I have one of these on bench. New electrolytics, new TungSol preamp tubes, new Winged C EL34s.
Played great for a while (a month) then got it back with one bad power tube and the story about fireworks in one tube. Replaced it with a new one. Fired it up and saw it myself along with incredibly loud noise.
I quickly shut it off and swapped in known good power tubes and it did it again in the same position (second from the left looking from the front). Swapped that tube out for another know good one and it was fine. I figured there may be some arcing issues at the socket so I replaced all of the octal sockets.
I put in the set that had worked before and when I took it out of standby it arced in the second power tube again. I put it in standby and swapped tube 2 and 3... Took it out of standby and it was fine.
I'm kind of afraid to put those Cs in there and let it go so I'm asking for advice here.
From what I remember, the voltages looked fine.
Have any of you had any experiences like this? Any ideas?
Tony
Orange OR120 Fireworks
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dorrisant
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Orange OR120 Fireworks
"Education is what you're left with after you have forgotten what you have learned" - Enzo
Re: Orange OR120 Fireworks
What are the plate and screen voltages on the output tubes ? I've had poor results with trying to use some current production output tubes in vintage Orange amps.
I watched a pair of JJ E34L's toast before my eyes, in a matter of seconds, in a '74 OR80 before I could take any voltage measurements or set bias.
I thought I had a couple of bad tubes so I put in a different pair of JJ E34L's and they toasted as quickly as the first pair.
I literally watched the red JJ paint on the tubes turn brown in a few seconds before my eyes.
These JJ E34L's probably would have had a normal lifespan in a more common amp (with sub 500V B+ and Screens) but they weren't up to the voltages in this OR80.
Before I installed more tubes I turned the bias pot to max neg voltage and put in a pair of Shuguang (Valve Art) EL34B's----- these tubes lasted long enough to take voltage measurements and set bias to 60%.
The Screen Grid voltage was very high but slightly lower than the plate voltage--- I don't remember the exact numbers----- I installed a dropping power resistor in the Screen supply, re-biased the amp---- I played it for hours to test it out-----then for more hours the next day.
The owner picked it up and was still playing it without problems the last I heard from him---- over a year after the service.
Many current production EL34's will not handle the voltage levels that the orig Blackburn Mullards have listed on the spec sheet----- In most tube guitar amps this is not a problem but vintage Oranges can be an exception.
So one could run high quality old production EL34's only or limit the voltage (screen grid is most important) so that many new production EL34's will last a reasonable amount of time in some of these vintage Orange amps.
Or always run a variac or bucking transformer to control supply voltage.
I watched a pair of JJ E34L's toast before my eyes, in a matter of seconds, in a '74 OR80 before I could take any voltage measurements or set bias.
I thought I had a couple of bad tubes so I put in a different pair of JJ E34L's and they toasted as quickly as the first pair.
I literally watched the red JJ paint on the tubes turn brown in a few seconds before my eyes.
These JJ E34L's probably would have had a normal lifespan in a more common amp (with sub 500V B+ and Screens) but they weren't up to the voltages in this OR80.
Before I installed more tubes I turned the bias pot to max neg voltage and put in a pair of Shuguang (Valve Art) EL34B's----- these tubes lasted long enough to take voltage measurements and set bias to 60%.
The Screen Grid voltage was very high but slightly lower than the plate voltage--- I don't remember the exact numbers----- I installed a dropping power resistor in the Screen supply, re-biased the amp---- I played it for hours to test it out-----then for more hours the next day.
The owner picked it up and was still playing it without problems the last I heard from him---- over a year after the service.
Many current production EL34's will not handle the voltage levels that the orig Blackburn Mullards have listed on the spec sheet----- In most tube guitar amps this is not a problem but vintage Oranges can be an exception.
So one could run high quality old production EL34's only or limit the voltage (screen grid is most important) so that many new production EL34's will last a reasonable amount of time in some of these vintage Orange amps.
Or always run a variac or bucking transformer to control supply voltage.
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dorrisant
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Re: Orange OR120 Fireworks
Thanks for the reply!
I'm getting these voltages:
Plates- 546 to 547
Screens- 542 to 543
Bias at pin 5- -61
All of these seem stable and all within a volt from tube to tube.
The bias is set at the lowest (most negative) setting.
I went ahead and inserted a 1.5k dropping resistor in the screen supply. Then I took these voltages. No red plating but there is a noticeable hum that gets louder if I turn the bias up.
The actual Winged C datasheet says max plate voltage is 800 but also states max screen voltage is 500... So maybe I should put a dropping resistor in there for the whole thing? From what I have been reading, it seems the plates should be at about 510.
Any further thoughts?
Tony
I'm getting these voltages:
Plates- 546 to 547
Screens- 542 to 543
Bias at pin 5- -61
All of these seem stable and all within a volt from tube to tube.
The bias is set at the lowest (most negative) setting.
I went ahead and inserted a 1.5k dropping resistor in the screen supply. Then I took these voltages. No red plating but there is a noticeable hum that gets louder if I turn the bias up.
