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 STC Model 562 Restoration Chassis.
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 Return to top of page · Post #: 31 · Written at 9:33:22 AM on 4 July 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3967

There are stand alone capacitance & Inductance meters which also measure DC ohms.

There are traps with voltmeters and some modern equipment as they are not designed for Valve radio & High voltage in general. Some digital's are incapable of handling RF and are confused by it, or can catastrophically flash over due to it. You need to be very careful as to what you buy.

Because of the way they operate they are hopeless with fluctuating, dirty input. Also be aware of what was used to measure voltage originally. Most of the good circuits tell you what type of meter was used. The analogue meters load the circuit significantly (not B+) VTVM, Digital & high impedance meters don't: So they will read higher than the analogue and the higher the K of the resistor, the greater is the difference.

With that set having new caps only the correct capacitance & voltage rating is of significance. Mica cap failure is not as common as that of Wax Paper & Electrolytic types. The other thing I use for non polarised caps (No neg or positive) is an insulation tester with a range of voltages, to use for leakage testing them. An ohmmeter will only pick up a dead short. One end of the cap or resistor need to be out of circuit to test it (in most cases).

Check the circuit and beware: Some of those valves had filaments / heaters floating above the chassis & in some other cases that filament / heater winding was centre tapped. That means that the correct voltage is measured pin to pin at the socket. The dial lamps in a lot of them also floated & can be shorted to ground if you are not diligent. That can fry the transformer winding. Make sure the meter is on AC for that lot.

You can leave the rectifier out to measure filaments & heaters as that will avoid damage if there is a B+ fault.

No one said this was going to be simple: There is a learning curve & the faulty sets steepen it.

Be very careful playing with the rectifier. Its filaments float. If you power with it out. The big pins 1&4 will have 5V AC across them (bit higher off load) Pins 2 & 3 should have roughly the same AC volts to Centre tap. Measuring across those pins with a meter that cannot handle at least 1KV is looking for smoke.

N.B. Electronic equipment runs on smoke: If it escapes the device is more often than not: Stuffed.

The normal approach is to get the voltages right after you sort out the obvious defects. I normally run the IF alignment frequency through a set next, to see if the signal can get from the mixer to the speaker (is it working). One of the initial tests due to the attrition rate of speaker transformers is to crack a 9V battery across the primary of the OP transformer & listen for sound. pins 2&3 2A5 (plate & screen) set not powered.

Alignment requires a Signal Generator.

Did you get the circuits I sent?


 
 Return to top of page · Post #: 32 · Written at 9:36:08 AM on 4 July 2017.
Captgogo's Gravatar
 Location: Sydney, NSW
 Member since 22 May 2017
 Member #: 2114
 Postcount: 120

Hi Harold,
I did download the circuit from Radiomuseum you suggested seem identical to the one Lankshear used in his EA article of STC 1 Restoration that I had.
This one at least gives some values for Capacitors and Resistors .
Thanks George.


 
 Return to top of page · Post #: 33 · Written at 11:12:40 AM on 4 July 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1490

Hi George.

Simple voltage and resistance checks will find 99.9% of faults in old valve radios. And unless someone has been really fiddling with the IFs, you won't need a signal generator to do an alignment. Helps, but not essential.

This thing is so simple you don't need tools like a signal generator to identify the stage where the signal is being lost. DC voltages will do that for you in most cases.

As a kid I knew a "radio mechanic" who used nothing but his finger and a screwdriver to fault find radios. Listening to the noise made when touching a grid cap with a finger. Voltage measurement was done by looking for the size of the spark when you shorted a pin to chassis!

These things are REALLY SIMPLE compared to what I work with in my day job!!


 
 Return to top of page · Post #: 34 · Written at 12:51:48 PM on 4 July 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3967

Spark is good, I fixed an ignition coil tester a few years back & it measured EHT pass fail with a spark gap. Works on my electric fences as well.

These sets may be simple, but with these things you do have to be very careful as to where you put your fingers and beware of the limitations of the test instruments.

