#1
There's a short article here where some guy is talking about hot-swapping preamp tubes to compare the differences in tone:

http://reviews.ebay.com/Want-a-better-amp-Change-your-preamp-tubes_W0QQugidZ10000000001202478?ssPageName=BUYGD:CAT:-1:LISTINGS:2

So get yourself a few 12AX7's, maybe an NOS or ANOS (almost new old stock = used). Play an open G chord and listen to your amp with the stock tube. Listen to the volume, lows, highs,"punch" and clarity of the tone. Now put your amp on standby and swap in another 12AX7

Has anyone here done this? is it always safe to do it when the amp is in standby? and why is it necessary to keep the amp in standby? and how much effect would swopping the preamp tubes have on your overdriven sound?
#2
First, the function of your stand-by switch is to allow the tubes' heaters to warm (thanks to the 6.3 Volts supplied by the power transformer) the cathodes to initiate the emission of electrons in the tube while blocking high voltage coming from the rectifier to prevent what is called "cathode-stripping" (to force electrons out of too cold cathodes).

When you hot-swap a tube, you cut the H/V with the stand-by swtich to allow you to remove the first tube safely and then to snap the new tube in while keeping the other tubes (power tubes like 6L6, EL34, 6550 and sometimes the rectifier tube like the 5Y3 on older amps) ready for your next try. Just remember that this new tube needs a bit of heating too, so letting the new 12AX7 warm for 30 seconds or more on stand-by won't hurt.

Have fun and remember to be extremely careful if you ever open the chassis of your amp : 400 V or so may stay present on the power supply capacitors even if your amp has been off for a while... Shocking experience, they say !
#3
Ta for the informative reply, the thing I'm wondering is, would I not be better off just switching off my amp altogether before swapping the tubes, I realise I might have to wait a minute or so longer, but I will probably be recording before and after clips anyway, so it should be easy to make a comparison.

Regarding the dangerous voltages, my understanding is that the valve amps are designed and layed out in such a way that you will not go anywhere near any dangerous voltages if all you're doing is swopping valves, so there shouldn't be any risk with doing that, should there? also, how long would I have to leave my amp off to be sure the power caps have discharged themselves, and is there a way of speeding that process up?
#4
You don't have to worry about it at all unless you actually open up the amp chassis, which you don't need to.

When I build/repair tube amps I just short the capacitors out.

And yes, it's just fine to swap them with the amp on standby. You can't hurt it.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
#5
OK ta, slightly OT question, what are some good makes of ECC83 tubes? (I've got some 'TAD's in mine at the moment)
#6
Quote by That_Pink_Queen

When I build/repair tube amps I just short the capacitors out.


Good idea, only once discharged... Otherwise, you can have nice sparks, depending on your P/S capacitance, or hurt capacitors a little (they are not usually meant to supply such currents so fast). I would suggest to short them instead with a 50 kiloOhm 10 W with insulated alligator clips to allow them to discharge properly, then short them out with a wire to prevent the charge from rebuilding (especially true on old oil ones).

The formula for calculating capacitors' complete discharge time is (in essence) T = 5 * R * C, where R is discharging resistance (say the 50k - 50 000 Ohms - aforementioned) and C the total capacitance (for exemple's sake, 200µF, or 0.0002 Farad), which gives us a nice 50 seconds of discharging time before working safely (inside) !

the thing I'm wondering is, would I not be better off just switching off my amp altogether before swapping the tubes


If your amp has been on for a while, don't ! Sound gets better with tube amps as they stay powered longer (not on standby, btw !), so powering it down completely "could" hurt your sound if you take much time between your tries, because the whole circuitry would now sound a little different, not only the new 12AX7.
#7
^Yes, I didn't mention it but I use a 10k resistor.
10 watts is overkill, 2 works just fine.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
#9
I have a question too. Now, i know ecc83's and 12 ax7's are essentialy the same/compatible but, lets say, i have a groove tube ecc83 in my v1 and v2 and i want to put a tung sol 12 ax7 in the v2 position, can i do this safely or do i need to put one in v1 as well or are they not close enough to the same value etc?
Last edited by diesect20022000 at Sep 26, 2006,
#10
Quote by Mr Songwriter
OK ta, slightly OT question, what are some good makes of ECC83 tubes? (I've got some 'TAD's in mine at the moment)


So far that is of course all in personal taste but, for what i do i like Eh power tubes (6l6gc) and tungsol at least for my gain but, i haven't tried them on clean. I like my groove tubes for cleans so far. I still want to try mixing them if possble. I do know that chineese are commonly used in the gain stage of preamps and groovetubes are used in the clean stages. I like the tung sols the best so far though. I hear alot of positive things about JJ's for metal but, i am not sure. Groove tubes a re a good all around tube for sure though, they are punchy war and clear and notes are pretty destinguishable from others. They aren't quite as high gain as i would like, but, i am being over anylytical i think because, they are great tubes and i don't NEED to replace them i just want to see what i can do.
Last edited by diesect20022000 at Sep 26, 2006,
#11
You can mix ECC83's and 12ax7's just fine.
You can also try any 12a*7 combo...like 12ay7, 2au7, etc. etc.

