so.. why do some valve amps chew through tubes quicker than others?

kt66

Is the OP using JJ valves? 

ecc83

Re screen feed resistors. Was not sure so have checked. The Artisan 15 and 30 both use 1k 1W MFs and although they run the 84s AT about the Pa limit the amps did not seem overly hungry? They also produced the specified power at visible clipping and that at 230V from a Variac. There is therefore no need to run the bits off output valves.

Dave.

chrissmith

 Are JJ valves no good then? ( I cant remember what's in there, but curious what brands people think cut the mustard. (NB not buying mullards, they are ridiculous ££

ICBM

JJ power valves are good - among the most robust modern brands, although some of them seem to bias a bit differently from average for the type. I’m not a big fan of their preamp valves - I don’t like the way they sound, and I’ve had a few of the 12AX7s fail in cathode-follower positions (which are harder on the valve than normal), eg V2 in classic Marshalls.

chrissmith

Interesting, thanks ICBM. What do you think is a good choice for reliable, good value 12AX7... Sovtek? Electro Harmonix? - I used to be able to name factories, but now it's ''brand'' - and I've lost track of what is made where.

ICBM

chrissmith said:

Interesting, thanks ICBM. What do you think is a good choice for reliable, good value 12AX7... Sovtek? Electro Harmonix? - I used to be able to name factories, but now it's ''brand'' - and I've lost track of what is made where.

Shuguang - the bog-standard cheap Chinese valve you will see under many brand names, but always easily identifiable by the double chrome strip on each side of the plate structure.

EH sound good but seem to be quite variable quality-wise, and Tung-Sol sound even better but seem to have a common problem with microphonics - and neither are reliable in cathode-follower positions, which Shuguangs are.

randella

nick79 said:

I had a Mesa mini rec that got needed new el84's after about 10 months.. Used once or twice a week, loud but never fully cranked. Seemed a bit excessive to me.. 

That’s interesting, my Mini Rec output valves have lasted a long time. It still has the original Mesa 84s in there, or at least the ones that were in the amp when I bought it second hand. The only valve that’s needed replaced was the ECC83 in whichever position buffers the effects loop. Go figure. 

Like @JayGee says (I suspect the Mini Rec has the same power amp as the 5:25) the 25W output rating is a pretty epic 25W, from only two 84s. I expected to have to change them much sooner. 

ICBM

randella said:

That’s interesting, my Mini Rec output valves have lasted a long time. It still has the original Mesa 84s in there, or at least the ones that were in the amp when I bought it second hand.

If it's a fairly recent Mesa they will be JJs, they're using them now. (Previously Sovteks and Shuguangs.)

randella said:

The only valve that’s needed replaced was the ECC83 in whichever position buffers the effects loop. Go figure.

That's a cathode-follower I think - it is in most of them - so no surprise. Hope you didn't fit a Russian (any kind) or JJ... if so it will probably go again sooner or later.

randella said:

Like @JayGee says (I suspect the Mini Rec has the same power amp as the 5:25) the 25W output rating is a pretty epic 25W, from only two 84s. I expected to have to change them much sooner. 

Fixed-bias Class AB isn't normally as hard on the valves as cathode-biased - not only is it usually run a lot cooler, it's actually more efficient so you can get more output power and less wasted plate dissipation (which is what really cooks the valves) at the same time. Mesa also run the screens on a slightly different arrangement to most other amps - the 'Dyna Watt' circuit - which reduces screen current and helps with valve life.

randella

@ICBM - interesting as ever. Thanks. 

The FX buffer I replaced will (I'm pretty sure) have been a JJ. I had a gig the following night and they were all I had to hand. I've got a bunch of them for some reason that escapes me.

If the worst happens I can switch out the loop on the amp, but then I lose my boost and reverb so I'd rather not have to in the middle of a set.

What's the best bet in that position? The Shuguang you mentioned earlier?

ICBM

randella said:

What's the best bet in that position? The Shuguang you mentioned earlier?

Yes, or any old-production type.

randella

ICBM said:

randella said:

What's the best bet in that position? The Shuguang you mentioned earlier?

Yes, or any old-production type.

Thanks again.

*randella goes off to change his valve and think about buying a Helix* 

fftc

ICBM said:

chrissmith said:

Interesting, thanks ICBM. What do you think is a good choice for reliable, good value 12AX7... Sovtek? Electro Harmonix? - I used to be able to name factories, but now it's ''brand'' - and I've lost track of what is made where.

Shuguang - the bog-standard cheap Chinese valve you will see under many brand names, but always easily identifiable by the double chrome strip on each side of the plate structure.

EH sound good but seem to be quite variable quality-wise, and Tung-Sol sound even better but seem to have a common problem with microphonics - and neither are reliable in cathode-follower positions, which Shuguangs are.

Can you please tell me where is the best place to get these from?

jpfamps

chrissmith said:

Got to find a good one in Berkshire.  I do know one, but he charges - ''a lot''.  Any recc's v welcome. Send by message if you like.

Out of professional interest what do you call "a lot"?

ecc83

jpfamps said:

chrissmith said:

Got to find a good one in Berkshire.  I do know one, but he charges - ''a lot''.  Any recc's v welcome. Send by message if you like.

Out of professional interest what do you call "a lot"?

Good question! I guess most of you have caught the odd glance of the BBC's "Money for Nothing"? THOSE guys ain't doing it for bottle tops!

Dave.