and Restoration Discussion Forum

matthewhouse · 19th Oct 2006, 9:01 pm

Hello all,
I have just 'finished' repairing this Hacker radio. Basically it was dead, and a check on the AF11Xs showed that all five had shorts to the can, and the sets operation was restored by snipping the 5 screen leads. I have now fitted modern TO72 replacements and the radio worked, but was rather quiet. Tilting the radio back and forth would increase and then decrease the volume, after close inspection i noticed that the core in L5 was rattling up and down the coil. A section of really thin rubber belt was inserted into the coil and the core screwed into the hole, the core now sits tight, and there is now lots of power coming from the speaker.

But on testing i have noticed that when tuned into a MW station, you always hear another station in the background, off tuning is silent. I have also noticed when L5 was 'tuned out' the station was quiet but the background station can still be heard clearly. I'm sure someone here knows exactly what causes this but I'm fairly new to radios, so would like to know where the problem is likely to lie. Otherwise this is a fantastic radio.
Thanks in advance.
Matty

Mike Phelan · 20th Oct 2006, 8:42 am

Matty
L5 is the oscillator coil (I think it is the same as RP25 - don't have a cct for RP31) and it is quite possible that the ferrite pot inside the coil is loose - it is held in with wax. Stock fault.

Moving the core will "move" the tuning and gradually weaken the RF gain.
I would be inclined to do a complete IF and RF alignment and then see what you end up with.

Do you have a circuit?

Paul_RK · 20th Oct 2006, 1:00 pm

The RP31 is in the RP18 "family" rather than the RP25 one, which makes L5 the second IF transformer.

I'd be of Mike's mind as to its being time to try realignment, bearing in mind all those transistor changes anyway: the behavior of your background station certainly confounds me. So far, though, I've fought shy of IF realignment on Hackers: they're not designed as other sets, and Hacker themselves warn that peak-tuning the coils is very likely to result in instability. Hence the recommended AM alignment procedure involves an oscilloscope and a wobbulator, and most of us lack at least the latter

Paul

matthewhouse · 20th Oct 2006, 8:00 pm

Hello, thanks for the replies, I was afraid of that. Unfortunately I don't have a manual, an oscilloscope or a wobbulator

. I think I shal have to live with this problem, unless some test gear appears on eBay that is! Another good reason to complete a realignment that i didn't mention is that one of the tuning caps rotor plates fouled the stator plates most of the way round when I received this radio.

matthewhouse · 21st Oct 2006, 3:37 pm

Update! Reading Pauls reply about peak tuning coils can cause instability, i adjusted L5 so that it was a little below the peak setting, and the background stations have gone! Many thanks for info.
Matty

Paul_RK · 21st Oct 2006, 6:20 pm

Hello Matty,

Excellent news there! I'll admit it hadn't occurred to me that a peaked L5 could be causing that symptom. What would happen if all the IFTs were peaked doesn't bear thinking about...

Paul

Top Cap · 22nd Oct 2006, 4:36 am

Hi, I wonder what transistors you used in place of the AF117's?
If you fitted a modern type, was it a Germanium or Silicon as the latter would require adjustment of bias components. A good replacement for the dreaded AF117's appears to be the AF125 or AF127 as described here:-

http://hometown.aol.co.uk/oldradiopa...conductors.htm

Les

matthewhouse · 22nd Oct 2006, 10:47 am

Quote:

I wonder what transistors you used in place of the AF117's?

Hi Les, the transistors I used were AF125's for the 115's and AF127's for the 117's, and as it happens they were from that gentleman!

Matty

Top Cap · 22nd Oct 2006, 7:50 pm

Hi Matty, I had good reason to guess you had used those as I don't think baby would have sung with silicon ones fitted direct

.
Strange the apparant I.F. breakthrough though. I once did your trick of cutting the screen leads of the AF's (not a Hacker) and I had a degree of instability.
I should not say this but we cured it by fitting a small disc cap between the gap in the cut screen lead

