Valve change time...advice please!!

siraxeman

AC30HW2X due for a change at least on the power valves....so, are the reissue Mullards (Russian made) worth the extra ? £83.99 for a matched Quad...or are they just hyping on the old UK name ?  Or what about S'vetlanas at £40 posted from Russia

http://www.ebay.co.uk/itm/6P14P-EL84-6BQ5-Closely-Matched-QUAD-NEW-NOS-Strong-Millitary-Same-Date-/182009595009?hash=item2a609e0481:g:RckAAOSweW5VV4YW

Last time I changed the valves nearly 2 yrs ago I just put in a full set of JJs - pre and power valves. And a Sovtek GZ34. This time around methinks i'll just change the big bottles as pre valves are usually good for longerer right ? So a new quad of EL84s and a new GZ34...any advice ? The JJs in my amp sound ok to me but methinks 2 yrs almost with regular gigs must mean they cant be as good as they once were and best not to push my luck and wait for one to die on me mid gig......!! Only thinking of trying different to JJs this time around because I've heard some saying JJs in AC30s can sound a bit harsh...so!

My new (used) Mesa Express I bought via this forum is over a couple of years old now and well the previous owner gigged it some and so methinks for peace of mind and knowing its good healthy best sounding valves in I want to but it a pair of 6L6GCs.....thinking JJs ? But advise me if otherwise!

cheers dudes  

jpfamps

I'd stick with the JJ EL84s.

You'll notice a difference mainly because you will be replacing old valves with new.

2 years of regular gigs with an AC30 is about right I'd say for a valve change as, I'm sure you know, they run the EL84s very hot.

MESA amps run their valves quite cool, and 6L6s generally last longer than EL84s, so a valve change may not be needed, but for peace of mind it's not a bad idea.

MESAs are fixed bias, which you can't adjust, so they recommend you use their (expensive) own brand valves, to ensure correct biasing. Some vendours now sell other brands selected to work in MESA amps if you want to, eg

http://www.tube-town.net/ttstore/Tubes/JJ-Electronic/TT-Tone-Selection-JJ-6L6-Mesa-GRY::4373.html

siraxeman

cheers will heed your advice  

ICBM

Stick with the JJ EL84s, and get a JJ GZ34 while you're at it - Sovteks are crap.

I don't like JJ preamp valves though - I'd go for almost anything else, especially for V1 - probably a Tung-Sol or a "reissue" Mullard, which aren't but they are a decent enough modern valve.

jpfamps

ICBM said:

Stick with the JJ EL84s, and get a JJ GZ34 while you're at it - Sovteks are crap.

I don't like JJ preamp valves though - I'd go for almost anything else, especially for V1 - probably a Tung-Sol or a "reissue" Mullard, which aren't but they are a decent enough modern valve.

I've not had great results with the Tung-Sol 12AX7s; I've not found them that reliable, and I'm not convinced they sound that great.

I like the EH-12AX7s, especially in Fender amps, and the JJ-ECC803s, which is a long plate ECC83 / 12AX7. Not tried the JJ-ECC83-MG yet.

The standard JJ-ECC83 is not my favourite sounding, but is cheap and reliable.

ICBM

I've had more failures with JJs than Tung-Sols, strangely. Probably just small-sample randomness.

EHs seem OK too.

maw4neu

I thought that EH's are just rebadged Sovteks

jpfamps

maw4neu said:

I thought that EH's are just rebadged Sovteks

They are made in the same factory as Sovteks, but have a different plate structure.

keir

I've had quite a few tungsol 12ax7s go microphonic recently, I agree on the JJs they just sound really dull / flat to me.

Maynehead

maw4neu said:

I thought that EH's are just rebadged Sovteks

EH and Sovtek valves are both manufactured by the New Sensor Corporation in their Russian factory, but the EH 12ax7s have a different internal structure to the Sovtek WA and LPS valves, so are not simply rebranded.

There isn't really a current production 12ax7 that's a one size fits all, and I've tried a LOT. It all depends on the amp and the characteristics you want to enhance or reduce. I personally don't think JJ 83s are a bad preamp valve, just another option for shaping your sound. However, if you are looking for a relatively neutral sounding valve, then the JJ 803s, EH, or the Chinese Shuguang 12ax7-c (got a couple in my amp) should fit the bill. The Tungsols have nice bass and sparkly top end but are quite dull in the mids, so beware. If you are taking out all the JJ 83s however be prepared to lose some low end, and the amp may not sound as "big" as it did. I'd think about keeping some in the amp, in non essential positions and saving some money in the process.

Cabicular

I'm having a lot of good results with groove tubes valve sets at the moment
Just chucking that in there the gain raiting system on the power valves actually makes a noticeable difference

ecc83

My (admittedly limited) experience with so called "matched" sets of valves showed then to be not very!

I would just buy 4 EL84s of the same brand from the same place and yes, JJs. and swap them about for minimum hum. 

I found the TAD GZ34 to be very rugged. Pre amp 83's? EH tended to the microphonic. TAD 7025 high grade were good.

Dave.

Cabicular

I do check mine with the Orange Valve tester and they do seem to match (although I think all that thing actually tells you is that they contain glass..)

crunchman

Unless they are a lot cheaper I'd buy from a reputable supplier here rather than Ebay from Russia.  I've had valves go bad with a few hours of playing on them.  Someone who will replace it for you without any hassle might be worth paying a bit extra.

On preamp valves I've always found the EH 12AX7 a bit harsh sounding and the JJ a bit warmer.  That's my personal taste.  Others might like the extra bite from the EH and find the JJ muddy.

I don't know if you'd need to replace the rectifier valve with the power valves.  I thought rectifiers lasted for years.

