22 Apr
2005
22 Apr
'05
12:33 p.m.
From: ard at p850ug1.demon.co.uk
Hi
Higher quality AM receivers used the two diode tubes.
One diode was for the detector while the other was
used for the AGC. That way the loading could be optimized
for each function.
Dwight
It has a B9A (9 pin miniature) base,
Certainly, multifunction tubes were around - the
first ones were the dual
diodes and rectifiers of the 1920s, then later twin triodes, extra diodes,
and yes, to the ultimate Compactrons.
The most complex common multi-section valve in the UK (i.e. with the most
sections), is the triple diode triode. It came with a variety of heater
ratings -- the EABC80 (6.3V heater), UABC80 (100mA series string heater,
by far the most common version) and the oddball PABC80 (300mA series
string heater). It turned up in numerous AM/FM radios in the 1960s, where
it was used for the AM detector (1 diode), FM detector (the other 2
diodes) and audio ampifier (triode). so there must be some commoning of electrodes going on,
probably the
cathodes.
-tony
22 Apr
22 Apr
3:29 p.m.
Dwight K. Elvey wrote:
Hi
Higher quality AM receivers used the two diode tubes.
One diode was for the detector while the other was
used for the AGC. That way the loading could be optimized
for each function.
Dwight
I wonder if the quality of AM radio ( not counting the decline in music
taste)
has gone down since every thing uses soild state diodes as compared to tube
diodes.
23 Apr
23 Apr
12:03 a.m.
On Fri, 22 Apr 2005, woodelf wrote:
I wonder if the quality of AM radio ( not counting the
decline in music
taste)
has gone down since every thing uses soild state diodes as compared to tube
diodes.
No. Narrow IFs and lack of design attention due to declining
worthwhile content on AM (plus novelty of FM in the '60s) and
other factors all conspired to make it sound crappy.
Preferring the sound of tube audio is fine; insisting it's
"superior" puts you with the tinfoil hat crowd.
You can simulate a tube diode with a silicon diode, a battery to
remove some of the .7v quantum bias, a huge series resistor a huge
parallel resistor and a bunch of capacitance everywhere to
everywhere. Don't forget inductances at VHF. Toss in 5 watts for
heat and shot noise. They suck. A circuit designed to work with
them does a great job. Ditto solid state, minus the resistors,
capacitors inductors and heat.
4:24 a.m.
Hi,
Tom Jennings said:
On Fri, 22 Apr 2005, woodelf wrote:
I don't know about the US, but UK am stations still transmit decent audio
even if the radios ain't much good. I have a couple of xtal sets - one
modern design and a replica cat's whisker design - and with good Sony
or Sennheiser hi-fi phones the audio is excellent on our local stations.
--
Cheers,
Stan Barr stanb at dial.pipex.com
The future was never like this!
I wonder if the quality of AM radio ( not
counting the decline in music
taste)
has gone down since every thing uses soild state diodes as compared to tube
diodes.
No. Narrow IFs and lack of design attention due to declining
worthwhile content on AM (plus novelty of FM in the '60s) and
other factors all conspired to make it sound crappy. 
2 May
2 May
9:45 a.m.
> I wonder if the quality of AM radio ( not
counting the decline in music
> taste)
> has gone down since every thing uses soild state diodes as compared to
tube
diodes.
No. Narrow IFs and lack of design attention due to declining
worthwhile content on AM (plus novelty of FM in the '60s) and
other factors all conspired to make it sound crappy.
10:17 a.m.
>>>> "Geoffrey" == Geoffrey
Thomas <geoffreythomas at onetel.com> writes:
> No. Narrow IFs and lack of design attention due to
declining
> worthwhile content on AM (plus novelty of FM in the '60s) and
> other factors all conspired to make it sound crappy.
>
Geoffrey> There was a design - in the late 60's?- which used a
Geoffrey> detector which demodulted both upper and lower am sidebands
Geoffrey> and fed the result to separate speakers. Apparently the
Geoffrey> effect during night time fading was exceptional. Anybody
Geoffrey> recall anything about this - Tony ? Sorry if this is ot.
Don't know about back then, but recently (within the past year) there
was an article about a receiver using that approach. It probably was
in the ham radio publication QEX, and I think that it was by Wes
Hayward -- or at least he was connected in some way.
paul
2:11 p.m.
Hi,
Paul Koning said:
Most of the fading is due to phase cancellation between the two sidebands.
The usual technique is to eliminate one sideband and treat the signal
as a single-sideband one, using either the transmitted carrier or a
locally synthesised phase-locked one. My Racal RA1792 has facilities for
an independent sideband system that would allow seperate demodulation
of the two sidebands, but I've not found the relevant hardware yet...
To get back to computers for a while, this Racal receiver has provision
for remote computer control and I'm currently investigating the SCORE
(Serial Control Of Racal Equipment) protocol it uses, with a view to
writing a remote control program so I can control the receiver from
downstairs and stream the audio over the network. It's even more-or-less
on topic - the radio dates from 1987.
--
Cheers,
Stan Barr stanb at dial.pipex.com
The future was never like this!
>>>> "Geoffrey" == Geoffrey Thomas <geoffreythomas at
onetel.com> writes:
> No. Narrow IFs and lack of design attention
due to declining
> worthwhile content on AM (plus novelty of FM in the '60s) and
> other factors all conspired to make it sound crappy.
