Pro Reverb 1x15

[lowell]

Anyone know about these? I do not see a schematic w/ a 1x15 anywhere. It's also a silverface w/ master volume. The speaker in here is not stock and it's a 15" 8ohm. I'm trying to replace it w/ a better speaker but the chassis says "4 ohm load." Any info on this? I was gonna get a Eminence Big Ben 15" 8ohm for it.

[JoeM]

Does the part number on the OT match the 2X12 Pro Reverbs OT number?

[lowell]

Yes it is 022848 which is in the list of possible part #s. However what does that tell us? There are no specifics as to what OT # is for what speaker configuration.

http://www.webphix.com/schematic%20h...-bmstr_rev.pdf

[JoeM]

The schem you linked to shows the Pro Reverb and Bandmaster using that OTconnected to a 4 ohm load. I've never seen a Pro Reverb with a 15". I believe that OT is 4k with a 4 ohm speaker load.

http://www.mouser.com/ProductDetail/...XlCgZp1zEEpUJ0

[lowell]

Hi okay. So I have a question that is probably asked a lot on here. I understand how OTs function like gears, matching the high z of power tubes' plates to the low z of a speaker. I also understand how in a solid state amp with no OT, the speaker load can largely determine output power. In tube amps however I don't think that this is the case. Maybe the effect of a larger secondary load may reduce highs a bit, but not reduce power so much. Thoughts? I'm just thinking it may be okay to put this 8ohm speaker in here. (the 15" in the amp now is also 8ohms)

[g1]

It is still the case for tube amps. You will get maximum power transfer when impedances are properly matched. You can see it by measuring output power into dummy loads of different resistances. You will get less power to a mismatched load. That being said, typical (older) Fender setup is matched when the internal speaker is used, but mismatched when you plug a second cab into the ext.spkr. jack.
I would be inclined to go with the stock 4 ohm value so the amp is delivering full power, however if the owner finds the amp "too loud" and would prefer less power, then the 8 ohm would be an option, the caveat being that in my opinion the Fender OT's are robust enough to handle the mismatch.
Also, in the case where the owner always uses an ext. spkr., it may be desirable to run an 8 ohm in the cab along with an 8 ohm ext. spkr., so once again the amp delivers full power into the load.