project 1951 Pontiac Chieftain

[PhilA]

Whoooeeee, got myself confused for a moment there.

I sat down and stared at the half-disassembled chassis on the desk, and started poking at it with my meter to try and recall what the hell I was doing. I started with the power transformer, which was the key item I had transplanted from the '56 set.

 

Going by the '51 diagram, I test across the coils, got about 500 ohms on the secondary (good) about 1.2 ohms on the primary (also good) but about 270 ohms from primary to secondary (bad!). I went go dig on that there Interwebs and found a circuit diagram for the '56 set- it is connected center tap to center tap, primary to secondary and secondary to input (float) for reasons unknown so the readings I get are accurate.

 

I need to re-draw the circuit diagram afterwards to reflect the transplanted power supply. The rest stays the same (except the tube heaters are the 12V versions rather than 6).

 

Getting back to sorting out just WTF I was doing with the bloody thing.

 

 

Phil

[PhilA]

See? Wot the fug.

1951:

 

And 1956:

 

Why is the secondary center tap connected to the primary center tap?!

Answers on a postcard plz

 

Phil

[Asimo]

It makes the HT rail 12 whole volts higher to have the secondary CT on the +12v rather than 0v. Possibly some sort of transient cancellation going on with HT and LT currents both flowing in that choke?

What frequency does the vibrator switch at?

[PhilA]

4 hours ago, Asimo said:

It makes the HT rail 12 whole volts higher to have the secondary CT on the +12v rather than 0v. Possibly some sort of transient cancellation going on with HT and LT currents both flowing in that choke?

What frequency does the vibrator switch at?

That's kinda what I was thinking. Vibrator switches at about 45-50Hz, from memory

[PhilA]

Redrawn the correction on the diagram.

 

 

Now to order the parts I don't already have in stock.

Phil

[PhilA]

Now $38 poorer. Those should be in by the end of next week and I can start on this in earnest.

 

Phil

[Zelandeth]

That is an...interesting...power supply setup.  Definitely not something I've come across before, though granted I've never worked on automotive radio gear from that period.

There were some odd things around back then though.  Especially when mains energised speakers were involved, there were some "inventive" hum cancellation designs out there.

Then of course there's Philips.  They just seemed to take joy in going out of their way to design circuits doing very ordinary things in as different a way as possible to everyone else on the planet...much to the dismay of any poor service engineer! 

[hairnet]

how many twinkies in your order :D

that diagram makes my brain hurt

oh to be good at shit like that :)

 

[somewhatfoolish]

thermionic valves = witchcraft.

[PhilA]

44 minutes ago, Zelandeth said:

That is an...interesting...power supply setup.  Definitely not something I've come across before, though granted I've never worked on automotive radio gear from that period.

There were some odd things around back then though.  Especially when mains energised speakers were involved, there were some "inventive" hum cancellation designs out there.

Then of course there's Philips.  They just seemed to take joy in going out of their way to design circuits doing very ordinary things in as different a way as possible to everyone else on the planet...much to the dismay of any poor service engineer! 

Fun times with vibrator power supplies!

Ours not to reason why. I just scoured the eBay for the 12V variants of those tubes, $55 was the best I could do for tested ones.

 

Phil

[PhilA]

Glad I re-evaluated what I was looking to buy because this set is a hybrid of "alternative" tubes.

 

What fun there is to be had with old stuff.

 

The people having the most fun appear to be selling the parts.

[PhilA]

A'ight, tubes ordered.

Hopefully in the next few weeks we'll have some music happening.

 

Phil

[Zelandeth]

4 hours ago, somewhatfoolish said:

thermionic valves = witchcraft.

Being honest, I find the three legged fuses called transistors far more baffling!

[PhilA]

5 minutes ago, Zelandeth said:

Being honest, I find the three legged fuses called transistors far more baffling!

Well, they're mostly doing the same thing. Kind of. 

 

The transistors I don't trust are the modern ones that are tiny and rated at many Watts. 

[mat_the_cat]

5 minutes ago, Zelandeth said:

Being honest, I find the three legged fuses called transistors far more baffling!

I recall repairing an inverter some years ago, where the transistors on the output stage had failed. Probably due to the inrush current required for a CRT TV, which dates it somewhat! I replaced what I assumed were thermal transfer pads (between the FETs and the aluminium case) with heat sink compound, not realising that the pads were for electrical isolation

They certainly lived up to their nickname of fire emitting transistors!

[PhilA]

The only thing that makes me a little sad about this is the tubes are all housed inside like metal cases for noise suppression.

