Changing valves: questions from a beginner...

[Antag]

OK, I have a confession to make: in 25 years as a guitar player, I've never changed a valve in an amp :oops:

I've been thinking about changing valves in my Engl Savage 120 after reading a few forums.  Not that there's anything wrong with the Savage with its stock valves - every time I play it loud I wonder why I even look at other amps.  But if I could warm it up a little bit & perhaps tame a little of the high gain channels' top end with a valve change, then why not.  So I have several questions - would really appreciate the advice of the amp tweakers & experienced techs on here:

Q1: Changing preamp valves.
Am I correct in my understanding that I can safely change any of the 12AX7/ECC83 preamp valves simply by swapping them for another valve of the same type with the amp switched off (& obviously with the valves cold :))?

Q2: Changing poweramp valves.
Everything I've read about this sounds scary (I've never looked inside an amp either :)) & I think I'm going to leave well alone.  But am I correct in my understanding that changing the power valves requires the amp to be rebiased?  & that not doing so will result in unpleasant consequences?

Q3: 12AT7 for the phase inverter
I read this comment on another forum: "For V6, 12AT7's push the power amp a bit harder and work the power tubes, giving you a nice open pushed sound and pulling out some of the typical Engl compression".  Also read a bit about using a 5751 for V1.  What do people think about this?

Q4: Engl Savage valve positions
OK, so V7 & 8 are the 6550 power valves, but does anyone know what the 6 ECC83 valves do?  I'm guessing that V6 is the phase inverter & V1 the first input gain valve.  I've read a few posts/comments that it "doesn't matter" what you put in V5 & people seem to stick any old ECC83 in there - why?

Q5: The sleeve thingy around V1
Looking at the preamp valves, V1 has this 4-sided metal cover on it.  The rest only have 2-sided spring-clip covers.  Any idea why? (to hold in some heat perhaps?)

[MrBump]

I can't really give you any technical advice, but if you want some sort of reassurance I'm in pretty much the same boat as you - I've been playing since 14, that's 24 years, and I only got around to changing the power valves in my Orange last month!

It was kinda scary - I read LOADS online, about how the various figures are calculated, then just went for it, and I'm glad I did - my Orange sounds so much better than it did.

I suspect your Engl will be somewhat easier to maintain than my Orange.

Mark.

[James C]

No helpful advice from me, but I have a vested interest in this thread...... 1 more for the valve changeing n00b squad!

[jibidy]

Pay a man who knows  :lol:

[jpfamps]

Q1: Changing preamp valves.
Am I correct in my understanding that I can safely change any of the 12AX7/ECC83 preamp valves simply by swapping them for another valve of the same type with the amp switched off (& obviously with the valves cold :))?

That's correct.

Q2: Changing poweramp valves.
Everything I've read about this sounds scary (I've never looked inside an amp either :)) & I think I'm going to leave well alone.  But am I correct in my understanding that changing the power valves requires the amp to be rebiased?  & that not doing so will result in unpleasant consequences?

If you install a decent pair of valves in your amp, then chances are they will work fine (assuming they aren't way out of spec)

However, it is adviseable to get the bias checked when you change power valves to be confident your amp is working optimally. If it is biased too cold it won't sound so good, and too hot then you will shorten the life of the valves and possibly endanger other components. However in my experience you have to run the valve pretty damn hot to cause significant "co-lateral" damage, and you will notice if this is happening because the grey plates in the valves inside the valves will start to glow orangey/ red.

Q3: 12AT7 for the phase inverter
I read this comment on another forum: "For V6, 12AT7's push the power amp a bit harder and work the power tubes, giving you a nice open pushed sound and pulling out some of the typical Engl compression".  Also read a bit about using a 5751 for V1.  What do people think about this?

A 12AT7 in the phase splitter won't drive the valves any harder. 12AT7 has less gain than a 12AX7.

5751 also has less gain than a 12AX7.

Whether you like the sound of these valves in these positions is entirely subjective and perfectly safe for your amp, so need to suck it and see (hear).

