What Not To Do With Your Tube Amp

Phostenix · 10-14-2009, 02:32 AM

I was searching for info on the Crate Stealth GT50 that came up in another thread & I came across this youtube video. Ouch!

YouTube - Crate Stealth GT50

Glasgow · 10-14-2009, 04:34 AM

So, that's not a feature?

Chuck H · 10-14-2009, 04:46 AM

When my amps do that I intentionally crank it up until the offending tube blows up

. I don't recommend this unles you are sure of the rest of the amps ability to handle a tube failure. If it can, it's great fun creating smoke and flashes.

Chuck

Phostenix · 10-14-2009, 04:20 PM

OK, I'll bite. I've always heard that power tube failure put the output xfmr at risk. What design feature(s) makes you "sure of the rest of the amps ability to handle a tube failure"?

tboy · 10-14-2009, 09:09 PM

Thanks, I really enjoyed that.

imaradiostar · 10-14-2009, 09:27 PM

Quote:

Originally Posted by Phostenix

OK, I'll bite. I've always heard that power tube failure put the output xfmr at risk. What design feature(s) makes you "sure of the rest of the amps ability to handle a tube failure"?

The confidence that you have the knowledge and spare parts to build something better!

jamie

Chuck H · 10-15-2009, 02:49 AM

A failing tube can cause problems for the PT also.

For starters, I almost always use a false CT for my heater wind. If anything like a plate to heater short happens the resistors will blow and open the circuit. Having an OT thats able to handle spikes, shorts and off loads is also a good idea. Some builders think that cheesey OT's are part of the tone of certain amps. I think that can be true, but doesn't have to be. I use beefy OT's. Screen grid R's rated carefully can double as fuses that will open if there is a gross failure. I'd rather blow a screen grid R than an OT any day. A rock solid bias supply is a good idea. If anything goes wrong with the bias supply while a tube is failing it can take out the other tubes too. This is substantially more stress to the rest of the amp than one tube failing. Part of the game is knowing what components to over rate and which ones should be rated to intentionally fail if things go grossley bad. Some guys think they're building a reliable amp by over rating ALL the components, but IMHE this is a bad idea.

The same conditions that are bad for tubes are often the same as whats bad for the OT. So it may just be more of a coincidence than a fact that blown tubes and OT's seem to go together. I'm speaking specifically of an open load. I would never intentionally run an amp into an open load to blow up a tube. For that matter, I would never intentionally blow up a good functioning tube. But if one is already failing, and all other parameters are in check (no open load), well... It's an observation in curiosity at that point.

There are other things like flyback diodes and fusing the B+ rail but I never use them.

I've blown up many tubes (and of course some peripheral components) but I haven't lost any transformers... Yet

Chuck

Edit: I always shut the amp down immediately after the event so that any persistant shorts won't be stressing the amp unchecked.

Phostenix · 10-15-2009, 04:35 PM

Thanks, Chuck! My silly post ended up providing some good info!

10-14-2009, 09:09 PM	#5
tboy Site Janitor Join Date: May 2006 Location: Behind The Zion Curtain Posts: 295 Member's Picture Albums	Thanks, I really enjoyed that. __________________ -tb

10-15-2009, 02:49 AM	#7
Chuck H Old Timer Join Date: May 2007 Location: pacific north west Posts: 1,225	A failing tube can cause problems for the PT also. For starters, I almost always use a false CT for my heater wind. If anything like a plate to heater short happens the resistors will blow and open the circuit. Having an OT thats able to handle spikes, shorts and off loads is also a good idea. Some builders think that cheesey OT's are part of the tone of certain amps. I think that can be true, but doesn't have to be. I use beefy OT's. Screen grid R's rated carefully can double as fuses that will open if there is a gross failure. I'd rather blow a screen grid R than an OT any day. A rock solid bias supply is a good idea. If anything goes wrong with the bias supply while a tube is failing it can take out the other tubes too. This is substantially more stress to the rest of the amp than one tube failing. Part of the game is knowing what components to over rate and which ones should be rated to intentionally fail if things go grossley bad. Some guys think they're building a reliable amp by over rating ALL the components, but IMHE this is a bad idea. The same conditions that are bad for tubes are often the same as whats bad for the OT. So it may just be more of a coincidence than a fact that blown tubes and OT's seem to go together. I'm speaking specifically of an open load. I would never intentionally run an amp into an open load to blow up a tube. For that matter, I would never intentionally blow up a good functioning tube. But if one is already failing, and all other parameters are in check (no open load), well... It's an observation in curiosity at that point. There are other things like flyback diodes and fusing the B+ rail but I never use them. I've blown up many tubes (and of course some peripheral components) but I haven't lost any transformers... Yet Chuck Edit: I always shut the amp down immediately after the event so that any persistant shorts won't be stressing the amp unchecked. Last edited by Chuck H; 10-15-2009 at 02:58 AM.

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10-14-2009, 04:34 AM	#2
Glasgow Member Join Date: Aug 2007 Location: Portland, OR Posts: 48	So, that's not a feature?

10-14-2009, 04:46 AM	#3
Chuck H Old Timer Join Date: May 2007 Location: pacific north west Posts: 1,225	When my amps do that I intentionally crank it up until the offending tube blows up . I don't recommend this unles you are sure of the rest of the amps ability to handle a tube failure. If it can, it's great fun creating smoke and flashes. Chuck

10-14-2009, 04:20 PM	#4
Phostenix Senior Member Join Date: Jul 2009 Location: Phoenix, AZ Posts: 291	OK, I'll bite. I've always heard that power tube failure put the output xfmr at risk. What design feature(s) makes you "sure of the rest of the amps ability to handle a tube failure"?

10-15-2009, 04:35 PM	#8
Phostenix Senior Member Join Date: Jul 2009 Location: Phoenix, AZ Posts: 291	Thanks, Chuck! My silly post ended up providing some good info!

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YouTube - Crate Stealth GT50

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