I've found on early Marshall Amps, that when the surface between the pot body and the chassis become tarnished or compromised with age, literally loosening them off, giving them a good old twist around and doing the nuts up again usually cures this. Sometimes wedging a screwdriver between the chassis and the pot and giving them a tweak will show the bad earth up. Sounds like nonsense I know, but I've seen it so many times now, and let's say I work on Marshalls exclusively in my day job. Interesting amp Stu, I've never seen inside an Orange amp before. Thanks for the video. DW

@stuartukguitarampguy5830

2 жыл бұрын

Hi. Goiod thoughts but I'd alreadybeen around with my huge thick earthing cable and tried everything.

@torquilmacd

Жыл бұрын

​@@stuartukguitarampguy5830 Are you sure that your thick grounding wire was getting a good enough contact to the pot casing when you tried to ground the pot casing through the wire? I'm asking because the pot casing looks quite black/tarnished.

@stuartukguitarampguy5830

Жыл бұрын

@@torquilmacd Hi Yes absolutely. I tried everything with that amp!

this one could be the best video yet. excellent Stuart.

@stuartukguitarampguy5830

2 жыл бұрын

Thanks David! I MUST learn to hold the camera steadier though!

I used to mend tube amps in my Uni days while studying electronic engineering ... I've had experience with Vox Marshall Orange and various other lesser know amps .... Hum emanates from three causes or combination thereof .... First check the HT filter caps ... and check the diodes in the bridge rectifier ... Next check the earth connection from the power socket to the amplifier chassis any break or high impedance will cause hum . There usually is a separate ground circuit routed through the amplifier which is only for audio signal and usually a 10 ohm wire wound resistor can be used to connect the ground circuitry to the EARTH ground going to the mains socket . Check that all input jacks have a grounding connections to remove stray input hum . You can try looking at the HT line using a scope to determine if there is any noise on that line ... ( any noise would not affect the push pull output tubes as the anode winding centre tap to HT is a common mode ...) Lastly change all the potentiometers ... and check their cases are well grounded to chassis .

@stuartukguitarampguy5830

3 ай бұрын

All good advice thanks

Excellent troubleshooting notwithstanding, my favorite parts of the movie were @14:18 & @15:09, with Stu's portrayal of an electromagnetic interference generator --- that made me "LOL!"

@stuartukguitarampguy5830

2 жыл бұрын

Ee' lad I'm a natural mimic, me...

"The orange amps were designed by Matthew Mathias and manufactured by Cliff Cooper in Huddesfield, Yorkshire, England. Cliff Cooper also had a retail store in London by the name of Orange. Cliff marketed his amps under this name in London and the South while selling them under the name of Matamp in the Midlands and the North. This was a common practice at the time, because the north and south of England were so different in style and taste."... That's from Aspen Pittmans book The Tube Amp Book.....

@stuartukguitarampguy5830

2 жыл бұрын

Very interesting thanks. I didn't know ANY of that! I wondered why it was called a Matamp! Hmm... Stuamp... doesn't quite have the same ring...

@Nomdeguerre

2 жыл бұрын

That is not even remotely close to the truth. Cliff wanted to built his own amps as his store was selling mostly used gear, but as he was no tech he needed someone to build the amps for him. At the time, Peter Green owned a Matamp Series 2000 (which he used on their hit single Albatross). This amp got Cliff intrigued and contacted Mat to ask him to build the amps for him. Mat's condition was that they had to say "Matamp". Cliff didn't like it but eventually agreed to call the amp "Orange Matamp". The very first prototype was a Series 2000 amplifier put in a new head case designed by Cliff. It had thicker edges with a "picture frame" look, Orange tolex and the Orange Matamp front panel. The following 10 prototypes had more power and three added "Depth" settings and was used on tour with Fleetwood Mac. Matamp amplifiers have always been built in Huddersfield since 1962. Orange didn't start making their own amps until they moved their production to Bexleyheath circa 1971 and could finally drop the "Matamp" off the front panel. Very few, if any Matamps were built during the Orange Matamp era as Matamp had a hard time keeping up with sales.

great repair my matew just got one of my girlfriend .must share this channel with him .great work

the fact that hum is more apparent at half or 3/4 of volume is due to the impedance which is maximum there,that said it could be a microphonic coupling cap or a bad grounding connection anywhere

@stuartukguitarampguy5830

2 жыл бұрын

Ah, interesting insight thanks.

Fender had this problem and fitted a brass plate behind the pots and earthed the pot boddies to it. I have used this method on sound city amps and it works.

