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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 10th Oct 2021, 8:00 am   #21
vintage_8bit
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Martin. Yes the cartridge is a rare survivor. It's a shame the suspension rubber has a small offset.

When I first got the player home I initially just wanted to check out its condition so just changed what was required to safely power, which was the electrolytics and the 3 decoupling caps. I will now give the amp a more detailed examination. Paying attention, as advised to the feedback as the gain appears down. Colin
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Old 10th Oct 2021, 12:38 pm   #22
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Default Re: Pye, Black Box Mk1 1954, cartridge.

The amplifier is simpler than it appears at a glance, only a single triode gain stage, so the cartridge output is critical. The typical 220K anode load is always worth a check too.
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Old 10th Oct 2021, 1:24 pm   #23
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Not necessarily relevant to your "fault" but are both halves of the output transformer primary intact? One section is notorious for going o/c on this model/

N.
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Old 10th Oct 2021, 1:56 pm   #24
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Nick. Both sides are good thankfully. I did scope the output previously with a sinewave input and the output looked clean, with no crossover distortion.

Bill. The 220K anode load is 240K. Which is well in tolerance. What I did notice & at the time I assumed it was a factory change as it looks original, is R9 & R7 are both 57K. Parts list calls up 47k hi-stab. Colin
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Old 10th Oct 2021, 3:45 pm   #25
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Hi Colin, both 47 and 56k resistors fitted on production in these amps

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Old 10th Oct 2021, 6:53 pm   #26
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Amplifier gain is mainly determined by the feedback resistors R16, R4 and associated capacitors. Are they all OK? In particular, has R4 gone high? As I mentioned, you can always play with the values, say increasing R16, to reduce the feedback and increase the gain.

Martin
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Old 10th Oct 2021, 10:18 pm   #27
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Thanks for the great input gents.

We now have more volume, I found......

C6 & C8 leaky. All capacitors are now changed anyway.
R4 4.7K was high by about 20%. (Top end of tolerance)
The earth terminal for R4,C1, & R12 was lose.

When I get a new cartridge & a better record ill let you know what it sounds like. Probably try a known good records first. All the ones I have here are in bad condition. Off to the record shop tomorrow for some mono bargains! Colin.
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Old 11th Oct 2021, 8:11 am   #28
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Default Re: Pye, Black Box Mk1 1954, cartridge.

You might find it harder to source good Mono LPs that you think. The majority of used LPs now sold, especially those in Charity, shops will be Stereo. Just think of the relative volume of Mono LPs pressed in the UK between c.1950 to c.1965, then in Stereo from c.1965 to c.1995.
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Old 11th Oct 2021, 12:07 pm   #29
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Regarding the availability of mono LP’s. In the Carmarthen Market the lady stall holder has a large number of classical and pop mono LPs.
Every time I visit I have to be very careful or I’ll end up upsetting my wife with “ not another load of records”.
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Old 11th Oct 2021, 12:18 pm   #30
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Default Re: Pye, Black Box Mk1 1954, cartridge.

I've just got back from the charity shop with around 20 45's a couple at least are marked mono so ill have a look & listen later.
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Old 17th Oct 2021, 10:44 pm   #31
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Story so far. I did not realise how many of the records now available are stereo, as mentioned by Edward. So I have now fitted an STC8 stereo output cartridge. I now have even more volume. So I think all is well with the amp and cartridge. Thanks to all for the advice.

Next is the UA6 deck stripdown as this is a gummed up and the turntable bearing centre is loose. Colin
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Old 18th Oct 2021, 6:52 am   #32
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Interesting, as I don't recognise that "STC8 Stereo" cartridge - do you mean a BSR TC8S? The tone arm of your BSR UA6 is only wired for Mono. A photo or fuller description of it would help. Even so, I'm pleased you are getting an improved performance. You say it is "louder" but at the expense of the increased volume, is there any detectable distortion?
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Old 18th Oct 2021, 8:52 am   #33
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Default Re: Pye, Black Box Mk1 1954, cartridge.

I Just checked the cartridge part No, see attached images. I can hear some distortion but all my records are in bad or unknown condition and I havent any known good ones that I would play on this yet. I Intend to find my self some known good ones that ive heard on a known good player. Then I can make a better judgement. I would say a bit too much treble as it is. But otherwise Im happy about the sound. I think the cartridge is new old stock. L & R pins are just wire wrapped, so ive used the existing tone arm wiring. The arm was set at 8 grams. Colin
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Old 18th Oct 2021, 12:00 pm   #34
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Yes, this is new manufacture BSR TC8S clone. It gives c.400mv output and might possibly slightly overload the amplifier. Try it at 6 grams. These cartridges have a poor vertical compliance and will wear Stereo LPs quicker than the later "flip-under" cartridge types e.g. Acos GP91/3 and BSR X5M series which track at c.4-5 grams.
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Old 18th Oct 2021, 2:27 pm   #35
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Edward. Thanks for the info. I won't be putting any treasured records on it then. When the deck is back together ill have a play with the tracking weight & cartridge loading, currently about 800K. The deck is having a complete strip down so might be a few days before the next power up. Colin
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Old 1st Nov 2021, 10:25 pm   #36
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Default Re: Pye, Black Box Mk1 1954, cartridge.

I have now got it all back together. It sounds quite good, with the lid closed. Voice seems a bit too prominent, but the base is reasonably punchy. I'm playing just 45's. Distortion I can here is acceptable to me with these old records.

I did try adjusting the feedback with no improvement. I found placing a couple hundred pF across the input gave a slight improvement but I left the amp as original.

I also looked at the cartridge output on a scope whilst playing a record. I then injected a 1kHz sinewave of around twice the output I saw from the record playing. The output at the speaker still showed no sign of distortion. So I don't think the amp is being over-driven. The amp also sounds good if an external signal is applied.

So I think it's as good as it will be with the cartridge fitted, which is now tracking at 6 grams. Colin
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Old 2nd Nov 2021, 7:40 am   #37
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Default Re: Pye, Black Box Mk1 1954, cartridge.

Thanks for this update, something we don't always get. Don't tinker wih the amp's design especially the feedback loop. What you have now is as good as it can ever be. But you might find that a new cartridge could be a revelation?
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Old 2nd Nov 2021, 9:21 am   #38
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Default Re: Pye, Black Box Mk1 1954, cartridge.

The volume control (actually a loudness one) on the BB is right up front so you can't overdrive the amplifier unless you turn it up too far. Adding a few hundred k of series resistance might increase the relative bass level with the added advantage of losing some excess signal voltage.

If you know the nominal outputs of the original vs new cartridges, a starting point would be the resistor which scales the voltage at the top of the volume control to leave the same as the original cartridge's.
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