Tube advice for my Tremoverb head

[xkalibur38]

Ok, here's the deal. I've got this Tremoverb head and it's amazing. But I keep telling myself it could be so much better with new tubes. I got it used a few months back, and it seems that the sound quality may be taking a slow downhill turn. It currently has 4 Groove tubes GT6L6 GE's in it. They all have a side that turned bright silver. Tha guy I got the amp from gave me 1 set of mesa 6L6 GC STR 430 tubes labeled 19 AC RED at the bottom. can I change out just 1 set of tubes? If so which tubes on the amp do I change (not sure which tubes on the amp are sets) But also the mesa tubes have that bright silver coloring on the tops of them, does this mean they might mot be any better than current said tubes? Sorry for the stupid questions, just wanting to breathe a little life into this amazing amp and I can't afford to re-tube it.
Also, is there anything I should check on the reverb, because it currently is not working, though the trem works fine. The "rca" looking cable is plugged in so I'm lost on that one.

Thanks in advance!

 

[94Tremoverb]

The silver is *meant* to be there - it's called the 'getter' - it's if it's not, or if it starts to turn white, gray, pink, rainbow-colored, or transparent, that the tubes are getting near the end of their life. If the silver looks normal, there isn't necessarily anything you can tell about the condition of the tubes at all. If there are other signs of overheating - 'smoky' looking stains on the inside of the glass, or marks that look like water stains on the gray boxes inside (which are the plates) then they are also suspect - but you can easily have worn-out tubes that look perfectly OK, or even ones that look damaged that will work well enough... at least for a while.

The easy way to tell if they're really worn or not is to try replacing them with a known good set. You can run just two tubes, or a mix of different tubes (of the same type) but it won't clearly show whether the others are worn, since you'll either get a mixture of the characteristics that may hide what you're trying to find, or just less power if you're only running two tubes.

It's at least as likely that you have a preamp tube going out, and again the best way to find out is just to replace each one in turn with a known good tube, and see if the amp sounds suddenly better when you replace a particular one. It's possible that they're all getting a bit tired, but more likely that it's just one.

The reverb fault is most likely to be a broken wire in the reverb tank itself - this is very common, more so than even the RCA cables... but there should be two of those - one thicker gray and one thiner white - so if there's only one that will be the problem! Or it could be the reverb tubes, which on this amp are V1 (reverb return, same as the input gain stage for the amp, which is very unusual) and V5 (reverb send). V1 to 4 are the row at the front side of the amp, starting nearest the input jack, and V5 and 6 are the two nearest the power tubes starting at the same end.

If you don't know the history of the amp at all, you *may* be best just to replace all the tubes, but it probably isn't necessary unless you think they are all likely to be really old or the amp has been used hard. Keep the old ones as spares, since you know they at least work.

 

[xkalibur38]

Awesome, so my mesa set of tubes could very well still be brand new as the previous owner had said. Like I had asked before, can I replace just one set of tubes? And if so, does it matter which two tubes i replace? Also, given the current groove tubes in the amp, would my bias need any kind of adjusting to put in the mesa tubes. They're all 6L6's but I didn't know if there was some variation that would require such adjustments.
I will look a little further into my reverb situation and try to pull out the tank. There are 2 wires going to it a grey one and a thinner white one. I may just have to save up and get all new pre amp tubes, as I'd like to try my own combination of tubes. Plus it very well could fix both my reverb and sound quality at the same time. Because as you said, I have no idea of the amps history. I was told the tubes had very little hours on them. But of course can you really trust a stranger from craigslist especially when they are getting the better end on a trade? I was also told it had the "hollywood mod" and it does have the green light cap on it, but other than that I have no idea if there's any truth to that either.

Thanks for your quick and informative advice!

 

[94Tremoverb]

You can certainly replace just two of the tubes - do either the inner or outer pair (it makes no difference which) - but if the ones that are in it are nearly new, there's probably no point. Some people report that you get a more complex tone by running two different pairs though, so try it if you want! Unless it's been modified, like all Mesa amps the Tremoverb does not have a bias control - it's preset to a safe conservative value. So just plug and play. For what it's worth, I fitted mine with a bias control, and was surprised by how *little* difference even quite different bias settings made to the tone - not none, but I'm not sure I would bother unless you want to experiment for curiosity, the factory setting is fine.

