Flakes

Hi there

I am trying to find information on a battery set that I have picked up.
It is an STC 511 "D". I have looked at the AORMS lists and it is not listed.

Does anyone out there have any info on this set. I am after the Voltage for the A and B supply, Frequency of the IF and any other relevant information that people might have.

I have tried looking through the net but I can't find anything that looks like it. The only thing I found was a STC 511 witch is a mains powered set.

My valve line up (Well according to the Layout sticker!) is as follows:

1P5G, 1A7G, 1P5G, 1H5G, 1Q5G
(I cant read the valve types at the moment as I haven't stripped it down yet.)

It was probably made around 1941.
The Chassis was/is type 511

The type 510 batt set is NOT the same!

Thanks

Daniel.

STC830

Hello Daniel

Can you read the ARTS&P prefix letter? This will set the year of manufacture.

550P and 258G have the same line-up
http://www.hws.org.au/RadioHistory/manufacturers/STC.htm

Graham

Marcc

http://www.thebakeliteradio.com/Circuits/STC/

Try the above, but agree that pattern does not fit the cloth.
I would before speculating, look at the valves and see what they are.

The numbers on those valves mentioned tell me they are octals and may actually be pre 1940 as thats when the minatures started to appear.

These are 1.4Volt filaments designet to run off a dry cell. These are still available at some Hobby shops as they are used for the glo plug on model aeroplane motors. Do not even think about using 2V. "D" cell yes.

Looking at the valve specs I would not see the HT being above 90V. The filaments are polarised and should be taken into account as they are often part of the bias. Pin 2 of 1Q5 is F+ use that as a guide.

The set may have "C" Batteries or be back biased. We need more info.

I say that as I have had to repair the damage on an Airzone (in Silicon Chip) which was caused by cooking the back bias.

Marc

Flakes

Ok....

The set is from 1941

I have checked the valves. All correct ones in correct places

It has had a recap by someone in the past....

The set is ALMOST! dead.

I hooked it up to my battery eliminator (1v and 90v) and all you get is static at full volume as the gang becomes closed. There is NO shorts in the Gang!

Do you have a copy of the 550P or 258G?

I have also tried tuning the valve set across the band with a transistor set near by. I cannot get any interference sound in ether radio.

I am lost at the moment without a diagram as what i find is a complete mess. All the wire is green and twisted around itself and other components.

I have made sure that i got the polarity of the connections right before i applied power so I haven't blown it!

Thanks

Daniel

STC830

Daniel

One is '40/'41, the other '46


1940/41 550P DW Portable 5 455 1A7G, 2*1P5G, 1H5G, 1Q5G AORSM '40/41 302 AORSM '46 328

1946 258G 258 Bat. DW Con. 5 455 1A7GT, 2*1P5GT, 1H5GT, 1Q5GT AORSM '47 432 TMRSM 94 49/7/0

I only have '37 to '40/'41.

I can send by email or send to Brad to post.

http://www.southcom.com.au/~pauledgr/STC.htm
(how old is your radio at bottom of page) says 511D is not in AORSM, but does say it is a battery radio, 1941, 455 IF.

Graham

Flakes

Hi Graham

Amy info on them would be of a help. Please send what you have so i might be able to sort this out.

Thanks

Daniel

flakelartpg.com.au

STC830

OK Daniel, sent.

Marcc

1V on the filaments is too low, there may not be enough emmision for the oscillator to start , yet alone other valves to run properly,

If it was recapped with paper caps, they will likely have to go, I have had two Midwest's pass through this year, that are now on their third (at least) set of caps.

Any electrolytics should be treated as suspect if they are older types. Static tends to indicate its audio may be working to some extent.

Be careful, with some power supplys earthing the set to mains earth causes them to go haywire. Use a 0.01 cap to mains earth. That includes the antenna.

Marc

Flakes

Hi

Is it possible that STC produced kits (or Kits were made using STC parts) the Front end of my set dosnt resemble the cct that you sent to me.

I have been looking at RT&H dvd that i got a while back and have discovered what looks to be a closer match for the converter / IF amp. It is called 1941 portable set from Jan 1941.

My set uses the detector and audio amp that is in the STC but the front end is almost the same as the RT&H design.

