How about an 'Open bonnet' tutorial?

[MarcusBlacksmith]

Hey all,

Like many guitarists, I'm not very technically minded when it comes to valve amplifiers (yet).

I can gut a computer in under 10 minutes, but when it comes to high voltage electronics I gibber like a schoolgirl on LSD.

However, if I'm going to own a valve amp, there's nothing for it but to learn how to navigate my way around its innards safely. I mean simpler things like changing pre-amp tubes, or in my case, checking that the cable is plugged in to the reverb tank. Tube Bias is something I'm quite happy to leave to a good tech ^_^

So, what's the procedure? Treat me as if I'm even more stupid than I look: how do I open the amp properly (RV50H in my case).

What can I touch safely? What should I definitely avoid bumping into? Should I be grounding myself while changing tubes, etc, and what's the best way to ground myself?

How should tubes be handled to avoid damaging them?

How do I play 'Castles Made From Sand' without sounding like a dead possum? (Well, okay perhaps the answer to that question is obvious)

Look forward to your responses

[VintageJon]

Assemble a clip lead with a 240 Ohm to 1K 5 to 10W resistor in series with one end, insulate lead on end without resistor.

Clip resistor-end to chassis and then clip other, isulated, end to filter cap of your choice. (Orange amps have no standby so you're OK with these instructions. (Lack of Standby is the only design-argument I have with Orange, what are they thinking? SS rectifier and no Standby????)

Measure voltage on plates. When it falls below a few volts you are safe to work. LEAVE it there til work is completed...

With caps discharged and everything off, amp unplugged, you can touch everything.

CARDINAL RULE: Keep one hand in back pocket and use the other hand ONLY
as fatal shocks come from one-hand-on-chassis-andone-hand-on-HV.

Avoid dropping tubes, let them cool. In fact DON'T MOVE THE TUBES WHEN THEY ARE HOT.

-Jon

[vdub]

As long as you do not expose the circuit you are ok, so if you want to change valves switch off stanby switch and leave power on for a few minutes this should discharge any high voltage from caps, then switch it off unplug and let it cool, change valves. If you want to peek inside do the same but once open make sure again that caps are discharged. do not ground yourself - that could kill you. If you work with live amp (ie setting bias) work with only one hand making sure you do not touch a chassis

[Andy H.]

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by MarcusBlacksmith</i>
<br />Hey all,

Like many guitarists, I'm not very technically minded when it comes to valve amplifiers (yet).

I can gut a computer in under 10 minutes, but when it comes to high voltage electronics I gibber like a schoolgirl on LSD.

However, if I'm going to own a valve amp, there's nothing for it but to learn how to navigate my way around its innards safely. <font color="red">I mean simpler things like changing pre-amp tubes, or in my case, checking that the cable is plugged in to the reverb tank. Tube Bias is something I'm quite happy to leave to a good tech ^_^</font id="red">
So, what's the procedure? Treat me as if I'm even more stupid than I look: how do I open the amp properly (RV50H in my case).

What can I touch safely? What should I definitely avoid bumping into? Should I be grounding myself while changing tubes, etc, and what's the best way to ground myself?

How should tubes be handled to avoid damaging them?

How do I play 'Castles Made From Sand' without sounding like a dead possum? (Well, okay perhaps the answer to that question is obvious)

Look forward to your responses
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">Hey Marcus, is everyone here answering what you asked, or just telling you how to go about doing what you said you weren't going to yourself anyway...?

Yeah, big difference between the guts of a 'puter, and inside a valve amp. Don't even think about earthing yourself if you do go inside your amp. You do that inside a computer to protect its delicate ICs from damage from static electricity. Not a problem in amps - worry about protecting <i>yourself</i>! What would be a problem would be touching something hot (volts wise) while yourself being grounded. The current would then go straight through you, and the reason Jon said only ever to use one hand in the amp is to prevent that. Specifically to prevent a current going from one arm to the other, (right across your chest), and standing a good chance of stopping your heart!)

I'd say that either you want to learn the basics you can do without going under the chassis and exposing the circuitry, or else you want to learn to go in there safely. If it is the latter then listen to what Vintage Jon said about how to get rid of the high voltages safely. Be aware though that capacitors can partially 'recharge themselves' when first discharged - something called the 'memory effect'. Can give a nasty surprise, so you've been warned...

From what you are saying though I'm guessing you are just wanting some more basic amp advice. If you don't go under the chassis, (ie you can't see the circuit board), and don't poke anything into the valve sockets then you shouldn't directly come in contact with any high voltages. (And remember that the voltages in valve amps ARE high - <i>way</i> higher then mains voltage - definitely potentially deadly.

You don't need to go in there to change preamp valves of course. It is generally safe to just swap out preamp valves when sufficiently cool. Rather then just pulling them directly up out of their sockets, a slight side to side or circular rocking motion can help ease them out if a bit stiff. Note that the pins in the valve bases will only match up with the socket in one direction, so never try to force a valve back in - check the orientation is correct because 99% of the time you'll just end up bending a pin because it wasn't...

(BTW if you ever do bend a pin on a valve don't just try to bend it back - you'll likely crack the glass base. Instead a good way is to take the refill out of a ballpoint pen, silde the outer pen sleeve down as far as the bend in the pin, and gently bend it back <i>without putting any twisting force at the valve base itself</i>.)

See my post here for diagnosing 'microphonic' valves:
http://forum.orangeamps.com/viewtopic.php?t=2662

And my post here for advice on swapping preamp valves singly rather then all at once:
http://forum.orangeamps.com/viewtopic.php?t=4077

As to your reverb connections, there are no dangerous voltages, and you'll do no harm connecting it the wrong way.
(Topic currently being covered here):

http://forum.orangeamps.com/viewtopic.php?t=6411

Let us know about any more specific questions Marcus. But it is really good and wise to know your limits with HT (high tension = high voltage) circuits. Personally I let a good tech do my biasing and just check everything else seems AOK while in there. I'm well aware myself how easy it is for a small slip to become a big problem, and I'd honestly say to anyone who isn't 100% sure what they are doing just to leave it to a pro. I'm sure our resident amp techs won't argue with that too loudly... [:p]

Andy.

[MarcusBlacksmith]

Hi Andy,

Thanks, that's exactly the sort of information I've been looking for (and somebody should sticky your thread ).

You're correct in that I'm not planning on exposing anything below the chassis just yet. So far I should only be possibly changing the reverb valve, and checking the connection to the reverb tank - both above the chassis, right?

But it's all good information - Jon's comment vis a vis not earthing could just well save my life - if, for example, I'm unable to find a tech who can bias anything other than Marshalls ^_^

[VintageJon]

Marcus,
You are in no danger changing a pre-amp tube or working on the reverb cables.

I live in the High Volt lethal interiors, so I can let you know the how and why of that.

Nice post Andy! (Howdy to ya...)

-Jon

[MarcusBlacksmith]

Cheers, Jon, I'll be sure to ask if the time comes.

I do have another daft question for you all, though. How do I remove the amp from the wooden sleeve? I can't see or maneuver well enough to properly check the reverb cables without doing that.

The cable was resting on top of the large transformer directly below the reverb tank, so I manipulated it away from there, carefully. However, I can't get close enough to check that they're actually properly connected.

TIA,
Marcus