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Old 22nd Jun 2024, 5:42 pm   #121
SiriusHardware
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Default Re: Valve radios with VHF?

Yes, that was also part of what was handwritten on the circuit diagram in the back of my service manual.
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Old 22nd Jun 2024, 6:34 pm   #122
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Default Re: Valve radios with VHF?

Quote:
Originally Posted by stevehertz View Post
Quote:
Originally Posted by factory View Post
Another one that is an import, a Philips Stereo Vienna (Danish), the FM band is mono and only covers the lower end. I've yet to try this it came with no speakers, it can use 5 ohm speakers, or 800 ohm electrostatic speakers. I should probably check for known problem paper based capacitors first, even though the seller told me it was working.

David
So where does the 'stereo' bit come in if it doesn't receive stereo FM broadcasts? On the gram input only I assume? Philips seem to have used this 'stereo' description on a few sets that are, in RF terms only mono. A bit naughty really.
This radio might predate the decision which FM stereo multiplex system was chosen. There are connections on the back for stereo tape & phono use. For me it needs the FM adjusting up to 108Mhz, this bothers me more than the lack of stereo part.

David

Last edited by factory; 22nd Jun 2024 at 6:54 pm.
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Old 22nd Jun 2024, 7:50 pm   #123
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Default Re: Valve radios with VHF?

Oh yes I totally agree, I was being more observational regarding the stereo aspect. As you say, being able to receive stations up to 108MHz is more important. Hope you manage it.
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Old 23rd Jun 2024, 2:17 am   #124
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Default Re: Valve radios with VHF?

When reading about the Hacker Mayflower shelf-filter modification mentioned upthread, I wondered if Hacker itself had seen the apparent frequency response problem, and if so, then why did it not include an appropriate filter. There was precedent for this kind of approach. For example, Ekco include a bass boost filter in its A274 and A277 models (although not in the C273 console version).

Of course, it could have been that Hacker was satisfied with the overall frequency response. With a table radio receiver, the speaker is the weakest link. The drive units must share an open-backed cabinet with the electronics, and the cabinet dimensions are probably determined more by aesthetic needs than by the needs of the speaker. However the speaker system is configured, the result is likely to be well away from that achieved with a reasonable hi-fi system, the deviation vector being variable in direction and magnitude. Presumably then the setmakers would “voice” their receivers to best suit the intended markets and likely users, perhaps varying this by model and size, and over time. In the case of the Mayflower, it seems possible that it was aimed at those who used their radios for extended listening to programme content. In that case, voicing to sound “right” on uncompressed (or minimally compressed) male spoken voice might have been a reasonable target.

The Hacker literature included the following commentary:

“Can be used for working in existing high fidelity installations, either as an ideal radio tuner, or to provide radio programs of ample power output without distortion to feed even the largest high quality loudspeakers”.

To this end, the RF and AF sections were well above average, and in the case of the AF section at least, perhaps noticeably more than would be required simply to serve the internal speaker. But the high fidelity application also demanded an overall flat frequency response. That mitigated against equalization for the internal speaker, unless such was switchable. An additional switch would have been an unwelcome complication in what was intended to be a receiver with relatively simple controls.

Returning to the Ekco case mentioned above, although the A274 and A277 table models had a bass boost circuit, this was omitted on the C273 console. This had the same speaker drive units (one circular, one elliptical) in a bass reflex cabinet, allowing the desired frequency response to be obtained without equalization. Ekco did not claim suitability for driving high fidelity speakers, the extension speaker sockets being for the usual purpose. It did though claim that the RF section, via the tape output, could be used as a high-grade VHF tuning unit. Ekco used fairly standard RF and AF circuitry, albeit that the EL84 output stage had distributed loading of the partial cathode loading type.

An interesting point is that in the A274, the elliptical speaker was mounted with its major axis vertical, whereas in the A277, it was horizontal, evidently to suit the different cabinet proportions. The conventional wisdom is that major axis vertical results in less treble beaming. But horizontal seems to have been the modal choice for table receivers, including the Hacker Mayflower, probably mostly for aesthetic reasons. There was an early precedent in the form of the HMV 1250 FM receiver of 1949, which had a 13.25 inch (major axis) elliptical speaker. It also had separate RF and AF sections. The former was quite elaborate (and used in modified form by the BBC as its HR/12). The AF section had a push-pull output.


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Old 23rd Jun 2024, 2:47 am   #125
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Default Re: Valve radios with VHF?

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The optimum valve used for FM decoding took some time to be developed, it was the ECC85 from 1954 that paved the way.

I was under the impression that the ECC85 was developed (by Telefunken?) to facilitate the use of “economy” single-valve FM front ends rather than for high performance. The latter could be obtained by using an ECC84 cascode RF amplifier in conjunction with an ECC81 or ECF80 mixer-oscillator, using either two or (preferably) three gangs, but the two-valve approach appears to have been unacceptable economically to many setmakers. Also, the components/assemblies industry soon offered ready-made single-valve FM tuners, thus relieving setmakers of the need to design and build their own.

