Run vintage OR120 as OR80 permanently - safe?

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vintagecharlie
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Run vintage OR120 as OR80 permanently - safe?

Post by vintagecharlie » Fri Jul 08, 2016 9:49 am

Hello all,

i am new to the forum and this is my first post here.

Recently i got my hands on a vitnage Orange OR120, looks like 1978 according to the serial number (015xxxx range). This is my first ever Orange amp, i tested it with 2 (outer tubes from the quad) tubes, as there was one not working tube from the quad the amp arrived with. On the first run-through it went fine and sounded good (with a strat), the second time i had it wide open - at about 70% volume and a Les Paul in front, then it popped the mains fuse and went dead. I suspect it was the tubes, so i put in a new pair of EL34s and just checked shortly with a new fuse - it works - so the transformers are fine and luckily no parts seem to be burned (HUGE relief). So off it goes to my tech for testing, before irun it wide open again.

I would like to run it permanently as an OR80 (i run it into a load box and the line out signal then goes into my DAW - this is one reason why i would like to avoid running it on all 4 tubes, as i am afraid, that being played wide open, it might surpass the max wattage that the load-box can handle (180w)) and from what i have read, the OR80 and OR120 are basically identical, including the transformers. But still, i also have read that the plate voltage rises considerably, when 4 bottle amps are run on 2 bottles. So now i am not sure, if it was simply an old/bad tube or it simply was run on too high plate voltage.
Also the amp was previously set on 240v and i left it during testing there, thinking it would not harm to lower the plate voltage (i am located in Europa - 220v outlet, which probably gives a bit more than that realistically). But that also means that the heaters don't get the full 6.3v, right?

Sorry for the long post - just a bit of context and background. So basically my question is, can an OR120 be run safely with 2 tubes permanently and what is needed for it to operate safely. Just correct bias, or i would still have the problem with too high plate voltages? How high are the plate voltages in an OR120 and how high are they when it is run on only bottles? Secondly, i would put the amp on 1/2 the load of the cab (e.g. head on 4 ohms running into load of 8 ohms). Anything else that needs to be taken into consideration?

Thank you very much in advance and best regards,

VintageCharlie

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Re: Run vintage OR120 as OR80 permanently - safe?

Post by Gladmarr » Fri Jul 08, 2016 3:05 pm

Basically, yes. Just remember when you halve the number of tubes, you must halve the value on the impedance selector for the same speaker load. 16 ohm load gets set to 8 ohm on amp, 8 ohm load gets set to 4 ohm on amp, etc.

fiveightandten
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Re: Run vintage OR120 as OR80 permanently - safe?

Post by fiveightandten » Fri Jul 08, 2016 10:46 pm

Plate voltages can vary, but from my experience they are usually in the low 500V range...in 70's OR-120s, i've seen them range from about 500V up to 520V or so. Though, i'm in the US, and this is running on US voltages (124V or so at the wall, running on a 115V or 118V tap, depending on the amp). Plate voltage will raise when pulling 2 EL34s out, but not considerably. You'd probably see 5V or 10V at the most.

Your concern about the heaters being starved is valid. They likely are a little low if you're running 20V low on the input voltage. It's easy to lower internal voltages, but a bit harder to go up. You could modify the heater circuit with some sort of a voltage doubler in there, then take the voltage down. Or, you could run a small filament transformer with the proper winding ratio for 220V input and run the heater lines off that. You could also just run the amp off a VARIAC (variable transformer) and run it at 240V, which would solve your issues without modification to the amp.

Make sure your load box is safe. Personally, i've had issues with tubes red-plating while using load boxes and I just don't trust them to be safe for the amp in the long term.

You should have your tech check the heater voltages to see what the amp is getting. If it's lower than 6V, i'd say that's too much of a drop. If it were me, i'd probably run the amp on a VARIAC to run it at true 240V. Though the filament transformer would be my 2nd choice. I would NOT drill the chassis of the amp to mount it and NOT drill any new holes in the amp to run the wiring. There are ways to get around it, but there isn't a lot of free space inside the OR-120 chassis.