You can check your reverb tubes like this: first, set the FX loop to Bypass, and pull V4, which is the furthest tube from the input jack in the row of four - this is the FX loop tube so it isn't needed when the loop is bypassed. Use this tube to test V1 (closest to the input jack, half of it is used for the reverb return) and V5 (nearer the input jack of the row of two, which is the reverb send). If either of those substitutions brings the reverb on, replace that tube permanently. If it's not that, you can test the reverb cables and tank like this: with the amp running and the reverb turned up about halfway, shake or bump the amp. If you get the typical reverb crash, you know the return side is working. Then, swap the gray and white cables and turn the reverb up full, and bump the amp again - it won't be as loud even if the tank is OK, but you should get *some* noise - if so, you know the send side is working. (Now put the wires back where they should be!) If either of those things doesn't work, you've got a bad connection or a broken wire in the cables or tank, and you will know which end to check - or get your tech to, since it will probably involve soldering if it's in the tank.

Most Tremoverbs I've seen have a green jewel light, so that isn't a sign of anything having been changed. What's the "hollywood mod"?

 

[xkalibur38]

Ok, when you say inner and outer tubes do you mean: inner = the two tubes closest to the input jack, and outer= the two tubes furthest from the input jack? For some reason I was thinking a little different. If 0=the tubes i didnt change and 1= the tubes I did, I swapped it like this: 0110. I let the amp warm up, but never turned off the standby and then realized I could be doing this all wrong. Hopefully that didn't cause any damage, but I had to make sure before going through with it. I've scoured the internet looking for this advice and found nothing.
Also the pre amp tube in V1 is an str spax7a, can i replace that with the 12ax7 in V4 to test the reverb? The spax7 has a rubber or plastic cover on the tube and the tube had a metal shield over it.

 

[94Tremoverb]

You did it right. "Inner" and "outer" are the pairs of power tubes as you look at the row of four. Using your code (which is good, and makes things very clear for anyone else reading) it wouldn't really make much difference even if you had changed 0011 or 1100 - if all the tubes are OK, it will still run and won't cause any harm. But to keep the power section well balanced, which will give the most power, fullest tone and the least hum, you need to change 0110 or 1001, or even 0101 or 1010 - as long as each half of the power section has one each of the tubes, it's OK.

You can use a standard 12AX7 to test a SPAX7A position, it just may be best to get another SP for a permanent replacement if the tube does prove to be the problem.

 

[xkalibur38]

Well, it's not the tubes causing the reverb to fail. It does seem to sound a little better though with the loop on bypass, as before I had been using the loop as a master volume. I'm not sure how dificult it will be to get the reverb tank out as it is in such a tight space, we shall see though. Thanks for such quick responses, you've been a great help!

 

[xkalibur38]

Hey Hey, sorry to dig up my old thread. I just now got around to getting the reverb tank out after removing the chassis. However the tank appears to be glued together. I defiantly didn't want to pry it apart without knowing that it was intended for that. The two wires seem just fine though. Still no reverb, and as I said before I checked the reverb driver tube too. Anyone have anymore advice to get my reverb going. I've had this amp for waaaay too long to never have heard it's reverb. Thanks in advance!

 

[94Tremoverb]

If the fault is in the tank you do need to get it apart - it shouldn't be glued together, as far as I know. You can find out for certain if it's the tank if you pull the Output cable (the grey one) from the tank, and touch the end with the amp running and the reverb on - if you get the usual loud buzz like you would from a guitar cable, the return circuitry in the amp is fine. If you then connect that cable to both of the tank jacks in turn, and get no crash from one of them when you shake the tank, the tank is faulty. If the tank is OK, the fault must be in the send circuit somewhere, most likely the transformer (very rare but can occasionally be blown).