@goodun2974

2 жыл бұрын

40 or 50 years after those amps were built, it is a good idea to unbolt all those pots, and the input jacks, and clean both the brass ground plane and the faceplate where the shaft nuts tighten up against it. The payoff is a significant reduction in hum and noise. However, Fenders aren't the same as modern high gain amps, where a similar shared ground plane often tends to act as a ground loop. Ideally, audio grounds should never be tied to the chassis via the body of the pot and its mounting hardware.

@stuartukguitarampguy5830

2 жыл бұрын

Hi Stewart, yes but I'm not convinced this was the case here as I'd already tried with my massive thick grounding cable and it made no difference. Possible though, I guess. I've also seen Uncle Ted go to the trouble of doing this mod (it's a fair bit of work) only to have zero effect on the hum.

Thanks for another great video Stuart. I thought u said u didn't play guitar. You were rocking at the start of this video!!

@stuartukguitarampguy5830

2 жыл бұрын

Ha ha. I'm a bit of a one-trick wonder on the guitar.

Great info here. Thanks for sharing. I have a 77’ or80

@stuartukguitarampguy5830

Ай бұрын

Thanks.

Hello and thank you for the great and informative video. I own an Orange OR120 since 30years which was in a horrible condition. I bought a specially fine tuned set of tubes 15 years ago. Then "Radio Moscow" reception was gone, but the hum was not completely gone. When I move the controls back and forth, it sometimes gets better and sometimes worse. I haven't changed the capacitors yet. But I had planned to do that soon. It would be so nice to be able to play the amp again, because it sounds amazing. But when I take it to the studio or a big concert with digital mixing consoles, they chase me away ;-) Thanx a lot, groovy greetings from germany, Kay

@stuartukguitarampguy5830

4 ай бұрын

Hi I hope you manage to get it sorted. Hum can be quite hard to locate and fix.

Love your videos!

@stuartukguitarampguy5830

2 жыл бұрын

Thanks Jeff!

Very interesting video and noise problem! The wire soldered to the pot is called a 'gimmick' capacitor. It creates a small capacitance of a few picofarad to ground. I have seen this used in high frequency oscilloscope probes to tune the probes compensation. That said, the small capacitance of the wire affecting a large improvement in hum reduction seems to indicate there is a high frequency noise issue present. I would say a high frequency noise with mains frequency noise riding on top of it.This could be an oscillation or high frequency noise spikes caused by diode rectification. The rectifier and first bulk strorage cap are nearby so the noise field could be coming from these components. Regarding the giant grounding wire tests, this is a great too for finding low frequency hum issues. But at high frequencies, it will have inductance due to the loop area and may not be effective at shorting high frequency noise. To me, it does not look like the noise is due to pots and jacks being tightened or bad filter capacitors. An oscilloscope would have been a good tool to try to identify the cause of the noise. A hope probe with the ground lead shorted to the tip of the probe is great for locating noise fields. Great video Stuart! I really like watching your videos. I have learned some very helpful things from you.

@stuartukguitarampguy5830

Жыл бұрын

Thanks for your interesting insights John.

Certainly a strange one..! That hum was bad, but your experience shone thru..Nice fix Stuart, and a cool relic..Ed..UK..😀

@stuartukguitarampguy5830

2 жыл бұрын

Cheers Ed.

Love your videos, and your giant ground cable chasing hum, excellent practice I think. My thought was the shield on the inputs and pot, you are only to ground one side of a shield. All those shielded cables running right past the very same area. The giant cable wouldn't have done anything to make it go away in that case. So I wonder if you checked the shielded cables to see if it was grounded on both sides or just one as it is supposed to be. Many people make that mistake, perhaps another tech before you or a previous owner that didn't know what they were doing, saw an ungrounded shield on one side and decided to ground it causing the loop. 50+ year old amp may have seen many techs and well wishers over the years. Perhaps your aerial found the center between and as you said 180 degrees out of phase killed a lot of it. Another potential fix would be to hot shield to the B+ but only one side.🙂

@stuartukguitarampguy5830

2 жыл бұрын

Great thanks. Yes I'm pretty sure I cjecked those shields. The odd thing about this one is that NOTHING made even a 1% difference to the hum. I've never had that before.

Great experiments ✊🏻👍🏻🙏🏻 very interesting

@stuartukguitarampguy5830

2 жыл бұрын

Thanks Thomas.

This was quite a poser, Stuart. Your patience is extraordinary. If I'm not mistaken, that model was used by Blue Cheer. It was indeed intriguing to see and hear it in real time. I'm glad you had a duet of EL-34 handy. As I understand it; tubes are becoming scarce. Enjoy your evening.

@stuartukguitarampguy5830

2 жыл бұрын

Thanks Alex. I can do you a great deal on a pair of EL84s - just £200 to you my son...

Valco amps often used a similar bent bracket of sheet metal as a shield for the control pots; Danelectro went one further in the cheapness department and used a piece of cardboard with aluminum foil on one side of it as a control shield!