The actual Winged C datasheet says max plate voltage is 800 but also states max screen voltage is 500... So maybe I should put a dropping resistor in there for the whole thing? From what I have been reading, it seems the plates should be at about 510.
Any further thoughts?
Tony
"Education is what you're left with after you have forgotten what you have learned" - Enzo
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Stevem
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Re: Orange OR120 Fireworks
New electrolytics does not mean that they are good, the ESR could be way above spec.In the passed 3 years I have started to check all new caps I install first for their ESR .
The hum could be from the bias voltage so I would check the level of AC ripple riding on that bias voltage, also that the bias voltage is fairly stable as the amp gets cranked up some.
Looking at that screen voltage and to keep the amp from popping tubes and coming back I would up those screen resisitors to 2K even if it may change the amps responce by 2 to 3 %.
The hum could be from the bias voltage so I would check the level of AC ripple riding on that bias voltage, also that the bias voltage is fairly stable as the amp gets cranked up some.
Looking at that screen voltage and to keep the amp from popping tubes and coming back I would up those screen resisitors to 2K even if it may change the amps responce by 2 to 3 %.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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dorrisant
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Re: Orange OR120 Fireworks
Yes, I installed a bad cap before. I have two ESR meters now. I always check new caps as soon as I get them in from the vendor.
Tony
Tony
"Education is what you're left with after you have forgotten what you have learned" - Enzo
Re: Orange OR120 Fireworks
You might consider a voltage regulator that does 110AC. What's your wall voltage? You could try JJKT88's if you think the heater current is up to it. I might try JJ 6CA7's as well, those are pretty sturdy, but unfortunately I wouldn't trust tubes that had already shown fireworks.
Are you seeing sparks in the tube? Or is it more like a thermal meltdown (if that makes sense)?
I sure wish they made 600v screen EL34's.
Are you seeing sparks in the tube? Or is it more like a thermal meltdown (if that makes sense)?
I sure wish they made 600v screen EL34's.
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dorrisant
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Re: Orange OR120 Fireworks
Yes I am seeing sparks inside the tube... Pretty pink an blue ones. Reminds me of a Roman Candle.
"Education is what you're left with after you have forgotten what you have learned" - Enzo
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Leo_Gnardo
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Re: Orange OR120 Fireworks
Makes ya wonder - what tubes DID work with Orange 120's & 80's - tough-as-nails real Mullards? @ 1974 I saw Hot Tuna play with a stage full of Oranges - at least a dozen - and Jorma complained "half the s#!t up here isn't working." 40 years later . . . it ain't any better.dorrisant wrote:Yes I am seeing sparks inside the tube... Pretty pink an blue ones. Reminds me of a Roman Candle.
Yes, reducing the SG voltage is a good move, also increasing the SG resistors to 1500 or 2000 ohms.
I've tried EL34 variants with some degree of success.
6CA7 - EH - no meltdown BUT a jingle bell noise accompanies every note. Good if you're playing the Winter Festival.
KT77 - JJ - also no meltdown BUT an unfriendly-sounding overdrive, when you do manage to push it into clipping. OK for unclipped signals, very Hi-Fi.
down technical blind alleys . . .
Re: Orange OR120 Fireworks
That sounds like half the JJ and EH power tubes I buy. It's very stressful.Leo_Gnardo wrote: 6CA7 - EH - no meltdown BUT a jingle bell noise accompanies every note. Good if you're playing the Winter Festival.
I bought a quad of these for the sole purpose of stress testing in a 550v screens amp. I wussed out, since I'm not in a state to blow $85 right now and I just don't trust their datasheet which claims 800V, I'm calling bull@#$% on that JJ.Leo_Gnardo wrote: KT77 - JJ - also no meltdown BUT an unfriendly-sounding overdrive, when you do manage to push it into clipping. OK for unclipped signals, very Hi-Fi.
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Leo_Gnardo
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Re: Orange OR120 Fireworks
Aw, don't you wanna give credit to JJ for copying Genelex's KT charts.eddie25 wrote: I bought a quad of these for the sole purpose of stress testing in a 550v screens amp. I wussed out, since I'm not in a state to blow $85 right now and I just don't trust their datasheet which claims 800V, I'm calling bull@#$% on that JJ.
So far the only more-or-less successful way to withstand hi B+ is to run the screen grids at half B+. Ampeg SVT's, Musicman, a couple others do this and get away with it. Would be a heckuva mod to do to old Orange and many other amps.
down technical blind alleys . . .
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gingertube
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Re: Orange OR120 Fireworks
This is not atypical of big amps with concertina phase splitters.
Consider what happens to the grids of the output tubes attached to the anode side of the concertina when B+ is applied by switching out of standby.
The coupling cap is uncharged (0V across it), when B+ is switched on you get a LARGE positive spike to the output tube grid. The spike goes away as the ccoupling cap charges.
That means you get a large spike in tube current too BUT note this happens on the push pull side fed from the concertina anode. This also happens with the side fed from the cathode but the voltage spike is 1/4 or even 1/5th that on the anode side.
