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Old 3rd Jun 2021, 8:48 am   #1
Edward Huggins
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Default The ubiquitous BUSH SRP31D

This portable record player, and it's earlier versions, sold in their 1,000s and there are many still in use and for sale Online.
Yet I have never understood the design philosophy behind these....
The ECL86 PP amp is easily capable of delvering 6 watts at low distortion levels, but not here. Bush used Celestion as their main source of loudspeakers, and there was a very nice 8" x 6" unit in the then range, but not here.
So why did Bush chose to downrate the amplifier's output to a modest 3 watts and why choose such a perilously small 6" x 4" speaker?
Was it to save costs? Was it to soak up available gain to allow for a rather complex tone control arrangement?
I don't quite get it. Views?
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Old 4th Jun 2021, 2:43 pm   #2
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Default Re: The ubiquitous BUSH SRP31D

Those who have a BUSH SRP31D that works well will know it's a very fine piece of equipment and can deliver surprisingly good sound.
Regarding the 6" x 4" speaker, maybe space constraints dictated the use of a speaker this size. A 8" x 6" unit would certainly not fit in the front panel without a radical redesign of the case. I play my Bush quite loud at times and I constantly marvel at the quality of sound and volume this smallish speaker delivers.
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Old 5th Jun 2021, 7:05 am   #3
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Default Re: The ubiquitous BUSH SRP31D

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Those who have a BUSH SRP31D that works well will know it's a very fine piece of equipment and can deliver surprisingly good sound.
Regarding the 6" x 4" speaker, maybe space constraints dictated the use of a speaker this size. A 8" x 6" unit would certainly not fit in the front panel without a radical redesign of the case. I play my Bush quite loud at times and I constantly marvel at the quality of sound and volume this smallish speaker delivers.
I agree and brings back as to the age old debate as to whether the tweeter makes any difference to the overall sound. Guess to those of younger years who have great hearing it possibly does?
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Old 5th Jun 2021, 8:09 am   #4
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Default Re: The ubiquitous BUSH SRP31D

Simple. There's always a manufacturing cost Vs saleability equation to consider, and that's what Bush addressed. Back then, people were far less bothered about high quality sound. It was all about pop music and being able to play the latest hits. People were happy to listen in on two inch speakers in transistor radios, so the sound eminating from that record player would have been considered to be more than adequate, pleasing in fact.
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Old 5th Jun 2021, 8:14 am   #5
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Default Re: The ubiquitous BUSH SRP31D

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Originally Posted by Ekcoman View Post
...whether the tweeter makes any difference to the overall sound. Guess to those of younger years who have great hearing it possibly does?
I'd say very probably. I've a radio with a front panel on/off switch for its tweeter, and I can barely discern any change it makes: the "loudness" switch next to it still has a marked effect. Then, last summer, I was walking with my wife down a very quiet road I knew well some fifty years earlier, and mentioned how on such a day back then the verge would have been alive with the sound of grasshoppers. Her response: "Can't you hear them?"

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Old 5th Jun 2021, 2:08 pm   #6
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Default Re: The ubiquitous BUSH SRP31D

At a guess this was a simple result of the previous ECL83 going from current to maintenance status, and being ousted by the ECL86. Minimal design changes required whilst transistorised units were on the horizon.
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Old 5th Jun 2021, 2:52 pm   #7
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Default Re: The ubiquitous BUSH SRP31D

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Quote:
Originally Posted by Ekcoman View Post
...whether the tweeter makes any difference to the overall sound. Guess to those of younger years who have great hearing it possibly does?
I'd say very probably. I've a radio with a front panel on/off switch for its tweeter, and I can barely discern any change it makes: the "loudness" switch next to it still has a marked effect. Then, last summer, I was walking with my wife down a very quiet road I knew well some fifty years earlier, and mentioned how on such a day back then the verge would have been alive with the sound of grasshoppers. Her response: "Can't you hear them?"

Paul
(Laughs). Often just a matter of wax and a good clean out. But yes, I know what you mean. My limit is 10k these days. Still covers most of the music spectrum though.
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Old 5th Jun 2021, 4:39 pm   #8
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Default Re: The ubiquitous BUSH SRP31D

I agree with Edward It does seem a strange choice I have had to replace these speakers when servicing these record players as the original is sometimes clapped out. I suppose it depends on how loud and how often it was played? The space is the problem there isn't much depth to spare so a replacement has to be one of the types with the larger but flat magnet. I also replace the tweeter with a modern one but again the space is a problem the tweeter can get a bit close to the valves.
It is a bit of an unconventional design compared to how others built record players at the time ....
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Old 5th Jun 2021, 11:03 pm   #9
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Default Re: The ubiquitous BUSH SRP31D

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Originally Posted by Ekcoman View Post
I agree and brings back as to the age old debate as to whether the tweeter makes any difference to the overall sound. Guess to those of younger years who have great hearing it possibly does?
I was given one as a teenager and it certainly sounded much better than similarly shaped alternatives from Dansette, Elizabethan or Fidelity that I'd used. The tweeter made a dramatic contribution - as did the bass and treble tone controls and the use of a decent cartridge.
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Old 5th Jun 2021, 11:18 pm   #10
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Default Re: The ubiquitous BUSH SRP31D

My guess is a larger speaker in the enclosed space would result in feedback through the cartridge.
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Old 6th Jun 2021, 4:59 pm   #11
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Default Re: The ubiquitous BUSH SRP31D

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My guess is a larger speaker in the enclosed space would result in feedback through the cartridge.
I agree, you would need a very spacial deck suspension system to handle much more power with out problems.