@Dr_Reason

2 жыл бұрын

But they used tone cardboard. (and imported aluminum foil)

@stuartukguitarampguy5830

2 жыл бұрын

No expense spared!

I enjoyed it. Thanks!

@stuartukguitarampguy5830

2 жыл бұрын

Great, thanks for watching!

Plus one for remaking and cleaning all the threaded and soldered grounds , if it isn't tube or capacitor related .But as you say , there are other possibilities . What fun !!!! 😂

@stuartukguitarampguy5830

2 жыл бұрын

Fun... fun... ah yes, I do recall having fun once....

Howdy. Absolutely great. A common problem with high impedance circuits. They easily pick up stray fields. Is the hum 50/60 Hz or 100/120 Hz ? To me the pitch suggest the latter. Would be worth the effort to check with an oscilloscope. It bewilders me why amp. manufacturers don't comply why the Rule n:r one. Never use the chassis as the minus/ground conductor. Use a separate minus wire as a ground bus. Connect the stage minues to the bus in the order of signal propagation. The bus should be connected to the chassis only at the input jack. The filter cap.s should be connected to the bus at the bus other end. The end tubes should have their own minus wires connected to the same end bus point as the filter cap.s. The filter cap.s should be mounted free floating from the chassis using screw bushings with the clamping collars. Pot.s should also be mounted using bushings and a casing grounding wire should be soldered onto the casings. This wire should run from pot to pot and be connected to the chassis only at the same point as is the minus bus. Regards.

@stuartukguitarampguy5830

2 жыл бұрын

Hi Eugene. Yes that's absolutely the way to do it!

looking forward to new vids soon I hope..cheers!

Serial 016! Nice.

I'd suspect that the volume pot wasn't grounded, but I'm guessing that you tried that. Still, this has the feel of the old days when someone would have to hold television rabbit ears antenna *just the right way*, or the channel wouldn't come in.

@stuartukguitarampguy5830

2 жыл бұрын

No it wasn't that as I'd already used my thick piece of cable to ground this and that. Do you remember that Mr Bean episode where he's trying to get the TV working? Hilarious.

Replace all potentiometers and those wires on the volume pot should be replaced too. 😂🚜🚛

Hi Stu, I wonder if screening the pot with some metal foil tape to the chassis might have helped? I have a valve Ferguson record player here that is doing a similar thing, I plan to add a few micro volts of out of phase juice to the hot fader tag trying to fix it!

@stuartukguitarampguy5830

2 жыл бұрын

Hi. Nice idea but I'd already used my thick piece of grounding cable to check for grounding issues.

The most sensitive part of the amplifier being so close to the HT Caps is not good. Would be worth removing the volume pot to get it away from the HT to see what effect it had.

@stuartukguitarampguy5830

2 жыл бұрын

Yes agreed, not good layout. You'll recall how my 'aerial' went crazy if I moved it anywhere near those caps.

"OK, the ACME HumReducer Mk. II" 🤣

I bet it's a problem with the chassis not grounding the pots correctly as there is clearly a lot of corrosion there.

@stuartukguitarampguy5830

2 жыл бұрын

Hi Scott. Nice idea but I'd already used my thick piece of grounding cable to check for grounding issues.

This was one of Jimmy Page's favorite amps. I have always wanted to have one.

@stuartukguitarampguy5830

2 жыл бұрын

Interesting. They are quite rare these days.

FYI: that pot labeled "max" on the topside of the chassis is tied to the Depth control on the front panel

@stuartukguitarampguy5830

Жыл бұрын

Ok thanks.

Hi Stuart... love the vids... just a thought ... on the input female jack did it ground out properly without the male plug in it .... I've run into the input jack ground sleeve being dirty and somewhat worn and not connecting for the continuity for the ground.

@stuartukguitarampguy5830

2 жыл бұрын

Hi Christie Tbh I can't I can't remember as it was a while ago. I probably would have tried that. Good thought though.

Guitar pickups are often encased in wax to reduce noise. Is it possible to encase a pot?

Always very instructive... but why not try and replace the volume pot?

@stuartukguitarampguy5830

2 жыл бұрын

Thanks. Why? That wasn't the issue.

If you remove the pot completely

I have that schematic

What I have a newbie problem with is how to get the metal module out of the housing? I don't want to just force pull it out, out maybe should I? 😅

@stuartukguitarampguy5830

Жыл бұрын

Hi Radek Do you mean getting the chassis out of the orange wooden housing? I don;t recall there nbeing and particular problem with this. Once the 4 screws are out it should just slide forward.

Hi Stuart you may have tried and I missed it, but did you ground the can sheild on the pai?

