The radio is a Japanese AGS AM/FM, circa about 1964. This same radio was also sold as a Rincan, I believe. (I posted earlier about subbing a tube for testing. It was in very rough condition from laying in a damp crawlspace or similar for many years, and I didn't want to waste time on a dud.)
I procured the 12DT8 tube I needed, repaired a bad connection and cleaned pots and sockets. With new Pioneer speakers salvaged from a pair of car speaker cabs, the radio was performing nicely with excellent reception, and loud enough to rattle the windows!
I polished up the cabinet and did some rust removal,then tried the chassis back in the cabinet. After about 3 hours total of play, the volume dropped to about half on both AM and FM.
Here is the tube lineup:
Two 12DT8 for the FM converter,
a 12BE6 for AM,
two 12BA6 IF amps,
a 12AV6 detector and a 50C5 power tube.
We are still running the selenium rectumfrier but it is not bad yet. I haven't changed the filter caps, but I brought them up to voltage gently with a variac and there is negligible hum with good B+ voltage readings. The volume pot is quiet and I get a good response from it, but max volume is a fraction of what it was. Has one of the audio amp stages stopped working?

It sounds like a case of capacitoritis. I would recheck my B+ and while the set is playing, put your finger on any one of the numerous bypass/coupling caps in the unit. Check for heat. Failing this you will havw to drag out the silliscope and check waveforms.

Lou

:The radio is a Japanese AGS AM/FM, circa about 1964. This same radio was also sold as a Rincan, I believe. (I posted earlier about subbing a tube for testing. It was in very rough condition from laying in a damp crawlspace or similar for many years, and I didn't want to waste time on a dud.)
:I procured the 12DT8 tube I needed, repaired a bad connection and cleaned pots and sockets. With new Pioneer speakers salvaged from a pair of car speaker cabs, the radio was performing nicely with excellent reception, and loud enough to rattle the windows!
:I polished up the cabinet and did some rust removal,then tried the chassis back in the cabinet. After about 3 hours total of play, the volume dropped to about half on both AM and FM.
:Here is the tube lineup:
:Two 12DT8 for the FM converter,
:a 12BE6 for AM,
:two 12BA6 IF amps,
:a 12AV6 detector and a 50C5 power tube.
:We are still running the selenium rectumfrier but it is not bad yet. I haven't changed the filter caps, but I brought them up to voltage gently with a variac and there is negligible hum with good B+ voltage readings. The volume pot is quiet and I get a good response from it, but max volume is a fraction of what it was. Has one of the audio amp stages stopped working?
:

If reception is still good, then yes an audio problem.
Check the B+ on the plate of the 12AV6. This radio could use a total re-cap job. This includes the filter capacitors. Also this set being in a damp spot for storage, could now have the silver mica migration problem in the IF cans. The detector side may already be leaking, that's why low volume.