I hope that helps a bit.

-Nick
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vintagecharlie
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Re: Run vintage OR120 as OR80 permanently - safe?

Post by vintagecharlie » Sat Jul 09, 2016 5:59 pm

So with a bias setup modern production EL34's can endure these high plate/screen voltages (from what i know, the screen voltages are the real problem, which, unlike plate voltage ratings of EL34's can be in the 450-500v range)?

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Re: Run vintage OR120 as OR80 permanently - safe?

Post by fiveightandten » Sat Jul 09, 2016 8:07 pm

vintagecharlie wrote:So with a bias setup modern production EL34's can endure these high plate/screen voltages (from what i know, the screen voltages are the real problem, which, unlike plate voltage ratings of EL34's can be in the 450-500v range)?
I've been running modern (and relatively cheap) EL-34s in my '71 head (see sig pic) for many years now. It sees about 510V to 515V on the plates and similar screen grid voltage and i've never had a tube fail in it. It is a non-master volume amp, so the tubes see hard use. I mainly run Electroharmonix EL-34s in it these days, but i've run Svetlana (not winged C, which I used to run as well) and JJ as well, without issues.

Modern EL-34's are decent from my experience. Some other tubes, like modern GZ34s are absolute garbage. But I, personally, don't worry about EL34s. I like EHs for a budget EL-34. Winged C (formerly known as Svetlana) are my favorite modern EL-34.

-Nick
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vintagecharlie
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Re: Run vintage OR120 as OR80 permanently - safe?

Post by vintagecharlie » Sun Jul 10, 2016 1:19 am

Thanks for the info - that sounds relieving. I have a pair of Winged C EL34s btw. which i actually planned to use for this exact amp - so good to hear that they should work fine.

It would be a likely scenario that the mains fuse blew because of the old tubes failing or could it be a different fault that lead the fuse to blow? Isn't it the HT fuse that blows with failing tubes?

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Re: Run vintage OR120 as OR80 permanently - safe?

Post by fiveightandten » Sun Jul 10, 2016 6:18 am

vintagecharlie wrote:Thanks for the info - that sounds relieving. I have a pair of Winged C EL34s btw. which i actually planned to use for this exact amp - so good to hear that they should work fine.

It would be a likely scenario that the mains fuse blew because of the old tubes failing or could it be a different fault that lead the fuse to blow? Isn't it the HT fuse that blows with failing tubes?
The HT fuse will blow if there is too much current being drawn through the B+ rail, or if there is a short. Dodgy tubes are usually responsible for it, often due to a partial short in the tube.

Whenever you blow a fuse in an amp:
1) Pull ALL the tubes out of the amp.
2) Replace the fuse and power the amp on without tubes in it.
3) If the fuse blows, it's a problem with the amp.
4) If the fuse didn't blow without tubes in the amp, start loading with TRUSTED tubes that you know are good.
5) Rectifier tube first (if there is one). Power on and see if the fuse blows again. If not, move on.
6) Pre-amp tubes next. Power on and see if the fuse blows again.
7) Power tubes last. Power on and see if the fuse blows again.

Use the results of this to narrow things down. It's important to note that if step 3 didn't pop the fuse, it doesn't necessarily mean there isn't a problem with the amp. Though in this case, you will likely find that the amp is just fine and the issue was a bad tube.

-Nick
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'71 GRO100 || '96 OR-80 || AD30 || '64 AC-50 || AC-30TBX || Hiwatt DR504 || HI-TONE HT30
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a.hun
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Re: Run vintage OR120 as OR80 permanently - safe?

