Hi
I am working on an STC Model 141C, I cannot find the exact schematic for this C variant of the STC 141. I have been on both Radiomuseum and Kevin Chat's sites but to no avail.

I noted in my search that a few years ago our supportive member GTC emailed one to someone who was also looking for this schematic.
If it not too much trouble I would appreciate receiving a copy of this, I assume my email is unhidden and I will check now and hopefully unhide it.

Though this Radio is working it does not have much volume, on checking the voltages it appears that though the Transformer is providing the correct voltage to the Anodes of the 6X5 the B+ is close to half what I would expect. The Electrolytics look like they were recently replaced and the choke read about right in DC Resistance about 260ohms. So, I would like the correct schematic to help me track why the voltages a low.

Thank you, George,

The schematic is in the AORSM volume 6.

I'll send a copy of the STC manufacturer sheet to Kevin Chant and post a link here once uploaded.

That way it can be shared with anyone who is interested.

There is no guarantee, that the filter capacitors are the correct ones, nor wired correctly. It is therefore not a good idea to run it.

They seem to have been playing Ducks & Drakes, possibly due to war time supplies. One model has a 6A8 pentagrid another 6K8 another 6J8

and then there is the output tube. 141C should have 6A8 and a 6V6; choke is in negative.

Looks like a "reflexed" set B+ at 6v6 plate around 220V

I have all four circuits.

I guess on this low end model the same dial would be used for all three mixers mentioned, so that tracking may not be accurate depending on whether it is 6A8, 6K8 or 6J8.....
Is this the case, or does the fact that there are different model numbers mean that a different dial was in fact used, or some other modification to help with tracking depending on the valve?

Thanks, Monochrome TV,
I do not have the AORSM Volume 6. So, appreciate you sending it to Kevin for all to share. I look forward to our confirmation once it is uploaded.

Marcc,
It is a reflexed circuit, with a negative choke, the valve lineup in mine 6AG8,6G8G,6V6G and 6X5G which is correct for the C variant and 141C is stenciled on the chassis.
I am not that familiar with Reflexed circuits, which is why I would like the exact schematic for this model.
I also do not intend to run it until I have the schematic and address the low voltage B+

STC830,
Not sure if they did vary the dials for each variant and will check this more closely as I have a 141B as well, which I have not looked at as yet it has been worked on by someone else as it was described as restored when I purchased it a year ago.

All of those pentagrids will run in the same hole. However due to design, there can be band spread variances. So, I would guess that the part numbers of the RF coils & perhaps dials, are different. 6A8 is the most unstable and 6K8 usually has an 8mF cap on the oscillator plate to stop it "fluttering" (RCA).

In an Astor JJ and some others, if you substitute a 6A8 with a 6J8, it will compress the band and you may find yourself listening to an Aircraft NDB at the low end.

In the reflexed circuit, the 6G8 is actually amplifying RF as well as audio, that saves one tube. Do be cautious with modern caps around the 6G8 as that is an area where serious radiation & induction along with lead dress & shielding can cause destabilisation.

With a tube like 6G8 some DVM's will not like it. The analogue meter will not see RF, but some DVM's will and give a wrong reading. There have been cases where the RF has caused a DVM to flashover internally. So it is important to note if it can handle RF.

Do note that some front end Oscillator & Antenna RF coils have mysterious, often unmarked Mica caps on them. Do not touch. They are there to get the coil into spec during manufacture.

Here is the link to the service document.

https://www.kevinchant.com/uploads/7/1/0/8/7108231/stc_c141.pdf

While one needs to check all resistors, as you get rid of all the electrolytic and wax paper caps; R12, 13 & 14, have an attrition rate and are usually out of spec.

Thanks once again MonochromeTV, for the schematic. Thanks Marcc, I always check all resistors but I will look closely at R12,13 &14 and most likely change them.

I usually find that if you sort out any bad wiring, resistors & caps, after making sure the transformers are ok. They normally, for me, have better than 95% chance of firing up & then revealing the niggly faults.

Rather unusual set, with the filter choke being in the earth circuit. Still, I guess it must be ok in theory.

Good luck with the repairs.

One theory says it keeps the HT off of it & more reliable? I have seen sets with one in HT and one in earth.

I do love it, with this sort of arrangement, it usually causes absolute havoc on a forum I am on. It gets lots out of their comfort zone and causes utter confusion, as to which way, or where the filter caps go, polarity wise.

Talk about getting out of the comfort zone: Its incredible.