Tuesday, February 9, 2016

1975 Marshall Super Lead!

 Well, here is the beast of rock nation.

  These amps are from the days when things were innocent to the point of being kinda dumb. Rock stars didn't wear ear plugs in these days.

  I was once coaching a group of kids for an after school program where they had a rock band. They played well. The final performance was to be for their parents at the end of the term. They were figuring out the order of the set and decided to put "Hotel California" 3rd out of 4th. I approved and said "yeah that's perfect timing for people to put their cigarette lighters in the air like this" They replied rather baffled: "people used to put their lighters in the air????"

  I said "oh man, you kids will never have any idea how disgusting a rock n roll concert once was." One of the fathers looked at me with a nod and said "yup."

  So these amps are some of the greatest inventions in modern history, or should I say, a great piece of evolution. Marshall merely copied Fender and his tweed Bassman amp and made it louder. Much, much louder. I've owned several of these, the first being a 1977 50 watter, the next being a 1974 100 watt Super Bass. Then I went through a series of Plexis. A 1966 Super Pa, '67 Super Lead, '67 JTM 50. These are hands down my favorite amps. The early ones simply look gorgeous. Heck, they made Jimi and Cream even more attractive to look at. That Gold face, black cabinet and silver grill along with Persian carpets screamed psychedelic.

  This one is a later model from '75. All original except someone added an fan which it doesn't really need. It's also been converted to 6550 tubes. Big sound with those tubes. I do prefer EL-34 tubes in these but, this is one ballsy amp.

The blue cap is from this amp, find me the date code:

  28th week of 1975. Now by this point in rock history, the stars were demanding amps to be brighter and have more distortion. This one isn't a Master Volume model, but it's dangerously bright. I don't like that. I prefer the sound of the earlier Plexi models. But, this is easy to alter. Just take out the damned bright cap across the volume knob on the bright channel. In this amp it's a .005. Try a 50pf or 100pf. Or leave it out so you can actually turn the treble knob up! I left the circuit alone cause this works for the owner.

  Also try taking a patch cord and putting between the low input on the bright channel and the high on the normal channel. I used to do this. I'd turn up the normal channel then add the bright channel for just a bit of hair.

  When this amp came to me it sounded terrible and had a nasty hum with plenty of crackly junk going on. I re-capped the power supply, changed a couple bad load resistors and cleaned it thoroughly. Also removed all the pots and cleaned the chassis where they are mounted to. This is routine. It gets gunky back there and causes problems cause this is where all of your signal path gets grounded to. Clean it. It will only take 5 minutes! Then make sure everything is nice and tight. Screws, nuts and bolts. Marshall amps, unlike Fender amps have mechanical grounds. In other words, the grounds aren't soldered to the chassis. They are soldered to lugs that are bolted to the chassis. For quietest operation, clean them all.

  I replaced the output tubes with Sovtek 6550 tubes. The plate voltage in this amp is 525V! I wouldn't trust any modern EL-34 tubes with that kind of juice. I'm running these at a conservative 35ma each. The preamp tubes, 2 were RCA, one was a Telefunken, all 12AX7 of course. I left them alone except for cleaning the pins which were filthy. They sound great and no modern tube can match these. I don't know what the good people at Telefunken were doing but, their 12AX7 had a 100k+ hour life span. And this was a smooth plate version, highly sought after. As per usual, that tube had both sides pretty close to being matched. I've sold dozens of these and use them in my own amps. It's rare that I get a mis-matched tube, even at this age!

  Also replaced the broken handle:

  Some before shots of the old caps:

  The filters are pretty easy to replace except for this one which feeds your preamp tubes. Fortunately by this point they put a longer ground lead on it so you can just pull it up from the chassis, unsolder it and solder in your new cap.

  In this particular amp I took some liberties with the power supply. The main filters rather than use the stock 50x50 caps I chose to use 350uf caps built by JJ. In series this gives you a total of 175uf. The next stage I went with the stock 50x50 caps followed by a 32x32 feeding the phase inverter and 16x16 for the preamp tubes. My customer wants that thunderous low end. JJ builds drop in replacements that go up to 800uf! That's pretty extreme. I've built a couple Plexi clones that used this high of a filter and gotta say, nothing wrong with a tight bottom. I chose to use a much smaller 16x16 for the preamps just cause that's what the old ones use. It's a bit faster response supposedly.

