I found a new schematic for the Crestline GA – 5′s by accident on ebay. I thought I was buying an original manual / schematic that came with the Skylarks, but instead I got a reproduction. Sigh. The good news is that the schematic is very different than any other I’ve seen. Some very exciting stuff in here.
New Find : A Totally Different Crestline GA-5 Schematic
August 7th, 2010 · Amp Repair, Gear, Schematics, Skylark Rebuid
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Skylark Rebuild : Last things first
December 6th, 2009 · Amp mods, Skylark Rebuid, Uncategorized
This is what the old girl looks like right now :
Skylark Faceplate with plenty of rust (click for fullsize image)
Now it’s not going to matter one bit if I don’t do anything about the looks, but it would be nice to get her cleaned up. There is no way I am going to be able to clean around the silk-screened lettering or lines. So the whole thing is going to have to come off. I don’t even know how you clean these things.
Now, the chassis is actually just a single piece of metal, bent and punched. I’m not sure if it’s steel or aluminum but either way, it’s easily bendable.
Here is a picture of one out of the cabinet :
5T Chassis out of cabinet and looking from behind
So I suppose I could just have one remade. That would surely cost more than the amp, but I’d come out of it with the specs for new metal, which would be a good thing for anyone else trying to do this. Then I would need to get the art redone or redesign something. Again.. favors or money and no improvement in the sound.
I’m leaning towards leaving it, for obvious reasons, but very early in the process I’ll have to make the decision.. anyone have any thoughts?
→ No CommentsTags: 753397·GA-5·Gibson·Gibson Skylark·Mods·Skylark
Admin Notes : Spam Blocking and missing Images
December 5th, 2009 · Uncategorized
Ok.. I’ve installed a comment spam blocker. If you get blocked please grab my email address and let me know.
Also, the fix to WP was a hack so I have to change up some URL. If you have problems with pictures or sound, lemme know.
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Rebuilding a Skylark
November 28th, 2009 · Amp Repair, Amp mods, Gear, Skylark Rebuid
Regular readers (hahaha…. I kill me) will remember that I bought two Gibson Skylarks. One of which I fixed immediately and the other sat waiting. This is a story about the other.
This is a Gibson Skylark in the “Crestline” series. It is one of the many amps released with the GA-5T model number. This was made sometime in the early 60′s as the later model “Whiteface” amps would be released in ’65. This is not as popular as the true Class A SE Skylarks from the 50′s so it cost me $202.50 with shipping a couple of years back. It’s not working right now and I’ve decided to refurb it.
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Old user accounts are gone..
November 28th, 2009 · Uncategorized
Sorry about that.. took me a complete reinstall to get WP back to gold.
Feel free to join in!
The Real McTube wrap up
October 10th, 2009 · Gear, McTube
Sorry to both of you who read this.. I’m keeping busy :-)
So where are we ? I built out my McTube clone and it actually worked. Here are a couple of pictures :
So yeah, she’s nice looking .. I’m a fan of the clean look. The back has the instructions / names of the controls. The three banana plugs on the top are for heater and plate voltages (recall that my power supply is separate).
Here are the guts.. quite a bit less nice looking :
So what happened here is I didn’t carefully lay out the components before hand. I ended up with a lot of bare wire crossing a lot of other bare wire and naturually got some interference. In fact. I got an AM radio station and had to tie some ground points together before I got a good sound.
How did it sound? Well, I plugged it into a crappy Frontman 15B (that I got for 13 bucks) and it sounded like a tube amp. Not a great tube amp, but a tube amp nonetheless. It would be very fun to A/B with this setup and a good solid state amp to really get a chance to play with the ‘sound’ of tubes.
For a distortion box, I would tweak it I suppose, because I don’t have anything that can give you that barely hanging on sort of distortion and this doesn’t get there, although it gets pretty close.
If I were to use this more often, it would need a complete rewire. I will probably consider it though because as always.. I have a plan
→ 2 CommentsTags: homebrew·McTube·pedal
Real McTube : We have Power.. again
May 9th, 2009 · Amp mods, McTube
This time, I have done most of the job (I’m missing a pilot light but I’ll add that later.)
As you may recall, I chose to break out the power supply because I thought it might be useful in other cases. In fact, if I were to mock up the preamp of the Crestline Skylarks (130V on the plate) , this would be damn near spot on. It’s a bit light for blonde Skylark/Champ (165V on the plate) but you can’t have everything.
