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Old 20th May 2019, 6:35 pm   #1
cathoderay57
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Default Hacker Hunter

Hello folks,
I have been fortunate enough to have been gifted a Hacker Hunter (S/N 22709) in unmolested condition. See pics. It came complete with a Hacker power unit VP408. It has not been run for at least 15 years. I tested the power pack and it produces a healthy 17.7v DC of the correct polarity (centre pin negative). I plugged it into the radio and switched on... Well, it produced clear sound on FM for about 1 second then went silent. Turning power on and off repeated the performance. The power pack was still producing juice on-load. So the next move was to download the manufacturer's service data from this website, which I now have. That's it for today as I have driven back to Bristol from Harrogate this morning and from Edinburgh to Harrogate the day before, so I'm giving my braincell a rest now. I'll check the voltages against the service sheet tomorrow when I'm thinking more clearly. Cheers for now! Jerry
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Old 20th May 2019, 9:09 pm   #2
cathoderay57
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Default Re: Hacker Hunter

Hello again, well I wasn't as tired as I thought and couldn't resist having another stab at the Hacker. First off I removed the AF amplifier board and discovered an extra transistor not shown on the service sheet. Mine has two BC148 pre-amp stages. I've called the second stage Tr1a in the voltage measurements below; spec values from the manufacturer's service sheet are shown in brackets:
Tr1 BC148 Vce 8(7); Vcb 6.05(6.35); Vbe 0.63(0.625)
Tr1a BC148 Vce 8.52(?); Vcb 7.75(?); Vbe 0.59(?)
Tr2 OC71 Vce 0.23(0.28); Vcb 0.06(0.25); Vbe 0.16(-)
Tr3 BC159 Vce 9.16(9.2); Vcb 8.53(9); Vbe 0.62(0.65)
Tr4 AC176 Vce 9.29(9.2); Vcb 9.18(9.1); Vbe 0.09(0.13)
Tr5 AC128 Vce 8.2(8.8); Vcb 8.1(8.55); Vbe 0.1(0.13)
As I was measuring the voltages, the sound came up very gradually, distorted at first but gradually improving in quality. I could not measure any detectable changes to the voltages as this was happening but maybe a capacitor was slowly reforming. There is still some distortion if I crank the volume up. Looking at the voltages the only one that stands out to me is the OC71 Vcb which seems too low. I have not attempted to tweak any of the presets on the AF board. My main area of expertise is in valve circuits so any advice at this point would be welcomed. In the light of the above I'd be inclined to check C7 (40uF) in the collector circuit of the OC71 and then maybe C8 (400uF) the LS coupler? Cheers, Jerry
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Old 20th May 2019, 9:19 pm   #3
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Default Re: Hacker Hunter

You have the RP38A, there are some differences, manual available on the Yahoo Hacker Radio Groups.
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Old 20th May 2019, 9:38 pm   #4
cathoderay57
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Default Re: Hacker Hunter

Hi Frank, thanks for the tip. Cheers, Jerry
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Old 21st May 2019, 2:51 pm   #5
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Default Re: Hacker Hunter

Had another crack at it today. I unsoldered and tested the following capacitors for leakage; component numbers now relate to the RP38a schematic, not the RP38 used before:
C10 400uF (470uF found fitted)
C9 40uF
C8 125uF
C5 2.5uF
C39 2.5uF (on main board next to volume control).
All reformed satisfactorily with leakage resistance >1MOhm.
When I reapplied power everything worked as it should. I cut the link and set the quiescent collector current of the O/P transistors to 3mA (it was a shade high). I'm now going to quit while I'm ahead. It is a nice radio and looks and sound very good. Cheers, Jerry
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Old 21st May 2019, 3:17 pm   #6
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Default Re: Hacker Hunter

My opinion for what’s its worth is the RP38A was the best Hacker radio they released at that particular time. We were a Hacker dealer and I had the choice of the range, I think 1973-4 or thereabouts and I thought it was better than the Sovereign.

Others may differ of course.

