Pre-war amp, not sure of make

[thelonious_crunk]

Three terminals on speaker seems odd. I was actually wondering if this was a type of field coil speaker, but that would require four terminals I believe.

Yes it only has 3 on the actual speaker. The 4 prong cable is going to the OT where 3 wires are coming off to the speaker. Says 5999PP on OT.

[thelonious_crunk]

Right, that looks like a PP amp wiring, so the metal can tube should be a 6L6 as well.

The seller said the large 6l6 tube didn't light up. He said it worked a charm for years and years though and played by his father in law

[thelonious_crunk]

There are 3 of what appear to be identical cathode bias resistors. Two of them read 250 ohms, while one reads 230 ohms and leads to a 6SF5. Not sure if that one has begun to bite the dust.

Also looking for modern replacements for the large bias resistors, 200ohms "C 10 F", utah 3000 ohms, and an Ohmite Brown Devil 20000 ohms. Are these just like standard small resistors now?

But yeah...appreciate all your help so far. I'm pretty novice to working on amps. I am gonna carefully rewire it, recap, and reflow any cold joints since they are all oxidized. Also make fresh new spots for the grounds to the chassis. Just waiting for parts to arrive and will keep updated.

[vintagekiki]

little help

1)
little more help ... ...


the rest is a classic

2)

[Helmholtz]

There are 3 of what appear to be identical cathode bias resistors. Two of them read 250 ohms, while one reads 230 ohms and leads to a 6SF5. Not sure if that one has begun to bite the dust.
Also looking for modern replacements for the large bias resistors, 200ohms "C 10 F", utah 3000 ohms, and an Ohmite Brown Devil 20000 ohms. Are these just like standard small resistors now?

If resistors measure within 20% of nominal value, I'd leave them alone.
Larger sized resistors mean they have/require a higher power rating.

First targets should be to draw a schematic, get the amp working and do some measurements.

[mozz]

"Power transformer putting out around 39 ohms"
I'm taking that as you measured the resistance of the primary and it's 39 ohms. You need to measure the secondary too, it should be a few hundred ohms. Probably have to disconnect a wire because of components attached to it. I would also measure the filament wires as if a tube is not lighting up that may be a major problem. That will be less than 1 ohm usually. I'm saying it's a field coil speaker because they often use the octal plug just like this and run up to the speaker/field coil assembly.

[Helmholtz]

I'm saying it's a field coil speaker because they often use the octal plug just like this and run up to the speaker/field coil assembly.

So what do you think is the small transformer mounted to the speaker frame, where the 3 wires connect to?
Certainly not a field coil, which needs to be in place of the speaker magnet.

I don't see a need to measure PT winding DCRs at this point. Just pull the rectifier and measure PT secondary voltages.

[The Dude]

Aside from the PT, I don't see a second transformer as part of the chassis, so I was thinking the transformer mounted to the speaker must be the OT.

[thelonious_crunk]

Aside from the PT, I don't see a second transformer as part of the chassis, so I was thinking the transformer mounted to the speaker must be the OT.

The transformer on speaker reads "5999 PP". A similar if not identical Utah one on Google says its 12w

[glebert]

So what do you think is the small transformer mounted to the speaker frame, where the 3 wires connect to?
Certainly not a field coil, which needs to be in place of the speaker magnet.

I don't see a need to measure PT winding DCRs at this point. Just pull the rectifier and measure PT secondary voltages.

I am not saying that it is a field coil speaker, but the Rola shown on this page (http://djcarlst.provide.net/FieldCoi.htm) looks a bit like the OPs to me.

[Helmholtz]

I am not saying that it is a field coil speaker, but the Rola shown on this page (http://djcarlst.provide.net/FieldCoi.htm) looks a bit like the OPs to me.

Yes, looks similar indeed. But seems to use more than 3 wires. With only 3 wires the field coil would have to be in series with the CT, what would cause a lot of sag.

But it's easy to find out if the speaker carries a permanent magnet or a coil: See if it attracts a screwdriver.

[The Dude]

My question would be: If it's not the OT, then where is the OT? I don't see a 3rd transformer in the amp. At any rate, it should be simple enough to figure out by simply looking at how it's wired.

[Helmholtz]

My question would be: If it's not the OT, then where is the OT? I don't see a 3rd transformer in the amp. At any rate, it should be simple enough to figure out by simply looking at how it's wired.

I never had a doubt that it's the OT. But the question is about the speaker magnet: Permanent or solenoid.

[vintagekiki]

Testing of an unknown transformer

It is enough that the two near turns are in mutual short-circuited, the DC primary resistance will be 39 ohms, but the transformer will be hot and the primary fuse will be blow.
The transformer is tested "upside down" by applying 6.3V from another transformer, to 6.3V connector transformer under test (TUT) and measure the voltages at his connections.
If the bulb light, it is a sign that the TUT has turns in mutual short-circuited.

Attention
On transformer under test, dangerous voltages appear.

[thelonious_crunk]

Yes, looks similar indeed. But seems to use more than 3 wires. With only 3 wires the field coil would have to be in series with the CT, what would cause a lot of sag.

But it's easy to find out if the speaker carries a permanent magnet or a coil: See if it attracts a screwdriver.

No magnet! Does it become magnetized when powered on?