I had a look at the 56 in Lankshears book. As I expected 2A5 has a "Humdinger: arrangement so its heater voltage will be near half if you measure them to chassis: V3 same deal. Measure across pins.

He does give voltages in the second article.

What is of concern is the screen grid voltage and that is likely why there are two 500V Electrolytic's in series. On startup, with an #80 even that the bias train represents a loading B+ will surge to over 500V before the heaters cause the valves to conduct & pull it back to normal.

I would definitely put a voltage divider across those two per previous.

Note that I fix commercially & have equipment permanently set up for things like calibration so its easy for me to use it for fault finding as well: Time is money in a commercial situation; So my techniques will vary accordingly, but I do share them.

Ultimately 83V has to go if the AWA data is correct? Others say 2A?

Note to get reception that needs an external antenna.


 
 Return to top of page · Post #: 35 · Written at 10:21:39 AM on 6 July 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3967

I was going to post on the tube pinouts but the system died.

I believe these to be read wrongly.

The big pins are the heaters; Looking wiring side the left one is pin one & the first small one, pin 2 (normally plate) pin 3, Screen: Going clockwise. The big pin on the right is pin 6.

Grid one is actually the top caps of that lot and pin 4 of the 2A5. Cathode & suppressor 2A5, pin 5; Suppressor (g3) on 57 & 58 pin 4.

I believe this is now making radio noise, the bias train was incomplete. This open circuit due to a missing wire between the "candohm" resistor (tapped) & the volume control which is the path to ground


 
 Return to top of page · Post #: 36 · Written at 8:49:35 PM on 6 July 2017.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 878

Re the label: will put together an email and send it to you. Might take a few days as I am on the road at the moment.


 
 Return to top of page · Post #: 37 · Written at 7:35:44 AM on 7 July 2017.
Captgogo's Gravatar
 Location: Sydney, NSW
 Member since 22 May 2017
 Member #: 2114
 Postcount: 120

No problem and much appreciated STC830.
Regards George


 
 Return to top of page · Post #: 38 · Written at 8:02:09 AM on 7 July 2017.
Captgogo's Gravatar
 Location: Sydney, NSW
 Member since 22 May 2017
 Member #: 2114
 Postcount: 120

An Update, as this site as had quite a few outages, I gave up tying to get on for a few days.

But thanks to both Marc and Ian through direct emails, I am please to say that I have this wonderful Radio up and running with great reception and am thrilled that I did not need to do to much to get it going once the circuit was followed and a few missing links were connected.
I also replace the twisted wire to the dial globe as it's insulation was failing a and short was imminent and have done some other minor safety mods.
I have just finished cleaning it and getting the Dial turning smoothly.
I am waiting for an repo 3 core twisted lead to come in matching the original and I will put in a dedicated earth connection.

To anybody reading this that is looking to embark on a project like this and like for me it is your first project, with the generous advise on this site you will be surprised and thrilled and what you can do. I have learnt some much from the wonderful people this site, even things I had learnt many years ago and have since long forgotten.

I am looking for the unique chasis colour paint, even though it cleaned up ok, there is enough rust pitting to make it worth while to do partial touch up if I can match the colour. I do not want to make it look brand new that defeats the look and feel of this piece of history but just want to make it look a bit cleaner if that make sense.

I have now gone back to the Cabinet to finish the top with help from Vintage Pete, you can read my journey on this exercise in the General Discussion Forum.

Thank's once again to all of you and I look forward to kicking off another restoration soon.
George.


 
 Return to top of page · Post #: 39 · Written at 5:05:11 PM on 7 July 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1490

Re using paint to touch up the chassis rust - in my experience, this always looks bodgy.

If you aren't going to do a full strip-down, all parts off, sandblasting and either plating or painting, use automotive cutting compound. It will strip off the worst of the rust and pitting, cover it up with colour from what's already there and slow down the rust.

Depends on how bad it is, if you have mostly paint it's worth trying first.