This one, for instance, emits an impressive bright mauve glow when it operates (argon gas discharge) and the others you'd see the glow of the cathode heaters. The 14C5's are glass but the heaters on those are just a pin-prick of orange light on the top.

Being plate beam devices when you crank 'em up they do glow blue inside in time with the music...

 

Phil

[LightBulbFun]

45 minutes ago, PhilA said:

The only thing that makes me a little sad about this is the tubes are all housed inside like metal cases for noise suppression.

This one, for instance, emits an impressive bright mauve glow when it operates (argon gas discharge) and the others you'd see the glow of the cathode heaters. The 14C5's are glass but the heaters on those are just a pin-prick of orange light on the top.

Being plate beam devices when you crank 'em up they do glow blue inside in time with the music...

 

Phil

ya know i dont think iv ever seen one of those metal can tubes opened up before

interesting domed envelope, looks a lot like the worlds biggest fluorescent starter/starter glow bottle!

[PhilA]

21 minutes ago, LightBulbFun said:

ya know i dont think iv ever seen one of those metal can tubes opened up before

interesting domed envelope, looks a lot like the worlds biggest fluorescent starter/starter glow bottle!

You're not far off. That one is a cold cathode full wave rectifier. They're normally potted in, which is why you don't see them. This one isn't, it is just prevented from rattling with a paper wad inside.

Phil

[LightBulbFun]

17 minutes ago, PhilA said:

You're not far off. That one is a cold cathode full wave rectifier.

yeah, on that note id love to get a MAR, gawd knows where id (safely!) put it but id love to get one! 

19 minutes ago, PhilA said:

They're normally potted in, which is why you don't see them. This one isn't, it is just prevented from rattling with a paper wad inside.

ah interesting  

reminds I had a Halson 60-M Radio that had a very similar looking *ahem* "vacuum tube" that I quickly found out the hard way was actually a resistive dropper/ballast resistor after I poked it shortly after turning the radio off!

[PhilA]

Yup, those get quite warm. This only has one dropper, to bring 250v down to 200v. 2W 1.8k resistor in the bottom left of the chassis.

I was amused that the paper holding that one in looked rather like someone had stuffed a Ferrero Rocher wrapper inside it.

[PhilA]

Setting the bench up properly.

 

Discovered my Wavetek 159 is well out of spec so set about calibrating it. Need to drag the oscilloscope in and I don't have the enthusiasm for that now so tomorrow that can happen.

Fun fact, the Wavetek 159 can be controlled by the Commodore PET microcomputer.

I'll stick to punching the numbers in on the keypad.

 

Phil

[PhilA]

All set up and ready to go.

 

Phil

[busmansholiday]

That's an impressive setup there Phil.

 

I've got exactly the same...................

 

led torch!

[hairnet]

14 hours ago, PhilA said:

All set up and ready to go.

 

Phil

mad professors lair

[PhilA]

One piece arrived already. 

That's the equivalent of it being brought to the post office in Rome on Saturday afternoon and being delivered in Birmingham on Monday morning, regular mail.

Impressed with that

 

Phil

[hairnet]

14 minutes ago, PhilA said:

One piece arrived already. 

That's the equivalent of it being brought to the post office in Rome on Saturday afternoon and being delivered in Birmingham on Monday morning, regular mail.

Impressed with that

 

Phil

https://www.google.com/maps/dir/Rome,+GA,+USA/Birmingham,+AL,+USA/@33.8905551,-87.1094028,8z/data=!3m1!4b1!4m14!4m13!1m5!1m1!1s0x888aa4c0629e40fb:0x2850c5f9bcf31d2b!2m2!1d-85.1646726!2d34.257038!1m5!1m1!1s0x888911df5885bfd3:0x25507409eaba54ce!2m2!1d-86.8103567!2d33.5185892!3e0

not that far away

*nerd leaves

[PhilA]

The ground tang broke off the chassis lug as I bent it down so I improvised and made a new lug.

 

All fixed, reassembled. I tried hooking it up to a 9v pp3 battery and the output of the transformer pegged my meter set to 1500VAC so I would say it's working.

 

Phil

[PhilA]

I just dissected the volume and tone control.

You know the button on your HiFi marked "loudness", which generally tends to make everything sound a bit better all the way across the volume range?

Well, this radio has that, automatic loudness compensation. That's pretty sharp for an old car radio.

 

Phil

[Asimo]

Is that "loudness" done with a capacitor  tapped into a fourth terminal  into the volume pot's track?

[PhilA]

4 hours ago, Asimo said:

Is that "loudness" done with a capacitor  tapped into a fourth terminal  into the volume pot's track?

It is. The pot is split 25/75 and there's a capacitor on the upper and another plus a resistance on the lower.

Very basic but it works.