Another Hacker Hunter RP38A

[Hybrid tellies]

After successfully repairing a couple of Hacker Sovereign RP25s for other people I have not had much luck with my own three. So I turned to my attention to my Hacker Hunter RP38A which I bought from the NCVF a few years ago. Thanks to mhennessy’s Hacker Hunter survey I was aware that this was a made up set with the chassis or cabinet being swapped over earlier in its life.

It had obviously been got at by the phantom dabbler as some of the coils had clearly been tweaked, the cabinet has suffered a very small dent to one of the teak sides and the front aluminium grill has quite a few noticeable dents. But apart from this it was all complete with no missing knobs, a nice straight telescopic aerial and the tuning dial was in good condition.

After connecting it up to an 18v supply from my workshop psu I was greeted by a loud beating howling noise when the volume was turned up, but worked OK on all three bands at a low volume setting. The calibration on all bands was way out, but using my RF scanner and small communications receiver placed very close to the radio I was very relieved to find that the IF frequencies on both AM and FM were spot on and that the phantom dabbler had only messed about with the front end coils and trimmers. With this in mind I decided to concentrate on the cabinet and motor boating fault.

Dismantling was nice and easy and I was able to remove the front aluminium grill and straighten out the worst of the dents although not perfect it’s a lot better than it was. I decided to leave the slight dent in the side wooden panel as it did not detract too much from the looks of the set. Finally with a good dust out and wipe over the cabinet was far more presentable.

I then decided to tackle the audio motor boating problem. I found that the audio motor boating and screeching fault varied when I moved the audio input cable feeding the audio amp/output board. After scrapping cleaning all the pins and tightening the sockets the fault had cleared, but after refitting the chassis back into the cabinet the motor-boating fault came back with a vengeance. This time it was slightly different, it was clear on minimum bass but turning the bass up to half way the motor boating started even at low volume levels and the only way to stop it was to turn the radio off and turning the bass control back to minimum before switching back on. Removing the chassis again I first checked all relevant electrolytic capacitors which measured spot on. It was whilst checking electrolytic capacitors C2, C5 and C10 on the amplifier board that I noticed a hairline crack on the PCB underneath the main plug and socket feeding pin 2 to the bass control. Soldering a small wired link across the crack cleared the fault. A quick check on the mid-point voltage of the output transistors showed it to be spot on at 8.9v, amplifier idle current at 13ma with the total idle current at 20mA which is correct according to the manual.

Whilst I had the chassis out I noticed the coils on the ferrite bar aerial had moved and were loose, so following the RF alignment procedure in the manual I repositioned them and secured using some thin insulating tape then continued with the full AM RF alignment using off air stations as my signal generator is out of action. For the medium wave alignment I used R Bristol on 1548Khz, for the high end of the band, BBC R5L on 909Khz for the mid band and R5L on 693 for the lower end. For Long Wave I used three stations France Inter on 162Khz, BBCR4 on 198Khz and RTE1 on 252Khz.

On FM I followed the RF alignment as per the manual using Radio 2 on 89.30 and 89.90Mhz, Kiss FM on 101Mhz and Somerset Sound on 95.50 and Heart on 96.30Mhz. I had to reduce the signal by disconnecting the telescopic aerial to reduce the aggressive AFC action so I could get the alignment spot on. The FM band can be tweaked to tune higher than 101Mhz but I would prefer to see the correct dial calibration so I did the FM RF alignment as per the manual. After a couple of hours I had the RF alignment spot on across the dial on all 3 wavebands probably better than when it was new, sensitivity and selectivity on all wavebands also looked good. I noticed the core position of the AM Oscillator coil T1 was still protruding the top of the can after a conversation with “mhennessy” my mind was put at rest by telling me this was normal for these radios. I used a dab of tipex on the coils and trimmers I adjusted to stop any possible mechanical drift.