Glad you got it sorted, one problem they can have is a high noise level with the volume control turned down, usually the first audio transistor.
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Old 21st May 2019, 3:25 pm   #7
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Default Re: Hacker Hunter

Yes, they're full of the dreaded Lockfits, though they don't seem to be misbehaving in this case. I must admit I'd be tempted to perform a quick Lockfitectomy while I had it on the bench - suitable replacements only cost pennies.
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Old 21st May 2019, 3:58 pm   #8
cathoderay57
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Default Re: Hacker Hunter

Hi Paul, by Lockfit I assume you are referring to the BC148 transistors? Cheers, Jerry
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Old 21st May 2019, 4:10 pm   #9
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Default Re: Hacker Hunter

BC148/159 on the audio board, also BF194/5 in the RF/IF stages.
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Old 21st May 2019, 4:26 pm   #10
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Default Re: Hacker Hunter

Thanks Paul, I've got a few BC108 lurking around somewhere so I'll probably replace the BC148s next time if it gives any more trouble. The other possible cause of the original fault was maybe a dirty preset pot that I could have disturbed whilst poking about, although apart from RV4 when I set up the quiescent O/P current I didn't attempt to adjust any of the others. Cheers, Jerry
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Old 21st May 2019, 5:33 pm   #11
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Default Re: Hacker Hunter

You can replace the BC159 with most PNP Si types - BC55x, BC32x, 2N3906 etc. Ideally it should be a low noise part, but it doesn't really matter in this application.
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Old 21st May 2019, 8:07 pm   #12
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Default Re: Hacker Hunter

Personally, I agree that it's best to wait until they start to play up. They're not all bad.

I've no idea why they specified a BC149 for T4 when the two preceding transistors are BC148. There is no requirement whatsoever for it to be a low-noise transistor, given that there is unity gain between it and the loudspeaker. Note that it's an AC128 in the very similar A205 amplifier used in the Sovereign II and others. If any transistor was critical, it would be T1. But the surrounding resistors (and volume pot) will no-doubt make a larger contribution to the noise than the transistor itself.

The most common cause of problems with Hunters is the switchbank, and it's worth giving it a good clean if you haven't already. Similar comments apply to the 5 pin connector on the amplifier, and also the headphone socket. After that, determine whether the fault is with the amplifier or the IF/RF stages. One question to help with that: is the fault present with both AM and FM? Another step to narrow it down some more: connect an external source of audio to the top of the volume control. Or connect an amplified bench speaker to the top of the volume control. Lots of ways to divide it up without expensive test gear...

It's worth checking the underside of the audio PCB for corrosion from battery leakage. I've had one or two quite subtle faults caused by that - inspection with a magnifier was necessary to find the damaged track. When that's happened, it affected the solder too - complete removal and replacement with fresh solder was required.

Frank is right about these - they are lovely sets. They sound and measure better than the Sovereigns, but a good Sovereign has the edge in RF sensitivity. Trouble is, now you'll have to get hold of a Sovereign to see if you agree with us
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Old 21st May 2019, 10:02 pm   #13
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Default Re: Hacker Hunter

Quote:
Originally Posted by mhennessy View Post
Personally, I agree that it's best to wait until they start to play up. They're not all bad.
I've got into the habit of swapping them out if I have a Lockfit radio in bits and access is easy (that excludes BF194/5s in Mullard modules for obvious reasons). I just see it as preventative maintenance. It's rather like wax caps in valve radios - it's difficult to test them definitively and they cause strange symptoms when they go wrong. It's a judgement call though, and many people will decide not to change them.
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Old 21st May 2019, 10:14 pm   #14
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Default Re: Hacker Hunter

Thanks for the replies - useful tips inc suitable equiv devices. The fault was definitely somewhere in the audio section - sound rapidly distorted and disappeared regardless of the selected freq band. No sound at all touching pin 4 so fault must have been downstream of the volume control. If the fault returns I'll certainly check the plugs & connectors. It has quite a good dynamic range for a small set. I suppose the only slightly disappointing thing is FM only goes up to 101MHz whereas my other transistor set a Roberts R700 goes up to 108. As I mostly listen to R4 that's not a problem! Classic FM reception (101.5?) in this location is not great anyway. Cheers, Jerry
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Old 21st May 2019, 10:22 pm   #15
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Default Re: Hacker Hunter