Post by a.hun » Sun Jul 10, 2016 10:01 am

Hi Nick. Nice to see you busy here again. :D (More than I've been lately...)
fiveightandten wrote: Whenever you blow a fuse in an amp:
1) Pull ALL the tubes out of the amp.
2) Replace the fuse and power the amp on without tubes in it.
3) If the fuse blows, it's a problem with the amp.
4) If the fuse didn't blow without tubes in the amp, start loading with TRUSTED tubes that you know are good.
5) Rectifier tube first (if there is one). Power on and see if the fuse blows again. If not, move on.
6) Pre-amp tubes next. Power on and see if the fuse blows again.
7) Power tubes last. Power on and see if the fuse blows again.

Use the results of this to narrow things down. It's important to note that if step 3 didn't pop the fuse, it doesn't necessarily mean there isn't a problem with the amp. Though in this case, you will likely find that the amp is just fine and the issue was a bad tube.

-Nick
You really sure about suggesting pulling all the preamp valves though? The rest, fine, but...
viewtopic.php?f=3&t=51844&p=615689&hili ... mp#p615689" onclick="window.open(this.href);return false;

Good to see you are fairly happy with most modern EL34s these days. Yeah, I'd certainly prefer the =C= SEDs, but they are sadly drying up now.


@ vintagecharlie, hi, and welcome to the forum! :D

Think Nick and Gladmarr have basically covered it. Most important things here I think are indeed to run the amp one impedance step down to compensate for the changed output impedance, and to be really sure the loadbox you are using it up to it. If it is a quality commercial one rated for 100W power handling it probably isn't. If it is (realistically) rated for 150W it should just about be safe with an OR80.

Sometimes running hard into load boxes (and especially reactive rather than purely resistive ones) can get a bit iffy. Though if the load's impedance / resistance is reasonable for the amp (and it is highly enough rated for power handling) than usually the main thing that'll happen is showing up any amp / valve problems which would have happened anyway running that hard into speakers. Problem of course is that the sheer volume when actually doing that tends to cause you to run more moderate amp settings. Running quietly it is much easier to get silly - been there myself.

I sometimes run my OR120 fairly hard into my THD HotPlate, (rated for about 170 - 180W realistically), and that is probably pretty marginal for full attenuation with the amp working hard for any length of time.

I did once blow the HT fuse (only) though on my old DR103 Hiwatt by basically maxing it out into the HotPlate. (Tone controls, everything on full - bit stupid really as didn't sound that great that way, but was curious. ;)
Diagnosis: arced power valve(s), very probably what happened to yours. Fortunately my old Mullard EL34s survived this (usually do apparently) so replacing the HT fuse was the extent of the damage for me.
(Additional advice was not to always totally trust the impedance rating of the Hotplate or other reactive loads as that - by definition - varies a lot at different frequencies and the impedance curve may not correspond that closely to the real speakers you use. Actually rather safer with a resistive load that way and some of these happily also sound very good.)

Can happen though and my Orange is probably slightly more powerful real world (with the old Teslas I still run in it) than the Hiwatt. Both are monsters of course - even a healthy OR80 with decent valves still is frankly!

What sort of load are you using with it?


Andy.
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In the bathtub of history the truth is harder to hold than the soap, and much more difficult to find!

vintagecharlie
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Re: Run vintage OR120 as OR80 permanently - safe?

Post by vintagecharlie » Sun Jul 10, 2016 11:27 am

Gibson Power Stealth, which is basically identical to THD Hot Plate, just rebranded, 8 Ohm, 180w power handling. And, yes, hence i want to run it as an OR80, as i suppose it can max out at double of the 80w rating. I have been running my JTM 45/100 clone with all 4 valves without issues this way for a long time. A Hiwatt DR504 seemed to work well too with this resistive load.

I popped the MAINS fuse in my case, not the HT fuse, hence i am wondering what might be the cause for the MAINS fuse popping. Interestingly i ran the OR120 for about 30 mins into the hot plate on Load setting with a strat without issues, including some couple minutes at 100%, but the fuse was blown when i ran it through the hotplate on -12db through an 8hm cab (amp set for 4 ohms, hot plate being 8 ohm too) and played through les paul and i was, IIRC not above 60-70% on the gain (fullest FAC setting) (which i would consider a normal use, as this is a spot where the amp delivers good tones before getting fuzzy).

