Valve Swappin' Compatability; *n00b* Alert!

[ShortCon]

Hello all! This is my first foray into valve amps and I'm quite excited by the 'tweakage' possibilities, but am unsure of just what I can get away with.

The skinny: I recently (last night, actually!) bought an AD30HTC on eBay. I've been reading many of these forum posts on tube swappage and have yet to find an answer to what may turn out to be the simplest of questions: Can I swap out the EL84's for some other kind of power tube, i.e. EL34's, 6L6's 6V6's, or am I restricted to just auditioning EL84's from various manufacturers to shape my tone? Also, would the same apply to the preamp valves?

Thanks in advance for your patience!

[ShortCon]

EL34's? But it comes stock with EL84's. Is that what you meant?

[Simon Wicks]

Yup, just el84s i'm afraid. Nine pin sockets...

Just make sure they are matched quads and they dont red-plate when being used. You can however swap in pretty much any 9 pin pre-amp tube. ecc83, 82, 81 etc.. Theres loads of different variants. The pre-amp tubes can be had fairly cheap off Ebay allowing you to experiment with tubes to get your best tone.

[ShortCon]

Sorry, but what is red-plating? I'm an utter newborn to the world of valves, but I'm doing my damndest to catch up quick. Thanks.

[irish_admiral]

If you look at the base of the power valves (the larger EL84s) when they light up, and see whether they glow red around the base. This is usually an indication that the amp isn't correctly adjusted (biased) for the valves.

Most EL84s are fine - you can just pop them in and go. It is far better to get a matched quad (ie. the sort of performance each valve gives is the same in the quad).

It is normal for each valves to have an orangey-red glow caused by the filament inside it. It's not normal to have it right at the base of the valve (ie. redplating).

[Simon Wicks]

If you look inside any valve, you'll see a box like structure or cylinder structure (or two in dual triodes). The outer plate should not glow. It should remain cool (ie not glowing). The only bit of the vale that should glow is the heater which occurs on the inside of the box structures. You'll see them start to glow when the amp is switched on.

When i said red-plating, i mean that if the amp is putting out too much heat, the box inside the tube will glow red, or in severe case orange or even white! You should check in a darkened room aswell. Any faint red glow on an el84 tube indicates the bias is not correct.

The bias basically regualtes the flow of electrons within the tube. These types of amps are know as cathode biased which basically means that any matched quad of el84s will work. However, if you see red plating, you need to get a tech to raise the cathode resistor value. I wouldnt worry too much about the AD30 though, it should handle any tubes you put in. Though old tubes from the 70's and before might need a tech to change out the cathode resistor.

When choosing tubes, let your own ears be the judge. I'm quite snobbish compared to most here when it comes to valves. I only use new production valves as a stop gap or test bed for my amps. I prefer the older tubes for my amp. Thats me though. Also modern amps tend to like the newer tubes more than older tubes.

Also, watch about poking inside amps unless you know a bit. They can kill you. Changing tubes is pretty safe but the innards are dangerous.

Have fun and ask away if theres anythign you want to know! There are some pretty knolwedgable guys here.

[ShortCon]

Thanks for bringing me up to speed, guys.

[Andy H.]

Yes, to be clear on red plating, it isn't the normal glow of the (low voltage) heater filament which is often visible near the top and / or base of valves which you have to worry about. It is as Simon says the plates themselves (the outer part of the metal 'box' structure inside the valves glass bottle) which you don't want to see glow at all.

For example the second valve from the left here is red plating a little. See the strip of dull red glow about halfway up the valve?



Always worth checking your power valves (any amp!) now and again in a darkened room for any signs at all of this. It isn't healthy and if you see it (even slightly!) shut the amp down and get a tech to check the biasing. (Only real exceptions might be known very hot running amps (eg Vox AC30) if fitted with particularly strong old valves (eg real Mullards) which will probably come to no harm with some mild red plating. Any other amps / valves are at serious risk if you ignore red plating as things can literally go into meltdown.

(See the pics about halfway down this page...)
http://forum.orangeamps.com/viewtopic.php?t=10331


Andy.

[Neiloler]

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Simon Wicks</i>
<br />Yup, just el84s i'm afraid. Nine pin sockets...

Just make sure they are matched quads and they dont red-plate when being used. You can however swap in pretty much any 9 pin pre-amp tube. ecc83, 82, 81 etc.. Theres loads of different variants. The pre-amp tubes can be had fairly cheap off Ebay allowing you to experiment with tubes to get your best tone.
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Just to clarify, make sure that you're not trying to stick these tubes (ecc83, etc, commonly known also as 12AX7s...) in your power tube sockets. EL84s have the same socket, but NOT the same ratings and are NOT interchangeable.

I'm sure Simon didn't mean this, but just to clarify. I'd hate to hear of a new post in 2 weeks that read "hey, so I plugged in some tubes, and I blew my amp up....help...."

[Simon Wicks]

Good poitn! Many wouldnt of realised this! (i didnt at first)