Fender Super 60

[eschertron]

Just picked up one of these from eek!bay and began testing it out. It came without speaker or tubes (as promised), but also came with evidence of one helluva drop (not promised). The PT mounting tabs are bent and the presence knob is bent out of alignment, still turns though. Once I got tubes, I put it one a lightbulb limiter and brought it up. Off the limiter now.

The clean channel makes a popping, crackling noise. I tried turning every control, nothing affected the noise. Well, maybe the presence control took a little HF out. Noise with ALL controls turned fully down. Finally I pushed the drive channel button. Dead quiet. I had to plug in a guitar to see if the drive channel worked at all!

The amp works, drive channel has only the hiss expected from turning up the gain, clean channel works but has the noise on it. With the noise audible when all controls are down, and is affected by the channel switching, should I be looking at the control voltage circuitry? Do LDRs go bad and make this noise? I appreciate any and all comments.

The schem can be found at this site Fender Super 60 | Ampwares

[eschertron]

So I played a bit more:

The 'bacon frying' noise is loudest when I flip the standby switch. Almost "oh cr** I'm gonna blow the speaker" loud. It tames a bit when the amp warms up more.
Plugging into the power amp in jack cuts out the noise totally.
After coming to equilibrium, the noise is faint-ish and might be possible to ignore while playing. Also the faint remnant noise is the same on both clean and drive channels. But only after - the noise is not noticeable on the drive channel until the clean channel gets quiet.

[eschertron]

I guess I love my 'alone time'

There's this thread http://music-electronics-forum.com/t39307/ which includes a full parts list and a transparent view through the PCB. That'll help trace the circuits. Thanks, G-one!

[TomCarlos]

I never noticed this amp before. I just did a quick check on YouTube.... this looks like a nice amp! I hope you get it up and running to your liking.

At this point, check everything!

Tom

[Leo_Gnardo]

I never noticed this amp before. I just did a quick check on YouTube.... this looks like a nice amp!

You bet! I think the Super 60 (and its variants) a "sleeper", an excellent amp that doesn't get enough attention. Twin-clean on one side, smooth refined distortion on t'other, all in a portable 1x12. I often recommend 'em to customers looking for an affordable quality amp. About once a year one appears on local Craigslist, typically $350-400. Little bit of a PITA working on the PC board, that's all. I call 'em "Boogie killers."

[DRH1958]

Yep, with a dropped amp, anything can be wrong. PCB construction and about 8-10 slide on connectors, so keep track of them. Definite PITA to work on. The knobs are on their own board, so I'd start there given that the presence knob is bent. Even though turning the knobs doesn't matter, these could still be a problem, they might be completely out of the circuit from broken traces/solder joints or shorted. I owned the Super 112, the brother to this amp and had it apart, bad screen grid resistor. BTW, I'd be in contact with the fleabay seller asking what he plans to do about this. The buyers have all the power right now. ebay will side with you. Did the seller insure the purchase?

[eschertron]

regarding the troubleshooting: I hear ya about checking everything. I would, though, like to have a hypothesis based on theoretical or practical reasons why the noise only on the clean channel.

Some of the discussions I've followed recommend replacing all the 1W resistors. Looking at the schem, I see ten. 2 on the screens: not channel-dependent. 5 in the HV rail: again not channel-dependent. The three remaining are in the bias/control voltage circuit. Since channel-switching control is in this circuit, I think there may be a relationship. Now armed with the PCB layout, I can scope some of these points.

I'm still trying to figure out how the LDRs are supposed to work. The third leg throws me. Is the LDR a NO/NC device, or do both the resistors conduct with light? I downloaded the spec sheet but didn't really see the answer.

232545.pdf

regarding the sale: after reviewing the pictures in the listing, I can see that the PT is a little cocked. So the damage occurred before the sale/shipping. I can ask the seller about the noise, but since the amp 'basically' works as advertised, then... :shrug:

Thanks, everyone, for your comments and suggestions

[Jazz P Bass]

The Super 60 is an awesome amp!

Without hesitation I would flip the main board & check out the solder job.

If the soldering looks deficient on the largest heatsinking parts, I would simply reflow the board.

#!: It's a combo amp. Everything is vibrating

#2: It 'took a hit".

Then, if it is still doing odd things, you can troubleshoot the issue.