Mike
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Old 6th Jun 2021, 10:07 pm   #12
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Default Re: The ubiquitous BUSH SRP31D

I had one of these as my second record player [my first being a fidelity ] I was delighted with it but it want long before it was connected up to the big 12 inch speaker in the defunct 50s radiogram in the dinning room .That big cabinet and the large speaker sounded really good especially when playing a good thumping Motown track
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Old 8th Jun 2021, 4:22 pm   #13
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Default Re: The ubiquitous BUSH SRP31D

Surely its very ubiquity indicates that it was a near-optimal balance of performance, styling and cost?
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Old 8th Jun 2021, 4:42 pm   #14
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Default Re: The ubiquitous BUSH SRP31D

It does seem odd that they didn't use a class A design. I can't see there's any real advantage in P-P at these output powers.

It certainly sold well though. My schoolfriend's older brother had one (he was a 17 year old mod with a Lambretta). My first girlfriend at university also had one (I thought it was very amusing that she was using something so ancient - this would have been in 1974).
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Old 8th Jun 2021, 7:26 pm   #15
Edward Huggins
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Default Re: The ubiquitous BUSH SRP31D

I completely agree. Indeed an ECL86 in class A could offer up to 4.5 watts if needed. A rather strange use of a down-rated PP amplifier, hence my original query here......
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Old 8th Jun 2021, 8:21 pm   #16
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Default Re: The ubiquitous BUSH SRP31D

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Originally Posted by paulsherwin View Post
I thought it was very amusing that she was using something so ancient - this would have been in 1974).
They were certainly still being produced in 1968 from what I've seen, so potentially "only" 6 years old at the time
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Old 8th Jun 2021, 8:23 pm   #17
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Default Re: The ubiquitous BUSH SRP31D

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My guess is a larger speaker in the enclosed space would result in feedback through the cartridge.
You may well be right, but the Hacker Cavalier wasn't much bigger but managed to fit in a 10" x 6" speaker, and the difference is very obvious.
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Old 8th Jun 2021, 8:37 pm   #18
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Default Re: The ubiquitous BUSH SRP31D

In January 1963 according to WHICH MAGAZINE the SRP31C it's predecessor, was considered a BEST BUY along with the DYNATRON CARNIVAL GR8.
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Old 8th Jun 2021, 8:46 pm   #19
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Default Re: The ubiquitous BUSH SRP31D

I've repaired countless numbers of these over the years, & I also remember them from new.
At the time , when I still had really good hearing, i.e I could still hear a 15.625Khz line whistle, I thought that they really had the edge over most contemporary models.

I still think that they sound pretty good now, but as others have said, it was a bit of an odd design. Certainly sound better than the early transistor Bush record players which followed.

David.
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Old 9th Jun 2021, 6:31 am   #20
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Default Re: The ubiquitous BUSH SRP31D

Quote:
Originally Posted by Edward Huggins View Post
So why did Bush chose to downrate the amplifier's output to a modest 3 watts and why choose such a perilously small 6" x 4" speaker?
Was it to save costs? Was it to soak up available gain to allow for a rather complex tone control arrangement?
I don't quite get it. Views?
We may never know. If you take a design, you can analyse it and find out its performance, you can build one and measure it and these things converge on a result.

But if someone asks (pays) you to design something and gives you a set of specs, then there is a very large number of different ways you could do it. There is more 'information' in the finished design than there was in the spec you got landed with. So where did the extra information come from? Choices had to be made which weren't constrained. Free choices, or maybe hidden constraints?

Maybe they wanted to use up a batch of those speakers which had been in stock. Maybe the amplifier was being targeted at a grander machine and the plan got changed mid-stream? Maybe someone just fancied trying a push-pull design derated to give low distortion and a good clean sound.

Even weirder things happen in R&D.

Back in the seventies, HP's spectrum analysers were plug-ins for existing oscilloscope models. They were working on a big integrated high performance unit (Project codename 'Doomsday Machine' was a bit of a give-away) but all the affordable ones in their future plans were plug-ins. A student in that division was working in R&D and he scrounged the receiver core of a base model plug-in. Built his own power supply and integrated it with a home computer board he was playing with. The analyser receiver got tuned by DACs where once there had been pots, and a TV format raster scan display completed the thing. He was playing with software driving it when it got noticed. It had a major effect on plans. All thinking of further plug-ins was dropped and it seeded HP's family of portable spectrum analysers. Billions of dollars of the resulting families have been sold. Not bad for a student playing around, eh?

Designs sometimes get steered dramatically by some spark of inspiration, by personal likes and hatreds.

It's good that there are things off the beaten track, these sometimes produce total junk, sometimes they show the way ahead. They are usually interesting, though.

The Bush SRP31 record player is an undoubted classic. They sold plenty. The people who bought them in the day loved them. OK, they weren't an absolute premium product, but they were better than average and a lot better than many. They managed to make the Fidelitys and Dansettes of the era look poor.

The design business is weird. Unless you've been in it, the discrepancy between the simplicity of a spec and the complexity of a finished design isn't something you'd notice. Where do you get the missing info? Sometimes tossing a coin is as valid as any other method (just don't let anyone see you!). But you do get opportunities to make arbitrary decisions.

When someone hands you a set of specs to do a design for, don't just accept them trustingly. Test them to destruction! Could you design something that meets all the specs but is actually useless for the intended purpose? This comes out as a yes surprisingly often. But, if this is so, you needed to know about it so you could see the pitfall.

Working as a paid designer can be very frustrating, but sometimes it can be great fun. Sometimes you get to play around a bit. But please don't tell today's MBA gang, if they thought people were enjoying things, they might feel the need to do something about it.

David
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