Also i was thinking about building a reactive Aikens Dummt Load for this and other amps i have. So in your experience reactive loads can put more strain on the amp than a real cab? In theory it should be the same? I would build it for a 300w power handling to have some over-head.

a.hun
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Re: Run vintage OR120 as OR80 permanently - safe?

Post by a.hun » Wed Jul 13, 2016 12:09 pm

vintagecharlie wrote:I popped the MAINS fuse in my case, not the HT fuse, hence i am wondering what might be the cause for the MAINS fuse popping. Interestingly i ran the OR120 for about 30 mins into the hot plate on Load setting with a strat without issues, including some couple minutes at 100%, but the fuse was blown when i ran it through the hotplate on -12db through an 8hm cab (amp set for 4 ohms, hot plate being 8 ohm too) and played through les paul and i was, IIRC not above 60-70% on the gain (fullest FAC setting) (which i would consider a normal use, as this is a spot where the amp delivers good tones before getting fuzzy).
Well hopefully if it is at the tech's now and they 'know their Oranges' (not just funny coloured Marshalls by a long way!) they'll find out why the mains fuse blew. Sorry, I was thinking HT fuse too, though you did say 'mains' right enough. :oops:
Also i was thinking about building a reactive Aikens Dummt Load for this and other amps i have. So in your experience reactive loads can put more strain on the amp than a real cab? In theory it should be the same? I would build it for a 300w power handling to have some over-head.
I'd say 'potentially' so. It really depends on different load / cab / amp combinations. For example here is some advice I got by mail from my old tech John P when I had that Hiwatt problem. (John is a very good tech BTW, knows more about amps than almost anyone out there, same guy quoted on that link I gave earlier) .
John Phillips by e-mail wrote:HT fuses blowing with the Hotplate is not too surprising, and is not necessarily (too) serious. I like the Hotplate (soundwise) but it has a major disadvantage in that it doesn't have the correct impedance curve to duplicate a real speaker, and this can put a lot of extra stress on the valves, especially at full attenuation with the Deep and Bright switches turned on. It's likely that a power valve arced over - it may or may not be permanently damaged, old Mullards usually survive this sort of thing but modern ones tend not to… try replacing the fuse and watch the power valves carefully when you switch from standby to fully on - if one arcs again, you'll probably see it.

If you're really cranking the amp up with the Hotplate, it's best to set the amp to one impedance step below the Hotplate's specified impedance - eg 4 ohms with an 8 ohm Hotplate - which brings the load back into a safer range. It should handle a cranked 100W amp OK, anyway. Maybe pushing it with the Orange, but the Hiwatt is slightly less extreme, in fact.
That was the sort of thing I meant really. And in this case with two valves pulled you might actually have been better using an (unavailable!) 2 ohm amp output... ;)
Aiken is of course another guy with spot on amp knowledge. (His FAQs have long been among my own personal amp bibles!) So though I've not found any links to his dummy load it should be very good. He is a great guy and would probably be able to advise specifically about use with that amp.


Andy.
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Ever tried to outstare a mirror?

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Re: Run vintage OR120 as OR80 permanently - safe?

Post by skylark » Sun Jul 24, 2016 9:46 am

Hi folks! Iam the same guy behind vintagecharlie username. I could not log in with my previous user and do not receive mails from the forum, so i was forced to create a new one in order to be able to log in.

So i got the OR120 back from my tech - he tested it and all was fine. He thinks that the old mains fuse simply was on its last leg - nothing wrong with the amp. It is now biased properly with a new pair of EL34s (i run it as an OR80) and i tested it properly now. I also had the chance to compare it to a Marshall JTM 45/100 clone side by side. And i was blown away by the fact how similar they sound (of course, while both amps are in the tonally overlapping region, not the extreme settings of either one). I did some recordings and A/B'd side by side - they sound close to identical. I like the cleans on the JTM 45/100 better (but the Orange cleans also sound really nice), i prefer the way the JTM cleans up with the volume knob and i prefer how it sounds with overdrive/fuzz/distortion pedals.

