I bought a 1960 Gibson Maestro Standard GA-45 amp today. It has a terrific sound with my mic (Shure PE-5H), but only when I really crank it up; at that point it gets really fun. It's 16 watts, with four original 8" Jensens. It sounds particularly good outdoors, which is why I bought it: for big-stage festival gigs. It's in great working order.
I suspect that it might benefit from swapping in some slightly hotter preamp tubes.
Can somebody in the know tell me:
a) what the standard preamp tubes are for this amp;
b) what I might swap in in order to hot rod it
My mic drives the HG2 and other smaller amps pretty hard, but it's not super-high output and hot preamp tubes seem to compensate well for this.
Ya can't go wrong with Daves advice ,..e-mail him for his input on hot roddin your amp ---------- Simply Unique Kustom Mic's By Rharley
Last Edited by on May 16, 2010 8:42 PM
There aren't always options for easy tube swaps with some tubes. This amp appears to have some tubes that may fall in that catogory. The 5879 is a medium gain 6.3 volt filament, sharp cut-off pentode amplifier. I don't see any plug in swaps listed anywhere. That's the beauty of the 12A_7 series tubes, there are so many options. You may be able to do something with the phase inverter or power tubes, but that of course is not hot rodding the preamp.
I'd call Skip, and say, help! If anyone would know of a swap he would. 707.678.5705
Gibson Maestro GA-45 schematic shows- rectifier 5Y3, power tubes 2x6V6, phase inverter 12AX7, vibrato 6SQ7 and input tubes 2-5879s. (David Barrett's site shows a 12AY7 as PI, so it could be either)
I've always thought those amps looked real interesting. I think they may have been designed with accordians in mind. I have a friend with a Maestro/ 15" speaker, recapped, fresh tubes, all up to spec, but not very loud.
Mark B will surely respond and he is very knowledgeable. Congrats on the new amp, If you want the schematic email me, it's in PDF format and I saved it. JD
Last Edited by on May 16, 2010 11:24 PM
The best advice I've ever gotten about re-tubing various guitar amps to voice them for harmonica is from Bob Pletka, the owner of Eurotubes. You can contact him via phone or email through the Eurotubes web site.
If you call by phone you almost always have to leave a message and wait for a return call, but he 's pretty good about calling back, and is a very nice guy, very patient and very helpful as well as EXTREMELY knowledgeable. Well worth the time and effort.
The Eurotubes site appears to be solely guitar oriented, but Bob has substantial expertise about tube selection and substitutions to voice guitar amps for harp. Let him know whether you are looking for a clean sound, nasty breakup, crunch or whatever and he'll tell you what you need for your particular amp, or what different options you should consider and why. Eurotubes also sells JJ tubes which IMHO sound pretty good. I like them because to my ear they sound warm and not at all harsh.
One thing I learned from Bob Pletka is that certain amps may sound "fatter" for harp if you use a tube with an unbalanced triode in the phase inverter slot like an 12D/W7 (or its European equivalent, an ECC832) But this doesn't work in all amps.
For example, it works in a Blues Jr, and a Super Reverb, but does not do anything in a Princeton Reverb. It depends on the design of the particular amp. Some people claim it really doesn't help very much in any amp, but my experience is that it does actually improve the tone for harp in certain amps. I have no idea if it would work in a Gibson Maestro or if it did whether it would reduce gain instead of increasing it.
Last Edited by on May 16, 2010 10:20 PM
Check this site out some good info in tubes:) http://www.triodeel.com/tubedata.htm
Maestro GA-45- rectifier 5Y3, power tubes 2x6V6, 12AY7, 6SQ7 and 2-5879s
do a cross ref with the info above not sure about the other tubes didn't look that far i was melting down,but if the amp has a 12AY7
its a Low gain tube this is why it has low output you got a spare 5751 laying around, pop that in see how it goes the output should have a massive boost:)
5Y3 rectifier, 2X6V6 power tubes, 12AY7, 6SQ7, 5879.
Try pairing dissimilar 6V6's. I did this at Rick's suggestion with my '41 Gibson...One hot Raytheon and one mellow GE blackplates. Did my Little Walter Showcase and didn't need to mic OR lineout.
