Output valve blown?

[Jigster]

Hi, don't know if this is doable on a forum - and I am planning a visit to an amp tech VERY soon - but last night my Orange head farted out - there was some smoke drifting out the top grill and I've checked the output valve fuses and they are both well blown - of course without being able to see it it's difficult - but I'm worrying that the smoke means more than just the valves, BUT the fact that the fuses have gone in the way they should when a valve pots out makes me hopeful that this is just all it is??

Any thoughts appreciated.

Ta

[DHA]

[quote name='Jigster' post='672879' date='Dec 3 2009, 09:35 AM']Hi, don't know if this is doable on a forum - and I am planning a visit to an amp tech VERY soon - but last night my Orange head farted out - there was some smoke drifting out the top grill and I've checked the output valve fuses and they are both well blown - of course without being able to see it it's difficult - but I'm worrying that the smoke means more than just the valves, BUT the fact that the fuses have gone in the way they should when a valve pots out makes me hopeful that this is just all it is??

Any thoughts appreciated.

Ta[/quote]

smoke is never a good thing, could be lots of things. Hopefully just a resistor but could be the output transformer.

Needs the tech to look at it.

Dave

[Moos3h]

I'd expect it's more likely the transformer

[umph]

[quote name='Moos3h' post='673936' date='Dec 4 2009, 09:28 AM']I'd expect it's more likely the screen resistor[/quote]

[Jigster]

sorted

[DHA]

[quote name='Jigster' post='691228' date='Dec 22 2009, 08:13 AM']sorted[/quote]
what was it?

[Jigster]

i think at the end of the day it's inconclusive - and I REALLY don't have the mental powers to understand it all, suffice to say, I called an amp tech, but the general scenario was this:

I bought the Orange head without a cab, and put a new cab on order. Meanwhile, whilst waiting, I used it once in anger at a reh studio and went though a sealed 8 ohm cab (think it was a 6x10 but may have been 8x10) anyway, no probs, played great. Then used it a 2nd time with the cab I'd ordered, 1x15 also 8ohms, but ported - and that's when it blew, lingering brown looking smoke coming out of the top grill and output valve fuses blown etc. (altho to say, according to the amp tech, the output valve fuses were the wrong kind to start with - they were slow cut rather than instant cut) Coincidence? Why did the head blow then, and not before with the sealed cab, this is what remains inconclusive really.

Anyway, so then i took it to the amp tech and this is what he put in an e-mail: "Two of the four 6550s in the Orange had suffered screen meltdown. This happens, for sure, but two at a time failing quickly after trying a different speaker load makes double-checking the suitability of the speaker important" - [b](which of course I did, the head has an 8ohm match as does the cab, so essentially, I didn't mis-match)[/b]

He continues:

"Very Low impedance is a possible problem for the AD200, since the anode voltage is very high (~700V) - low Z loads draw current while leaving a high instantaneous anode voltage, and potential anode hotspots. On the other hand, if the resonance peak(s) present substantially more than 8 Ohm within the Bass spectrum, these may cause rapid decrease of anode voltage and a sharp rise in the screen current. Although the Orange runs the screens well within spec (<400V) you could certainly get screen meltdown with unsuitably high impedance peaks - all dependent on frequency. Many drivers have their resonance curve pushed upward in frequency when enclosed in a small cabinet, which (depending on where they start from) may be dangerous for a valve bass amp."

When I collected the amp head he also mused on whether ported cabs are suitable for valve amps generally - which I know has seen a lot of discussion on Talk Bass and maybe on here (?) - I really don't have the knowledge to argue anything either way, maybe a ported cab [i]doesn't[/i] suit and I should get a sealed one, (altho was speaking to Jeff at Matamp last week about this and he said ported cabs were fine, and not to pay any attention to that)

Suffice to say, the head is fixed, I played it again and all works fine. I've returned the 1x15 (superstition I guess, fresh start I guess) and am now considering what to get next to match with the Orange. (maybe a Matamp)

All thoughts welcome - but keep it simples

[umph]

[quote name='Jigster' post='692143' date='Dec 23 2009, 10:22 AM']i think at the end of the day it's inconclusive - and I REALLY don't have the mental powers to understand it all, suffice to say, I called an amp tech, but the general scenario was this:

I bought the Orange head without a cab, and put a new cab on order. Meanwhile, whilst waiting, I used it once in anger at a reh studio and went though a sealed 8 ohm cab (think it was a 6x10 but may have been 8x10) anyway, no probs, played great. Then used it a 2nd time with the cab I'd ordered, 1x15 also 8ohms, but ported - and that's when it blew, lingering brown looking smoke coming out of the top grill and output valve fuses blown etc. (altho to say, according to the amp tech, the output valve fuses were the wrong kind to start with - they were slow cut rather than instant cut) Coincidence? Why did the head blow then, and not before with the sealed cab, this is what remains inconclusive really.