Q4: Engl Savage valve positions
OK, so V7 & 8 are the 6550 power valves, but does anyone know what the 6 ECC83 valves do?  I'm guessing that V6 is the phase inverter & V1 the first input gain valve.  I've read a few posts/comments that it "doesn't matter" what you put in V5 & people seem to stick any old ECC83 in there - why?

You would need schematic to assess what all the valves do. Negative feedback in gain stages can reduce the effect different valves have on the sound. V5 may say drive the fx loop. My guess is that people have tried different valves in V5 and not heard much difference.

Q5: The sleeve thingy around V1
Looking at the preamp valves, V1 has this 4-sided metal cover on it.  The rest only have 2-sided spring-clip covers.  Any idea why? (to hold in some heat perhaps?)

Sounds like V1 is shielded to prevent EMI on the first couple of gain stages (there are two triode gain stages in each valve). The signal is lowest and gain highest at this part of the circuit so any extraneous interference is worse here.

The shield inhibits valve cooling, which would explain why it is not on the other valves.

[Antag]

Many thanks for the great detailed reply! :)

5751 also has less gain than a 12AX7.

Whether you like the sound of these valves in these positions is entirely subjective and perfectly safe for your amp, so need to suck it and see (hear).

Use of a 5751 seems quite prevalent for V1, reducing the gain a bit (not a problem for even the most rabid of us metalhead - the Engl has SO MUCH gain anyway you'd have to be certifiable to use it >3 o'clock :twisted:) but also warming it up & taking "fizz" on the really high gain settings.  Might give it a go.

Q4: Engl Savage valve positions
OK, so V7 & 8 are the 6550 power valves, but does anyone know what the 6 ECC83 valves do?  I'm guessing that V6 is the phase inverter & V1 the first input gain valve.  I've read a few posts/comments that it "doesn't matter" what you put in V5 & people seem to stick any old ECC83 in there - why?

You would need schematic to assess what all the valves do. Negative feedback in gain stages can reduce the effect different valves have on the sound. V5 may say drive the fx loop. My guess is that people have tried different valves in V5 and not heard much difference.

Interestingly I stumbled upon a couple of schematic diagrams for the Savage & both seem to imply that V5 does have something to do with the FX loop.  But the Savage has two FX loops (though only one of them is active at any one time - you can make loop 1 a "master" loop which deactivates loop 2, or have one loop for each main channel) - does this bit of diagram make any sense?  Are they basically saying that V5 is acting as a driver for whicever FX loop is switched in?





If V5 is the loop driver, are there any valves that are known to be particularly good in this position? Worth paying extra for "balanced" valves like for the PI?  If not, I may as well just leave it stock...

[Dmoney]

V5 is indeed driving the loop.

what you put in there probably depends on what effects you use in the loop, if any at all.
I use JJ ECC83's as a good standard tube. I wouldnt worry if i used one in a loop since i don't really use fx loops.

I can tell you V5 is the driver. But i have no real experience with playing with FX loops related tubes.

[jpfamps]

If V5 is the loop driver, are there any valves that are known to be particularly good in this position? Worth paying extra for "balanced" valves like for the PI?  If not, I may as well just leave it stock...

It's not worth paying extra for balanced valves for use anywhere in a guitar amplifier. The balance of the phase splitter does not depend on having a balanced valve (even assuming that having a balanced phase splitter is beneficial).

[Elliot]

It might be worth trying a 5751 in the V1 position (I wouldn't go any lower in the gain chart) - I use them in the V1 of my amps and like the difference - in gain terms, its like loosing 1 to 2 notches on your amp's volume control but it often has a sweetening effect (well, I think so, but I use Fender amps, so there is no comparison with an Engl) and is good if you also use OD type effects.

You can also get some good NOS Philips JAN 5751 on ebay for roughly the same price as a new 12AX7, so its no real loss to experiment with.  I wouldn't bother putting them anywhere else except V1.

[Roobubba]

If V5 is the loop driver, are there any valves that are known to be particularly good in this position? Worth paying extra for "balanced" valves like for the PI?  If not, I may as well just leave it stock...

