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Old 4th May 2021, 2:19 pm   #1
vinrads
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Default My Hacker Herald just repaired itself.

I listen to my beloved Hacker every day mostly radio four , I began to notice a lack of bass and volume whilst loud enough I thought was lacking , anyway today it was playing away nicely , went to switch it off when I touched the knob I heard a click ,up came the volume and the bass , a static discharge cured the fault , I am suspecting the lock fit transistors .Mick.
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Old 4th May 2021, 2:54 pm   #2
agardiner
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Default Re: My Hacker Herald just repaired itself.

Reminds me of the good ole days, where knowing exactly where to 'bash' the product would be a fix.
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Old 4th May 2021, 3:58 pm   #3
Nickthedentist
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Default Re: My Hacker Herald just repaired itself.

Yes, probably those transistors, but the multiway plug/socket on the AF amp panel is often suspect too. As are the presets on the latter.
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Old 4th May 2021, 4:27 pm   #4
mhennessy
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Default Re: My Hacker Herald just repaired itself.

This is a puzzle!

I think I'd start by looking for bad solder joints and connections, including the 5 pin connector. I'd also have a close look at the volume pot - given that the knob is plastic, I'm wondering if it was the mechanical disturbance (rather than static) that made it come good?

At least the Heralds don't have those switched sockets (headphone and gram input) that go intermittent. And there's no waveband switching that includes the audio path - as there's no need to switch between AM and FM detectors. That reduces the possibilities...

If the volume was constant but it was just the bass going, I'd look for an intermittent connection between pin 2 of the 5 pin connector and ground (assuming RP30/31/32 or RP35/37). Turning the bass to minimum has the effect of shorting that to ground. I have had that before, and it was a fault with the bass potentiometer (I think I was able to repair it, but it was 10 years back).

To get into more detail about the amplifier, we'd need to know which Herald you have... But I'd take a look at the output cap (C10 if RP35/37) - they don't tend to go intermittent, but anything is possible.

Of course, the speaker itself could be seizing on the magnet, but I'd expect that to come with some distortion.

Could it be Lockfits? In this instance, I'm not so sure. And because of the intermittent nature of the fault, how long might we have to wait after you changed them before we can be 100% it was those? That's a tricky one. Suffice to say - assuming it's the A205 amp (RP35/37) - then it's more likely T1 than T2, but I can't square the loss of bass and the loss of volume. I think I'd be looking elsewhere before blaming those. But if there's an audible noise with the volume at minimum, then they are probably worth changing separately...

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Old 4th May 2021, 8:51 pm   #5
vinrads
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Default Re: My Hacker Herald just repaired itself.

Thanks Mark this is why I am thinking it is a semiconductor at fault , the set is working ok apart from lack of bass and a bit low volume ,as I reached to turn the radio off I felt a slight shock ,a static discharge, possible before I touched the knob ,that's when the volume increased along with an increase in bass , Its not unusual for me to get a shock when I get up of the arm chair and touch something .Mick.
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Old 4th May 2021, 9:39 pm   #6
mhennessy
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Default Re: My Hacker Herald just repaired itself.

Yes, I can definitely see how that makes sense, it's just that I'm not sure what semiconductor fault could cause the symptoms you had. I'm probably over-thinking it

So which set is it? I'm guessing RP35 or RP37 as you mention Lockfits?
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Old 4th May 2021, 10:55 pm   #7
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Default Re: My Hacker Herald just repaired itself.

The audio lockfits (BC148/149/158/159) do seem to be the most troublesome.
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Old 5th May 2021, 10:10 am   #8
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Default Re: My Hacker Herald just repaired itself.

I once had a pile of salvaged lockfits back in the 1970s and noticed that some had gold flashed pins and most did not.
I wonder if that made a difference to reliability?
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Old 5th May 2021, 11:45 am   #9
chriswood1900
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Default Re: My Hacker Herald just repaired itself.

I think the trouble with most lockfits seems to be the poor quality of the encapsulation which allows moisture in.
With the regard to the original audio fault one thing I've seen a few times is with electrolytics which are starting to fail improving after power has been applied for a little while, I first noticed this whilst repairing a Ferrograph 7 audio board.
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