Try swapping the 12AY7 for a milspec 5814, 6211, 5965, 6829, for better distortion before feedback; or 5751 for hi-gain/ volume . If you can find a 6072-A, ( milspec AY7 ) try that too. I think an ordinary 12AX7 or 7025 would prolly be too gainey.
Electrolytic caps OK ?
Try a complete solder remelt. Not as time consuming as one might think. Remove all tubes beforehand, and mark.
What are the recommended volts ? If it's less than 117, use a Variac. ( I know there is some OPINION out there against using variacs ) I DO use one...even with my newer amps.
The Maestro is kind of odd...more of a jazz styled amp, but pretty cool looking.
I am looking at a similar amp in a 25W 4X8 configuration for a likewise purpose. It's still 63 pounds for only 25W, when the YGL-3 does 125W bridged ( but an UGHHLY 80 Lbs. )
@ JDH...Oh, absolutely. I found a nice 5lb. unit with a Kill-O-Watt. Just had to make sure of grounding. Paid $40 for the variac and $30 for the KAW. Essential for vintage units. New stuff ? No.
Oh...just wanted to add that where I usually play, it is very close to the Diablo Canyon nuclear power plant. I have played at places where wall voltage was 125+ ! Yeow !
Also, the Kill-A-Watt comes in handy for checking all sorts of energy usage.
Last Edited by on May 17, 2010 3:40 PM
HYVJ wrote: "One thing I learned from Bob Pletka is that certain amps may sound "fatter" for harp if you use a tube with an unbalanced triode in the phase inverter slot like an 12D/W7 (or its European equivalent, an ECC832) But this doesn't work in all amps." The 12DW7 has the most beneficial effect in some amps with a "long tail phase inverter", the GA45 does not use a long tail phase inverter.
Increasing the value of the 200ohm 6V6 cathode resistor is probably more practical than using a variac, *if* plate dissipation is high (check first). Try 250ohms at 5W? Your tech should make sure that the 6V6s aren't drawing more than 40mA each & that dcvoltages are within limits dictated by caps.
If you liked the tone without a variac then you don't need a variac. They are not essential for vintage amps. 99% of vintage amp owners do not use them. Gibson didn't typically run their tubes as hard voltage-wise as Fender.
As Little Joe says, ensuring the electrolytic caps are in good order is very important.
You are not very clear on what you are trying to change about it. Do you think it is not sounding good at low volumes, but it is at higher volumes? Does it sound too one dimensional? If you got it for big stage situations, and it sounds good cranked, then why worry, that is how it will be used?
If it is all standard, then my suspicion is that you won't want to change values of hard wired components. That limits what a good amp tech can do.
I know it has vintage speakers, but with 4x18 speakers, you could swap in some other speakers. If you want louder then some more efficient ones, if you want more bass response, then some heavier magnet speakers. If you want more depth of tone, then mixed speaker types (the strategy taken in the Sonny 4x10's and some other modern harp amps).
It may be as simple as getting a hotter mic for this particular amp.
These are all answers that vary depending upon what your goal is for the sound of this amp. Cheers, Walter
@Walterharp: The speakers are the one thing I have absolutely no desire to mess with. They're great. They're why I bought the amp.
I bought the amp from an acquaintance who lives not far from me and read my post about being interested in the 4x8" configuration. He purchased the amp from Mark Baier at Victora amps. He told me that Mark had gone through it and brought it up to spec. This consisted, as far as I can tell, of replacing EVERY capacitor and resistor with new components. That's not what I would have done, and I'm sure that Skip Simmons would be aghast as such manhandling, but it means that the amp is noiseless, if not perhaps as free-breathing and funky as it would have been if a lighter touch had been used.
As for Walterharp's question: Jeez, man. I bought an amp I love, but I'm trying to make it better. I suspect that every single person who has weighed in on this thread--including you--understands exactly where I'm coming from. I'm trying to tweak it so that it produces that rich, wonderful sound at a slightly lower volume level. If I can do that by changing out a preamp tube, why not? Although I've got a hotter mic, I'd prefer to find a way of making it work with the mic I've got.
