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Old 22nd Apr 2017, 9:31 pm   #41
mhennessy
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Default Re: Radio sound quality - some measurements

Quote:
Originally Posted by Philips210 View Post
Quote:
Originally Posted by Thyristor View Post
I don't currently own an R700, but have owned and repaired several over the years. They are good performers; but a real PITA to work on; IMO better than the R600/R606, but, ofcourse, out-performed by the R707.
I can second that. The R700 must be the worst Roberts radio for servicing.
I have found my R700s today, but I've no plans to work on them just yet. I did go inside one about 7 years back, and don't remember it being as bad as the R707.
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Old 22nd Apr 2017, 9:57 pm   #42
Philips210
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Default Re: Radio sound quality - some measurements

Hi Mark.

The biggest difficulty with the R700 is the way the component leads are squashed flat after insertion. I think the R404 used a similar manufacturing technique. This makes it pretty awkward to say the least for servicing. I do however like the R700 which I believe was Roberts first AM/FM transistor set from 1966.

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Symon
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Old Yesterday, 5:32 pm   #43
mhennessy
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Default Re: Radio sound quality - some measurements

A few more...

Grundig Music Boy 208, Elite Boy 210, and Elite Boy 600.

I'm especially fond of the smaller sets from Grundig. When working, they have excellent sensitivity and always great sound quality. Hard to restore cosmetically, as we know...

The two older sets have a tone control, which follows Grundig's usual practice of either cutting the bass lift, or cutting the treble. The Elite Boy 600 has a simple 2-position tone button that provides treble cut only.

For the first 2, there are 3 curves, showing tone at min, mid and max. For the latter, the two positions of the tone control switch.

The 4th image shows all 3 sets on the same chart (tone at mid or up). The similarities between them is startling - Grundig clearly had a definite "house style". The Music Boy 208 is blue, Elite Boy 210 is black, and Elite Boy 600 is red.

The Music Boy 208 is the most extended at both ends, but the least smooth overall. The Elite Boy 210 is the smoothest, but least extended at HF. The Elite Boy 600 the best compromise... All very impressive for such small, lightweight sets.

For balance, here's something else:

The Dynatron Elan TP38.

I have a fair few Dynatron sets, but hardly any of them work. Here's one that does, in fetching teak-veneered plywood!

Basically, it's not great. The 4-by-7" Fane loudspeaker has no bass or treble! To get the curve shown, the bass and treble controls were turned up to max. It's fine for AM
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Old Today, 7:55 am   #44
Radio Wrangler
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Default Re: Radio sound quality - some measurements

Your neighbours must now think you've got some strange tropical bird, with all the loud and slow 'whoooop' noises...

David
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Old Today, 8:07 am   #45
Hybrid tellies
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Default Re: Radio sound quality - some measurements

Great work Mark, very interesting results.
I agree what you say about the Hacker Hunter RP38A with the Elac speaker.

My other two best sounding radios are my Bush TR130 which makes listening on AM a pleasure, its very sensitive with a very loud 1w RMS output through its Celestion speaker.
My ITT Tiny Super sounds really nice on AM and FM through its small elliptical Fosters speaker.
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Old Today, 12:09 pm   #46
mhennessy
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Default Re: Radio sound quality - some measurements

It's surprisingly not very loud, David, especially if you're trying to keep the volume control within the scope of a loudness tapping. I'm keeping the FM mod down as well, as a lot of these basic discriminators become a quite non-linear as you approach 75kHz. I have a choice of pseudo-random noise or a fast sweep - it only takes about second or two to capture the readings. Averaging is an option, but hardly worth it here...

Simon, I think I've found the box containing my ITT radios. I don't have many, but hopefully a couple that are similar to yours. I remember them having very good FM sensitivity.

It'll be a few days before I can get back to this - other things have cropped up.
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Old Today, 1:21 pm   #47
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Default Re: Radio sound quality - some measurements

Re: The Grundig Yacht Boy 210 having excessive loudness, presumably to make it sound more impressive to make its thinner plastic cabinet seem as if it is more like a solid wooden one, the loudness components can easily be removed, either lifting one end of the marked components or taking them out all together. It would be useful if they could be switched in and out but not very practical to fit a switch. Disabling the loudness circuit makes the radio sound more natural, the tone control gives more than adequate range to suit listening tastes, either pushed in for bass or pulled out to put the coupling capacitor in circuit to reduce the bass. The circuit diagram shows the components to lift in red, though the print values aren't very clear. Experiments could be made to either remove the top or bottom part of the loudness control from the volume control, or to substitute different values of resistors and capacitors in the loudness circuit.
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Old Today, 2:56 pm   #48
mhennessy
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Default Re: Radio sound quality - some measurements

I posted a clearer version of the schematic of my N210 here: https://www.vintage-radio.net/forum/...554#post371554

The proposed mods would remove all EQ, leaving you with the "raw" response of the loudspeaker+cabinet - which would be severely lacking in bass and perhaps treble too. Some EQ is necessary.

Earlier I described how it actually worked quite well with a "broadcast" that wasn't Optimod'd to within an inch of its life. The problem is not so much the design; it's modern music and broadcasts.

An attenuator ahead of the volume/tone control PCB would preserve the original design intent while rendering the set compatible with today's broadcasts. Alternatively, reducing the gain of the power amp - subject to loop stability - would work.
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Old Today, 3:54 pm   #49
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Default Re: Radio sound quality - some measurements

The mod works very well as I have done it to my Yacht Boy after I was disappointed at how it sounded with an extension speaker. After the removal of the components the extension speaker sounded normal, the internal speaker has good bass extension without being overblown and the tone control set to around three quarters gives a natural treble response. Changing the value of 611 could compensate for any change in frequency response but in practice isn't necessary, the radio whether on internal or external speakers sounds more natural, or maybe neutral. Additional attenuation could be fitted to the input of the volume control as the input signal is larger but only noticeable if the volume is turned fully up.
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