Possible fixes
- limit the problem with diode clamps on output tube grid side of coupling caps, anode to the cap, cathode to 0V. These clamp diodes can also be put from output tube grid pin to cathode pin if you prefer. If you want to allow the grids to go just a little positive use 2 or 3 diodes in series.
- mod the standby circuit such that it ONLY affects output tubes by switching screen supply or similar. That is let the preamp and phase splitter run all the time and just switch the output tubes.
I've seen amps with concertina splitters blow B+ fuses as they switch out of standby from this problem.
It can also happen with amps with cathode bias, you get large tube current till the cathode bypass capacitor charges. Worst I saw was a cathode biased amp with a concertina splitter, switching out of standby was blowing the B+ fuse about every 3rd time. I modded that amp such that the standby switch was no longer a standby switch but a grid mute switch (The OR120 looks to be fixed biased so that would not be an option).
Stop abusing the tubes and they will stop failing on you.
Oh, big grid stops on the output tubes will help too.
Cheers,
Ian
Consider what happens to the grids of the output tubes attached to the anode side of the concertina when B+ is applied by switching out of standby.
The coupling cap is uncharged (0V across it), when B+ is switched on you get a LARGE positive spike to the output tube grid. The spike goes away as the ccoupling cap charges.
That means you get a large spike in tube current too BUT note this happens on the push pull side fed from the concertina anode. This also happens with the side fed from the cathode but the voltage spike is 1/4 or even 1/5th that on the anode side.
Possible fixes
- limit the problem with diode clamps on output tube grid side of coupling caps, anode to the cap, cathode to 0V. These clamp diodes can also be put from output tube grid pin to cathode pin if you prefer. If you want to allow the grids to go just a little positive use 2 or 3 diodes in series.
- mod the standby circuit such that it ONLY affects output tubes by switching screen supply or similar. That is let the preamp and phase splitter run all the time and just switch the output tubes.
I've seen amps with concertina splitters blow B+ fuses as they switch out of standby from this problem.
It can also happen with amps with cathode bias, you get large tube current till the cathode bypass capacitor charges. Worst I saw was a cathode biased amp with a concertina splitter, switching out of standby was blowing the B+ fuse about every 3rd time. I modded that amp such that the standby switch was no longer a standby switch but a grid mute switch (The OR120 looks to be fixed biased so that would not be an option).
Stop abusing the tubes and they will stop failing on you.
Oh, big grid stops on the output tubes will help too.
Cheers,
Ian
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dorrisant
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Re: Orange OR120 Fireworks
Ian, what value of diodes would you recommend?
Should I do anything about the excessive voltage on the screens?
Tony
Should I do anything about the excessive voltage on the screens?
Tony
"Education is what you're left with after you have forgotten what you have learned" - Enzo
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gingertube
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Re: Orange OR120 Fireworks
Tony,
Just ordinary power diodes will do (1N4007 or similar). They are reverse biased and therefore OFF in normal operation. Just there to handle switch out of standby spike.
The screen voltage is a problem particularly for El34 which are not known for robust screens.
Some of the schematics I've seen for Orange Amps of that vintage show 110V and 120V taps on the mains tranny. If yours is like this, then make sure you are on the 120V tap.
Increase the screen resistors, 1K are minimum for EL34 when run within their specs. I would be using 2K2 5W at least for the voltages you noted. Don't be afraid to go higher (like 4K7) if it does not add to much compression to the amp for your liking.
If this were not an original ORANGE but a home brew amp I would strongly recommend rewiring to take the screen supply from the half voltage node on the main capacitor bank but that would destroy its "originality".
My (limited) experience is that the Winged C Svet EL34 are the best of the modern production. They cetainly seem more robust than the JJ although I've managed to destroy some of each.
Cheers,
Ian
Just ordinary power diodes will do (1N4007 or similar). They are reverse biased and therefore OFF in normal operation. Just there to handle switch out of standby spike.
The screen voltage is a problem particularly for El34 which are not known for robust screens.
Some of the schematics I've seen for Orange Amps of that vintage show 110V and 120V taps on the mains tranny. If yours is like this, then make sure you are on the 120V tap.
Increase the screen resistors, 1K are minimum for EL34 when run within their specs. I would be using 2K2 5W at least for the voltages you noted. Don't be afraid to go higher (like 4K7) if it does not add to much compression to the amp for your liking.
If this were not an original ORANGE but a home brew amp I would strongly recommend rewiring to take the screen supply from the half voltage node on the main capacitor bank but that would destroy its "originality".
My (limited) experience is that the Winged C Svet EL34 are the best of the modern production. They cetainly seem more robust than the JJ although I've managed to destroy some of each.
Cheers,
Ian
Re: Orange OR120 Fireworks
Interesting, i always though Fender left the stnby off the 5E3 as it was a budget model, tighter margins/save some dough, but after reading this maybe they knew better??? I have one on my clone, never an issue, if I get bored I might change it to a mute.gingertube wrote:It can also happen with amps with cathode bias, you get large tube current till the cathode bypass capacitor charges. Worst I saw was a cathode biased amp with a concertina splitter, switching out of standby was blowing the B+ fuse about every 3rd time.