I like EH preamp tubes, and JJ power tubes. JJ pre tubes are good too.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
#12
Quote by That_Pink_Queen
You can mix ECC83's and 12ax7's just fine.
You can also try any 12a*7 combo...like 12ay7, 2au7, etc. etc.


Yes I was wondering about that, I might give it a go.

I like EH preamp tubes, and JJ power tubes. JJ pre tubes are good too.


I'm not looking for an out and out metal sound, just maybe a smoother, well defined and non-harsh OD sound, and from what I'm hearing, Tung-Sol and EH might be what I need.
#13
Quote by That_Pink_Queen
You can mix ECC83's and 12ax7's just fine.
You can also try any 12a*7 combo...like 12ay7, 2au7, etc. etc.

I like EH preamp tubes, and JJ power tubes. JJ pre tubes are good too.


Very cool thanks! I thought so but, i didn't want to go on a whim and hurt my baby you know? One of these days i will have to get some JJ's too and see how they are. I like a bright and punchy sound and i am doing well with what i have now but, still have to try some more combos first to be sure. Thanks again!
#14
well the sound you described i would suggest Groove Tubes for your preamp. Very smooth and rich. I hear good things about ruby tubes (medium gain) for that too. I like the tung sols for distortion though because they are quite metalic but, not harsh....still musical which is important for me because i am a sucker for melody. My groovetubes are beautiful though, sounds like what you described for the preamp/v2 stage
#16
Quote by diesect20022000
well the sound you described i would suggest Groove Tubes for your preamp. Very smooth and rich. I hear good things about ruby tubes (medium gain) for that too. I like the tung sols for distortion though because they are quite metalic but, not harsh....still musical which is important for me because i am a sucker for melody. My groovetubes are beautiful though, sounds like what you described for the preamp/v2 stage

Groove Tubes are rebranded, as are Ruby's. Groove's are usually Sovtek's, I believe. Just buy Sovtek's and all the others straight from the manufacturer, rebranded = no no most of the time..

They are too expensive for what they are when they are rebranded and "tested".
#17
Also for the record, Sovtek has several types of gain levels and various tubes in each class. There are three different (that i have seen) 5881 types which are color coordinated red of course being highest gain so i assume they distort at lower volume more than that of the others. I personaly have only used the reds and i liked them actualy. Preamp wise being renamed dosn't affect the tonal characteristics i previously described. I actualy did some research on the groovetube/sovtek thing. Now they are owned by the same company essentialy but, are still manufactured to original specs hence the name keep. It works much like energizer and duracel or hotweels versus matchbox. They are under the same ownership but, not made the same way. This i can assure you is the reason that if you were to purchase one or the other (which i have) they do NOT sound the same. Groovetubes are still warmer and rounder as where the sovteks take to higher gain better and are a little more harsh/brittle in tone. Check Groovetubes homepage for further info. I generaly just email companies as well if i really need info.
Last edited by diesect20022000 at Nov 8, 2006,
#18
Not all tubes are Chinese/Russian...
EH and Sovtek tubes are made in the Reflector plant in Saratov, Russia IIRC. Lots more are made here too.

JJ's are made in the old Tesla plant in Yugoslavia I think.

With NOS tubes there is TONS of rebranding...the brand name has almost nothing to do with who manufactured the tube in some cases.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
#19
Yeah that was essentialy the message i was trying to convey. That was actualy what i meant i just over generalized because alot and in fact the majority are manufactured in plants over seas now but, not all of them and chances are to get a genuine American made tube you will have to get refurbs/NOS tubes. JAN/Phillips are one such tube/valve. I actualy like the russian tubes, EH 6L6 EH's are what i use now. My amp came with Sovtek 5881WXT+'s in it and those were pretty nice to be honest. It all depends on what you are looking for tonaly though. Of course, just because they are manufactured elsewhere doesn't mean they sound different if they are constructed to the same specifications.
Last edited by diesect20022000 at Nov 8, 2006,
#20
My tubes wore thin so i opted to try some other ones but, i would get the Sovteks again in a pinch.
#21
I'm saying that GrooveTubes are usually incredibly expensive, not that they are bad. JJ's, Sovtek's, and so on are all cheaper and sound the same or better in the case of JJ's
#22
More expensive sure but, i don't think 16.00 is really that expensive. Sure they are more expensive but, you get what you pay for plus in most cases you don't have to replace all of your preamp tubes. the gain cicuit in mine is v1 and v2 so those two would be replaced for gain change/swapping. If you can't afford good tubes then cheap ones will do but, the chinese ones tend to be on the harsh side sounding more solid state than alot of people would like i would think anyway. JJ's sounding better is also a matter of opinion as are the rest of our statements on what to get for tone. The only real way to know is to try them but, i know personaly JJ's don't do it for me at least preamp tube wise.
Last edited by diesect20022000 at Nov 10, 2006,