[g1]

The solder side should be looking at you so you shouldn't have to flip the board for solder inspection, resolder anything suspicious. Preamp tube sockets should be looked at closely or just resoldered. The 1W resistors that were mentioned, maybe they meant plate resistors in the preamp? That and preamp tubes could cause the kind of noise you mentioned.
I think in the other post replacing components without board flipping was discussed?

And beware of the temptation to straighten that bent pot. More often than not the shaft will just break, and some of these pots and opto's are NLA.

[DRH1958]

You are correct g1, the solder side is indeed facing up when taken apart. This link won't help solve any problems, but is informative nonetheless. From the guy who designed it. Kind of him to get back to the guy and go into this with so much detail. This was right after Bill Schultz brought Fender out of the darkness(CBS) in 1985. Telecaster Guitar Forum - View Single Post - Rivera-era Fender amps club

[eschertron]

The solder side should be looking at you so you shouldn't have to flip the board for solder inspection, resolder anything suspicious. Preamp tube sockets should be looked at closely or just resoldered... I think in the other post replacing components without board flipping was discussed?

Yes. Good suggestion! The layout sheet, which you provided in the other thread, contains the info that makes this possible.

And beware of the temptation to straighten that bent pot. More often than not the shaft will just break, and some of these pots and opto's are NLA.

Yes. I rejected the idea of trying to un-break the pot shaft. Also, since the PT is fastened by machine screws with the nuts loose (or lose-able) inside the chassis, I'll wait until the main board is out before worrying about straightening the legs on the PT.

[eschertron]

Furthermore...
It seems that the crackling noise persists less and less with each power on. Also it won't crackle with a brief power off. I waited several hours to power up and scope the bias/control voltage line. All voltages look normal, no noise on that line with crackling evident at speaker. The crackling is gone (or reduced by several magnitudes) within a minute. So maybe the previous user just lived with it

Earlier I'd tested the power amp in jack. Kills noise, hiss, and all other preamp garbage. Pulling the preamp tubes: V1 no change, V2 kills the noise (at least for this test!). So plate resistors near the front may be suspect?

To amend a previous observation: I do hear the crackling on both clean and drive. I swear it wasn't like that before. But then, each power on and the conditions seem to be slightly different.

Regarding suggestions for inspecting/reflowing solder points: At first blush everything looks OK. I have only chopsticked a portion of the board, will continue inspecting and probing. I noticed the screen resistors have been replaced at some point (they are on the topside of the board now) and one is showing evidence of crispness.

But to repeat what I've said in previous posts: the amp sounds good for what it is, barring the crackles. The clean channel is a little 'dim' compared to the drive channel, but that may be just the design. I can look at that later, as other discussions have been made about that point. Thanks, all.

[TomCarlos]

Is this correct? If you put a signal into the Power Amp Input the crackling does not exists? If you go through the Pre-amps the crackling comes back? And you hear it on both the Clean and Distortion Channel? Doesn't that indicate the problem is between the power amp and the Pre-amp channels?

[eschertron]

Is this correct? If you put a signal into the Power Amp Input the crackling does not exists? If you go through the Pre-amps the crackling comes back? And you hear it on both the Clean and Distortion Channel? Doesn't that indicate the problem is between the power amp and the Pre-amp channels?

Tom, that is right. My first encounter with the amp gave me indications that were slightly different and more confusing (to me at least). Now I am ready to question bad plate resistors (or any other component) that can produce such high levels of sizzle. And I agree that it is likely to be part of the gain structure before the power amp.

I just finished inspecting the amp. I popped out the main board and, finding it appeared a little 'greasy', cleaned it with some head cleaner and Q-tips. I pulled out the input section board as well, to fix a jumper that I broke while wiggling the main board around. I have touched up a few solder joints too. Because the worst of the noise is only if the amp has been cold for a while, I'm not really sure if the problem is better now or not. I'll have to see tomorrow when I power up if there's any change to the issue.

[TomCarlos]

I am trying to find an old thread that addressed this. The suggestion was to replace the Plate Resistors. It looks like V101 A&B have 100K 1/2w. V102A has a 220K 12w and V101B has a 100K and 220K, both 1/2w. And since you are at it, you might as well change the Plate Resistors on the Phase Inverter - V103 A&B. Resistors are inexpensive- If you lift one side to test them, you might as well go ahead and replace them.

I once checked a resistor that measured ok but it had an issue when heating up. I know some guys like to stay with Carbon but I ended up using Metal Oxide resistors for the plates. Give that a try.