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Old 26th Nov 2020, 9:59 am   #541
barretter
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Default Re: BBC TV: The Repair Shop

Quote:
Originally Posted by dave walsh View Post

The extended HF range meant that the treble controls always had to be turned down somewhat or the hiss from the master tapes [used to produce the vinyl LP] would intrude when a record was played.

Dave W
Perhaps he didn't get the high frequency reduction part of the phono pre-amp quite right.
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Old 26th Nov 2020, 10:06 am   #542
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Default Re: BBC TV: The Repair Shop

Ref post #539/40, thanks for info, I learn something every day.
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Old 26th Nov 2020, 11:20 am   #543
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Default Re: BBC TV: The Repair Shop

From what we saw of the underside of the amp the build quality was excellent. It was a sympathetic restoration and I loved the array of test equipment on show. I wish they had shown more of the restoration but I suppose that soldering in components isn't as visual as making a wheel from scratch.

I wish I could make a holder for a PP3 battery as well at that.
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Old 26th Nov 2020, 11:22 am   #544
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Default Re: BBC TV: The Repair Shop

Referring to David's post 526 about the ball- pein hammer & the wooden spokes - that upset me more than the fannying about with the radio/radiogram.
Yes, treasured family household items deserve preservation/restoration. Thus enhancing loving memories of departed loved ones. No argument. However, this program's production team takes the pathos & tear-jerking to the extreme. Definitely OTT, and it belittles the good nature of the family member who brings in the particular item.
Right enough, I got the impression that the "radio expert" has cleaned up his act a bit. So maybe some of the points raised on this long running thread have filtered back to him.
Thank God Fred Dibnah was also on our screens again last night. The difference between his programs & drippy drooly RS is like chalk & cheese.

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Old 26th Nov 2020, 11:50 am   #545
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Default Re: BBC TV: The Repair Shop

I haven't seen the programme yet but possibly the battery was for providing grid bias? Dad helped me build a valve amp in the early 1960's from a design in one of the mags and that used a PP9 for grid bias.

I shall be interested to watch the spoked wheel repair. As a young child I vividly remember fascinatedly watching my neighbour, a semi-retired rag and bone man, making and fitting a new spoke to replace a broken one of his handcart wheel, finally making a circular wood fire to heat the steel tyre to red heat to shrink fit it on completion.

According to the preface of my 1960's edition of the Concise Oxford Dictionary, "tyre" replaced "tire" in British English in the Edwardian era. Likewise "colour" for "color". The spellings and grammar in Victorian literature sometimes seem very American to modern UK readers.

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Old 26th Nov 2020, 11:52 am   #546
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Default Re: BBC TV: The Repair Shop

Can't wait for a pulpit restoration.

Lawrence.
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Old 26th Nov 2020, 12:05 pm   #547
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Default Re: BBC TV: The Repair Shop

Quote:
Originally Posted by G4XWDJim View Post
I was impressed by the quality of the front panel lettering, done it would seem with white paint and a fine brush.

There was a fleeting glimpse of a control perhaps the band switch labelled 160-80-40 and probably 20 although I couldn't actually see the final numbers. That could mean that it contained an amateur band receiver so was the builder a radio amateur or SWL. There weren't enough views of the front panel to see what the other controls were labelled as.
Hi,

I've had look at the Mullard circuits for valve amplifiers and found the 3 valve preamplifier and it has 5, 7 & 5 KHz Low pass and 20, 40, 80 & 160 Hz High pass filters

I've attached two pictures of a 3 valve preamplifier I must have bought at a Swapmeet or Audiojumble.

As for the soppy nature of the show I'm OK with that and stick to my earlier post (#537)….. I'm happy with being a soppy 'ole Terry

Regards
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Old 26th Nov 2020, 12:51 pm   #548
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Default Re: BBC TV: The Repair Shop

Thanks for the pic in post 548 which showed the frequency range of a high pass filter as 160-80-40-20 which happens to coincide nicely with the lower frequency pre warc amateur bands. Something to be learnt every day. I didn't know that.

Jim
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Old 26th Nov 2020, 1:17 pm   #549
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Default Re: BBC TV: The Repair Shop

Just a reminder to Stay On Topic it's wandered a lot in the last dozen or so posts.

Cheers

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Old 26th Nov 2020, 5:24 pm   #550
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Default Re: BBC TV: The Repair Shop

It would be unusual if the builder had done it all with original design, so I wonder where the sections of it might have come from.

The classic push-pull EL84 amplifier of the period was the Mullard 5-10. I spotted an ECC83 in a close-up shot (Real Mullard and yellow marking to boot) Or could it be a copy of the leak TL12?

With the Mullard modules in the tuner, is this a collection of circuits out of the Mullard book? That long slide pot for tuning looks odd with just a 9v battery, there isn't enough voltage for getting the best out of varactors.

