When BBC 2 first came on the uhf tuners were using tiny valves, but when I tried to use them this way, I often found that the inbuilt inductance etc,
of the circuit made it impossible to get above around 200 mhz. Obviously
when Transistors came along this changed, then came te problems with capacitance making them unstable, but I digress, I just wondered how they managed to get these valve uhf tuners to work on band 4 and 5? I suspect its tied up with the way they were tuned using effectively tuned lines, but they worked surprisingly well.
When BBC 2 first came on the uhf tuners were using tiny valves, but when I tried to use them this way, I often found that the inbuilt inductance etc,
of the circuit made it impossible to get above around 200 mhz. Obviously
when Transistors came along this changed, then came te problems with capacitance making them unstable, but I digress, I just wondered how they managed to get these valve uhf tuners to work on band 4 and 5? I suspect its tied up with the way they were tuned using effectively tuned lines, but they worked surprisingly well.
On 14/04/2022 09:56, Brian Gaff (Sofa) wrote:
When BBC 2 first came on the uhf tuners were using tiny valves, but when I >> tried to use them this way, I often found that the inbuilt inductance etc, >> of the circuit made it impossible to get above around 200 mhz. Obviously
when Transistors came along this changed, then came te problems with
capacitance making them unstable, but I digress, I just wondered how they
managed to get these valve uhf tuners to work on band 4 and 5? I suspect its >> tied up with the way they were tuned using effectively tuned lines, but they >> worked surprisingly well.
They were very noisy and got worse and worse very quickly.
Bill
Brian Gaff (Sofa) <briang1@blueyonder.co.uk> wrote:
When BBC 2 first came on the uhf tuners were using tiny valves, but when
I
tried to use them this way, I often found that the inbuilt inductance
etc,
of the circuit made it impossible to get above around 200 mhz. Obviously
when Transistors came along this changed, then came te problems with
capacitance making them unstable, but I digress, I just wondered how they
managed to get these valve uhf tuners to work on band 4 and 5? I suspect
its
tied up with the way they were tuned using effectively tuned lines, but
they
worked surprisingly well.
The initial problem was inductance in the cathode leads which was common
to the input and output circuits and gave unwanted frequency-dependent feedback. By using dual connections to the cathode, each circuit could
be connected separately to remove the common inductance; then the
remaining inductances of the lead-outs were taken into account in the
tuning components. Even the humble EF80 had dual cathode connections.
As the frequency went up further. the earthed grid configuration became almost universal, but the 'acorn' triodes with metal-to-glass seals and special 'bulkhead' valve holders were expensive and inconvenient. For domestic tuners, valves with very short lead-outs were developed and
multiple grid connections were distributed around the base pins to effectively put an earthed screen right across the middle and earth the
grid in many places (thus reducing stray inductance). Some
manufacturers turned the electrode assembly on its side to give shorter leads.
There is a lot of information on valve development in Philips Technical Review and the Mullard adverts in Wireless World arond that period.
--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
On 14/04/2022 09:56, Brian Gaff (Sofa) wrote:
When BBC 2 first came on the uhf tuners were using tiny valves, but when
I
tried to use them this way, I often found that the inbuilt inductance
etc,
of the circuit made it impossible to get above around 200 mhz. Obviously
when Transistors came along this changed, then came te problems with
capacitance making them unstable, but I digress, I just wondered how they
managed to get these valve uhf tuners to work on band 4 and 5? I suspect
its
tied up with the way they were tuned using effectively tuned lines, but
they
worked surprisingly well.
They were very noisy and got worse and worse very quickly.
Bill
In article <jbqqe2Fmv4pU2@mid.individual.net>, williamwright <wrightsaerials@f2s.com> scribeth thus
On 14/04/2022 09:56, Brian Gaff (Sofa) wrote:
When BBC 2 first came on the uhf tuners were using tiny valves, but when >>> I
tried to use them this way, I often found that the inbuilt inductance
etc,
of the circuit made it impossible to get above around 200 mhz. Obviously >>> when Transistors came along this changed, then came te problems with
capacitance making them unstable, but I digress, I just wondered how
they
managed to get these valve uhf tuners to work on band 4 and 5? I suspect >>> its
tied up with the way they were tuned using effectively tuned lines, but
they
worked surprisingly well.
They were very noisy and got worse and worse very quickly.
Bill
PC88 RF amp and PC86 Local Osc/Mixer..
Then came transistor tuners and made decent reception possible:)
Especially for us out in the sticks trying to receive Xtal place at some
65 miles distant!. Converted quite a few TV's to take a transistor tuner
with decent results!.
BF180 and BF181 was it in them;?...
--
Tony Sayer
Man is least himself when he talks in his own person.
Give him a keyboard, and he will reveal himself.
In article <jbqqe2Fmv4pU2@mid.individual.net>, williamwright <wrightsaerials@f2s.com> scribeth thus
On 14/04/2022 09:56, Brian Gaff (Sofa) wrote:
When BBC 2 first came on the uhf tuners were using tiny valves, but
when I tried to use them this way, I often found that the inbuilt
inductance etc, of the circuit made it impossible to get above around
200 mhz. Obviously when Transistors came along this changed, then came
te problems with capacitance making them unstable, but I digress, I
just wondered how they managed to get these valve uhf tuners to work on
band 4 and 5? I suspect its tied up with the way they were tuned using
effectively tuned lines, but they worked surprisingly well.
They were very noisy and got worse and worse very quickly.
Bill
PC88 RF amp and PC86 Local Osc/Mixer..
tony sayer <tony@bancom.co.uk> wrote:
In article <jbqqe2Fmv4pU2@mid.individual.net>, williamwright
<wrightsaerials@f2s.com> scribeth thus
On 14/04/2022 09:56, Brian Gaff (Sofa) wrote:
When BBC 2 first came on the uhf tuners were using tiny valves, but
when I tried to use them this way, I often found that the inbuilt
inductance etc, of the circuit made it impossible to get above around
200 mhz. Obviously when Transistors came along this changed, then came
te problems with capacitance making them unstable, but I digress, I
just wondered how they managed to get these valve uhf tuners to work on >> >> band 4 and 5? I suspect its tied up with the way they were tuned using
effectively tuned lines, but they worked surprisingly well.
They were very noisy and got worse and worse very quickly.
Bill
PC88 RF amp and PC86 Local Osc/Mixer..
The noise figures for those triodes were pretty good because they didn't >suffer from the partition noise of a pentode. I suspect there would
have been other causes for the noise, such as poor gain distribution in
the early stages of the receiver or mechanical problems in the tuner
made worse by the heat of the valves.
The Eddystone 770U used a 6AM4 in earthed grid configuration and a 6AF4A >oscillator with a 'crystal mixer'; it covered 150 to 500 Mc/s in six
ranges. With an I.F. bandwidth of 20Kc/s the S/N ratio was 15dB for 10 >microvolts input (75 ohms) modulated at 30%. A double triode was used
in cascode as the first I.F. amplifier because the signal was still too
low at that point for a pentode to give a good S/N ratio. All the
television sets of that era (as far as I remember) used a pentode in
that position, so that might have accounted for the higher noise level.
The higher gain of a transistor tuner may have delivered a larger signal
to the first I.F. stage and that would be wbere the improvement in S/N
ratio occurred.
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