To be honest, i am a bit surprized why people say that the Oranges are much darker than Marshalls - at least the old ones seem to be voiced extremely similar to OR120. The Orange of course has tons of more gain and it can get SUPER bassy if needed. But within the rather normal range of the gain know (up to about 50%) it acts and sounds very similar to a JTM. Past 50% on the gain the circuit obviously rolls down treble and the sound gets progressively darker and leads into a territory where it is clear, why stoner metal guys love this amp. Indeed it is right, what i've read by other users - when Orange is really cranked, it starts to get dark and becomes like a thick fuzz. In contrast, the JTM starts to sound like a thinner and more spitty type of fuzz once it is close to max volume. So they "fall apart" in a very different way.

But, yes, the OR120 turned out to be a super versatile amp (i am still stoked at how well the tone controls work on this circuit - compared to Marshall and even Hiwatt) - from clean to mean, to doom :D

Thanks for the suggestions and comments!

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Re: Run vintage OR120 as OR80 permanently - safe?

Post by Kristian Ford » Sun Jul 24, 2016 2:25 pm

I'm thinking of doing this as well.. :wink:
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Re: Run vintage OR120 as OR80 permanently - safe?

Post by skylark » Sun Jul 24, 2016 9:17 pm

Been playing around with the controls of the OR120 - it is probably one of the most cleverly figured out set of controls for an amp that i've seen around. Really extremely versatile. Also looks like it is possible to get cleans very close to those of a JTM 45/100 (just with less headroom and slightly different tonality - here i still clearly prefer the JTM). Digging this amp more and more (while as i got it, it seemed to be my least favorite). Everything written here on the forum about the versatility of the Baxandall seems to be true - that alone is very effective to sculpt the tone + the hf drive works perfectly and just how you would imagine "high frequency drive" - adds sligthly overdriven shimey sparkle, or when turned down low, smoothes out the tone. Don't use the FAC a lot, but can see how it can get extremely handy in a lot of situations, especially when residing in the higher gain settings - it is easy as pie to get really usable and different highly overdriven neck pickup sounds without everything turning into mush - very unique (ok, to an extent an EQ pedal would allow basically the same, but still - cool to have that in an amp).

Get the hype now. Love it!

skylark
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Re: Run vintage OR120 as OR80 permanently - safe?

Post by skylark » Sun Jul 24, 2016 9:37 pm

Kristian Ford, looks to be running well so far. But in general this should be perfectly safe with any Push-Pull amp that has 4 valves (i've done it on my JTM 45/100 previously too, but Oranges are new territory to me). Only it has to be biased properly and the impedance on the head has to be halved - my amp tech confirmed everyhting that the folks here already noted. If my Orange starts to catch fire, i will report here...

Again, thansk for all your input and advice!

a.hun
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Re: Run vintage OR120 as OR80 permanently - safe?

Post by a.hun » Thu Jul 28, 2016 8:49 am

Hey, great that the amp seems healthy skylark. Bit surprised by the Marshall comparison myself, but as you say the simple controls do make for a very versatile amp indeed. I tend to shy away from Marshall sounds myself - just not my thing - so I haven't explored how it works in that tonal range. But a mate of mine who was a very early OR user back in the '70s did say he used to set his FAC and EQ for that zone and was able to seriously scare Plexi users in other bands. Pretty nuts back then I suspect...

You'll have fun, there are definitely plenty of sounds to be had from the old ORs.

BTW you a Hiwatt owner too then? Here are my three favourite classic Brit amps, my '78 Orange OR120M Overdrive, '74 Hiwatt DR103, '65/'66 Vox AC30TB(B). :D
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Andy.
aNDyH. :wink:

Ever tried to outstare a mirror?

In the bathtub of history the truth is harder to hold than the soap, and much more difficult to find!

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