A radio I am working on actually put a weird noise through the speaker even when its disconnected but bolted to the chassis. Has anyone experienced this and why?
I will add that the previous owner had made some really stupid mistakes like disconnecting a filement and one speaker transformer wire.

The speaker is disconnected electrically and made a weird noise?

Or, more likely, the radio is disconnected from power but briefly made a weird noise through the speaker?

More info please Tallar, I'm intrigued.

2nd attempt. Whole thing locked up.

As the set has been Monkeyed with, if you are going to have a ghost of a chance of sorting it, you are likely going to have to go and get a marker and systematically, check every node & terminal and what is on it; in order to exorcise its Demons.

It is never unusual to get an oscillation after you turn it off, due to instability. Do remember that the filters will take a finite time to discharge and the heaters will also be effective for a finite time as they cool.

Marc

Marcc and BringBackTheValve

The secondaries from the transformer were discconected as I was fault checking. The radio was switched on and I noticed a weird noise coming from the speaker . I failed to mention that one of the speaker tags was still connected to a tag strip on the chassis. I also noticed that one of the secondaries on the original output tranny was cut off close to the transformer. This leads me to believe he may have removed a wire to a feedback circuit. the radio is a STC Bantam A5140AV

Come to think of it I did discover one of the wires going to the speaker tranny was cut and roughly joined . I resoldered the wire and put heatshrink on it.
I am thinking that the monkey rerouted the wire. I'm at my place of work so the radio is not in front of me.

That number came up as battery in the AORSM disk, which has decided to chuck a hissy fit, like the floppy drive on the old one. However it will likely not chuck a hissy fit with the disk in it, as its XP.

The battery version is downright conventional with the usual suspects. There is no feedback of of the OP Transformer secondary however,
one side is grounded, that does leave scope for the Monkey to have added something.

This is why, despite the Illusion of time wasting and the ruination of exuberance: Time may be better spent at this point, going over the circuit & debugging it.

I have actually had a set with plate resistors of every generation of them, all wrong and downright frustration as the majority, with others wrong value and accompanied by dud caps, on ceramic tag plates which are part of the Hammerlund formers inside cans. The set had eighteen valves. Most of the caps had been replaced before & the mess left. No wonder it was about as stable as a bucket of weeping Gelignite.

Marc

Marc
One of the mods the monkey did was remove the filement ground wire from the 6ba6 and probably wondered why the radio did not work.

Marc
A question , which pin on 6ch6 should have the speaker tranny connected to it?
If you look it up on radiomuseum the schematics are for a mains set and its marked as A5140 on the schematics

Fascinating, that's an interesting choice of tube: Its actually a video output type. http://frank.yueksel.org/sheets/155/6/6CH6.pdf

Pin1, NC Dead pin; Pin 2 Grid one; Pin 3 cathode; Pins 4 & 5 Heaters, Pin 6 Internal connect, dead pin; Pin 7 Plate Pin 8 Screen G2; Pin 9, Grid 3 Suppressor.

Transformer Pin7 to Pin 8; Pin 8 to B+

Amendment I managed to get the AORSM circuit & its different than the usual they are feeding the OP Transformer direct B+ and running the screen at a lower voltage after the unreadable 3W R12.

Other STC circuits are often the same & may need to be consulted to see what it is.

6CH6 is extremely common in STC post-war radios. Nobody else seemed to use that valve though.

Another STC peculiarity is the use of a 12AH8 for the frequency changer stage.


I think Marcc meant that the transformer primary goes to pin7.