Will it last?

[jnew]

Might kill the speaker but!
So what I've done is take my old 4X10 Marshall cab and make a new baffle to run two of the 10"s on top with 1 12" centered in the bottom. Pretty blown away at how good it sounds. I had a Vintage 30, 12" and liked it a lot but then put one of Jim's 20 watt PVC, Greenie type in. What can I say? I'm a Greenback kind of guy and this thing smashes so friggin nice. I'm just wondering how much I'm pushing it though. The PVC is 16 ohms while the two 10's are 8 ohms each. So you get the idea right? An 8 ohm cab but the PVC is seeing half the wattage which is dangerous business. But some other things going on, might let it live. For example, I am running a variac on the amp which is set at 85VDC. (50 watter BTW) But using a JTM-45 re-issue PT. Plate voltages are like 250. (really low) Amp screams but I think its output is far less than what a typical 50 watt would do. Is there a way to measure the output of the amp to get an idea of how close I may or may not be to killing the speaker?

[Lefty Lou]

Will it last? You've got one weird speaker impedance there chief. I suppose you could wire the three 8 Ohm speakers to 2.7 Ohms like the rare 57' Bandmaster (or Vibro-King amp) with 3 x 10"s, and use the THD 2.7 Ohm Hot Plate and feel completely comfortable with running the amp as you are now.

[jnew]

Whaaa?

No, the cab is 8 ohms total. The 12" PVC speaker is a 16 ohm and the two 10"s are 8 ohms each. So the two 10's are in series (16 ohms) and then those are paralleled to the 16 ohm 12" speaker. 8 ohms total. So resistance isn't the issue. Just concerned that the 12" rated at 20 watts will be ok. The 10's are 35 watts each but they're dividing up half the wattage of the amp. So roughly 25 watts to those (no problem there) and roughly 25 watts going to the 12" PVC (rated for 20 watts ) If it dies, I guess I could just send it back to Jim and have him re do it in a 60 watt. Or 65? Whatever his spec is. But so far, it lives. And sounds facking awesome.

[Scumback Speakers]

Animal. Living on the edge of power handling can burn you, sir! LOL

Let me know if it sputters and sparks out on you, sounds like you're testing the limits!

[jnew]

Indeed I will. In fact, you'll be the first to know.

[Lefty Lou]

Whaaa?

No, the cab is 8 ohms total. The 12" PVC speaker is a 16 ohm and the two 10"s are 8 ohms each. So the two 10's are in series (16 ohms) and then those are paralleled to the 16 ohm 12" speaker. 8 ohms total. So resistance isn't the issue. Just concerned that the 12" rated at 20 watts will be ok. The 10's are 35 watts each but they're dividing up half the wattage of the amp. So roughly 25 watts to those (no problem there) and roughly 25 watts going to the 12" PVC (rated for 20 watts ) If it dies, I guess I could just send it back to Jim and have him re do it in a 60 watt. Or 65? Whatever his spec is. But so far, it lives. And sounds facking awesome.

Apparently I need some new reading glasses however, as you've said the impedance issue is really a non-issue. I defer to Jim of course (being he's the resident speaker guru), just don't like the idea of low efficiency speakers being driven by higher efficiency heads. Like many guys here on the forum, I'd most likely be running (2) 4 x 12" low efficiency speaker cabinets using an attenuator and a Lar/Mar PPIMV installed in my head, if my tastes ran in that direction. Just for the speakers and transformers sake, I'd always be using at least 65 watt rated speakers with a 4 X 12" cabinet and a 100 watt head (or should I say a 160 watt to 170 watt head). Even then I wouldn't be running the heads flat out, but that's just me. BTW, I have a JTM45/50 amp that Jack McCallister of Mouradian Amps built for me with the JTM45 PT and JTM50 OT and depending upon whether or not you are using tube rectification as opposed to SS rectification also would come into play. Naturally you'd be a little bit safer using a GZ34 in this instance as opposed to a bridge rectifier.

[jnew]

Yeah, I think power wise, I might not be risking as much as I think. The PT is a JTM-45 re-issue from 1990 and the OT is a MM's 045RSL. And yes, also using a GZ-34 tube rectifier. So probably not a true 50 watter. In fact, I think the old literature on the JTM-45 RI's said something along the lines of a 30 watter so who knows. We'll just see what happens. If I smoke the speaker, no big deal. Need an excuse to get down and play a round of Golf with Jim anyways.

[Lefty Lou]

Yeah, I think power wise, I might not be risking as much as I think. The PT is a JTM-45 re-issue from 1990 and the OT is a MM's 045RSL. And yes, also using a GZ-34 tube rectifier. So probably not a true 50 watter. In fact, I think the old literature on the JTM-45 RI's said something along the lines of a 30 watter so who knows. We'll just see what happens. If I smoke the speaker, no big deal. Need an excuse to get down and play a round of Golf with Jim anyways.

Yeah, you're looking at like around 38 watts max. Go out and play golf before everything ices over!!!!!

[jnew]

Maybe not even that as I'm running the variac at 85VDC. It's probably pushing it but WTF, right?

[Lefty Lou]

Why the heck not?