It turns out that it already has a 12AX7 in it, so that particular solution may not work. The optimal solution might be to send it to Skip and have him put back in a few of the old caps and resistors, but before I go to the trouble and expense of doing that, I'll try the power tube mis-match tweak and see what happens. I'm also going to use the amp a few times--at the Chicago Blues Festival, for example, and maybe even at HCH--and see how I like it.
Last Edited by on May 17, 2010 7:51 AM
Sounds like Bruce Collins asked for a clarification:-).
A way to hardwire earlier main stage crunch involves the main tube bias, even on a cathode bias amp: as Mark suggests, make sure the main tubes are running at the cooler, crunchier, drier end of their bias range by changing the main cathode resistor. Cathode bias amp designers back in the day usually used a resistor value that was likely to result in safe bias with whatever tubes the buyer got at the drugstore, but today's higher wall AC voltage means the bias has shifted upward into a warmer, less crunchy mode. First you should figure out what's going on with that pair of main tubes that's in there; if they're running up toward 40 ma or over, go up on the main cathode resistor value till they're running about 30 ma. If they're running down toward 30 ma to start with, never mind.
But I think you should avoid that invasive & time-consuming process and do what some people have started doing with much bigger amps: use a Lone Wolf preamp pedal in front to get it going on at low volumes. You can use LW's solid state Harp Break pedal either to dial in some overdrive sound at lower amp volume, or as a clean boost to make that mic signal effectively bigger. You could also travel light with the pedal alone and get your signature tone. If you like blending in that Mouse amp, then you'll like the Harp Break. It's not a harsh SS clipping overdrive if you don't overdo it.
The tube Harp Attack will do those jobs also, with the same tone as your vintage single-ended tube amps if you crank up the pedal's drive. The LW preamps don't make the rig touchy because the pedals don't use a lot of gain to make their overdrive happen.
I daresay both the Harp Break and the Harp Attack will be available at the Hill Country gathering, so if you can wait a few days, you could try before you buy. I'd say run the mic directly into the LW pedal; the mic buffering by the LW pedals may well add a new dimension to the delay sound as a bonus.
Longterm hotrodding the GA-45, I'd just tighten up the power supply with a GZ34 rectifier and bigger main stage filter caps to make it louder/punchier and project bass better, but you'll have to adjust the main stage bias as noted above, and also adjust the preamp voltage downward to the original 5Y3 level. One version of that is to use the GZ34, or even a SS rectifier, but with a zener diode on the PT ground to bring the overall voltage down to 5Y3 levels. That keeps the original tone/breakup characteristics, but with a tighter, punchier note envelope for more stage presence. A tighter note envelope will probably work well with your preference for using delay. The tighter note envelope thing is a very common boutique harp amp approach--bigger filters and a tighter rectifier than they would have used in 1955.
"He purchased the amp from Mark Baier at Victora amps. He told me that Mark had gone through it and brought it up to spec. This consisted, as far as I can tell, of replacing EVERY capacitor and resistor with new components. That's not what I would have done, and I'm sure that Skip Simmons would be aghast as such manhandling, but it means that the amp is noiseless, if not perhaps as free-breathing and funky as it would have been if a lighter touch had been used."
Well, Mark's reputation and that of his company are pretty galvanised in the amp world, if "every" component has been replaced, then it will probably be with comparable components (proven US made, rather than Taiwanese resistors & Chinese caps...not that I have anything against them, they are just not the kind of thing to give a vintage amp buyer peace of mind when they look under the hood) & as long as equivalent values have been used, there's no reason why the amp won't sound as good as it could, or ever did. After all Victorias themselves are all made with new components & are still in demand.
For the amount of work it would take to replace every component I'd say you probably got a good deal on the amp, given the labour involved.
Resistors can be changed if they are seriously drifted or open (shot), filter caps & cathode bypass caps lose effectiveness with age, coupling caps can leak & kill tone...I'd give Mark the benefit of the doubt (just as I would if I gave an amp to Skip & it came back with new parts). They're both experts & I'd trust their judgement as such.
