Valve noob!

RedRabbit

Just after some general advice on swapping valves - what brands are good, what sort of difference to expect etc.

To put it in context I've just taken delivery of a Jet City JCA22H.  It sounds great but there's a little high end fizz to the sound and I seem to recall people saying you need to swap out the valves to get the best from it.

From what I've read on various sites it seems most folk are happy just swapping the preamp valves out (5 x 12ax7) but there seems to be a lot of mixing and matching of brands.  I'm a bit lost as too what's good and what the difference between brands are.

Are there any significant gains to be had from swapping out the power amp valves (2 x EL84) as well?

Finally will I need to re-bias the amp?  It says it's fixed bias but various folk say it'll still need re-biasing to get the best from it.  Is this only necessary for changing the power amp valves?

I'm quite handy so I've no problem with tackling these things myself but this is a whole new world to me and I know valve amps can be dangerous things to start tinkering with so I'd really appreciate any advice you guys can offer.

ecc83

http://starin.info/Product%20Info/Jet%20City/Manuals/JCA22H%20-%20Schematic.pdf

Yup, fixed (but adjustable!) bias but no current sense resistor on that schematic so you would probably use the OPT resistance method or fit a resistor if practical. 

But I suppose much depends on what sort of sound you are after? I guess the Top Chaps will be along to tell you the options. 

Dave.

Fortheloveofguitar

I spoke to a lot of guys on here about these being 'fizzy' amps. I was reliably informed that you need to dial down the presence control.

ThePrettyDamned

Assuming you've turned the presence down (it amazes me how many people will say they have a lot of presence, but leave it half way up...), it's a commonly modded amp. And I doubt it's fizzy out of the box anyway

Check presence and treble controls.

JohnPerry

I know others disagree but I've yet to own a tube amp that didn't benefit from having the preamp tubes swapped for some oldies, Mullards, Philips, that sort of thing. Even my Two Rock had a fizz to it that good old tubes fixed instantly

RedRabbit

Presence control has spent most of the time on 0.  The treble control hasn't really been past 2 o'clock.

Maybe fizz was too strong.  It was barely noticeable at rehearsals but if a valve change would smooth out the overdrive channel a bit it's something I'd want to be doing but I've no idea what valves are decent.  I'm not a high gain player - it's mostly classic rock.  Guns n Roses and Bon Jovi covers are as heavy as we get.

ChrisMusic

A slight off topic, but not really...

What do you guys mean by fizz ?

Is there an accepted definition? or is it as subjective as most other guitar terminology?

Thanks for any clarification  

ICBM

If you don't want to spend a lot of money on NOS or old tested valves (or take your chances buying untested ones), try JJs. Personally I think they have an odd muddy, midrangy tone, but that may be what you need in this amp… and some people seem to like them anyway.

Avoid Sovteks (the other main candidate for muddy valves) since they're also fuzzy-sounding and have a known problem with failure in cathode-follower positions, which this amp has two of.

RedRabbit

I've done some wider reading on this.  The terminology is new to me so bear with me...

Some people seem to be suggesting replacing the 12ax7 in the V1 position with a 12dw7 as it's shared between the two channels and the 12dw7 would act slightly differently for each (cooler for the crunch channel and hotter for the OD was my understanding).  Would this be worth trying and, if so, would it just be a straight swap between the two?

Also, having read a few brand comparisons Tungsol seem quite appealing.  Anyone have any experience with them?

ICBM

RedRabbit said:

I've done some wider reading on this.  The terminology is new to me so bear with me...

Some people seem to be suggesting replacing the 12ax7 in the V1 position with a 12dw7 as it's shared between the two channels and the 12dw7 would act slightly differently for each (cooler for the crunch channel and hotter for the OD was my understanding).  Would this be worth trying and, if so, would it just be a straight swap between the two?

Also, having read a few brand comparisons Tungsol seem quite appealing.  Anyone have any experience with them?

The 12DW7 substitution should be safe, if that's what you want to do to the two channels - although it will only reduce the gain on one channel, not increase it on the other.

Tung-Sols are nice-sounding modern valves, clear and quite bright. But definitely don't use them in any cathode-follower position (V3 or V4), they have a high failure rate there.

RedRabbit

Cheers, @ICBM.

That's exactly what I'd want out of the 12dw7 - clean up the crunch channel slightly and leave the OD as it is.

Currently thinking of picking up a 12dw7 and a couple of 12ax7s (probably a JJ and a tungsol).

From what I've read V1 will have the greatest effect on tone so I'm thinking I can take the opportunity to try out a few options there and then decide what if anything to put in the remaining positions.

RedRabbit

Thought I'd just follow up on this as I've just spent a couple of hours playing around with different valves and also comparing the Jet City to my Blackstar HT5.

First thing I did was have a good play through the Jet City without changing any valves to really try to get to grips with how it sounds stock.  I think I may have been harsh previously in calling it fizzy.  There's a rawness to the high end/upper mids that I'm not used to but after half an hour of playing it seems right.  The crunch channel is fine but dirties up a bit too quickly for me.  The preamp control takes you from clean to crunch before you're past 2.5.  The crunch sounds great but I'd like a bit more room to play around with the "just breaking up" sounds.  The OD channel has loads more gain than I'll ever need it sounds okay but lacks a bit of definition - definitely better for lead than rhythm at the moment.  Palm muted riifs not a strong point here.

I then decided to let the JC cool down a bit before swapping tubes around so unplugged everything and had a few minutes with the Blackstar.  Now I'd previously loved my Blackstar but it just sounds a bit bland next to the Jet City.  The overdrive on the HT5 seems hugely compressed and a touch too refined.  What it does have however is the definition that the Jet City was missing.  Oh well I guess you can't have everything.

With things cooled down and a good idea of what I was after I started playing around with putting different valves in V1 of the Jet City.  In the end I'd ordered 2 12ax7s (a JJ and a Tungsol) and a 12dw7 (A JJ was all I could find for this one).

First up was the 12dw7.  Great news is that it did exactly what I was hoping for and lowered the gain on the crunch channel.  With the preamp on 2 all I get is a bit of extra hair and some extra bite when I dig in.  The effect on the OD was equally good - a much warmer sound with a bit extra definition in the bass than I had before.  All in all I was impressed.

Next up was the Tungsol 12ax7 - ICBM was spot on with this one, very clear and bright.  A bit much for the crunch channel I thought (a touch too modern?) but worked great with the OD giving it plenty of punch and the definition it was sorely in need of. 

Finally the JJ 12ax7 - no surprises here after the 12dw7.  Pretty much as above but with more gain on the crunch channel.

So after a re-reading some of the advice from here and looking at the manual ecc83 I've done the following.

V1 now has the 12dw7 - a no brainer for me just for the extra control over the crunch channel
V2 has the tungsol - from looking at the manual it looks to me like V2 is the only position that only effects the OD channel so I thought it'd be a good home for this one.
V3 has the other 12ax7
V4 and V5 are remaining stock for the time being.

This seems to have given me the best of both the 12dw7 and the tungsol 12ax7.  Not sure the JJ in V3 make much difference but I figured I may as well put it in and keep the stock tubes as backups.

Frankly I'm amazed at how much difference the valves make.  I'd always assumed that it'd be fairly subtle but the tungsol in particular had a dramatic effect on the tone.

I tried all this through the 1x12 I keep at home.  It's fitted with a greenback so I just I don't change my mind bout the tungsol when I feed it through my 2x12 with V30s at rehearsal.