crate paloino 50 impedance , how to determine?

[georage]

Thanks for reading. Can anyone help me to determine the proper or safe speaker impedance for a crate v50 212 made in vietnam version? i just picked up this amp and it sounds great, but i noticed that the speaker jack is labeled 8ohms and the actual speakers are indeed 4ohms (2 8's in parallel)
this amp has been modified by someone who did a very clean job of replacing 5 big caps and moving them off the board to a remote area of the chassis. they did such a nice job that i find it hard to believe that they would put a 4ohm pair of speaks in an obviously 8 ohm amp. the speakers are also branded crate v series and look origional.

[georage]

im sorry it is a palomino amp. i wish i could edit posts but its out there now.

[DrGonz78]

I would make sure he didn’t also install a different output transformer. And if they did you think they would re-label the output jack. Did it mess anything up?

[georage]

anyway, the amp had a problem reported by the previous owner that it would shut down while he was playing and then come back on....the power tranformer is labeled "resetable thermal fuse". if the power transformer overloaded, that would make sense of the previous owners problem.
idk how a mismatch of the ot would overload the pt, but thats where im at.....is the ot modified? or is the speaker wrong or other haha. sorry for such a long post.

[g1]

Do you have a means of measuring the power output with scope and dummy load?
If so, it will normally put out less power into mis-matched impedance.
Running 8 ohm amp into 4 ohm load would probably make it run a bit hotter, so that could open the thermal breaker in the PT.
But also check the bias, it may just be adjusted to run hot.

[Jon Snell]

Thanks for reading. Can anyone help me to determine the proper or safe speaker impedance for a crate v50 212 made in vietnam version? i just picked up this amp and it sounds great, but i noticed that the speaker jack is labeled 8ohms and the actual speakers are indeed 4ohms (2 8's in parallel)
this amp has been modified by someone who did a very clean job of replacing 5 big caps and moving them off the board to a remote area of the chassis. they did such a nice job that i find it hard to believe that they would put a 4ohm pair of speaks in an obviously 8 ohm amp. the speakers are also branded crate v series and look origional.

This amplifier is switchable either 4R or 8R. Move the switch to 4R.

[g1]

I think there are various versions of this model, some with switchable impedance, some not. SLM and Loud versions were different from each other, and there were single 12 and 212 versions as well.

[georage]

i do have a scope and a dummy load g1. there is no impedance switch, there are only one set of secondaries on the ot. This is the blonde 212 made in Vietnam.

[g1]

i do have a scope and a dummy load g1. there is no impedance switch, there are only one set of secondaries on the ot.

What is your dummy load impedance? See how much power you can get with a sinewave, just before the output starts clipping.

[georage]

after a lot of searching old reverb ads and the like, im pretty sure the speakers are wrong. it looks like these speakers came out of a crate v50 with 8-16 ohm impedance in which the 8 ohm speakers are wired in series and there would be a ext speaker jack. It looks like the speakers that came in the palomino 50 said Palomino on them, not crateV. There are also a few different palomino 50 amps out there. some have el34s and some have el84s.

[georage]

my dummy load can do 4 8 and 16, G1. how do you calculate wattage with a scope? I understand reading the output voltage and what clipping is. Would that work like this? measure peak voltage just before clipping and divide by 4 or 8ohms to get amps them multiply by volts to get watts? How would that tell us if the amp can handle a 4 ohm load or not?

[Jon Snell]

The easiest way is to put a known load on the amplifier, say 8R.
With a signal generator set to 1kHZ sine wave, turn the level up until 8volts of signal is across your load, then switch to 4R. If the signal level stays the same, it is a 4R tapping, if it reduces, it is either 8R or 16R. Set to a 16R load and repeat, if the output signal stays the same, it is an 8R tapping.

[g1]

my dummy load can do 4 8 and 16, G1. how do you calculate wattage with a scope? I understand reading the output voltage and what clipping is. Would that work like this? measure peak voltage just before clipping and divide by 4 or 8ohms to get amps them multiply by volts to get watts?

You can do it like that, but first convert the peak volts to RMS (peak times 0.7). Or if you are working from peak to peak, divide by 2.8 to get RMS.
You should find that with one of the load impedances you can get more power before clipping, that should be the correct load impedance.
I myself use the E squared over R formula to calculate power (RMS volts squared, divide by load resistance).

[Helmholtz]

What power tubes does the amp use?
What is B+?
What is rated output?
Is there a schematic?

[g1]

put a known load on the amplifier, say 8R.
With a signal generator set to 1kHZ sine wave, turn the level up until 8volts of signal is across your load, then switch to 4R. If the signal level stays the same, it is a 4R tapping, if it reduces, it is either 8R or 16R.

I've never tried this method, so I could be mistaken. But it seems to me you could have a slight reduction into 4 ohms and still be putting out more power than into 8.