It's not worth paying extra for balanced valves for use anywhere in a guitar amplifier. The balance of the phase splitter does not depend on having a balanced valve (even assuming that having a balanced phase splitter is beneficial).

This is encouraging. The amp tech I took my 5150-II to when I first got it told me the same thing (having bought a set at that point... DoH!).

I kept the old valves, and I know that if I have any problems at a gig, I can substitute these (if possible) and the amp will be fine without rebiasing. I'm guessing that most similar valves would be fine also, but I think I'd still rather take the amp to a tech for a power valve swap and to give it an all round health check once every so often!
Preamp valves are another matter, though, I'll happily swap those about to check out the sound differences (although it's difficult to crank a 120W amplifier at home...)

[Antag]

Excellent, thanks for the advice everyone.  Think I'll leave the PI & FX buffer stock & experiment with the first 4 valves.  A 5751 in V1 seems to be a popular choice for both Savage & Powerball so I may give it a go - it would have to take a LOT of gain away before I didn't have enough on tap.

I have just two more questions.

Looking at either of the following 2 schematics, can anyone tell me what V3 is doing?  I'm guessing that given the position of 3A that it's some sort of eq buffer (like that thing the 5150 has, forget its proper name...) or is it more gain stages like 1/2/4?





& finally (& this is such a dumb question that I chickened out of asking it in the first post :lol:)  I read somewhere that handling a valve with bare hands shortens its life.  Really??  I may have failed chemistry O-level but I'm fairly sure sweat doesn't corrode glass.  Surely as long as I don't eat a bag of chips & some spare ribs before I change my valves & my hands are dry, it won't be a big deal?

[dave_mc]

i haven't changed valves yet either, but i think some of the engls have some technical stuff round the back which supposedy makes biassing a lot easier. if the savage has it (i think my savage se does, but i'd have to check), you might not have to open the amp up to bias it (if I've understood the Engl description correctly).

[HTH AMPS]

V3a and V3b in the Engl schematic above are just plain old gain stages - the first half drives the EQ from the plate (not the cathode like most Marshalls) and the second half is another gain stage.

handling valves with your bare hands makes no difference to lifespan whatsoever - they're not like halogen bulbs.

[BigK]

Excellent, thanks for the advice everyone.  Think I'll leave the PI & FX buffer stock & experiment with the first 4 valves.  A 5751 in V1 seems to be a popular choice for both Savage & Powerball so I may give it a go - it would have to take a LOT of gain away before I didn't have enough on tap.

I use a JAN phillips 5751 in V1 of my powerball and it is the single best £24 I have ever spent, it sweetens up the top end and warms up the mids and low end.

For the rest of the preamp I used JJ ecc83's which again had a warmer sound than the stock engl tubes.

I did notice a difference when I changed the Phase inverter on my powerball. Using a JJ it sound slighlty warmer and a JAN5751 was not quite as warm but alot clearer and had slightly less output (so you need the channel volume slightly higher) compared to a normal 12ax7/ecc83. Both seem to sweeten the top end a little and add a little warmth.

Have Fun! I was floored by how much difference the tubes made.

[Keven]

on a side note. i recently bought a Weber BiasRite after following topics here. my amp has an external adjustable trimpot for bias current so it's only a matter of getting an accurate reading of the plate voltage and idle current.

the unit is very well built, even though it cost me around 200$ CAD with taxes and shipping and all (i went for the quad octal version)

if your amp has an external adjustable bias pot, and you feel like learning. i think it'd be a very safe experience

otherwise... well, take it to a tech who knows what he's doing, but get one with common sense. some guys just like to sell valves, some others actually care about making your amp work right.

i've had a customer wait 3 months for an amp with '' dead rectifier tubes'' when in fact his entire power supply board had short circuited because of liquor falling into the amp, prompting a rectifier tube failure. (and a lot of other things gone bad....)

a week with my tech solved the problem. supposedly the guy my customer was working with would '' fix it up cheap''

my tech had to glue the board back togheter, and fix all the broken traces.

moral of the story. don't ask a friend of a friend who supposedly knows some stuff.