An Admission - I know nothing about valves

monquixote · August 2014

I've had loads of valve amps over the years, but I've never bothered to revalve them.

To be honest I tend to flip stuff so quickly that it hasn't really been a problem and when I've had stuff blow up I've just taken it to a tech and had the specific valve replaced with whatever he has in stock (usually groove tubes).

As a result when people talk about changing their valves it's a bit of a mystery to me what the difference is between say a Winged C and a Tung-Sol is.

I've now had my H&K Puretone for a while and I figure it might be worth getting it revalved especially as it seems to only have 2 12AX7s and 2 EL34s so it shouldn't be too much money to get it redone and I do rely on it for gigs. It's also class A and as I understand they eat valves a lot more.

The way I understand it the power amp valves take a beating, but you don't have to replace the preamp ones all that often.

So my questions are:

* Should I bother replacing the valves at all, or just ignore them till they go bang like I have in the past?

* If I do will I get any advantage from replacing the preamp valves as well?

* If I replace them what should I buy and is it worth paying extra for expensive brands?

vasselmeyer · August 2014

Is there some reason you think it needs revalving? Does it seem different from when you first bought it or are you just thinking about it because you want to see if it makes any difference. It won't be expensive and if it doesn't make any difference then you have some spares.

I don't bother with spare valves as, like you, I would have no clue how to change them. I can always use the Zoom G3 amp emulator to DI into the PA if the amp blows up during a gig and get it fixed later.

ICBM · August 2014

If it is genuinely Class A - it could be at that power - it won't eat valves much, if any, faster. The ones that do are the so-called Class A amps which are actually hot-running cathode-biased Class AB… ie most of them

. Typically with EL84s operated at well above 12W per valve at idle, ie any cathode-biased 2-EL84 amp which claims the standard 15W or 4-EL84 one which claims 30W. (Contrary to popular belief/myth/marketing BS, cathode bias and Class A have nothing to do with each other whatever.)

I would get a set of new valves, both preamp and power. You should always have spares if you're relying on an amp for gigging (plus any fuses the amp takes) anyway, so buying a set is not pointless even if the current ones are fine. Swap the valves - power valves as a set, preamp valves one at a time - and listen to what difference each makes. If the sound improves you can keep the old ones as the spares. If it doesn't, then it doesn't really matter which you use.

In my opinion it is worth buying old-production valves (US or European-made from the mid-80s or earlier, not Chinese or East-European no matter that they may be 20+ years old now), because they both last longer and sound better. They are getting really quite expensive now though, especially power valves and even if you avoid the most-hyped brands.

Of the modern-production ones, there unfortunately seems to be a reverse correlation between life expectancy and tone...

monquixote · August 2014

vasselmeyer said:

Is there some reason you think it needs revalving? Does it seem different from when you first bought it or are you just thinking about it because you want to see if it makes any difference. It won't be expensive and if it doesn't make any difference then you have some spares.

I don't bother with spare valves as, like you, I would have no clue how to change them. I can always use the Zoom G3 amp emulator to DI into the PA if the amp blows up during a gig and get it fixed later.

No I don't have any reason to think it needs revalving.

I'm planning on taking my amp to a tech because I want to get a scratchy pot replaced and so I thought it might be an opportunity to get it revalved.

The main reasons I was thinking about it is because I've heard people suggesting amps should be regularly revalved and because lots of people claim they swap out valves for various other brands and it makes a difference to the sound and I've no idea if this is BS or not.

I'm not too worried about having spares as I'd just go to my backup option of a Tech21 or G3 into the PA if it failed on me.

vasselmeyer · August 2014

If you do decide to revalve it you might try some of the solid state replacements (e.g., Jet City RetroValves) in the preamp section.

ICBM · August 2014

Suggestions that the valves should be replaced regularly mainly come from valve sellers

. Actually there is *some* truth in it, but mostly because they wear very slowly and subtly, so it can be hard to know when they have degraded a bit unless you compare them to new ones. But other than that - no, they don't need replacing until they fail… which can be years for power valves and up to decades for preamp valves, even with regular use.