I don't have a Hunter, but you should be able to tweak the oscillator trimmer to get a few more MHz at the HF end if there's something you want to listen to up there. I find I can usually move the range to pull in a local station on 106.8 while retaining R2 on 89.5.
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Old 21st May 2019, 11:18 pm   #16
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Default Re: Hacker Hunter

I get a great deal of pleasure from my hunter, for example when we had a violent thunderstorm overhead last year and I had to unplug everything. The hunter kept me company.
Mine also sometimes fades out when listening, but I know the problem: the selector switches. A quick push of all of them and then back to the required band will have it working a few more hours. Must get the servisol out!!
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Old 22nd May 2019, 6:58 am   #17
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Default Re: Hacker Hunter

Quote:
Originally Posted by McMurdo View Post
I get a great deal of pleasure from my hunter
These sorts of radios really are a class act. It is good to see the decent sized speaker and a well designed circuitry & interior and a decent wooden cabinet. More to the point though the radio is still almost as good as the day it was made many decades ago. Oddly this is now exactly what the world needs to counter plastic pollution and the curse of short lived appliances.

I have had little trouble with lockfit transistors in my Hacker radios....so far, perhaps I have been lucky. One thing that is not widely known is that Lucas used lockfits in some of their alternator regulators in the 1970's so they must have trusted them at least then, but I think the lockfit troubles took some decades to materialize.

Out of interest I've attached a photo of one of their boards, left hand image and you can see the lockfits.
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Old 22nd May 2019, 10:08 am   #18
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Default Re: Hacker Hunter

My Hacker Hunter RP38A is still full of lockfit transistors and has been working fine since I repaired it a few years ago. Its a joy to listen to.

Personally I have not had any problems with lockfit transistors but can appreciate a lot of people have both on tellies and audio equipment.
I think its down where the radio or TV has been stored over the years. If say its been in a damp garage, basement, shed then yes the lockfits have probably suffered long term water ingression. If stored in reasonably dry location they will probably be ok.

If your radio is working ok on all wavebands I would leave the lockfits in place.
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Old 22nd May 2019, 12:17 pm   #19
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Default Re: Hacker Hunter

As some may already know, I've gone into a lot of detail about Lockfits here: http://www.markhennessy.co.uk/articl...rs.htm#lockfit

Apart from complete failures - which can happen to any transistor - and ignoring the beefier types used as output devices with no or minimal heat sinking, the usual failure mode for these is an increase in noise.

Whether this increase in noise is a problem depends on where in the circuit the transistor is. Obviously, the earlier in the signal path, the more noticeable it will be. It's common to find T1 is noisy, whereas it's much more unusual to find T2 being a problem because T2 would have to be a *lot* worse than T1 for it to be audible at the output. Simple, really.

Of course, Lockfits were used for many other things. The RP25B uses one as a voltage regulator. The RP75 uses a couple to drive the tuning meter. If any of these went noisy, would anyone know?

What happens to a noisy Lockfit? I don't know if it will carry on getting noisier; I don't know if it will eventually fail completely. If the root failure mode is moisture ingress or similar, then perhaps that will indeed happen. But so far, there is no real data out there. And regarding them as "change on sight" will ensure that remains the case. Against that, a balance has to be made - especially if the set is difficult to dismantle and work on - but in a Hacker, I'd definitely regard them as "innocent until proven guilty".

I understand that others will have different views.
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Old 25th May 2019, 4:05 pm   #20
cathoderay57
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Default Re: Hacker Hunter

Hello again, well, guess what, the fault has returned. The fault seems to recur after the set has been switched off for >24 hours. I was still unhappy with the T3 (OC71) voltages so I desoldered it. On the Avo the Collector-emitter leakage resistance measured only 8.5k which didn't look good to me. I replaced it with a spare that had a measured leakage resistance of 500k. I also found a couple of discrepancies from the RP38A service sheet. On my radio, R10 is 82R (not 150R) and R11 is 180R (not 150R) but I left these as-is. I repeated the set up of the quiescent o/p current. With RV4 set to s/c I could only get the current down to 3.7mA (not the specified 3mA) and the sound became distorted. So I readjusted RV4 up to a clear sound threshold which gave a measured current of 4.7mA. The o/p transistors are still running cold to the touch so we'll see how it goes. Cheers for now, Jerry.
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