OK! So if Flyback voltages are bad with a Ultimate Attenuator..then...

[JubileeMan 2555]

Because my original thread exploded into another fight-fest over the safety of the UA... I'm starting a new thread with a new question:

If the flyback voltages are whats dangerous using a 4:1 ratio when using the UA... Is there any mods/tricks that can be applied to the amp that could either reduce the effect, or eliminate it all together without changing the 4:1 ratio at all? I saw someone mentioned an addition to the speaker jack or something... Diodes?

PLEASE if you have no answer to this question, don't comment on the actual use of the UA. I don't want another angery fight.

 

[JubileeMan 2555]

It's not just the voltage spikes, there is also the matter of the huge increase in screen grid current at 4x mismatch...you can't get around that.

Ok. Just checkin'

 

[Bussman]

Try a properly rated L-pad between amp and UA. It amounts to using an attenuator in front of your "attenuator" which is kind of ironic.

<edit>Never mind, I did not read the part about maintaining the mismatch... </edit>

 

[JubileeMan 2555]

It is a very simple task to to change the two metal-bodied power resistors inside the unit to a different value to match your amp...you could even put in a switch to switch between two or three different values to match amps of different impedances, assuming there is room inside the unit.

true, but apparently Mr. Ho has commented that hes tried many different OHM loads and found the 30 to present the best transparency. If I wanted to be safe, but sacrifice a bit of tone, I'd get a hotplate. But since I'm already using a PPIV that is pretty wicked, I just wanted the UA to achieve a "one-step-up" from the PPIV. If I start messin' with the design, I won't be getting its full effect.

 

[JubileeMan 2555]

That's the part that doesn't make sense...if 30 ohms gives the best tone and transparency for a 16 ohm amp, then how can it also give the best tone for an 8 ohm, 4 ohm, or 2 ohm amp? If you really wanted the same tone at all impedance settings, you'd have a switch that selected a 30 ohm load for the 16 ohm amp, a 15 ohm load for the 8 ohm amp, an 8 ohm load for the 4 ohm amp, and a 4 ohm load for the 2 ohm amp.

Randall Aiken

You may be right. But I can't say since I didnt' design the unit. It might have something to do with the reamping circuit thats built into the unit. Who knows.

But no worries. I don't want to risk the Vintage Tranny anymore anyways. I'm buying a Marstran OT thats got a 16ohm tap, so I'll be set.

 

[hasserl]

That's the part that doesn't make sense...if 30 ohms gives the best tone and transparency for a 16 ohm amp, then how can it also give the best tone for an 8 ohm, 4 ohm, or 2 ohm amp?

LOL! I guess it's just magic! A deep dark secret only an enlightened one can answer.

Sorry, I shouldn't be so glib about it. But I've taken a lot of heat from the fan boys. Isn't that question so obvious, does it really need to be asked?

 

[JubileeMan 2555]

I asked this thread not to turn into another worthless commentary on the UA. I just wanted an answer to my question.

I will delete the thread if it continues.

 

[reaiken]

You may be right. But I can't say since I didnt' design the unit. It might have something to do with the reamping circuit thats built into the unit. Who knows.

The reamp circuit is simply a complementary emitter follower, it (ideally) doesn't appreciably load the circuit it is connected to, so that wouldn't be the answer.

 

[hasserl]

I asked this thread not to turn into another worthless commentary on the UA. I just wanted an answer to my question.

I will delete the thread if it continues.

With all the inherent risks involved, I assume this is directed at me. My post was not a commentary on the UA, it was a facetious commentary (worthless perhaps, depending on your POV) on the lack of critical thinking by otherwise reasonable people when it comes to objects of desire.

 

[epluribus]

...on the lack of critical thinking by otherwise reasonable people when it comes to objects of desire.

This thread is about girls isn't it?

 

[Jahn]

Well I don't use it to go into an attenuator, I use it to go into a mismatched speaker cab, but I guess the idea is the same ... I use a Weber Z-Matcher. It matches impedance. So if you have a Vibro Champ pumping 4 ohms, plug it into a Z-Matcher, dial it up to 30 ohms and put it into your attenuator, wouldn't that work? Well, the Z-Matcher only goes up to 16 ohms, but hey it's closer at least.

 

[hasserl]

This thread is about girls isn't it?

It very well could be!!!

Or motorcycles, or cars, or.....(what's your poison?)

 

[Trout]

I was tinkering over the weekend on an amp that is very intolerant to mismatch.

In a nutshell, The OT is rated at 4ohm, I plugged it into a 4 X 12 cab set for 8 ohm. It caused the rectifier to arc to an untimely death in less than 20 minutes.

