Here is a thread how I biased it last night: https://tubeamparchive.com/viewtopic.ph ... 2cb66cf5e8VH100R just died after putting new tubes
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VH100R just died after putting new tubes
My VH100R just died after I have put new tubes and biased them. It was working for few minutes last night after I biased them and I did not wanna play it was late night. Today I woke up turned it on the power light flashed just for a split second and turned off. No light no nothing totally dead now. All the fuses are OK. Any ideas, what could have gone wrong Here is a thread how I biased it last night: https://tubeamparchive.com/viewtopic.ph ... 2cb66cf5e8
Here is a thread how I biased it last night: https://tubeamparchive.com/viewtopic.ph ... 2cb66cf5e8Re: VH100R just died after putting new tubes
Ok it was power fuse, although it was showing OK with the Ohm meter it was not working properly, I got new power fuse in and it works, now the question is why the power fuse died after biasing? Will the new die also? Or it was just a coincidence?
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Re: VH100R just died after putting new tubes
Sometimes it takes a couple days to get over a fuse blowing. 
Sometimes they give up. Sometimes there is not problem other than the fuse. Hard to know.
Check your bias and make sure you don't have a tube that decided to do something bad, suddenly.
Sometimes they give up. Sometimes there is not problem other than the fuse. Hard to know.
Check your bias and make sure you don't have a tube that decided to do something bad, suddenly.
Re: VH100R just died after putting new tubes
Typically fuses don't blow for no reason but they can.
Re: VH100R just died after putting new tubes
Are you sure you got the right fuse for the job? Mains fuses should be of the slow blow type.
Re: VH100R just died after putting new tubes
This fuse was in there for at least 8 years maybe even more, but I though slow blow fuses are for HT and Power fuse suppose to be fast acting ?
On the amp it does not say Fast or Slow blow it only says 1 Amp for HT and 5 Amps for Power fuse. For some reason I have bunch of fast acting power fuses and slow blowing HT fuses in stock from years ago, I guess somebody told me to buy those back then. So Colossal are you shore I should have Slow Blow on Power? Maybe that is the problem, maybe the amp was cold biased all this time and now when I got it where it should be - now I need Slow Blow on Power?
On the amp it does not say Fast or Slow blow it only says 1 Amp for HT and 5 Amps for Power fuse. For some reason I have bunch of fast acting power fuses and slow blowing HT fuses in stock from years ago, I guess somebody told me to buy those back then. So Colossal are you shore I should have Slow Blow on Power? Maybe that is the problem, maybe the amp was cold biased all this time and now when I got it where it should be - now I need Slow Blow on Power?
Last edited by Emetal on Sun Jun 09, 2013 1:59 pm, edited 4 times in total.
Re: VH100R just died after putting new tubes
I'we read that tubes that are biased too hot can blow fuse, but I thought I did everything as I am suppose to. Maybe my meter is not accurate, I will set bias lower for now and tomorrow (monday) buy new meter, this one I have is old and I am suspecting it's accuracy... Or maybe this amp can not handle GC type tubes, but again if it's within a biasing range of an amp then it should be OK? I am buying new meter tomorrow for shore. It's either that or this thing with Slow/Fast acting fuses thing from above..That is honestly all I can think of, if anybody has any other idea please shoot
Re: VH100R just died after putting new tubes
I used SB fuses on the mains and FB on the HT. You can use SB all around. Some do. When the time comes, the fuse will blow. Just ask my ex-wife.....
D
D
There are no stupid questions, just stupid people.......
Re: VH100R just died after putting new tubes
Yeah I am starting to believe that's what the problem is, I should have Slow Blow on the Mains, the reason it wasn't blowing before is probably because the amp was chronically running cold, now when I learned how to bias myself and got new tubes in, that Fast Acting proved not to be up to the job. Buying slow blow tomorrow and a new meter, what the hell, gonna treat myself
Re: VH100R just died after putting new tubes
Fuses can weaken over time as well due to the surge of current at start up.
But first check out the circuit to rule out a problem that has drawn excessive current.
Be a good time to use a light bulb current limiter.
Look for the sticky up above about building one.
But first check out the circuit to rule out a problem that has drawn excessive current.
Be a good time to use a light bulb current limiter.
Look for the sticky up above about building one.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: VH100R just died after putting new tubes
Anyone please correct me where I'm wrong... I don't know controls per se, so I'm commenting from a theory perspective only.
Do not substitute a slo-blow fuse in place of fast-reacting unless the f/r was placed there by mistake. The fact that the fuse blew as soon as you activated the amp indicates a short.