 
 Return to top of page · Post #: 40 · Written at 9:32:56 PM on 7 July 2017.
Captgogo's Gravatar
 Location: Sydney, NSW
 Member since 22 May 2017
 Member #: 2114
 Postcount: 120

I take your point Ian, not sure if you can tell from the pics I have posted previously, most of goldish paint is still there, it has peeled of some of the valve shields and on the top at the back is where their is rust pitting but still some colour. The colour is hard to match so I am unlikely going to even try.


 
 Return to top of page · Post #: 41 · Written at 4:25:33 PM on 8 July 2017.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 878

Re the label info: Can't send emails where I am staying - some sort of authentication problem - so have to sort that out first.


 
 Return to top of page · Post #: 42 · Written at 5:01:51 PM on 8 July 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1490

Hi George

I just had a look at the chassis pics and I believe it's beyond cutting compound.

If you don't want to attempt a bare chassis repaint (big job) there is an intermediate option that I think would work for you.

1. Remove everything from the chassis that will come off easily. Valves of course, covers, coil covers, the ARTS&P plaque (it's held by small rivets) and the transformer cover. The tuning gang and dial only involves a few wires and screws so this too for preference.

2. Mask off valve sockets, coils and everything you won't want to paint.

3. Use a small rotary wire brush to remove the paint and rust scale on the chassis, keeping clear of masked parts.

4. Similarly wire brush the coil cans, valve covers and the transformer cover.

5. Spray everything with an automotive touch-up can, chosen to match the pinky-gold STC colour. I had little trouble finding a matching colour at a large retail automotive shop last time I did an STC chassis.

6. When it's dry, remove the masking and reassemble everything.

7. Stand back and admire!

That cabinet is or is going to look so good after Pete's input it'd be a shame to spoil it with a tatty chassis.

Tart up the speaker using the masking technique too. Tyre black makes paper speaker cones look brand new!


 
 Return to top of page · Post #: 43 · Written at 12:25:14 PM on 9 July 2017.
Vintage Pete's avatar
 Location: Albury, NSW
 Member since 1 May 2016
 Member #: 1919
 Postcount: 1311

Automotive paints are a good idea.
They come in 2 types in a Can.
If you buy Acrylic Auto paint the gloss level comes out of the Can on the Dull side and needs to be polish to bring it up. The Advantage to this type of paint is it looks old!
So you can buff it up or dull it off!
The other advantages are that auto Acrylic paint is Tac dry in minutes so it wont collect dust like Enamel and look dodgy! To give you an idea of this ,you can spray cars in the backyard with it and achieve high grade finish without a booth etc etc, I did it for years that way ,when Acrylic was the all the Rage before 2 pack.
Your rust will wipe off with a bottle Deoxidine, but only if your going paint it .
Automotive paint is a good way to go as Ian says .
Look for Acrylic though not Enamel .
Pete

Note that Deoxidine wipes rust off and neutralise it .but on some metals it can stain so only use it on parts that will be painted.


 
 Return to top of page · Post #: 44 · Written at 12:44:31 PM on 9 July 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1490

Be very careful about letting any liquids other than distilled water or metho get into valve sockets, IF transformers etc. Also be careful with any corrosive material and aluminium. If you use deoxidine it's very important to wash everything down afterwards with copious amounts of metho.


 
 Return to top of page · Post #: 45 · Written at 3:06:44 PM on 9 July 2017.
Vintage Pete's avatar
 Location: Albury, NSW
 Member since 1 May 2016
 Member #: 1919
 Postcount: 1311

Yes Ian, Thats correct I was thinking along the lines of the items that were being removed from the chassis for painting.
Not in the chassis because it needs to be washed out.
Deoxidine rust convertor is what we pre wipe any panels with in the car industry prior to painting them.
Now talking about Automotive paint and why its a good option,
I had to restore a $5000 1959 metal frame lounge for somebody and so I repainted it in acrylic automotive paint and after it was finished it still looked 40 years old, because acrylic you have so much control over the gloss levels ,yes it comes out of the can or gun low sheen, but you can just polish it up as you said to get that old look rather than it looking new.
Pete

The lounge I restore is the same as this one in the BEE GEES first ever TV appearance.
https://youtu.be/aQrvo50eTrg


 
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