If someone came to me with a cap out of a 50yr old amp and asked me to install it into a gigging amp, I'd decline...& probably not that politely. :-)
Adam, the short answer is "No." A simple preamp tube swap will probably not get you where you want to be. There is lots of faulty advice offered in this thread, most of it speculative and potentially costly. It's easy to suggest expensive solutions to other people's problems.
Skip Simmons is a good tech, but as you suggest it is an expensive solution. If the amp has already been tweaked by Mark at Victoria and if Mark knew it was for harp, the amp is good to go. (Kim Wilson is an endorser of Victoria Amps, btw.) Perhaps you could contact Mark and ask him. He knows harp tone very well.
With only about 14 watts from two 6V6 power tubes, your amp will never have the volume to carry outdoor shows. Since it already sounds good at full tilt, and it will need to be mic'ed up anyway, I'd reccomend you leave it as-is for now. We all have the urge to tinker with old amps, but I've found it doesn't always bring marked improvements. In fact, it can make things worse.
I'd suggest you stick with your excellent HG2 and Premier amps when you need less ultimate volume and crank that Gibson when the opportunity presents itself.
Hey, I'd love to hear a recording of this new amp!
I don't know if it is safe to do or if it will work with this amp, but some amps overdrive and distort nicely if you actually REMOVE one of the power amp tubes.
adam, of course i understand the elusive goal of a perfect amp :-) just seemed lots of people were adding advice and you had not even made clear exactly what it was you wanted to change about the amp.
if you have a good (expensive) pair of matched power tubes and decide to use the mismatched gain inverter tube for any length of time, i suggest swapping out the power tubes as there is no need for matched power tubes at that point, and an unmatched pair goes for a bit cheaper. It is also possible that the uneven gain will cause the tubes to wear at a different rate.
getting the bias voltages adjusted would be an easy thing to do, but you might lose the punch and cut at higher volumes.
What do you guys think about a line out for this situation (if adam is going to a tech)? You lose the speaker tone, but also lose one more place for feedback to creep in.
@hvyj: Hmmmm. I run my 55 bassman with only one rectifier tube instead of two, but I was under the impression that your suggestion--removing one of the power tubes--was a recipe for disaster.
5F6H: I know Mark is very good. I also know, from my conversations with Skip Simmons, that even the best guys disagree. Skip's way--and he made this clear to me--was to use a light hand when swapping out old components. Mark's way is clearly not Skip's way. That's OK; even the best guys disagree. Skip's comment to me last year was that guys who don't know what they're doing start by taking out all the old stuff and replacing it with new stuff. This doesn't mean that a few very good guys don't sometimes do that--and that's your point, clearly. Point taken. I've got a big heavy bag of the stuff that was taken out, so no irreversible harm done. :)
@Walterharp: I'm not going to use a line out. I like the sound of the speakers.
Thanks for your suggestions, everybody. I'm digesting them. I will bring the amp to HCH and we'll see if we can't accomplish an on-the-spot tweak or two. We'll start with the Lone Wolf pedal.
Last Edited by on May 17, 2010 12:20 PM
Changing everything in a vintage amp upsets some people, but gives the gigging musician confidence that the amp should not fail.
BUT.
Personally, I'd rather keep the vintage stuff as original as possible and keep them for special occasions like recording or a few select gigs. Power supply caps would have to be replaced, but tone stack and coupling caps, only if they were leaking.( I have re-voiced an old Bandmaster to suit harp, but would have to put it back to original to keep its re-sale value up)
There are lots of modern amps/kits that can be voiced easily to suit whatever sound you want. They are comparatively cheap, reliable, and you can mod them in any way you like without feeling guilty.
I don't believe in old amp mojo. Old speaker mojo, maybe ?
@Walterharp - I've used the line out feature on my Double Trouble. It sounded good. While I've got a line out on my Mini Meat, I've only used it to record and it sounded fine.
I know Greg Heumann has used the line out on his Cruncher. He has also mic'ed it, too. It sounded fantastic. A buddy of mine has used a line out on a Gibson Falcon and it sounded great.