ICBM

crunchman said:

I don't know if you'd need to replace the rectifier valve with the power valves.  I thought rectifiers lasted for years.

They do - unless they're in Vox, Orange or other amps with standby circuits designed by someone who doesn't know you shouldn't hot-switch a rectifier valve to an empty filter cap.

But there's still no point in changing them unless they fail, since they don't degrade in performance until they do.

ecc83

Cabicular said:

I do check mine with the Orange Valve tester and they do seem to match (although I think all that thing actually tells you is that they contain glass..)

My test involved noting the bias voltage needed to set a specific Ia. "Quartets" seemed have about the same spread as the random bulk. But as I say, I only had a few sets to check.

But then apart from minimizing residual hum* I cannot see much benefit in closely matched valves for guitar amps? "They" almost always get the PI anode loads wrong anyway!

*Cept ICBM who likes a bit 'o' 'um and 'iss!

Dave.

jpfamps

I generally buy matched sets of valves and by and large they are well matched from the vendours I use (I re test then before fitting on a Maximatcher).

I think it is well worth buying matched sets as the valves will have been "burnt in" and thus hopefully and that would fail in short order have been eliminated.

Matched sets will have lower hum and in amps with adjustable bias you can set the bias optimally without fear of a valve over dissipating.

ecc83

jpfamps said:

I generally buy matched sets of valves and by and large they are well matched from the vendours I use (I re test then before fitting on a Maximatcher).

I think it is well worth buying matched sets as the valves will have been "burnt in" and thus hopefully and that would fail in short order have been eliminated.

Matched sets will have lower hum and in amps with adjustable bias you can set the bias optimally without fear of a valve over dissipating.

Not questioning your vast experience but, how do we know sets have been "burned in"? The few seconds it takes to test a valve would surely not constitute this process?

I have run valves to investigate grid current (seems high in some modern valve) and found that it takes one  to two hours for this to drop. The drop is dramatic however, some 2-4 100%!

This sort or burn in test would make valves much more expensive?

Dave.

jpfamps

ecc83 said:

jpfamps said:

I generally buy matched sets of valves and by and large they are well matched from the vendours I use (I re test then before fitting on a Maximatcher).

I think it is well worth buying matched sets as the valves will have been "burnt in" and thus hopefully and that would fail in short order have been eliminated.

Matched sets will have lower hum and in amps with adjustable bias you can set the bias optimally without fear of a valve over dissipating.

Not questioning your vast experience but, how do we know sets have been "burned in"? The few seconds it takes to test a valve would surely not constitute this process?

I have run valves to investigate grid current (seems high in some modern valve) and found that it takes one  to two hours for this to drop. The drop is dramatic however, some 2-4 100%!

This sort or burn in test would make valves much more expensive?

Dave.

The vendours I use burn the valves for 24 hour in as part of the matching process. I would not rely on valves that had been matched without this procedure.

This will cost extra, but I am in the business of repairing amps; I don't want amps coming back due to failed valves. Money well spent in my view.

Manufactures of course want to keep costs down, so often the "factory matched" or even unmatched is the cheapest option.

I check the matching before installation as, in my experience, valves can be damaged in shipping.

I also run amps for an hour or so after installation of new valves whilst monitoring the bias. In my experience the valves I get are stable and well matched.

Burning in reduces gas (and hence grid current) due to getter action and is required for ALL new valves before installation. Also full activation of the cathode requires that the cathode is energised for several hours.

Additionally burning gets valves through the "infant mortality" end of the bathtub curve.

The RDH4 recommends 56 hours of burning in!

ecc83

jpfamps said:

ecc83 said:

jpfamps said:

I generally buy matched sets of valves and by and large they are well matched from the vendours I use (I re test then before fitting on a Maximatcher).

I think it is well worth buying matched sets as the valves will have been "burnt in" and thus hopefully and that would fail in short order have been eliminated.

Matched sets will have lower hum and in amps with adjustable bias you can set the bias optimally without fear of a valve over dissipating.

Not questioning your vast experience but, how do we know sets have been "burned in"? The few seconds it takes to test a valve would surely not constitute this process?

I have run valves to investigate grid current (seems high in some modern valve) and found that it takes one  to two hours for this to drop. The drop is dramatic however, some 2-4 100%!

This sort or burn in test would make valves much more expensive?

Dave.

The vendours I use burn the valves for 24 hour in as part of the matching process. I would not rely on valves that had been matched without this procedure.

This will cost extra, but I am in the business of repairing amps; I don't want amps coming back due to failed valves. Money well spent in my view.

Manufactures of course want to keep costs down, so often the "factory matched" or even unmatched is the cheapest option.

I check the matching before installation as, in my experience, valves can be damaged in shipping.

I also run amps for an hour or so after installation of new valves whilst monitoring the bias. In my experience the valves I get are stable and well matched.

Burning in reduces gas (and hence grid current) due to getter action and is required for ALL new valves before installation. Also full activation of the cathode requires that the cathode is energised for several hours.

Additionally burning gets valves through the "infant mortality" end of the bathtub curve.

The RDH4 recommends 56 hours of burning in!

Fairy nuff! The valves I fitted in TVs in my yoof must then have been burned in pretty well (hardly ever changed valves in radios until the horrible ECL83 and Ul84s came along!) since I rarely had a failures inside a year and even line and field OP valves would last 3 years or more. In fact most faults were caused by marginal component ratings especially caps and resistors. Indeed the valves were often just a victim of cheap design not the cause.

Just a thought? Much is made of "NOS" valves. Might it be that a gaggle of modern ECC83s, burned for a week say might sound as good?

Dave.