The relative positioning of the ECC85 is illustrated by the Pye FenMan I and FenMan II models of 1955. The FenMan I, evidently intended to compete with the bulk of setmaker AM-FM receiver offerings, used an ECC85 front end, whereas the upmarket FenMan II had a two-valve, three-gang front end (EF80 and ECF80). Dynatron adopted an ECC85-based front end for its T10 tuner of 1955, but soon switched to a two-valve type (FE2) for the T10A, presumably for performance reasons. I don’t know if the FE2 was a Dynatron own-design or acquired from a third party, but proprietary two-valve FM front ends seemed to have been rather rare, if available at all. Hacker might not have been in a position to build its own for the Mayflower, in which case the single-valve ECC85 type from a third party might have been a forced choice. The higher performance British FM tuners of the valve era generally used two-valve front ends, with the ECC85 single-valve type sometimes found in the middle rank models. An exception was Radford, who used an ECC85-based D&W front end in its FMT1, but that I suspect was a forced choice if it did not want to build its own.


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Old 23rd Jun 2024, 7:15 am   #126
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Default Re: Valve radios with VHF?

Quote:
Originally Posted by Synchrodyne View Post
When reading about the Hacker Mayflower shelf-filter modification mentioned upthread, I wondered if Hacker itself had seen the apparent frequency response problem, and if so, then why did it not include an appropriate filter. There was precedent for this kind of approach. For example, Ekco include a bass boost filter in its A274 and A277 models (although not in the C273 console version).

Of course, it could have been that Hacker was satisfied with the overall frequency response. With a table radio receiver, the speaker is the weakest link. The drive units must share an open-backed cabinet with the electronics, and the cabinet dimensions are probably determined more by aesthetic needs than by the needs of the speaker. However the speaker system is configured, the result is likely to be well away from that achieved with a reasonable hi-fi system, the deviation vector being variable in direction and magnitude. Presumably then the setmakers would “voice” their receivers to best suit the intended markets and likely users, perhaps varying this by model and size, and over time. In the case of the Mayflower, it seems possible that it was aimed at those who used their radios for extended listening to programme content. In that case, voicing to sound “right” on uncompressed (or minimally compressed) male spoken voice might have been a reasonable target.

The Hacker literature included the following commentary:

“Can be used for working in existing high fidelity installations, either as an ideal radio tuner, or to provide radio programs of ample power output without distortion to feed even the largest high quality loudspeakers”.

To this end, the RF and AF sections were well above average, and in the case of the AF section at least, perhaps noticeably more than would be required simply to serve the internal speaker. But the high fidelity application also demanded an overall flat frequency response. That mitigated against equalization for the internal speaker, unless such was switchable. An additional switch would have been an unwelcome complication in what was intended to be a receiver with relatively simple controls.


Cheers
Interesting points but it has to be pure conjecture as to why Hacker didn't go the 'extra mile' to attain a flatter frequency response. A few reasons why they didn't could be that in doing so reduced efficiency, it would have cost more to make, and maybe it was considered that the sound was simply 'good enough', especially given that at that time hifi was not mainstream and most people's idea of good sound quality would not have been that high, intelligibility and clarity being higher on the list which of course the Hacker has in stock form. Apart from the set not using a filter to attain a flatter frequency response, as I have mentioned previously, Hacker seems to have opted for a simple, 'easy to use', uncluttered design that is devoid of lots of controls, even placing the single tone control at the back of the set! Had they wanted to address the lack of bass they could have added a bass tone control, but clearly this would have gone against the simplistic design. At the time, Grundig and many other sets were littered with very effective graphic EQ style tone controls and perhaps someone at Hacker thought it might put some people off, or they simply wanted a different approach for marketing reasons.
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Old 23rd Jun 2024, 10:05 am   #127
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Default Re: Valve radios with VHF?

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Originally Posted by stevehertz View Post
At the time, Grundig and many other sets were littered with very effective graphic EQ style tone controls and perhaps someone at Hacker thought it might put some people off...
I wonder what proportion of Mayflowers went into the role in which I first met one, a primary school's radio: only FM ever required (I actually have one of the adaptors the BBC offered to every school many years later when schools programming began on Radio 5 MW), and simplicity of operation very desirable.

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Old 23rd Jun 2024, 5:10 pm   #128
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Default Re: Valve radios with VHF?

A few more sets I have that I don't think have been mentioned:
EKCO A239 Large FM/AM set
STELLA ST236A Same chassis as a similar Phillips model
RIGONDA (?) Same size as the large German radios of the period and you also get a turntable (of sorts) if you lift up the top
MURPHY A242 Good sound but not over sensitive on FM
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