  So it was great to breathe life back into this fine amp. I miss the days when it was normal to rock one of these with a couple 4X12" cabinets. Voice of god I tell you! Nothing sounds this good to me. And the funny thing is for those who have a prejudice against these due to the years of bad music made by hair metal guys. These 4 input heads are actually a low gain amplifier. They can be FANTASTIC jazz amps. There is so much tone and they respond so well to your touch. I don't care for the later 900 and 2000 series at all. As my former boss Steve Melkisethian at Angela instruments said: "I know bad taste when I see it!" He refused to sell those 900 amps when they came out and he sold a lot of Marshall. I'm on the same page as he is.

  See.... what else can I say about these? I worked on a Dumble once. Belonged to Robben Ford. I couldn't understand for the life of me why people pay $40k for one of those when these just sound so much better! I'd take one, sell it and buy a few Plexis myself, or pay for a nice vacation.........yeah, that's what I'd do.


Wednesday, February 3, 2016

Late 50's Ampeg 518 "Dolphin Special"

 This may very well be my favorite rare amp. The absolutely beautiful sounding Ampeg Dolphin. Model number 518. I'm becoming a bigger fan of the early Ampeg amps the more I get to see them. Here in NY I see more oddball Ampegs such as this probably cause they were built nearby. Go to Michaels Music in Freeport, Long Island if you want to see and buy some rarities. He's often loaded with great old Ampeg product.

  Here's a link to his page:  http://www.michaelsmusic.com/

Ok, just click next to the word page! I know it's invisible. I work on old amps that should be in the landfill, not on computers so bear with me!!!

  Anyway, I couldn't find a schematic for this amp. The unusual bits are it was originally loaded with the famous Mullard EL-37 tubes. You can sub them out with common 6L6 tubes though. These amps are cathode biased so you don't need to fiddle with that, just drop them in and gig away.

  Also the original preamp tube is a 6CG7. This amp had corrections from the factory:

The 6CG7 tube was actually a 12BH7 in this case, and my eyes and experience says it came wired from the factory this way even though it says otherwise on the chart. Cool thing is, I can just drop in whatever 12A tube I like. 12AT7, 12AX7 or 12AU7 which is what I chose and my customer is way happy with his sound. The 12AX7 made this amp buck like a wild horse!

  I found a catalog picture of this amp from 1960 and the first preamp tube was listed as a 6SN7. They were obviously experimenting greatly at this point in the company history. The 6SN7 is a low/medium mu dual triode with an amplification factor of 20 just like a 12AU7.

  This amp has a very old school way of construction. The preamp and the power amp are separate. This allows for the preamp to have minimal noise entering it from the power supply. The only AC entering the preamp is the filament voltage. You could easily convert that to DC but why bother? When I finished the re-cap this amp became dead quiet!

     Shots of the power amp:

  And shots of the preamp:

Notice the beautiful old ceramic Jensen speaker! I don't know if it's original to this amp but I don't care either. It's a terrific match! I repaired a hole in the cone. There was one other repair from long ago as well. Sounds heavenly!

  One of the fun facts about these amps is the power amp was possibly a copy of an Acrosound high fidelity schematic. I know this cause the first amp I built was this one:

  I've built this amp using 6L6 tubes and 2A3 tubes as well. Great circuit. Ampegs have a lovely midrange to them, a bit fuller than a Fender. This I really like. Later Ampeg amps become too mid heavy for me but these early ones are right up there with my favorite Fenders and Gibsons of the day. I hate to use the word 'undervalued' but these amps, well, they aren't quite as sought after, and that's not a bad thing for those who dare to be different! One sold recently on Reverb for $495. My client who bought this paid $80 on Craigslist! Yeah, needed a lot of work but still, that's a lot of wonderful sound for the money!

  Here's one last shot of the super cool "Jet Age" styled control panel:

  Volume, treble, bass and 'ultra high' for you to enjoy the jet stream with!

  While I certainly don't need another amp, if I built anything new I may follow this path. No one else is and I think this is a great amp for a jazz player who likes a little bit of hair to their tone! I'm starting to hear more jazzers play through amps such as the Blues Jr. by Fender and it makes me really happy after nearly 45 years of Polytone and Roland Jazz Chorus blandness. Acoustic instruments such as my roommates oud would absolutely kill through this thing!