Anyway, so then i took it to the amp tech and this is what he put in an e-mail: "Two of the four 6550s in the Orange had suffered screen meltdown. This happens, for sure, but two at a time failing quickly after trying a different speaker load makes double-checking the suitability of the speaker important" - [b](which of course I did, the head has an 8ohm match as does the cab, so essentially, I didn't mis-match)[/b]

He continues:

"Very Low impedance is a possible problem for the AD200, since the anode voltage is very high (~700V) - low Z loads draw current while leaving a high instantaneous anode voltage, and potential anode hotspots. On the other hand, if the resonance peak(s) present substantially more than 8 Ohm within the Bass spectrum, these may cause rapid decrease of anode voltage and a sharp rise in the screen current. Although the Orange runs the screens well within spec (<400V) you could certainly get screen meltdown with unsuitably high impedance peaks - all dependent on frequency. Many drivers have their resonance curve pushed upward in frequency when enclosed in a small cabinet, which (depending on where they start from) may be dangerous for a valve bass amp."

When I collected the amp head he also mused on whether ported cabs are suitable for valve amps generally - which I know has seen a lot of discussion on Talk Bass and maybe on here (?) - I really don't have the knowledge to argue anything either way, maybe a ported cab [i]doesn't[/i] suit and I should get a sealed one, (altho was speaking to Jeff at Matamp last week about this and he said ported cabs were fine, and not to pay any attention to that)

Suffice to say, the head is fixed, I played it again and all works fine. I've returned the 1x15 (superstition I guess, fresh start I guess) and am now considering what to get next to match with the Orange. (maybe a Matamp)

All thoughts welcome - but keep it simples [/quote]
stopped reading after he said the mains fuse should be a fast blow fuse!

[Mr. Foxen]

That sounds well dodge. The valves are isolated from the speakers by the transformer, so not much going on at that end should affect them, thats why the transformer gets upset by misloading. Did you check the impedance of the cab with a meter? Just cause it says 8 ohms doesn't mean its so, practice room cabs can have bodged in new speakers.

[Jigster]

the reh room cab was fine, the one i bought was where the probs started - yes i'm aware that impedence is variable - so even tho i bought an 8ohm cab to match 8ohm on the head there cud well have been a mismatch going on -

[DHA]

[quote name='Jigster' post='692342' date='Dec 23 2009, 02:10 PM']the reh room cab was fine, the one i bought was where the probs started - yes i'm aware that impedence is variable - so even tho i bought an 8ohm cab to match 8ohm on the head there cud well have been a mismatch going on -[/quote]

Sounds like there was an open circuit between the amp and the speakers at one point. Most likely a duff speaker cable or jack, I would check it all again or you will blow it up again at some time.

[DHA]

[quote name='Mr. Foxen' post='692332' date='Dec 23 2009, 01:48 PM']That sounds well dodge. The valves are isolated from the speakers by the transformer, so not much going on at that end should affect them, thats why the transformer gets upset by misloading. Did you check the impedance of the cab with a meter? Just cause it says 8 ohms doesn't mean its so, practice room cabs can have bodged in new speakers.[/quote]

The transformer matchs the required load of the valves (Kohms) with the low impedance speakers. The transformer windings present and match a reflected load to the valves, so sorry to correct you but they are not isolated in terms of load and therefore current drawn. Thats why valves blow when you don't connect the speakers.

[Jigster]

[quote name='DHA' post='694366' date='Dec 27 2009, 04:47 PM']Sounds like there was an open circuit between the amp and the speakers at one point. Most likely a duff speaker cable or jack, I would check it all again or you will blow it up again at some time.[/quote]


how wud I check? the cab came with a cable provided so that won't be used again as the cab's gone back - when i used it with the reh room cab that was a standard extension speaker cable and was no probs - so hopefully am free of any dodgy cables or jacks

just had a thought actually - the cable that came with the cab was a speakon connection type and pretty hard to fit tightly, if that wasn't flush in would that create some kind of problem?