Hi Guys,
Does anybody know where I could find a schematic for the little STC C-141 radio. I have the A-141, B-141 and D-141 schematics which all differ greatly. The set I'm working on has had some oddball mods which I would like to correct and put right. Thanks in advance.
Dave

Kev Chant's site:

https://www.kevinchant.com/stc2.html

Thanks GTC,
Kev's site was my first go to, but I can't see one for the C variant.

I've emailed you the schematic and notes.

Received. Thank you Sir.

Had dealings with one of them in 2012. It was green & had a cracked case. I took pics of it. I still have the pics and there are pics of the inside of the pan. Sent photos to Brad (there are more)

I have the AORSM circuit I referenced to.

Did find some real interesting bugs in it

Marc

Thanks Marcc,
The set is quite original, but has had a replacement power tx fitted at some stage along time ago. There are just some strange mods inside that I want to correct. A screen resistor and large bypass cap (0.5mfd) has been fitted to the 6V6 and it has a 6v light globe in series with the choke. These are the 2 obvious ones, just not sure of any others. As I said, these are old mods, so I can only assume the radio was working fine.

The globe is interesting? I still use them as a Barretter. There is a "No Break" I made, here, and a globe is the current limiter to protect the PSU when the battery is run down. Metz did that with NiCad battery packs for their Flash guns. They had a "lilliput" size series barretter, as NICad could actually reverse polarise and the Barretter stopped the transformer etc. from being fried. Even with the pack presenting as a dead short (clever).

I would suspect that screen resistor is not a "willy nilly" thing to be messed with, without investigation. Check the Plate voltage: If with the new transformer, you have 315V plate (which PYE often did & applied it to the OP transformer body) then the 6V6 screen has to be dropped to 225V; Rendering it a quite legitimate mod.

The panel mount resistors would be ideal as a voltage dropper however there is always the option of choke input filter, or cutting down the size of the input cap as a means of lowering volts.

Some 6X5 variants had a terrible habit of going short and that was the demise of many transformers. I will tend to follow one AWA set and put 100 Ohm 1/2 Watt resistors in series with the plates. I.e. resistors "sailing with the wind" so they act as fusistors & fry instead of the transformer (not the only reason those resistors were there).

Marc

Thanks Marc,

The new Transformer has a slightly higher output voltage giving a screen voltage of 230V on the 6V6. Voltages across the board are around 10V above whats specified. The "fitted" screen resistor was 100k and bypassed with a 0.5mfd cap. so I don't really what thats about. I'm not sure that the previous repairer was overly knowledgeable though. The paralleled 30kohm resistors in the schematic (R10-R11) had been replaced with 1x 60kohm instead of a 15kohm resistor.

The light globe, I'm just not sure about. Other than adding some extra resistance between the centre tap and the chassis which is set by the choke. I didn't go into it too much other than running up the set with it in place which performed normally without it being lit.

A good idea with the 100ohm resistors on the 6X5 plates. A probable cause of the previous transformer failure.

I have the radio up and running well. It's quite a lively set and after an alignment, it's one of my better 4 valve reflex performers. For what ever reason, has a good immunity to the local electrical interference that many of my other house receivers succumb to.

Dave

I did try to reply early in the day & late, but this site seems to have big issues.

It is amazing how well many sets perform when brought into specs. Some repairmen did have a habit of fixing things with whatever was on the bench. I had to replace every Plate resistor in the RF on an American Midwest (16 Valve) and everyone of them, plus other bits were on tag plates in the IF & other cans. the cap count was around 64 or so from memory. Only autodyne sets I had seen with a separate RF exciter which is Colpitts.

If decoupling is good, a lot of crap that rides on the mains, gets killed, & chokes & field coils also help immensely. The globe still sounds odd, perhaps there was some weird idea that it would make a Barretter to save the transformer: Wattage would have to be critical (like mine & Metz). Fusistor would be much more predictable. Too much I squared R, can be useful for creating one. Its like never increase the wattage of a back bias resistor; fix what caused it to fry.

Marc

" For what ever reason, has a good immunity to the local electrical interference that many of my other house receivers succumb to."

I have been fixing an AWA Champion (failed on/off switch on the tone control) and soaking it while doing things on my computer. To my surprise it plays Sydney AM stations while next to the PC without noise from the PC, whereas my normal radio, a PLL AM/FM/DAB+ can only be operated at least 2m from the PC and 1m from its power supply.

Your reply answers my go figure Marcc.