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A Model 16X story
#31
OK, the paper arrived. I really want to get this rewind finished and reassembled this weekend. Then on to replacing the transformer on the speaker basket and new wires in the connecting cord.
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#32
Right! That is the transformer done. I didn't get time to fasten it back to the speaker or run the wiring yet, but we are definitely getting there.
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#33
Finally - some time to work on the radio.

I started the day by looking again at the cabinet. I gave the interior a really thorough clean/damp dusting to remove the last hints of rodent occupation. In the process, I found some additional areas that were separating, so applied glue and they are clamped up for the night. Then I removed the sound board to inspect the cloth, and to attend to the "fringe" trim that runs above it. This is a ribbed/castellated section of moulding that was loose and split from the batten which holds it. That was dismantled and reassembled carefully with glue.

Well, this is really the electronic section, so I made progress here. A 4 wire "umbilical" to run between speaker and chassis was twisted together. I fitted the transformer to the speaker basket, and completed wiring of the field and voice coils, and the umbilical and its plug. That is all ready to go. Next I need to make a checklist of final items. This will include:

1) Replace dial mechanism and shadow meter.
2) Complete chassis wiring of the 2 power supply caps.
3) Replace the 10 K wirewound pot for the interstation noise control. The original is bad.
4) Solder top cap connectors to the new flying leads for RF valves
5) Re secure the large wirewound resistor to the chassis.

We are getting there!

Cheers

Ed
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#34
Well, a little more work achieved today. More attention to the cabinet, gluing here and there. On the chassis, I replaced the wiring for the Interstation Noise Suppressor switch, checked and cleaned the switch. I bought some fiber sheet at the hardware store and punched out washers suitable to cushion the ceramic tube of the big wirewound - the originals had fallen apart. I put this back in place and completed the wiring. A new wirewound 10K potentiometer was fitted to the chassis again part of the noise suppressor circuit. Sadly the original has 2 or 3 breaks in the wire. A few other items of wiring were completed and tidied up. Lastly, I spent some time cleaning up the valve (tube) shields.

To add to the list - variac or dim bulb arrangement. Getting close now Icon_smile
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#35
Wow!! Keep going Ed!! I'm making popcorn now...
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#36
Lurking
--
Ron Ramirez
Ferdinand, IN
Я этого не понимаю
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#37
It's coming chaps, I promise, but work has summoned me back until the weekend, and Mrs H has not yet decided whether we will be travelling or not... And you wonder why this has taken over a year? Icon_smile
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#38
Well, we're not travelling. However another large project from Mrs H demanded attention/supervision, so progress was a bit limited. Since I had to run an errand, at least there was the chance to buy the bits for a "dim bulb" arrangement. However I did:

1) Fit new mains cord (with bulb tester connected for now)
2) Replace all the tube top caps, with the connecting wires dressed to length
3) Found a problem with the new volume control/switch - switch not engaging properly. Dismantled, fixed and refitted to chassis.
4) Cleaned tube sockets and the bandwitch contacts.

For today (I hope) Plug in and test the power transformer on its own -no valves- with a series bulb to check for problems. If all is well, replace dial mechanism tubes etc. and run a test.

There's also a bit of gluing still to do, veneer is lifted where the cabinet curves inward towards the speaker board. Speaker cloth needs to be reapplied as well, so I might do that.

Cheers

Ed
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#39
OK, I plucked up courage to plug in with all the valves removed, and a 40W bulb in the tester. These are 75 Ohms measured cold, and must be more if lit up. The transformer hummed quietly, and the bulb lit dimly, with about 35V across it, leaving 90 or so on the transformer primary.

I let it soak for a few minutes, and there was no change, and no sign of anything getting hot, making odd smells or smoke. Output voltages were about right if you take the 90 V input into consideration ~315-0-315 on the HT, ~4 v on the rectifier heater socket and a little over 5V on the other heaters.

Oh yes, and more wood glue...

Other things to do here in the mean time, but at this point things seem ready to complete wiring (dial & shadow meter assembly) and go for a careful test. I'll post more if I get there.

/Ed
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#40
I made some progress today, of sorts.

First, I powered up with all the valves except the rectifier, checked that they were all heating etc. Then I added the rectifier. With a 60W bulb, the highest power I have available, there was around 70V HT, no sound or signs of life. With no other option, I went for direct connection, measuring everything carefully. HT settled around 380V, but no sounds from the speaker or response to tuning. Nothing untoward, glowing red or emitting blue smoke.

Further investigation showed the audio O/P stage is alive. I could hear crackles when probing the type 42 output valves, and a distinct hum with a probe on the grid of the type 42 driver. This is good news for both my interstage and output transformers. However, I get no response probing at the volume control, or around the type 77 tube AF preamplifier that feeds the driver, which ought to be pretty sensitive, so something is amiss here. It could be a wiring error, or something else, but I ran out of time for diagnostics.

Lastly, the RF stages are drawing current, since the shadow meter's shadow grew large as the set warmed up. Tuning around produced no changes, but there was no aerial connected. I will at least check for oscillator activity on the Broadcast Band using another set as detector when I get another chance to tinker.

Hopefully more tomorrow.
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#41
Rather little time today, but I did compare the circuit diagram, parts layout and wiring. This unearthed (pun not intended) a couple of anomalies that I'll put straight before retesting. Today, however, was busied with helping my Son run experiments for his science fair project.

I do need to lash up a cradle, or some other device that allows the chassis to be worked on while upside down, so that there's no chance of wrecking the dial mechanism and shadow meter.

Cheers

Ed
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#42
Last evening, I got under the chassis and straightened out the wiring issues at the filter block cap. Things now match the wiring diagram on my service sheet, and trace correctly to their respective parts of the circuit.

I'm not sure this explains why signal was not making it through the 77 pentode before the power stage, but will check voltages etc. in the next work session. Wiring from the volume control, power and grid connections look to be correct, but check and recheck always helps.

I'd hit a bit of a nervous dither a couple of weeks ago, but enthusiasm for this radio is really picking up again Icon_smile
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#43
Here's a quick shot of the chassis after reassembly. I left the dial scale off for the time being to keep it safe.

   
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#44
Well that wiring check was worth the effort. I plugged in today, and instantly the valves were warm, there was some hiss from the speaker, and a loud buzz report when the #77 valve's top cap was probed.

Twiddling the tuning cap changed the noises.

I turned up the volume

I attached a 2ft clip lead to the antenna terminal

Stations - lots of them Icon_smile

Madam 16X lives again!
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#45
Congrats, Ed!
Any 16 is always worth it.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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