First symptoms were an occasional mild pop, it started to increase to several pops.
I put it in standby, for a few minutes while I switch guitar cords & guitar, Flipped the switch and it was like the 4th of July inside the GZ34.

I ruined 2 JJ GZ34's in this amp in under an hour.
I plugged the amp into a 2 X 12 4 ohm cab and now its perfect. I have had similar problems with this particular brand OT before, always the same scenario.
BTW, this amp already had diodes on the PT secondary to protect the rectifier, but the voltage/flyback was excessive enough to still be a problem.
Some combinations are simply destined to fail.

 

[Tone_Terrific]

I put it in standby, for a few minutes while I switch guitar cords & guitar, Flipped the switch and it was like the 4th of July inside the GZ34.

I ruined 2 JJ GZ34's in this amp in under an hour.

Any explanations of how the mismatch is reflected back to the rectifier tube?

 

[Uniphasian]

I was tinkering over the weekend on an amp that is very intolerant to mismatch.

In a nutshell, The OT is rated at 4ohm, I plugged it into a 4 X 12 cab set for 8 ohm. It caused the rectifier to arc to an untimely death in less than 20 minutes.

First symptoms were an occasional mild pop, it started to increase to several pops.
I put it in standby, for a few minutes while I switch guitar cords & guitar, Flipped the switch and it was like the 4th of July inside the GZ34.

I ruined 2 JJ GZ34's in this amp in under an hour.
I plugged the amp into a 2 X 12 4 ohm cab and now its perfect. I have had similar problems with this particular brand OT before, always the same scenario.
BTW, this amp already had diodes on the PT secondary to protect the rectifier, but the voltage/flyback was excessive enough to still be a problem.
Some combinations are simply destined to fail.

Trout - were you running through the UA? or just straight into the 8 ohm cab from the 4 ohm amp output?

 

[Trout]

Trout - were you running through the UA? or just straight into the 8 ohm cab from the 4 ohm amp output?

Straight in,

Had I put an attenuator on there, it would blow the tube instantly.

Now, that said, The OT in the amp is " advertised " as 4 ohm, but measurements show it to be closer to 2 ohm.

 

[epluribus]

Slightly OT, but if you're interested in a Q&D intro to output transformer loading, reflectance, etc., it doesn't get much more intuitive and easy than this:

http://www.wisc-online.com/objects/index_tj.asp?objID=ACE12607

If you like this little doo-dad, they have scads of them at Wisconsin Online, a website belonging to The Wisconsin Technical College System--free sign-up. Huge library of such educational objects, most of them just as cool.

--Ray

 

[Dave_C]

Because my original thread exploded into another fight-fest over the safety of the UA... I'm starting a new thread with a new question:

If the flyback voltages are whats dangerous using a 4:1 ratio when using the UA... Is there any mods/tricks that can be applied to the amp that could either reduce the effect, or eliminate it all together without changing the 4:1 ratio at all? I saw someone mentioned an addition to the speaker jack or something... Diodes?

PLEASE if you have no answer to this question, don't comment on the actual use of the UA. I don't want another angery fight.

I don't know if this has been mentioned yet, but have you considered a good iso box, like the Grendel Dead Room? That way, you're driving a real speaker inside a real cab inside a real [albeit little] room, so it's no more dangerous than running into your normal cab. You also get the tonal advantages of a speaker driven hard. Of course, as mentioned above, the iso box is a little speaker cab in a little room, so you do get the acoustic properties of both, just like your normal cab inside any normal room you play in. So, you need to factor that into the equation and maybe shop around.

I own a GDR now and have been through all the popular attenuators (including the UA) and, so far, would always choose the GDR over the attenuators...when I need attenuation, that is.

 

[alivegy]

Just buy a Weber Zmatcher, it's $100. Put it between your amp and the UA. The UA still has it's 30ohm input that it wants, my bassman still see the 4ohm that it was designed for. If anything it sounds even more like my bassman at volume than it did before and my headroom back. Since the bassman is 4 ohms and the UA is 30, I use the 2.6 and 16 ohm settings to get the proper match. My amp runs much cooler as well.

 

[767400]

I'm curious has any information come out with UA or Ho attenuators still having (possible fly back voltages) problems while using the 100 volt AC tap? I have one and did have an issue with one of my amps.

Also, if anyone is interested. My amp tech (great guy!) fixed my Bluesbreaker when it had a tube socket short, using an attenuator for the first time none the less. He installed a ceramic sockets and a little extra mod. He connected three diodes (IN-4007) in a series from pin 3 to ground for spike protection. I am hoping this modification will save any of my NOS tubes from damage. I love my Ho (I also love saying that) attenuator and the tone I can maintain while not blowing my ears out. This picture is a 1959HW 100w head with the diodes in place. I marked just one of them with a red arrow.