Television, 1947 style- 10
Well, progress has been in dribs and drabs- there have been few tasks that I've been able to tackle en bloc, as it were, and little tiny finishing parts have been trickling in. One of the better trickles this week was a package containing the two U31 rectifier valves:
They're pretty, but not as pretty (or large) as the U14s I was originally looking for. They are, however, much cheaper, and have an octal base, which means I don't have to buy still more valve sockets. Although I might now find myself short on octals when I come to build the amplifier stage..
I've also received a shaver socket in the post- ridiculously, this is a new, solid brass shaver socket for £3, which was cheaper than all the secondhand melamine ones on Ebay. This is to supply a 1:1 transformer, and proves to have been an inspired decision, as the lump mounted on the back of these things is pretty impressive. Behold:
After a certain amount of grappling and fudging I had added a tagstrip and tweaked it to fit onto the timebase chassis..
Which looks pretty presentable to me. It's now wired into place on the frame timebase, which means that the timebase/synch unit is now complete, apart from the absence of the frame output valve, the EL33. I'm still hunting for this, and keep getting outbid, primarily because I refuse to pay upwards of £25 for it. (Matched pair for £140, anyone?) This audiophile nonsense is very silly- they're not that rare, and they're certainly not worth £140 the pair. I'm not even convinced matched pairs are that important in a push-pull situation, but that's another story.
I've also more or less finished of the (admittedly simple) wiring under the PSU unit, including dummying up the two smoothing capacitiors and wiring up the small transformer as an optimistic HT choke. I must remember to double-check that the power transformer is delivering the correct voltage to the rectifier heaters before I actually power it up. I can't keep buying rectifiers..
So currently, the two chassis look like this:
Synch unit on the left, power supply unit on the right. Note also that the anode caps finally turned up, so the synch unit really is complete now. Aprt from that output valve..
I've also salvaged some pierced steel (it's an old office 'in' tray i found in a skip) to make the EHT cage that will live in that blank space at the back of the power supply. I won't mark and cut it until I've decided what is going in there. It will be the Osram big valve, plus an EHT smoothing cap, plus a.. something. Oddly enough, I was fixing a neon sign earlier this week, fitting a new 5Kv transformer. The old one was of course o/s, but I did salvage some useful silicone EHT cable. I might keep an eye out for a similar transformer, but a flyback overwind or a tripler would probably be safer.
I've been experimenting this week with EHT stuff, having salvaged miles of fine transformer winding wire from an old doorbell transformer (some useful laminations, too). I thought I'd experiment with winding a crude overwind-type transformer and see if I can produce something workable.
A few scrubby bits and pieces- the back of a sketchpad to cut a couple of card bobbin cheeks from, a ferrite core from an old FM tuner and the plastic tube that solder comes in (that stuff isn't cheap, incidentally). I used this to make a crude former that I could then chuck up in the Dremel, and then by plugging the Dremel in via my trusty (ex PYE televisions) variac, I could run it at a suitably low speed to wind the wire on. There are many types of coil winding, the one I employed is called, I think, 'disaster' winding.
I clearly don't take enough photos, because I failed to photograph the winding before I dipped it in wax. Anyway, that's what the gungy-looking thing on the left is. It was left to soak up as much wax as it could, and then left to cool. It's not very neat, so I might trim it down and dip it again, but it's probably not worth the effort at the moment, as it is all a bit experimental. These 'pie' overwinds should really be wave-wound, but you need a machine to do that and I don't have one.
The small coil on the right is the primary, and it's my intention to use this as the variable until I get a sensible output. There will almost certainly be an output, and it will probably be in the region of thousands of volts, but how long the overwind will last is another matter, or whether it can cope with any kind of load. To be perfectly honest, I don't even know how I'm going to mount the thing yet. A sign transformer does seem temptingly easy..
They're pretty, but not as pretty (or large) as the U14s I was originally looking for. They are, however, much cheaper, and have an octal base, which means I don't have to buy still more valve sockets. Although I might now find myself short on octals when I come to build the amplifier stage..
I've also received a shaver socket in the post- ridiculously, this is a new, solid brass shaver socket for £3, which was cheaper than all the secondhand melamine ones on Ebay. This is to supply a 1:1 transformer, and proves to have been an inspired decision, as the lump mounted on the back of these things is pretty impressive. Behold:
After a certain amount of grappling and fudging I had added a tagstrip and tweaked it to fit onto the timebase chassis..
Which looks pretty presentable to me. It's now wired into place on the frame timebase, which means that the timebase/synch unit is now complete, apart from the absence of the frame output valve, the EL33. I'm still hunting for this, and keep getting outbid, primarily because I refuse to pay upwards of £25 for it. (Matched pair for £140, anyone?) This audiophile nonsense is very silly- they're not that rare, and they're certainly not worth £140 the pair. I'm not even convinced matched pairs are that important in a push-pull situation, but that's another story.
I've also more or less finished of the (admittedly simple) wiring under the PSU unit, including dummying up the two smoothing capacitiors and wiring up the small transformer as an optimistic HT choke. I must remember to double-check that the power transformer is delivering the correct voltage to the rectifier heaters before I actually power it up. I can't keep buying rectifiers..
So currently, the two chassis look like this:
Synch unit on the left, power supply unit on the right. Note also that the anode caps finally turned up, so the synch unit really is complete now. Aprt from that output valve..
I've also salvaged some pierced steel (it's an old office 'in' tray i found in a skip) to make the EHT cage that will live in that blank space at the back of the power supply. I won't mark and cut it until I've decided what is going in there. It will be the Osram big valve, plus an EHT smoothing cap, plus a.. something. Oddly enough, I was fixing a neon sign earlier this week, fitting a new 5Kv transformer. The old one was of course o/s, but I did salvage some useful silicone EHT cable. I might keep an eye out for a similar transformer, but a flyback overwind or a tripler would probably be safer.
I've been experimenting this week with EHT stuff, having salvaged miles of fine transformer winding wire from an old doorbell transformer (some useful laminations, too). I thought I'd experiment with winding a crude overwind-type transformer and see if I can produce something workable.
A few scrubby bits and pieces- the back of a sketchpad to cut a couple of card bobbin cheeks from, a ferrite core from an old FM tuner and the plastic tube that solder comes in (that stuff isn't cheap, incidentally). I used this to make a crude former that I could then chuck up in the Dremel, and then by plugging the Dremel in via my trusty (ex PYE televisions) variac, I could run it at a suitably low speed to wind the wire on. There are many types of coil winding, the one I employed is called, I think, 'disaster' winding.
I clearly don't take enough photos, because I failed to photograph the winding before I dipped it in wax. Anyway, that's what the gungy-looking thing on the left is. It was left to soak up as much wax as it could, and then left to cool. It's not very neat, so I might trim it down and dip it again, but it's probably not worth the effort at the moment, as it is all a bit experimental. These 'pie' overwinds should really be wave-wound, but you need a machine to do that and I don't have one.
The small coil on the right is the primary, and it's my intention to use this as the variable until I get a sensible output. There will almost certainly be an output, and it will probably be in the region of thousands of volts, but how long the overwind will last is another matter, or whether it can cope with any kind of load. To be perfectly honest, I don't even know how I'm going to mount the thing yet. A sign transformer does seem temptingly easy..