Power On
Here we are with an unloaded 170V. Very nice. The switch in front is standby.
The Filament power is the bottom connector. 16.4V unloaded.
Plenty of room
That’s a 12 point turret board with the discretes on it. I should probably dress those wires.
That is with power down.
WARNING : Those are good sized caps and there is still plenty of juice in them. You’ll get a nasty shock if you short the leads with power down (and much worse with power up). I should switch in a couple of resistors to ground when the power is off, but I’d need a DPDT for that and I don’t have one handy.
Buttoned up and resting on the mothership
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A Little Status
May 3rd, 2009 · Amp Computer, McTube, Songbird, calculations
Since I am failing to complete numerous tasks at once, I thought I would describe their status
Amp Computer
The problem here was banana cables. At some point, the ‘Asshole Audiophile’ community got a hold of banana connections and now it’s damn near impossible to get banana cables at a reasonable rate. I wanted to use banana cables instead of say, posts and alligator clips. These guys : Circuit Specialists solved that for me. I paid a buck and a quarter per 20″ cable. Woot! Back on that soon, but the first two parts are in fab now! I haven’t decided on the mounting system yet, Cheap boxes or panel/rackmount. Tough call actually.
Real McTube III
This got some love yesterday. The power circuit is done but not boxed yet. I am going to box it separately from the foot pedal part because hey, it’s 140/12 power supply and it’s not like I’m gonna take it on the road. I wired up the heater stuff, LED and footswitch yesterday and may take a crack at the signal today. More on that heater circuit later, but these are the first two amp computer style components.
Real McTube Calculations
This is gonna take a while, I did the numbers and they worked out, but now I can’t find the book I used and describing this stuff is really painful. I’m back into the Rider book but that is the most annoyingly pedagogical book I have ever read. I’d love to find a good clean book on tubes, with our without the math but it must have full data sheet reading info
SongBird
I’ve started buying parts and will rip the old stuff out of the chassis soon. There may be some original Gibson Transformers on EBay soon. Maybe I will recreate the Crestline in the amp computer style. Maybe the 102C84 will get up there. That would be ridiculously hard to find anywhere else.
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A Game Changer – The Gibson GA 20 RVT Initial Review
April 23rd, 2009 · Gear, Songbird
I have purchased the best amp I have ever heard. This is a 2006 Gibson GA 20 RVT. It’s not perfect, I might have to mod it, but I am definitely in love. My strategies about building the Songbird and other things are all up in the air now.
Let see why..
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Real McTube : Some Notes on Rectification
March 29th, 2009 · Amp mods, Gear, McTube
The Real McTube II was designed with rectified filament voltages because Fred found that the original McTube could be noisy if not done impeccably well. The original McTube (appearantly) had the 12 V AC from the transformers going directly to the heaters on the tube.
That is the way it’s always done on the old amps and I’m surprised in retrospect that he didn’t remember the simpler trick. Better amps would place a 100 Ω potentiometer between the two sides of the 12 V tap from the PT. Of course, I’ve just remembered that too now that my rectified filament is done. Oh well.
So the way to determine quality with rectification is to ask how close you got to the desired voltages and how much ripple (AC in your DC) remains in the signal. The only way you are gonna see this is on a scope or a dedicated tool for this. You might get it measured with a DMM, but I never got that to work. If the ripple is complex, the DMM will not settle on a value so you will be seeing snapshots that make no real sense. Since the DMM is reading RMS, the highest number you see will be about 2/3 rds the total ripple.
Unfortunately, I didn’t take a picture of the ripple in the Skylark when I had it open. Suffice it to say that it was plainly visible. With a scope, it’s easy to see. You set the scope to AC (and you don’t have to worry about the DC voltage spec within reason) and you slowly dial down the volts/div.
For the McTube, on both the B+ and Filament voltages, there was practically no ripple. At 0.01 volts/div at the slowest sweep, I saw about 0.005 swing that took a bit over a second. My scope wouldn’t trigger on it but it was plain enough. Normally you expect to see something at 60 Hz at least and I saw nothing.
So I guess it cost me some extra parts, but that is a clean power supply.
Next time I get an amp opened, I’ll shoot a pic of the ripple.
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