OT :Modifying my amp's output stage?

[Connoisseur of Distortion]

I have an amp that i want louder. It makes a nice tone, but just not enough of it...

How practical (possible, that is) is it to add another set of output tubes in an amp? I imagine that i would need a new output transformer as well, more components to go around the extra power tubes, and of course more tubes.

thank you for your time.

[cd]

You've halfway answered your own question.  Provided you have the space to add two more output tubes, then you'd need to replace the OT, especially if it's undersized.  THEN you may have to replace the PT, since adding two more power tubes requires more heater current, and your stock PT may not be able to handle it.  AND even if the heater winding is up to the task, the HV winding may not be able to supply the current required.

Then don't forget to account for resale, since this kind of large mod will significantly lower the resale $, even if you think it's a beneficial mod, and even if it's professionally installed.

AND (you knew there was another one, right? I hope you have another speaker cabinet to handle the increased power, or your stock speakers can handle the increased power...

AND even if you get everything installed, kiss resale goodbye, then you turn it on expecting to blast your old bandmates away... and your amp is only 3dB louder.  Barely louder than before... yes, double your wattage and you "only" get 3dB in volume.  Yeah, I know how the low end will probably be way better, different speakers may make it seem louder, etc. but fact of the matter is, a 100W amp is only slightly louder than a 50W amp.  

OK, still want to go through with it?  You need a PT, OT, new tube sockets, tubes - might as well spend slightly more $ and build a completely separate SUPER SCALER amp (see www.londonpower.com, or TUT5 - enough info there to get you started, since it's way beyond the scope of this board).  At least, then you'll be able to sell your amp later on without regret.

[brett]

yes, double your wattage and you "only" get 3dB in volume.

Yep. Efficiency will beat power every time.  Adding a high-efficiency speaker or two might get an extra 5 to 10dB, which you'll never get with extra tubes.  I would say high efficiency means 95dB/W or higher.
Sammi speaker have a good reputation for tone and efficiency, and are cheap(ish) here in Australia.  I think the 12s are rated at 98dB/W, which means that a 1W amp will blast a room and 10W will blast a small hall.
I have a 94dB/W 12inch that I use with a 5W amp.  I rarely need to totally crank it for garage use (though I do).
have fun

[bwanasonic]

Without knowing the specifics of what amp you are talking about, the suggestion for a more effecient speaker is probably worth trying, but it may adverslely effect the tone. Have you tried running an external speaker cab? Maybe a 2X12 if you are currently using 1X12. I know it's not always practical to mic in some band scenarios, but that might be another route of experimenting. In general a question like this benefits from more info about what amp/speakers in particular, and what function you need it for (living room jam, pub gig, church/worship band, stadium gig, etc.).

Kerry M

[Connoisseur of Distortion]

thanks for the responses    

cd - i didn't even think about the PT.  :x  getting that and an OT will probably send me into the hundreds range... and that's not even considering the other stuff. i'm not a bit concerned about the resale value, as it was already modified before (someone did a mod to clean up a murky clean channel, and put in some sort of mesa preamp on the crunch channel) and it's a piece of crap anyways   . I know about the 3dB increase per wattage doubling, BUT i thought that the change would be very definately noticeable. as in, about time and a half as loud  :? . i guess i don't really get dB...

brett - thanks for the suggestion of speakers... and for an actual reference to a good value of efficiency! i never knew what a good range for a speaker was, but with that in mind i'll resume my hunt for new speakers.

bwanasonic - i have tried external speaker cabinets, but i don't have one readily available and it didn't seem like a truly worthwhile addition... my experiences with micing have been interesting but that's about all (my PA doesn't add much amplification, it is in fact quieter than my amp is). The irony is, my cabinet is a **** 4x12. i don't really have the cash on hand to purchase another, but the presence of bringing such a monster into a concert would be awesome    i tend to jam with friends (we're well isolated, i assure you) and play gigs around town. ALOT of venues seem to expect the guitars and basses to handle their own power (a real joke considering both guitarists in the band have been using combo's) and i really do want the presence of a stack. not to mention the hit.  

my amp is a BV60H, by crate. As i mentioned, it has already been heavily modified and i don't mind messing it up some more. it's running 60 watts, and i think 120 would get me the volume i am looking for... but maybe not. the cabinet is a crate 4x12, i have no info about it except it handles 40 watts per side.

comments, info, insights, opinions, and experiences appreciated. thanks cd, brett, and bwanasonic.  