Does the combination of preamp controls - especially those filters - fit anything known?

David
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Old 26th Nov 2020, 5:31 pm   #551
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Default Re: BBC TV: The Repair Shop

Quote:
Originally Posted by Radio Wrangler View Post
Does the combination of preamp controls - especially those filters - fit anything known?

David
David,

See Post #547.

I think it was a Mullard 3 valve pre amplifier. The power amplifier could have been a 5-10.


Regards
Terry
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Old 26th Nov 2020, 6:23 pm   #552
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Default Re: BBC TV: The Repair Shop

Re my story about a similar sized but solid state amp at 427*, I wonder if Barretter's interesting comment [at 451] about high frequency reduction in the pre-amp [in that bread board creation] might have legs? How would that give a false impression? I'd assumed that the presence of tape hiss meant a very wide bandwidth but is the suggestion that this is misleading and it might well have actually been system [thermal] noise-within the Transistors? I know little about the subject though.

I can only say that [subjectively] the overall quality of sound produced by this " lash up" seemed extraordinary at the time. I made the comparison with the valve amp in the first place, because the HF end seemed to be in several bands there. I had been impressed in 1972 because there were at least three controls covering the higher end alone [not just bass and treble] and this seemed to confirm what I was being told. On the other hand, I'm often inclined to suggest that there is a lot of psychology [codology] involved in the listening process itself, just as we see with our brains, not our eyes and that's why I tend to "focus" on the content rather than the very highest "quality".

Dave W

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Old 26th Nov 2020, 7:38 pm   #553
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Default Re: BBC TV: The Repair Shop

Sorry, Terry, I'd missed reading that, but I had looked at the photos! Yes, that's definitely the thing.

It definitely stands at the crossroads, those Eagle knobs put it at the late sixties, as, I think do the Mullard modules, yet it's mono. Transistor amplifier manufacturers had just moved from germanium to silicon, but were still working out how to do good designs. The Quad 303 was about to appear.

Enough things were all changing at the same time, so it's difficult to pinpoint where this fits in. It being mono seems anachronistic.

THey didn't linger on the speaker and the quick glance left me thinking 'Heathkit'

David
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Old 26th Nov 2020, 7:41 pm   #554
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Default Re: BBC TV: The Repair Shop

Yes, a Mullard 5-10 with the 3 valve pre amp with treble filter inductor from the Mullard book.
I think the tuner was also from a mullard tech pub that used their modules. I believe they used varycap tuning, so a PP3 may be a bit puny. PP9 would have been better.
No real need to make a battery clip as there are plenty of nice spring clip types about.

I noticed he had his scope on again, even before the work started, displaying a sine wave and I thought his reforming was a little on the rapid side.

Ed
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Old 26th Nov 2020, 9:21 pm   #555
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Default Re: BBC TV: The Repair Shop

I have to say I enjoyed the programme.

My only comment would be that the amplifier lacked bass.
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Old 27th Nov 2020, 10:47 am   #556
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Default Re: BBC TV: The Repair Shop

In 1975 I built a portable FM radio using LP1185/1186 modules in a large tupperware
box which worked well. 8V supply is fine if the highest frequency station available is 97.6.
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Old 27th Nov 2020, 10:59 am   #557
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Default Re: BBC TV: The Repair Shop

Quote:
Originally Posted by Radio Wrangler View Post

They didn't linger on the speaker and the quick glance left me thinking 'Heathkit'

David
Been there done that where I've posted and subsequently found there was an earlier post with a similar reply etc.

Yes, bang on it's a Heathkit Cotswold MFS Speaker. I had one of these, which I bagged at a Wotton Bassett auction along with a MA12. Sadly the speaker fell by the wayside when I was clearing out prior to the move I've found some pictures on-line.

Roberts used those Mullard 'LP' modules in the late 60's and early 70's radios.

I suppose another pointer (no pun intended) is the tuning dial is annotated with R2, R3 and R4 with no markings for Local or IBA stations.

Finally, as well as the Quad 303 there was the Crown DC300 'silicon' amplifier.

Regards
Terry
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Old 30th Nov 2020, 11:14 am   #558
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Default Re: BBC TV: The Repair Shop

Must admit I like the rural scenes in the programme - but the actual restoration work I don't believe for a moment is actually done there.
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Old 30th Nov 2020, 11:19 am   #559
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Default Re: BBC TV: The Repair Shop

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Must admit I like the rural scenes in the programme - but the actual restoration work I don't believe for a moment is actually done there.
Why not?
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Old 30th Nov 2020, 11:23 am   #560
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Default Re: BBC TV: The Repair Shop

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Must admit I like the rural scenes in the programme - but the actual restoration work I don't believe for a moment is actually done there.
Oh? A lot of it you can actually see it happening here, and with a lot of the big or fragile items there's no point in transporting them elsewhere.
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