.
I know, I know, Naughty! But surprisingly it worked.
Cheers
Les

19th Oct 2006, 9:01 pm	#1
matthewhouse Octode Join Date: Jul 2006 Location: Willand, Devon, UK. Posts: 1,023	Hacker RP31SW, IF problems. Hello all, I have just 'finished' repairing this Hacker radio. Basically it was dead, and a check on the AF11Xs showed that all five had shorts to the can, and the sets operation was restored by snipping the 5 screen leads. I have now fitted modern TO72 replacements and the radio worked, but was rather quiet. Tilting the radio back and forth would increase and then decrease the volume, after close inspection i noticed that the core in L5 was rattling up and down the coil. A section of really thin rubber belt was inserted into the coil and the core screwed into the hole, the core now sits tight, and there is now lots of power coming from the speaker. But on testing i have noticed that when tuned into a MW station, you always hear another station in the background, off tuning is silent. I have also noticed when L5 was 'tuned out' the station was quiet but the background station can still be heard clearly. I'm sure someone here knows exactly what causes this but I'm fairly new to radios, so would like to know where the problem is likely to lie. Otherwise this is a fantastic radio. Thanks in advance. Matty

20th Oct 2006, 8:42 am	#2
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: Hacker Herald SW (RP31sw) not quite right Matty L5 is the oscillator coil (I think it is the same as RP25 - don't have a cct for RP31) and it is quite possible that the ferrite pot inside the coil is loose - it is held in with wax. Stock fault. Moving the core will "move" the tuning and gradually weaken the RF gain. I would be inclined to do a complete IF and RF alignment and then see what you end up with. Do you have a circuit? __________________ Mike.

20th Oct 2006, 1:00 pm	#3
Paul_RK Dekatron Join Date: Nov 2003 Location: Fakenham, Norfolk, UK. Posts: 4,255	Re: Hacker Herald SW (RP31sw) not quite right The RP31 is in the RP18 "family" rather than the RP25 one, which makes L5 the second IF transformer. I'd be of Mike's mind as to its being time to try realignment, bearing in mind all those transistor changes anyway: the behavior of your background station certainly confounds me. So far, though, I've fought shy of IF realignment on Hackers: they're not designed as other sets, and Hacker themselves warn that peak-tuning the coils is very likely to result in instability. Hence the recommended AM alignment procedure involves an oscilloscope and a wobbulator, and most of us lack at least the latter Paul

20th Oct 2006, 8:00 pm	#4
matthewhouse Octode Join Date: Jul 2006 Location: Willand, Devon, UK. Posts: 1,023	Re: Hacker Herald SW (RP31sw) not quite right Hello, thanks for the replies, I was afraid of that. Unfortunately I don't have a manual, an oscilloscope or a wobbulator . I think I shal have to live with this problem, unless some test gear appears on eBay that is! Another good reason to complete a realignment that i didn't mention is that one of the tuning caps rotor plates fouled the stator plates most of the way round when I received this radio.

21st Oct 2006, 3:37 pm	#5
matthewhouse Octode Join Date: Jul 2006 Location: Willand, Devon, UK. Posts: 1,023	Re: Hacker Herald SW (RP31sw) not quite right Update! Reading Pauls reply about peak tuning coils can cause instability, i adjusted L5 so that it was a little below the peak setting, and the background stations have gone! Many thanks for info. Matty

21st Oct 2006, 6:20 pm	#6
Paul_RK Dekatron Join Date: Nov 2003 Location: Fakenham, Norfolk, UK. Posts: 4,255	Re: Hacker Herald SW (RP31sw) not quite right Hello Matty, Excellent news there! I'll admit it hadn't occurred to me that a peaked L5 could be causing that symptom. What would happen if all the IFTs were peaked doesn't bear thinking about... Paul

22nd Oct 2006, 4:36 am	#7
Top Cap Octode Join Date: Mar 2006 Location: Watford, Hertfordshire, UK. Posts: 1,270	Re: Hacker Herald SW (RP31sw) not quite right Hi, I wonder what transistors you used in place of the AF117's? If you fitted a modern type, was it a Germanium or Silicon as the latter would require adjustment of bias components. A good replacement for the dreaded AF117's appears to be the AF125 or AF127 as described here:- http://hometown.aol.co.uk/oldradiopa...conductors.htm Les

22nd Oct 2006, 7:50 pm	#9
Top Cap Octode Join Date: Mar 2006 Location: Watford, Hertfordshire, UK. Posts: 1,270	Re: Hacker Herald SW (RP31sw) not quite right Hi Matty, I had good reason to guess you had used those as I don't think baby would have sung with silicon ones fitted direct . Strange the apparant I.F. breakthrough though. I once did your trick of cutting the screen leads of the AF's (not a Hacker) and I had a degree of instability. I should not say this but we cured it by fitting a small disc cap between the gap in the cut screen lead . I know, I know, Naughty! But surprisingly it worked. Cheers Les