Need some help with Ohms

[dumbassbob]

I have a 100watt Marshall 1959 Plexi and a Attenuator, Reactive load like a SE100 called a PS Systems power tool,It runs at 8 ohms but the manual said you can run down to 4 ohms..Does that mean I can use the amp at 8 ohm into the power tool into a 4 ohm cab,I know you can't use @16 ohms I popped 4 power tubes..all my speakers are 8ohms so one cab is at 16 and the other is at 4 ohms.I don't want to blow it up I got off easy this time I thought I arced the tube sockets

[g1]

Is this it: http://www.pacair.com/mmamps/EB100S/...ool_Manual.pdf
If that's what you have, it says set your amp to 8 ohms. It has it's own solid state power amp that drives your speaker cabinet. It says the speaker cab can be as low as 2 ohms. If this is what you have, it should run either one of your cabs. The solid state amp will work fine with a 16ohm or 4ohm cab.

[dumbassbob]

Thats what I have,But I used a 16 ohm cab and my power tubes popped after 6 hrs of useing over 3 days,some one said it was BAD to use a 16 ohm load,I don't the amp up past 5 and I keep the speaker volume down Would my 4 ohm cab be safer

[Chuck H]

If the attenuator unit is a re-amp type, like an "Ultimate" or "Ho" attenuator, then the cabinet you plug into the attenuator has no reference to your amps tubes at all and cannot affect their working conditions for better or worse.

It is emminently possible that your tubes blew up for a different reason. If you don't have the opportunity to crank the amp very often and then, rather abruptly, put six hours of cranked up time on the power tubes, it could be that a poor operating condition is revealing itself.

Atenuators are often blamed for burning up tubes and output transformers. But the fact is that, were it possible, cranking the amp through a speaker cabinet to the same degree for the same amount of time would probably have caused the same failure.

Like I said, if your attenuator is a re-amp type system then the cabinet you plug into the attenuator has nothing whatever to do with the power tubes working environment. The tube failure would have been caused by something else like incorrect bias, gross imbalance due to age, intermittent bias supply, having the amps output impedance set improperly or an intermittent load connection.

[dumbassbob]

Ohm

Is this it: http://www.pacair.com/mmamps/EB100S/...ool_Manual.pdf
If that's what you have, it says set your amp to 8 ohms. It has it's own solid state power amp that drives your speaker cabinet. It says the speaker cab can be as low as 2 ohms. If this is what you have, it should run either one of your cabs. The solid state amp will work fine with a 16ohm or 4ohm cab.

Read this about it its a Reactive load with a built in SS power amp and FX loop really cool I think I had a Bad input Jack....My Marshall SLP only need to be at 5-6 to get the tone

[Chuck H]

Read this about it its a Reactive load with a built in SS power amp and FX loop really cool I think I had a Bad input Jack....My Marshall SLP only need to be at 5-6 to get the tone

Do you mean the input jack on your amp?!? Or the input jack on the attenuator? The input jack on the amp also has nothing to do with the power tubes working environment and nothing you do there can damage the power tubes. If you mean the input jack on the attenuator that would constitute and improper or intermittent load as I mentioned above. Not to mention that you should have heard something was wrong and discontinued using the amp before it blew up all the tubes. Even then, an open load would more likely cause a transformer failure and a shorted load probably wouldn't take out all the tubes at the same time. The most likely culprit is an incorrect bias condition or a bias supply failure that was excacerbated by cranking the amp.

[dumbassbob]

Ohms

Do you mean the input jack on your amp?!? Or the input jack on the attenuator? The input jack on the amp also has nothing to do with the power tubes working environment and nothing you do there can damage the power tubes. If you mean the input jack on the attenuator that would constitute and improper or intermittent load as I mentioned above. Not to mention that you should have heard something was wrong and discontinued using the amp before it blew up all the tubes. Even then, an open load would more likely cause a transformer failure and a shorted load probably wouldn't take out all the tubes at the same time. The most likely culprit is an incorrect bias condition or a bias supply failure that was excacerbated by cranking the amp.

My 2x12 cab input jack was loose,the ground part would move and it was Not bolted down tight. It was a cheap China one that's all I had at the time.I thought that might have some thing to do with it,Also what is the "Right" jack to use Switchcraft has differnt #11's some are shorter or have that tab

[J M Fahey]

*If* you used a cabinet with a loose jack connected to your attenuator/reamp, this device isolated it from your tube head, so no trouble there.
If you used it straight to the head, (or maybe the the attenuator has a bypass switch), yes.

[dumbassbob]

If the attenuator unit is a re-amp type, like an "Ultimate" or "Ho" attenuator, then the cabinet you plug into the attenuator has no reference to your amps tubes at all and cannot affect their working conditions for better or worse.

It is emminently possible that your tubes blew up for a different reason. If you don't have the opportunity to crank the amp very often and then, rather abruptly, put six hours of cranked up time on the power tubes, it could be that a poor operating condition is revealing itself.

Atenuators are often blamed for burning up tubes and output transformers. But the fact is that, were it possible, cranking the amp through a speaker cabinet to the same degree for the same amount of time would probably have caused the same failure.

Like I said, if your attenuator is a re-amp type system then the cabinet you plug into the attenuator has nothing whatever to do with the power tubes working environment. The tube failure would have been caused by something else like incorrect bias, gross imbalance due to age, intermittent bias supply, having the amps output impedance set improperly or an intermittent load connection.

What IS Intermittent Load,Bias...

