Valves, or as the Americans call them Vacuum Tubes.
I have been fascinated by valves from a young age and have owned several valve amplifiers like a pair of Quad mono blocks, there was something about the orange glow from the heaters and the leathal voltages they run on that kept me hunting for info on how they work and how not to kill myself!
Decca
SRG-707 Stereophonic Radiogramophone (incorporating VHF FM)
This is a valve amplifier AM & FM tuner with stereo record player (gramophone) chassis removed from the above mentioned unit.
It was bought off ebay and is another project that I have been working on rebuilding into a standard amplifier with all the original functions working.
The chassis was removed from the wooden cabinet (see pictures from link below) it was housed in and I set to work in repairing / restoring it into full working condition.
Valve technology has been around for at least 100 years and was very popular by the 1940 - 1960s but by the late 1970s the introduction of the silicone transistor meant that valves later became obsolete and transistors took over.
However valves are still in use today, many TV and radio transmitters use high power forced air cooled valves to transmit as they are capable of transmitting in the megawatts range efficiently, any solid state device would not be able to disipate the heat generated quick enough.
Audiophiles demand valve amplifiers for the supposed clear, warm sound and tone they produce, many makes of valve amplifiers like Quad, and Leak are worth hundreds or even thousands of pounds, even second hand they hold a hefty price.
Marshall and Vox still make valve guitar amplifiers and heads to this day.
The most common valve used today that everybody has seen / watched is a CRT (Cathode Ray Tube) they are used in TV and computer monitor screens, does not apply to plasma or TFT!
In this Decca chassis there is not one transistor or piece of silicone at all!
There are a total of 9 valves and one Germanium Diode they are:
EZ81 - Rectifier valve.
EB91 - VHF / FM detector valve.
EHC81 - AM frequency changer / 1st FM I.F
EF89 - AM I.F / 2nd FM I.F amplifier
ECC83 x 2 - Triode, audio pre-amp / tone.
EL84 x 2 - Pentode, audio output valves left / right channel
OA81 - Germanium Diode
The Pentode and Triode sound like something out of a Jackie Chan movie!
Once it was made safe to work on by replacing the original mains lead and earthing the chassis I set about replacing all the electrolytic capacitors, after 45 years the old ones had most probably dried out or dielectric broken down.
A few Metalized axial capacitors were also changed (replaced by the big yellow ones in the pictures) as after the unit got hot sound would distort heavily and the volume start to drop off.
Once virtually all the old capacitors were replaced and the unit was back up and running again I made a new back plate with modern speaker, RCA phono connections and fitted a modern IEC filtered mains socket and 2 Amp fuse and holder.
It is now fully working even the radio although it cannot pick anything up above 100 MHz on the FM band as back in the 1960's the range was 88 - 100 MHz FM.
If you wind to the end stop at the 100Mhz end you can just about get 102.7 Mercury FM a local radio station around the Crawley area, I live a few miles away from there.
Am still using it and as of yet I have not found a cover but am still looking.
After the chassis was removed the wooden cabinet went down my local tip.