I would suggest trying both a different times and record the results. I would listen to the recordings and decide from that.
"With only about 14 watts from two 6V6 power tubes, your amp will never have the volume to carry outdoor shows. Since it already sounds good at full tilt, and it will need to be mic'ed up anyway, I'd reccomend you leave it as-is for now. We all have the urge to tinker with old amps, but I've found it doesn't always bring marked improvements. In fact, it can make things worse."
Let the record show that I agree with this statement 100%.
Adam - There are two kinds of line-out circuits. The one in your stereo receiver comes straight from the pre-amp - it is not affected by tone controls or volume and is sterile. But on most guitar/harp amps, the line-out is driven from the signal going to the speakers - i.e., PAST the output transformer. The speakers remain active when you use the line-out. This signal represents 100% of the mic's tone, the preamp's tone, the power amp's tone, your tone settings and the volume setting. It does NOT represent 100% of the speaker-specific tonal characteristcs - however it doesn't represent 0% of that either. Speakers place an inductive load on the amp - so the speaker interaction actually DOES show up in the line-out signal too.
If you knew all that and still don't like the sound of a good line-out circuit, then fine. If you DIDN'T, maybe you want to give it another try. As Joe said, I've have very, very good response to line-out tone. The more the amp can provide enough sound on its own, the less the PA has to add to make it audible as well, so it becomes less critical. Really low power amps with line out are NOT a panacea for large-venue live performance. Note that the sound guy can BOTH mic and line-out your amp. The good ones will mix the two signals. The sound guys I've worked with really like the line-out.
I used my 1 Watt home built 1 x 10" tube amp at a very loud gig on Sat as everything was being mic'ed up via sound engineer.
I mounted it at head height on a PA speaker stand.
It worked superbly, I just stepped in front of it for the solo's and could hear it easily above the rest of the band. I was staggered at how loud it was at this height, straight into my ear ! Obviously not loud enough to fill the stage, but as a personal monitor, ideal.
The harp was coming through the monitors too, but not as loudly as I'd have liked, due feedback constraints.
I still prefer using my own PA and Bassman, but for gigs with in house PA and engineer, I'll use this set-up. ----------
I like the range of sounds that I get from miked harp-amp speakers, depending how on-axis or off-axis I go. Line-outs aren't for me. I'm sure they work great for others.
Since I do a lot of upper-octave playing and I need my lines to be legato, I need an amp that overdrives up there. Smaller amps in general work better for me, or at least this is the vector that I've followed through a lot of trial and error over the past 25 years. This is partly a function of my mic; the lower signal strength compared to Astatic-style mics means that I have an easier time overdriving the amp if I user a smaller rather than larger amp.
I've played large outdoor festival stages, quite a few of them, with a pair of small amps: a Premier 2x8 and a Kay 1x8, for example. About 12 watts, total. The Maestro--which is listed in the Gibson catalogue from that year at 16 watts, BTW, not 14--is plenty of power for the one-man thing I'm doing, even outdoors.
I did a few gigs back in the early 1990s with two Supers. I get a much better sound with much smaller amps. But I'm looking forward to working the Maestro into the rotation.
The best amplified harp sound I've ever heard was somebody at Manny's Car Wash in NYC in the mid-1990s who was Jimmy Rogers's sideman. He was playing through a solid state PA head that was cranked way up and plugged directly into the board. It was shockingly good. He had some off-brand Radio Shack mic. Amping the harp, as we all know, is an art, not a science, and the exception that proves the rule probably sounds better than the rule.
Last Edited by on May 17, 2010 2:24 PM
I've kept my Bassman all these years, I should say, solely for the reason that I just MAY have a big outdoor gig--such as this Philly Folk Fest Friday night in 1993--where I want real firepower and the amp has room to breathe. So I never say never to 4 x 10s. Notice the 1948 National that I've paired it with here. That little thing loved to overheat! The sound would just fade away. But it was such a pretty amp:
Mmmm. I totally agree with Greg on the Line Out circuit. I use it all the time now and never worry about being loud enough. Brian Purdy does a wonderful job with his Harpgear amps when it comes to line out!
