re-tube questions for a novice

samzadgan

So i am looking to change some tubes in my amp.

from doing a bit of research, i've decided, for now, to change the power tubes, the V1 tube and the Phase Inverter.

Again from some research I think the tubes I want are:

Power tubes: Sovtek 5881WXT

V1: Sovtek 12AX7LP

PI: Sovtek 12AX7LPS

The amp is a Jet City 50w Head…and the idea behind the whole change is to smooth out the dirt and remove some of the harsh highs and add some warmth.

apart from opinions, i'd also like to ask, when i'm ordering these preamp valves, theres a bunch of testing options. On the 12AX7LP it shows its been tested for V1 and PI, but on the 12AX7LPS it doesn't have that option…does this really matter??

any help would be much appreciated.

ecc83

Unless the quality has improved a lot since I was using them 3 years ago I would not go for Sovtek except perhaps for the PI, certainly not for a low noise input valve.

The 5881's might be ok I have not used them. Wait for ICBM to pronounce since my knowledge of the amp is zero but I doubt a valve change will make much impression on the sound. 

Since the 5881s will almost certainly need re-biasing you should look for a tech to do the work. Otherwise just buy one  pre amp valve and I have found the TAD 7025 HQ a good valve at a fair price. Most folks think JJs are pretty good as well. 

The trouble is the good stuff seems to change every 6 months or so! When I was bottle swapping, TAD 84s and 34s were fine. Now it seems they are not and JJs are much better. I have not had a lot of success with Rubies but YMMV.

Dave.

jacksparrow

Don't get sovtex 5881 if you want to smooth things out, my experience with those is the sound quite harsh go tad for power tubes.

also get your self a bias tool and learn how to set the bias yourself saves a lot of money and time taking it to the tech to bias it everytime you want to retube.

ICBM

It depends what you mean by smooth - some people like JJs across the board for that. (I find their preamp valves muddy-sounding, but many seem to like them.)

I would second avoiding Sovtek, especially the power valves. JJs are much more reliable as well as less grainy-sounding.

Don't forget the other two valves either - it's not only V1 and the PI that affect the sound, in fact in an amp like this with most or all of the distortion coming from the intermediate gain stages they may be more important than those. Definitely avoid Sovtek or any other Russian-made valve in V2 and V3, they have a high failure rate in these positions in a Soldano-type circuit.

I probably wouldn't do this in my own amp since I don't like smooth sounds (although the JC is a very bright amp, so it might take it well) but I'd probably try a Tung-Sol or EH in V1 and JJs for everything else.

Have a listen to this demo of the Jet City Retrovalves though, it gives a good idea of the tone differences between JJ, EH and Tung-Sol too:

See which you like best before you look at the reveal!

thermionic

That was interesting... I don't enjoy having my irrational prejudices disproved by evidence!

samzadgan

thanks @ICBM, thats really interesting…i preferred the clean tones of the retrovalves…but on Dirt the EH and Tungsol were the best. The JJ's weren't that great. I've read that JJ's tend to darken the tone, but it didn't sound like it did that on this clip.

When i say smooth it out, i'll put it in context…i play metal, but i play more stoner/doom type metal…so want the amp to have less high end sizzle and a more round smooth tone if that makes sense. I have kind of got there with the EQ settings, but there is that trace of high fizz still there.

as for power tubes…if i need to rebiase i might pass on those 5881. I'd like to try KT66, but they all seem to need rebiasing too.

ICBM

I don't like JJ preamp valves, I have to admit. To me they have an odd combination of muddiness and harshness, which I think you can hear in that clip quite well. Some people seem to describe them as 'warm' or smooth' though, so I thought it was worth mentioning.

Rebiasing is a fact of life with a valve power amp unless it's either cathode-biased (which is rare in 6L6/KT66/EL34-type amps) or set so conservatively that it doesn't really matter - and even then you're best to use 'selected' valves. (eg Mesa amps.) If you want to try KT66s it's no worse than trying different 6L6s. You can't even assume that a new set of the same valves it has in now will bias the same, to be honest!

What speakers are you using, by the way? They make a much bigger difference than valves.

samzadgan

I changed my cab…i use to use V30's and that was horrible…now i have a pair of Eminence Cannabis Rex, which have really helped. The bottom end is there and is thick and top end is smoother than before. 

I'll have to look into this biasing thing, and see if its something i can do. I am absolutely useless with electronics…i've never even soldered anything out of fear of killing anything.

ICBM

samzadgan said:

I'll have to look into this biasing thing, and see if its something i can do. I am absolutely useless with electronics…i've never even soldered anything out of fear of killing anything.

You don't need to solder to bias an amp . Although there is a small risk of killing yourself…

The best way is to get a 'bias probe' which is an adaptor which fits between the valve and the socket and allows you to read the valve current directly using a multimeter without risking touching anything live. But in most amps you still have to adjust a trimmer inside the chassis, and unless you want to take all day about it you need to do this with the amp powered up. There are ways of keeping yourself safe though.

samzadgan

Just watched a couple of video on biasing…it seems pretty simple actually…i just need that electronic thingy.

right…so on preamp valves I'm most likely going with the TungSol in V1 and some JJ's for the rest. 

then ill look into the KT66 for the power tubes…but right now, I'm playing mainly at bedroom volumes so not a huge need to change power tubes.