Different valves do change the sound. How much can depend on the amp design - some are much more 'valve-sensitive' than others - and how much you mean by "how much"

. Also contrary to popular belief, even the valve *type* (eg 6L6 vs EL34) cannot change the basic voicing of the amp, and the difference between different brands is smaller. But it can still make a substantial difference, particularly to the clarity and hence 'cut' and projection as well as to the tone. And it can also be *more* noticeable, not less, at gig volume with a band than in isolation.

Spares are still worth having even if you don't want to change them on stage - they could save you a trip to a repair shop at least, and can be useful for troubleshooting even if you do end up having to take it to someone. This amp is almost certainly cathode-biased, so you don't need to worry about that either.

ThePrettyDamned · August 2014

vasselmeyer said:

If you do decide to revalve it you might try some of the solid state replacements (e.g., Jet City RetroValves) in the preamp section.

Yeah yeah yeah yeah YEAH! Or the AMT ones.

It would be genuinely interesting to see what you think of the tones. I suspect it might lose *something* but in an amp like the Puretone (which is presumably quite valve sensitive compared to modern channel switchers) it would be interesting to know.

p90fool · August 2014

I like to think I know a little about it but I don't. I just revalved my JCA 20h with NOS Mullards because the cheapo Chinese valves they're shipped with are notoriously grainy and lacking in smoothness.

The difference? Sweet FA, I might as well have used mallards quite frankly.

However, I always revalve any amp I intend to use for gigging pretty well immediately, simple so that I have a complete known good set I can whack back in there in a few seconds. It really is just like having a couple of light bulbs in your kitchen drawer, it's silly not to.

Dave_Mc · August 2014

If you want to see what different valves do and don't want to learn the whole biasing shebang, just get a little single-ended 5 watter and you can swap valves all you like without biasing.

or even a cathode-biased bigger amp which also normally don't need to be biased.

that's what i do

)

JohnPerry · August 2014

p90fool said:

I like to think I know a little about it but I don't. I just revalved my JCA 20h with NOS Mullards because the cheapo Chinese valves they're shipped with are notoriously grainy and lacking in smoothness.

The difference? Sweet FA, I might as well have used mallards quite frankly.

However, I always revalve any amp I intend to use for gigging pretty well immediately, simple so that I have a complete known good set I can whack back in there in a few seconds. It really is just like having a couple of light bulbs in your kitchen drawer, it's silly not to.

it's odd, this. For the last few years i have routinely changed the preamp tubes in any new amp I've bought for old Mullards or Philips and in most of them the difference is night and day. Normally the sound is smoother, richer and with substantially less gain. But years ago I did used to have a couple of Carvins where I did this with no effect whatever. I have no idea why it makes such a diff in some and not in others.

monquixote · August 2014

Dave_Mc said:

If you want to see what different valves do and don't want to learn the whole biasing shebang, just get a little single-ended 5 watter and you can swap valves all you like without biasing.

Yeah, I don't really want to know about it TBH

As I get older I find that small differences matter a lot less to me than my playing on any given day and really I'm more interested in having something simple and reliable.

If it's going to make a big difference and last a long time then I don't mind dropping a few quid on a set of Philips 12AX7s, but if it's barely discernible cork sniffer stuff then I won't let it worry me.

Amusingly I just realised that my amp actually does have a socketed speaker I just hadn't noticed

@icbm it appears that my amp is 25W into 16 Ohms and 40w into 8. Does that sound like it's likely to be proper class A?

The manual says it doesn't require biasing as long as the valves are matched sets.

Dave_Mc · August 2014

No worries. Yeah you can definitely worry too much about the small things. I've only swapped valves on the easy ones to swap, I've never swapped any on my more complex amps

)

ThePrettyDamned · August 2014

I really noticed a huge difference when I swapped valves on my Laney lh50 but that's because the old power valves were genuinely shagged.