The problem may just be the tube(s) themselves. Open it back up, and make sure there is nothing obvious going on; like bent contacts or disconnected wires... Since the fuse has blown, you now also need to check the board for a carbon-path as a result of arching. If there is a carbon-path, it will need to be carefully removed from the pcb, as it will continue to arch in the same place.
Also need to check the bias diode to make sure it is still viable. You can check diodes using an simple Ohm meter with diode test function. A diode conducts current in one direction only. Place you probes on the diode, then reverse and check again. If everything looks good, replace the fuse and activate the amp WITHOUT the power-tubes installed. This should tell you if the issue is related to the tubes (circuit). You biased it, so I'm thinking something has gotten moved or the bias diode has possibly failed. Could also be a crumby set of tubes... I've been running into a lot of those lately.
Do not substitute a slo-blow fuse in place of fast-reacting unless the f/r was placed there by mistake. The fact that the fuse blew as soon as you activated the amp indicates a short.
The problem may just be the tube(s) themselves. Open it back up, and make sure there is nothing obvious going on; like bent contacts or disconnected wires... Since the fuse has blown, you now also need to check the board for a carbon-path as a result of arching. If there is a carbon-path, it will need to be carefully removed from the pcb, as it will continue to arch in the same place.
Also need to check the bias diode to make sure it is still viable. You can check diodes using an simple Ohm meter with diode test function. A diode conducts current in one direction only. Place you probes on the diode, then reverse and check again. If everything looks good, replace the fuse and activate the amp WITHOUT the power-tubes installed. This should tell you if the issue is related to the tubes (circuit). You biased it, so I'm thinking something has gotten moved or the bias diode has possibly failed. Could also be a crumby set of tubes... I've been running into a lot of those lately.
Re: VH100R just died after putting new tubes
Given that you retubed it worked for a bit and than failed.
The fuse is intended to blow to save the amp from voltage spikes.
Bring the amp up on a variac and make sure the amperage doesn't spike. If it does this indicates a problem. Since you didn't modify the circuit it would point to bad tubes, filter caps, transformer.
I would test the new tubes to make sure one did not die or short when it received high operating voltages. It's not uncommon to have new tubes go bad. It's why I stress actual operating voltage for testing and matching tubes. I average 3-7% loss during tube testing of new tubes.
The comment about your fuse still testing good on voltmeter I find interesting. You tested it for continuity? Its a work or won't work component. No moving parts except for the moment it fails.. I'm curious did you reseat your tubes at the same time you swapped fuses? You may need to clean / and retention the tube socket pins. One may have been lose or tarnished making intermittent contact which took out the last set of tubes and now caused this.
The bias shouldn't trip the fuse until after the tubes red plate go thermal and fail causing a B+ short.
The fuse is intended to blow to save the amp from voltage spikes.
Bring the amp up on a variac and make sure the amperage doesn't spike. If it does this indicates a problem. Since you didn't modify the circuit it would point to bad tubes, filter caps, transformer.
I would test the new tubes to make sure one did not die or short when it received high operating voltages. It's not uncommon to have new tubes go bad. It's why I stress actual operating voltage for testing and matching tubes. I average 3-7% loss during tube testing of new tubes.
The comment about your fuse still testing good on voltmeter I find interesting. You tested it for continuity? Its a work or won't work component. No moving parts except for the moment it fails.. I'm curious did you reseat your tubes at the same time you swapped fuses? You may need to clean / and retention the tube socket pins. One may have been lose or tarnished making intermittent contact which took out the last set of tubes and now caused this.
The bias shouldn't trip the fuse until after the tubes red plate go thermal and fail causing a B+ short.
My Daughter Build Stone Henge
Re: VH100R just died after putting new tubes
On the amp it says T5A for Mains and T1A for HT what does "T" stands for? Time delay?
Re: VH100R just died after putting new tubes
Correct denotes Time delay.. If you wanted to get technical nitty gritty
An abbreviation for 'threaded cylindrical multi-pin coupling .... Such fuses are usually marked with a rating prefixed by 'T', for example T5A for a 5 amp rated fuse.
An abbreviation for 'threaded cylindrical multi-pin coupling .... Such fuses are usually marked with a rating prefixed by 'T', for example T5A for a 5 amp rated fuse.
My Daughter Build Stone Henge
Re: VH100R just died after putting new tubes
Ok now I have a tube that is not glowing at all, I switched places and it is always the same tube, bad tube? Could something in the amp have broken the tube? Anything I can do to test that tube further?
I am checking all the pins and connections, will put old set of tubes (which are still good), revert the bias as it was until yesterday and see what happens..
I am checking all the pins and connections, will put old set of tubes (which are still good), revert the bias as it was until yesterday and see what happens..