I slotted the main chassis back into the cabinet and ran the set for a few weeks connected to my workshop PSU. It did not take long before the next fault showed up, a very intermittent noise fault on FM only. After weeks of gentle tapping around I eventually traced this highly intermittent fault to an intermittent pre-set PR1 on the FM demodulator circuit. I found a replacement 4.7K pre-set in my box of spares the only problem was there was no setting up advice in the manual. After a little chat to Tazman I checked and noted the resistance across PR1 in circuit, reversing the meter leads for two readings and out of circuit after gently removing the pre-set from the board. Fitting the new pre-set and adjusting it to match the resistance readings I had recorded I am happy this intermittent fault has been cleared as the radio has been running well for the last few months. As this pre-set is in the AM Limiting part of the FM demodulator I was not able to run a test as my signal generator is down, but mother nature came to my aid with a few good thunderstorms which I was able to compare the levels of impulsive interference on the weak Radio 4 FM signal alongside a few known good FM radios The results were very good proving that the AM limiting action of the FM demodulator was working well.

Everything was running well for weeks until one afternoon whilst listening to BBC R2 on FM reception suddenly went all noisy again, I froze staring at the radio with disbelief. Closer investigation revealed that the lower half of the FM band was full of very strong Spanish and Portuguese stations swamping out our local signals from Wenvoe and Bristol Ilchester Crescent transmitters thanks to an intense Sporadic E opening.

The nearly new PP9 batteries lasted months with the radio still giving reasonable results even when the 18v line dropped to 7v. Sensitivity is very good on all three bands easily pulling in all the available stations plus many more weaker and more distant stations. The sound quality from the large 8”x 5” Elac speaker is just amazing with plenty of bass and treble giving a very clear natural but powerful sound that can be heard around the house and into the garden with the volume only turned up by a quarter. I can understand why some of the members of this forum say that the Hacker Hunter sounds as good as or better than Hackers flagship radio the Sovereign.

Message to moderators I have cut this story down but if you still think its to long please delete it and let me know so I can try and cut it down in size again.

[Nickthedentist]

Great work, Simon.

Those pesky "domino" plug/sockets often seem to give the motorboating symptoms you describe. I've had to hard-wire one as the female parts had started to disintegrate.

Too long? Definitely not, but breaking it down into paragraphs (i.e. the odd bit of white space between sections) would make it much more easy on the eye

Nick.

[Hybrid tellies]

You are quite right Nick. It looked ok on the word document on my laptop but could do with more editing. Moderators can you please delete and I will add a shorter version. Thanks.

[mhennessy]

Nice write-up, Simon. Sounds like you've had most faults going

I agree the AFC can be a pain. During line-up, I disable it by short-circuiting C21...

I've never found the setting of PR1 to be all that critical in practice. I think you've done the best you can in this case though.

The more I listen to these sets, the more I wish they'd simply used that loudspeaker across all their sets. It's the best of the bunch, and given that it was only used on the Hunter, you can bet it was the cheapest. It's a lot better than what they used on the later Sovereign III sets (including the Super-Sovereign). I was pleased to see its return in the Sovereign IV.

No need to edit this down. All we need is a kindly mod to insert a few carriage returns here and there.

Cheers,

Mark

[Nuvistor]

Nice restoration, I also think the RP38A is one of the best. I have had mine since new, it is only when I think that it is about 40 years since it was bought, oh dear that long ago.
Frank

I also think the RP38A is one of the best

So do I, I was given mine by a fellow madoinian a few years ago, it gets used most days (I would say every day but I can't remember) they where made here.

[Radio Wrangler]

I was at an amateur radio sale in August and there were few Hacker portableswith sticker prices under £20 and you're making me wish I'd plumped for one!

David

and there were few Hacker portables with sticker prices under £20

I did work out than mine cost the equivalent of about £350 in todays money. About the same as portable 'phone today, I know which one I prefer.

[Tazman1966]

Nice write up Simon. I must get myself one one day....

[Hybrid tellies]

Thanks for the kind comments. This radio is my own first own Hacker so I gave it a lot of extra TLC. I agree about the Elac speaker but Hacker obviously thought that the Goodmans speaker was superior, Tas, the only thing that you might not like about these radios is the six lockfit Si transistors used in the RF/IF stages. I have always liked this family of transistors and found them to be very reliable but I know you and others have had a few problems with them.

[Tim]

Those separate amp boards and related connections are nothing but trouble IMHO. Even more so when they are subject to corrosion from leaky batteries. There is one(two actually) advantage though, in that they come out to work on, and you can always subsitute one frome another set to prove a fault.