I've never bothered swapping different valves around, but there are a/b comparisons that prove it can make quite a difference. I guess it depends on the amp?

monquixote · August 2014

ThePrettyDamned said:

vasselmeyer said:

If you do decide to revalve it you might try some of the solid state replacements (e.g., Jet City RetroValves) in the preamp section.

Yeah yeah yeah yeah YEAH! Or the AMT ones.

It would be genuinely interesting to see what you think of the tones. I suspect it might lose *something* but in an amp like the Puretone (which is presumably quite valve sensitive compared to modern channel switchers) it would be interesting to know.

I certainly won't be trying the Jet City ones.

I seem to remember hearing a comparison of them and thinking they sounded quite bad (and I like solid state amps).

ThePrettyDamned · August 2014

Yeah, probably a wise move - even the amt ones, it's a fair wad of cash to drop on something that you're, frankly, likely to not like as much. I don't think I would get them either.

Which is a tragedy - what if they're awesome?! It's the sort of product that needs plenty of extensive demos for before I'll realistically consider it.

digitalscream · August 2014

ThePrettyDamned said:

Yeah, probably a wise move - even the amt ones, it's a fair wad of cash to drop on something that you're, frankly, likely to not like as much. I don't think I would get them either.

Which is a tragedy - what if they're awesome?! It's the sort of product that needs plenty of extensive demos for before I'll realistically consider it.

The jury's still out for me - there aren't any demos from people who don't make everything sound bad. It strikes me that they're a great bit of kit to have in your emergency bag, though. Practically unbreakable compared to real valves.

ICBM · August 2014

monquixote said:

@icbm it appears that my amp is 25W into 16 Ohms and 40w into 8. Does that sound like it's likely to be proper class A?

That doesn't really make sense, unfortunately. Does it have an impedance selector?

If not and it's running mismatched into 16 ohms, it almost certainly isn't Class A. You can get 25W or even 30W from a pair of EL34s in Class A, but only with a correct match. If the correct match is into 8 ohms and gives 40W, it isn't going to be Class A.

I wouldn't worry about it though, it doesn't really matter as much as the usual marketing hype implies. Very few so-called 'Class A' amps actually are, and it doesn't stop them sounding good.

monquixote · August 2014

No it doesn't have an impedance selector.

The speaker out says 16 Ohms 25w 8 Ohms 40w. It is monumentally loud (much louder than the 25 Watt Supersonic I used to have)

That's a gut shot, not sure if it tells you anything:

http://carvinbbs.com/userpix/7879_6164_2.jpg

Does look a fairly simple and well made amp as the marketing blurb suggested.

I'm not bothered if it's really class A.

It's taught me that a lot of stuff about amps is balls. The Puretone is (supposedly) class A and EL34 and yet it sounds pretty much like a Fender amp when it's clean which I put down to the tone stack more than anything because if you bypass it, it really doesn't anymore.

ThePrettyDamned · August 2014

Can't sound like a fender with el34 man, it must sound British.

says Internet wisdom.

Blimey, it's a tidy looking amp!

ecc83 · August 2014

I cannot find a schematic for that H&K, nor even a user handbook but this review..

http://magazine.dv247.com/2010/02/12/hughes-kettner-puretone-head-review/

does say that an 8 Ohm load will pull 40W and 16 just 25W. I can only conclude that the design has a very "flat" output impedance similar to a solid state amp? This is contrary to most valve amp characteristics which tend to put MORE power into higher resistance loads thus "beating" to some degree loudspeaker thermal compression.

I am also intrigued by the two small PCBs either end of the chassis? They each have a ferrite inductor/traff on them. Anyone shed any light?

H&Ks blurb does state that the amplifier is "Pure Class A". Make of that what you will!

Dave.

monquixote · August 2014

It has a built in attenuator so perhaps it's that.

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An Admission - I know nothing about valves

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