[Chuck H]

Intermittent unintentionally. Not designed that way. "intermittent load" would mean the load is not presenting full time as it should because of a system failure. likewise with the bias.

[dumbassbob]

Ohms

Do you mean the input jack on your amp?!? Or the input jack on the attenuator? The input jack on the amp also has nothing to do with the power tubes working environment and nothing you do there can damage the power tubes. If you mean the input jack on the attenuator that would constitute and improper or intermittent load as I mentioned above. Not to mention that you should have heard something was wrong and discontinued using the amp before it blew up all the tubes. Even then, an open load would more likely cause a transformer failure and a shorted load probably wouldn't take out all the tubes at the same time. The most likely culprit is an incorrect bias condition or a bias supply failure that was excacerbated by cranking the amp.

If it is a 8 ohm reactive load and the manual said put my 100watt Marshall on 8 ohms,and it can take a 4ohm speaker load,but I had it at 16 ohms,and as soon as I saw it flashing blue and sounding harsh I shut it down.I did not bias these Valve Art EL34B

[Chuck H]

as soon as I saw it flashing blue and sounding harsh I shut it down.

Blue flashing isn't uncommon. Some tubes glow blue anyway and under heavy overdrive, with voltages jumping up and down, they flash. Harsh tone is subjective. Maybe that's how they sound. Did the tubes actually stop working or have you just assumed they're bad now that they flash blue and sound harsh?

I did not bias these Valve Art EL34B

That's a pretty bad thing considering that you intended to overdrive them into a dummy load for long time periods.

OK... Here's how I know the Ultimate and Ho atenuators to be. As long as your amps speaker output is plugged into the attenuators amplifier input the amp is safe. Provided all jacks and cables are sound. A small amount of the dummy loaded output (so small as to make no notable difference to the load your amp is playing into) is sent to an independant solid state amplifier that is now responsible for any and all volume you will hear. If this is how your attenuator works then now you should understand that when your amplifier is plugged into the attenuator properly the actual speaker cabinet is almost entirely isolated and not part of the load your amp is playing into. Therefor nothing about the speaker cabinet can cause problems with your amp. Only a problem with the actual load that your amp is using can cause problems with your amp. And in the case of the Ultimate and Ho attenuators the load your amp is playing into is not the speaker cabinet.

It's sort of like micing an amp. You stick a mic in front of your little amp at the gig because you need the PA to boost your volume. Nothing about the PA's speaker load can hurt your amp. The amp is isolated from the secondary amplification system. If the speaker in your amp is presenting an improper load or has an intermittent connection, that can hurt your amp. In this case the speaker in the analogy would be represented by the load in your attenuator.

Even with an improper load your not likely to lose all four power tubes. Perhaps an OT or one or two tubes. It's most likely a bias issue. IF the tubes are blown.

As for using an improper load for the attenuator output... I can only assume that the minimum load is a safety issue for the attenuators output. Any load higher than that will not damage the attenuator and certainly not your amp (since it is isolated from this system). You will simply lose output capacity.

[dumbassbob]

ojms

Blue flashing isn't uncommon. Some tubes glow blue anyway and under heavy overdrive, with voltages jumping up and down, they flash. Harsh tone is subjective. Maybe that's how they sound. Did the tubes actually stop working or have you just assumed they're bad now that they flash blue and sound harsh?



That's a pretty bad thing considering that you intended to overdrive them into a dummy load for long time periods.

OK... Here's how I know the Ultimate and Ho atenuators to be. As long as your amps speaker output is plugged into the attenuators amplifier input the amp is safe. Provided all jacks and cables are sound. A small amount of the dummy loaded output (so small as to make no notable difference to the load your amp is playing into) is sent to an independant solid state amplifier that is now responsible for any and all volume you will hear. If this is how your attenuator works then now you should understand that when your amplifier is plugged into the attenuator properly the actual speaker cabinet is almost entirely isolated and not part of the load your amp is playing into. Therefor nothing about the speaker cabinet can cause problems with your amp. Only a problem with the actual load that your amp is using can cause problems with your amp. And in the case of the Ultimate and Ho attenuators the load your amp is playing into is not the speaker cabinet.

It's sort of like micing an amp. You stick a mic in front of your little amp at the gig because you need the PA to boost your volume. Nothing about the PA's speaker load can hurt your amp. The amp is isolated from the secondary amplification system. If the speaker in your amp is presenting an improper load or has an intermittent connection, that can hurt your amp. In this case the speaker in the analogy would be represented by the load in your attenuator.

Even with an improper load your not likely to lose all four power tubes. Perhaps an OT or one or two tubes. It's most likely a bias issue. IF the tubes are blown.

As for using an improper load for the attenuator output... I can only assume that the minimum load is a safety issue for the attenuators output. Any load higher than that will not damage the attenuator and certainly not your amp (since it is isolated from this system). You will simply lose output capacity.

Thanks, I think because I didn't bias the tubes I might of hurt them or the bias caps are going bad I have been using some of my NOS tubes without the power tooll it is ok,but using the power tool I turn the amp up to 6 that is very loudI need to buy a bias probe

[dumbassbob]

Is this it: http://www.pacair.com/mmamps/EB100S/...ool_Manual.pdf
If that's what you have, it says set your amp to 8 ohms. It has it's own solid state power amp that drives your speaker cabinet. It says the speaker cab can be as low as 2 ohms. If this is what you have, it should run either one of your cabs. The solid state amp will work fine with a 16ohm or 4ohm cab.

Thanks It hard being a Dumbass