>
Geoffrey> There was a design - in the late 60's?- which used a
Geoffrey> detector which demodulted both upper and lower am sidebands
Geoffrey> and fed the result to separate speakers. Apparently the
Geoffrey> effect during night time fading was exceptional. Anybody
Geoffrey> recall anything about this - Tony ? Sorry if this is ot.
Don't know about back then, but recently (within the past year) there
was an article about a receiver using that approach. It probably was
in the ham radio publication QEX, and I think that it was by Wes
Hayward -- or at least he was connected in some way. 
22 Apr
22 Apr
7:11 p.m.
The most
complex common multi-section valve in the UK (i.e. with the most
sections), is the triple diode triode. It came with a variety of heater
ratings -- the EABC80 (6.3V heater), UABC80 (100mA series string heater,
by far the most common version) and the oddball PABC80 (300mA series
string heater). It turned up in numerous AM/FM radios in the 1960s, where
it was used for the AM detector (1 diode), FM detector (the other 2
diodes) and audio ampifier (triode).
Hi
Higher quality AM receivers used the two diode tubes. One diode was for the detector while the other was
used for the AGC. That way the loading could be optimized
for each function.
The main reason was to provide a 'delay' (in voltage, not time) for the AGC.
But most AM/FM sets didn't bother. They had a total of 3 diodes, 2 for
the FM detector, one for the AM detector. I've never seen a quad diode
valve (well, OK, I have, it was a double full-wave HT rectifier, but
that's not what we want here). And I've never seen a set that switched a
diode between the AM AGC and FM detector stages as approriate.
Whether there existed sets with, say, an EB91 (double diode, I think you
call it a 6AL5) for the FM detector and an EBC91 (say) for the AM dector,
AGC, and 1st audio, I don't know, and I am not looking for such a
schematic tonight!. When germanium diodes became common in domestic
radios, it was, of course, quite common to fit 4 them (or fit 2 for the
FM detector, and keep the double-diode triode valve for AM detector, AGC,
and 1st audio functions).
-tony
23 Apr
23 Apr
5:21 a.m.
On Sat, 23 Apr 2005, Tony Duell wrote:
>> ratings -- the EABC80 (6.3V heater), UABC80
(100mA series string heater,
>> by far the most common version) and the oddball PABC80 (300mA series
>> string heater). It turned up in numerous AM/FM radios in the 1960s, where
The EABC80 and UABC80 must have appeared around 1952. I have
Grundig 2012W from 1952 (2xEF41, ECH81, EABC80, EL41, EM34). There was an
all-current model, too (the 2012GW). Since then most radio sets became
boring (from the technical point of view) because they were built with the
same tubes (ECC85, ECH81, EF89, EABC80 and EL84, with very little
variations).
Whether there existed sets with, say, an EB91 (double
diode, I think you
call it a 6AL5) for the FM detector and an EBC91 (say) for the AM dector,
AGC, and 1st audio, I don't know, and I am not looking for such a
Of course it exists! It was very common then. Thinking of my Graetz 154GW
from 1950 with UB41 as ration detector and UBF80 for AM
and delayed AGC,
or of my Grundig 380W from 1951 with EAA11 and EBF15. Then there
were
other interesting circuits from K?rting (Syntektor 54W, synchronous
detector? don't know how it's called in English), or simple AM/FM radio
sets that used only one single diode for AM *and* FM (edge demodulator?)
Christian
5:31 a.m.
From: "Tony Duell" <ard at p850ug1.demon.co.uk>
Whether there existed sets with, say, an EB91 (double diode, I think you
call it a 6AL5) for the FM detector and an EBC91 (say) for the AM dector,
AGC, and 1st audio, I don't know, and I am not looking for such a
schematic tonight!.
-tony
The Hacker Mayflower 2 I have on the bench at the moment uses an EB91 as FM
detector, but appears to have no AGC (it is FM only). The is a preset (rear
mounted) sensitivity control on the 1st IF though. I suppose the idea is
that you were a set distance from the transmitter, so the sensitivity (gain)
could be fixed - when this set was built, FM broadcasting consisted of 3
stations (Third, Home and Light), all from the BBC, so the transmitters for
a certain area would be co-located.
There are a few other FM sets that use the EB91, but I don't have any to
hand to look how the AGC is derived.
Jim.
6:53 p.m.
From: "Tony Duell" <ard at p850ug1.demon.co.uk>
I am not in any doubt that the EB91 was used as an FM demodulator. What I
was asking about was sets that had effectively 4 diodes for FM
demodulator, AM detector and delayed AGC.
I've enver had the pleasure of working on a Hacker (what a wonderful
name!) valved radio. Their transsitor sets are some of my favourites,
though, particularly the RP18 Sovereign. It has separate IF strips for AM
and FM -- the only common stages are the audio ones. And a decent audio
amplifier and speaker specified to give 1.5 honest watts.
-tony
Whether there existed sets with, say, an EB91 (double diode, I think you
call it a 6AL5) for the FM detector and an EBC91 (say) for the AM dector,
AGC, and 1st audio, I don't know, and I am not looking for such a
schematic tonight!.
-tony
The Hacker Mayflower 2 I have on the bench at the moment uses an EB91 as FM
detector, but appears to have no AGC (it is FM only). The is a preset (rear
7099
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10 comments
9 participants
participants (9)
-
ard＠p850ug1.demon.co.uk -
bfranchuk＠jetnet.ab.ca -
cc＠corti-net.de -
dwight.elvey＠amd.com -
geoffreythomas＠onetel.com -
jim＠g1jbg.co.uk -
pkoning＠equallogic.com -
stanb＠dial.pipex.com -
tomj＠wps.com