[bwanasonic]

If you are just playing small jams and gigs, 60 watts should be MORE than enough. Maybe you need to tell your drummer to chill out? :wink:  I have played many a rowdy biker bar and small club, unmic'd, and with *enthusiastic* drummers, using a 55 watt 2X12 combo. If you are at all considerate of your audience's (and your own) ears, 120 watts is overkill in small clubs.  Maybe everyone else in your band needs to turn down :idea:

Kerry M

[vanhansen]

The problem is the amp.  I know from experience except I had the 120 watt blue doodoo head.  The other guitar player had a 50 watt Marshall and his amp blew mine away.  I had to turn mine up 3/4 of the way just to keep up with his on 4.  Plus those tube sockets and everything else are PC mounted, and not on a very good PCB either.

Good thing you're not worried about the resale value because there really isn't a good one for those anyway.  The fact is those things don't keep up very well.

You may have better luck with a Peavey Classic 50.

[cd]

Forgot to mention, a 10dB increase is a perceived doubling in volume.  So 3dB sounds like nothing.

Keep in mind, I presume the previous amp modder didn't do something to the power section to lower the power, like wiring the output stage in triode mode, or mucking around with the PI so it's not driving the output stage properly.  Make sure the amp is working properly to its max potential first.  Actually IIRC the iron in Crate amps is undersized which can limit frequency response - what are the dimensions of the OT?

You sound like you have very little $ and need the best bang for the buck - that without a doubt is to get the other people in the band to turn down.  Besides that, anything else is going to be pricey.  Four new speakers? $80-100 a pop.  Change OT, PT, add a choke, tube sockets, new output tubes?  $200-300 at least.

[thatjanke]

I have a 4x12 cab that I couldn't seem to get enough volume out of as well. I found that by simply lifting it off the floor and setting it on a 15" speaker cab (milk crates would do also) my volume increased tremendously.  

[brett]

Hi again.
Hmmm...
Something is fishy here.
Bwana is right - 60W should fill/kill a small room.  And it doesn't have to be a Plexi to do it.  My Musicman 65 is loud, even on its 18W setting.
Maybe there's a clue in that messing about that happened with the preamp.  Double-check that the output tubes are getting several volts AC on their grids.  

Also, check your plate voltages (Danger Danger Will Robinson!!!).  The pre-amp tubes (e.g. 12A..7s) should probably be running at 200 to 250V.  For power tubes, expect 300 to 400V for EL84s and the like.  A few amps (like my Musicman) go to as high as 700V (on a pair of EL34s).  For others, look up a datasheet, and check that they are running somewhere near capacity.

Good luck!

[Fret Wire]

Get a schematic and go over the amp to see just what has been done (modded) to it. Undoing the mods may be all that's needed. Just make sure you discharge the electro's first. And go over the simple stuff first: bad/weak tubes, dirty/low tensioned sockets, stress broken solder joints. loose pots/jacks, etc. 60 watts should be plenty loud enough for clubs. How old is it? You could have a failing electro. Funny, even though caps are better made today, they don't seem to last as long in newer amps.

[cd]

Good point: if you've never worked inside a tube amp with high voltages before, read this first:

http://geofex.com/tubeampfaq/taffram.htm

Then have a good night's sleep and read it again.

[vanhansen]

I have a 4x12 cab that I couldn't seem to get enough volume out of as well. I found that by simply lifting it off the floor and setting it on a 15" speaker cab (milk crates would do also) my volume increased tremendously.  

That's only because the sound waves were now coming straight at your head instead of your legs.  It's a good bet that the volume level didn't change at all, it just seemed like it did because you changed where the speakers were pointing.

[vanhansen]

This sounds exactly like what my BV120 did.  The freakin PC board got so hot it melted a few traces causing it to drop in overall volume.  It was like someone put the speaker cab in a box.  Took it in for warranty repair 3 times before I finally said "f--- it" and got rid of it.

If it's none of the things Fret Wire says to check, unload the sucker and get a better amp.  Save the headaches for playing too much.  

[fikri]

I think the mod for getting more output power with more tubes might not worth the effort, Maybe you should consider of building another power amp to fit your needs. I think a 50W amp is more than enough to play in such a small club. I've played with a 50W Marshall (no master volume) in such a noisy band with my handmade tube preamp, and it blows out everything the first time i open my guitar volume ! even the sound engineer could feel that  

[Connoisseur of Distortion]

i had a quick look inside the amp's chassis, and everything looks alirght...

the mods were done neatly (they even cleaned off flux) and everything looks good in terms of part quality...

i'm not feeling bold enough to take a measurement of the plate voltages right now, but i'll get to that later.

i'm really tempted to get a dB meter and see what it's delivering. also really tempted to go after a better cabinet (or to replace the speakers in this one). a friend told me awhile ago (which i for the most part ignored) that a good set of speakers will best a good amp.

[Connoisseur of Distortion]

question: when you say efficiency in speakers, do THEY mean sensitivity??  :?