Still... I cant get the thing to oscillate, I think that i might have a crook 1A7G?

Not having much fun!

Flakes

Has Anyone got any more info on this set, I can't be lucky enough to be the only person to have one?

Is it possable its a kit or just a limited run made by STC?

I am going to draw up a full diagram this weekend.

I have even borrowed a sig gen to try and help me find why it wont osc.

Marcc and STC830 (and others) where will the best place be to start with it?

thanks

Daniel

STC830

Daniel,

There a number of portables at
http://www.hws.org.au/redlands.htm
Hopefully it is one of them.

Another STC 1941 portable at http://www.southcom.com.au/%7Epauledgr/STC.htm

Can you please post a pic.

Graham

Flakes

Photos Here: Image Link

In the photos
1. The knobs are just some that i found in my bucket.. I know they are not the right ones. (If you have them and want to part with them let me know!)

2. Photo of the sticker on the back clearly states its a Code 511. THe valve positions are as marked

3. The speaker is a perm mag one and the cct was designed to have this because there is no HT connections like the ones with the electro magnet. this can be seen from one of the bottom shots of the Chassis.

4. Chassis Photos. You can see that it is complete and very tidy from above. Under is a completely different story!

5. I have replaced the 25μF cap that is across the 50Ohm bias resistor (this is the only electro in the set!)

6. All coils check out ok with my multi meter (Well DC anyway!)

I will try and draw up a diagram but things don't make sense. When i got the set the 50Ohm resistor was disconnected from the Speaker socket therefore no bias for the audio output valves.

I think there might be a cap in the wrong position done by someone who didn't know what they were doing.

As I don't have a valve tester or a spare valve I cant check out the 1A7G.

Marcc

Pentagrids are not renown for being reliable.

Make sure that you use a filament voltage of 1.4 to 1.5V and polarity is correct.

Compare the circuit to a 510. All that is different is the output valve, the circuit may well be the same up to there?

Check the screen divider resistors have not gone high on the converter.

What drew you to the conclusion that the oscillator was not working?

Marc

Flakes

I think that it is not oscillating because you only get sound when the gang is almost fully meshed. All slugs have been played with.

The cct is completly different. It has the 1P5 as a RF stage before the 1A7G, then the 2nd 1P5.

Drawing it up makes no sense. for example. The L.O. dosnt seem to be connected in a way that will make it oscillate. Maby i just cant follow what is happening in it.

I thought it was similar to a cct shown in RT&H Sept 1946 (page 39) but from what i can tell it is a little different because my set has an areal coil that connects the Loop antenna to the first 1P5.

Any Ideas??

Flakes

I think that it is not oscillating because you only get sound when the gang is almost fully meshed. All slugs have been played with.

The cct is completely different. It has the 1P5 as a RF stage before the 1A7G, then the 2nd 1P5.

Drawing it up makes no sense. for example. The L.O. dosnt seem to be connected in a way that will make it oscillate. Maby i just cant follow what is happening in it.

I thought it was similar to a cct shown in RT&H Sept 1946 (page 39) but from what i can tell it is a little different because my set has an areal coil that connects the Loop antenna to the first 1P5.

Any Ideas??

Flakes

I think that it is not oscillating because you only get sound when the gang is almost fully meshed. All slugs have been played with.

The cct is completely different. It has the 1P5 as a RF stage before the 1A7G, then the 2nd 1P5.

Drawing it up makes no sense. for example. The L.O. dosnt seem to be connected in a way that will make it oscillate. Maby i just cant follow what is happening in it.

I thought it was similar to a cct shown in RT&H Sept 1946 (page 39) but from what i can tell it is a little different because my set has an areal coil that connects the Loop antenna to the first 1P5.

Any Ideas??

Marcc

It's a Superhetrodyne if the oscillator is not working you will not get anything. This rather suggests it is.

The audio output from these sets is not much more than a quarter of a watt, so it will not blast you out of the room.

I would suggest that the majority of the problem is manifest in "tweedle dee or tweedle dumb" stuffing up the IF transformers and everything else by screwing the slugs.

In order to sort this out you are going to have to work backwards through the set. It would appear that the audio is trying to work, inject a signal (not big) into the centre of the volume control. Do be aware that those resistors with caps do fail and I would still recommend rough checking them.