@stuartukguitarampguy5830

2 жыл бұрын

Hi Monty. Couldn't quite understand what you meant. Did you mistype?

@montygore

2 жыл бұрын

sorry stuart. I mean grounding the pot sheild to ground. Love the videos.

May be worth replacing the bridge rectifier with one made from discrete UF4007 + snubber caps.

@stuartukguitarampguy5830

2 жыл бұрын

Interesting idea, but why do you say that?

@VintageSG

2 жыл бұрын

@@stuartukguitarampguy5830 Diode switching noise is a pain in the rear. It can, and does, induce noise in the most awkward manner. The noise often isn't seen on the power rails post rectification as it's mainly a spike reflected back the transformer. Noise post rectification gets squashed by any choke or filter cap, but that back EMF can get induced in nearby signal wires, appear in the chassis, generally be a pain in the arse. Stick an x10 probe on the rectifier, mains side, and see if there are any spikes. The UF series are ( generally ) quieter than IN, and it's super easy to add snubbers to a discrete rectifier. Bit of a straw-clutch, but cheap, simple and reversible.

@stuartukguitarampguy5830

2 жыл бұрын

@@VintageSG Ok useful info thanks.

The problem IMHO is the proximity of the two input jacks on that side close to the power transformer. I have had success with disconnecting this feature on these amps with consent from the owner of course.

@stuartukguitarampguy5830

2 жыл бұрын

Interesting. Where did you relocate them to?

@diedraak1

2 жыл бұрын

@@stuartukguitarampguy5830 I got permission from the owner to remove all wiring from those sockets. IOW they are no longer used. A bit of a bummer, but the amps is dead silent. On later revisions these sockets were no longer used in this position

Don't know about those ARS cans though.

Those 16+16uF mains caps are too small imho for this amp. The original caps were 50+50uF, i Installed 100uF and the amp is dead quiet and sounds very sweet.

@stuartukguitarampguy5830

Жыл бұрын

100+100 is a bit too big in my opinion. Maybe 50+50 would be better. 1000 MAY be ok but such a karge cap can cause a bit of a surge on switch on. Not 100% sure on this one tbh.

@crystaldive_tv9475

Жыл бұрын

@@stuartukguitarampguy5830 I joined the legs of each cap, so i ended up with 50+50. Do you remember how high the B+ was on the amp in the video? Unfortunately the one i had repaired already had replacement transformers and the B+ was at a whooping 500V without tubes installed, so i had to bias it quite low around 28mA plate current...

@stuartukguitarampguy5830

Жыл бұрын

@@crystaldive_tv9475 Hi Ok yes that's fine at 50+50. I donpt recall the B+ but 500V without tubes is ok, Would probably be about 465 with?

@crystaldive_tv9475

Жыл бұрын

@@stuartukguitarampguy5830 It's sitting at 490 with tubes, so im not surprised my unit had it's OT replaced once already... I also noticed from your video that my amp is lacking the 5w 10k dropping resistor sitting between those .047 coupling caps feeding the PI. Looks like each unit is a different amp with these ORST's...

Extremely interesting and what a pain. Poorly designed layouts soon show up fooling all but the best techs. We would like to believe the designer was accurate but too often a field fix is the only cure.

@stuartukguitarampguy5830

2 жыл бұрын

Hi Larry They barely 'designed' things back then, Just threw them together and hoped they worked!

I've not powered mine up in a while, but I think mine might.. do the same.... I could be wrong.

@stuartukguitarampguy5830

Жыл бұрын

It might have been a 'feature' !

@Combine_Harvester_of_Truth

Жыл бұрын

@@stuartukguitarampguy5830 Well, I know who to go to if I want my Orange Matamp fixed.:). Last person to work on it was Jeff Lewis at Matamp.

@stuartukguitarampguy5830

Жыл бұрын

@@Combine_Harvester_of_Truth I'll wear gloves so as not to erase his hallowed fingerprints...

Something about the way the input jacks are wired looks fishy to me.

@stuartukguitarampguy5830

Жыл бұрын

Your comment reminds me of the aircraft fault log. The pilot had written "Something loose in cockpit". The mechanic had replied with "Something tightend." !

Im sure a man of your calibre could have drawn a circuit diagram from the physical amp itself, whilst you had the chassis out. ( hope you did) 😉😉

@stuartukguitarampguy5830

9 ай бұрын

Yes I could but it's quite a long job. (I didn't!)

Enough with the ads.I’ll let you advertisers know the more you do the less I listen

@stuartukguitarampguy5830

7 ай бұрын

Hi Pat. The really annoying thing is I have zero control over this and also do not get paid a single penny! That's KZread for you!

@patreidcocolditzcastle632

6 ай бұрын

@@stuartukguitarampguy5830 all good love videos entertaining to my geek mind