1967 Fender Bassman amp

  Here's an amp I used to see all the time and haven't seen much of in a while. A good old '67 Bassman head built by Fender in Santa Ana California. These are to me some of the most consistently good sounding amps built by Fender, and are still relatively a bargain when compared to the earlier black panel amps. These are commonly known as the 'drip edge' series due to the aluminum edge around the grill cloth.

  This one is an AB-165 circuit. They started building this right around 1965. Not as desirable as the earlier AA-864 which, I ain't gonna lie here, is a better sounding amp. But these aren't bad by any stretch of the imagination. The AA-864 is relatively hard to find. I would describe it as more open sounding, the classic 'black panel' sound. These do have a bit more of a stuffy sound to them. You can convert one of these, it's a pretty big task so I wouldn't attempt it unless you have some serious skills. I've done several over the years with satisfying results. There is one thing I don't see talked about in literature and that is the output transformer may be wired out of phase on the AA-165. Once you do a conversion when you fire it up if it sounds like Armageddon (bombs falling, explosions, people screaming!!!) simply switch the blue and brown anode wires on pin 3 of your 6L6 tubes. Seriously, it's a scary sound!

  This amp just needed service. It had been off for about 25 years in storage. 5 out of the 6 tubes were original to the amp and unfortunately the 6L6 RCA tubes were shot. Always sad to see those go. I replaced them with Sovtek 5881 tubes, the thin base ones. They are rugged and sound decent. I like them the best cause I never get returns. All other glass is risky. The 12AT7 phase inverter tube I replaced with a NOS Sylvania. There are plenty of NOS 12AT7 tubes around, and in a Fender amp these, especially in the reverb driver circuit, take a lot of abuse. I get annoyed when I see new glass in these positions. The JJs and Sovteks fail. Don't be cheap and don't be lazy and besides, these often COST LESS than new glass. If you don't need premium Telefunken or Mullard, any garden variety RCA, Sylvania or G.E. will do.

  This amp received a full re-cap. Get those old, crusty electrolytics out of there! Yeah, they look cool and have those date stamps but, they need to go.

  Also check the power supply resistors. These were okay so I left them. Always replace the screen grid resistors though.

  I didn't convert this amp but did convert the bias supply. This is the era where Fender started to be more concerned with balancing the output tubes than actually biasing the amp properly. One tube stays constant, the other is adjustable. Not a terrible idea, Marantz has an individual bias pot for each tube, I like that. To do this really right you would need to add another pot to adjust overall bias, but we're just going to make it like the older amps.

  Now, on a late 70's model you need to leave that balance pot alone and add a bias trim pot. Here's why. Those amps are Ultra Linear. When one side drifts out the amp hums. I've seen people pay for a re-cap on one of those when all it was is the poor tubes aren't matched up right. I'm not a fan of ultra linear output transformers in guitar amps. The idea is low triode distortion at high pentode power. The result is an amp that is good for pedal steel or jazz but not as likable as the previous models.

 So Jef, what is Ultra Linear???

  Read this:   https://en.wikipedia.org/wiki/Ultra-linear


The Marshall Major, Park 150, Sunn amps, these are all Ultra Linear. I like these for bass. For guitar I like my distortion thank you!

  Anyway back to our Bassman. Once I got the amp re-capped and biased the amp ceased to hum and sounded great but still more needed to be done. Snap, crackle pop, hiss....... Here's an example of a big corporation trying to squeeze out every profit they can. Leo Fender was a perfectionist. He chose the best components available to him be it pickup wire or resistors, you know, the little things. CBS decided to buy resistors from Joe's Discount Resistor Shack, they probably just got a better deal on them. It's not unusual to have to replace EVERY load resistor in one of these along with the 220k and 470K resistors in that additional gain stage. Check them. In this amp all of them had drifted way out of tolerance. I replace them with new carbon composition resistors to retain that old, warm sound. There are plenty of choices. You can go with new Allen Bradley or Nichicon, Kemet, they are all good and I'm grateful I can buy these at Mouser, Antique Electronic or Mojo Musical. When I first got in the game I had to scour dirty, disgusting and often depressing HamFest or some poorly lit electronic supply houses. Ok, I did enjoy the HamFest and the surplus places, many of which are now gone were pretty special places. You met some really eccentric folks there. But that's ironic progress for you. A demand for a resistor that is by all means antique has created a new supply for us with picky ears! And that's exciting.

  It's the little things....