If its high in circuit, unsolder one end & check it properly; it probably still will be high. I normally check these as I do the caps (saves work later).

Once you are confident the amp is working then start aligning the IF's. That is always done last one first. I would suggest things will improve from there.

Check the outside plates of the tuning gang rotor, they are the normal ones to get bent. A bent oscillator one that is shorting will kill it. Lack of emmission and voltage or a weak valve will also see the oscillator die at high frequency.

Marc

Flakes

Well So Far...

I have checked the tuning gang. Its fine with no bent or rubbing plates.

I set the frequency gen that i borrowed to about 550KHz with AM tone modulation and was able to get a tone eventually out of the speaker by adjusting all the IF coils one at a time.

Now for the strange part..
I varied the frequency out of the gen a bit and the tone went away like it should. This is where it gets strange.... The position that I left the dial of the gen output was set at 450KHz By pure fluke! I started to get radio signals to tune over the band as i varied the radio tuning.

I switched off the tone part of the gen and now i am able to tune stations.... BUT ONLY WITH THE GEN SET TO 455 ish. If I turn the gen off the signal dies. if I vary the frequency of the gen I can make the signals completely die or at a certain point they come in strong almost to distortion. but when at this particular frequency i can't get any other station. I have to set it back at 455 again to find another station. Then you can vary the frequency gen at a completely different frequency to make the station die and then stronger. Returning the frequency gen to 455 allows tuning across the entire band pulling in stations weak but able to be heard.

Does this mean that my local oscillator in the radio isn't working and i have a dead 1A7G or something around the LO coil is wrong. The coil looks good and meters out ok with dc meter.

The way I hooked up the gen was to the antenna with a 0.05μF 400v cap (Just what i had sitting on the bench at the time).

Any ideas???

Marcc

The IF is likely 455KHz. There is a procedure in the Astor section of AORSM's & a couple of others.

In order to get the IF's back on track you need to put the signal into the last IF first and get it right before moving backwards to to the first one. Astor normally put the signal into the grid (cap still on) via a 0.01mfd cap (15- 50mW) They only use 200pF on the antenna.

Sort the IF coils out first. I normally use a CRO as that enables me to see the resonant coupling. The CRO would also show the oscillator to be dead or alive. You can also use a transistor radio of the same IF close to the oscillator and see if it can pick up the signal. the two will hetrodyne as the Gang is swung. If the oscillator is running.

It is likely that the oscillator coil has been "adjusted" and will be way off frequency. That is usually set with the dial at 600KHz.

If the set only tunes with the sig gen and a signal cannot be found with the transistor radio. Then start looking at everything around the Converter. Voltages resistors dry joints etc.

See how you go.....

Marc

Flakes

Thanks for that.

I will look tomorrow and get back to you. I dont have a spare valve. Do you know of an alternate that might do the job (i dont mind changing the heater voltage just for this valve to test and see if the set will work) All valve heaters are in parallel at the moment and i will sort something out if needed.

Marcc

The battery valves are not that easy to come by. A 1B7 has the some pin outs & filament voltage. needs slightly more screen current.

Heaters will have to stay in parallel. The fact that the sig gen causes signal to go through would cause me to suspect components first and valve last.

Check the oscillator coil as well, often when components are changed the fine wire gets broken at the lug. It could also have corrosion damage. I have seen as many as three coils lost in one radio, due to that.

Marc

Flakes

Hi Marc (and others that have helped)

Its been a while but I thought I would let you know. I have changed out ALL resistors in the set after one of them fell apart when trying to take it out to test. This still didn’t fix the radio. I tried looking at the LO with my CRO but couldn’t find anything happening. I then went to the multi-meter again to see a voltage but nothing…

I finally got a hold of a 1A7G. Put it in and now the set is working very well.

I set up the IFs using the sig gen that I borrowed to 455KHz using the method you suggested above and now the set is great (well as good as a 1940 battery set can be)


With a working set I got out my meter and as soon as I put it near the LO pins of the 1A7G the set stops. It is a decent digital meter so I thought that it wouldn’t load down too much just goes to show that you cant believe your test equipment all the time!