Peavey 6505 Plus on tour

[rf7]

A customer has a 6505 that's been in twice with similar issues. First it was the output jacks were intermittent. I replaced them with new jacks and sent him on his way. He brings it back, says that it worked fine for a week and then had the same problem. I put it on the bench and it's oscillating badly, so I remove the preamp tube cover, which is bent quite a bit (dropped amp???), and pull some 12AX7's to isolate the problem. After swapping tubes around, and cleaning/re-tensioning tube sockets, the problem is gone, with the original tubes back in place. New output jacks seemed to be fine. I ran the amp on and off for a couple of days and could not get the problems to re-occur. He takes the amp again, and calls me from the road again. It worked fine for a week and then started to act up again. He's pissed off, and I don't blame him. I don't trust the molex connectors in those amps, and this guys on a van tour, with the head probably getting tossed about a bit. Are these amps that touchy/unreliable?

How do I tour-proof this head? Switchcraft output jacks? Hardwire all of the Molex connectors? I really want to touch up all of the connector and pot solder joints when it comes in again. I should have done that the last time, but did not. My f-up. Aargh!

[Enzo]

You're guessing. The problem with the amp is that you have not yet found out what is wrong with it. I'm not picking on you. Whatever is wrong, you open the amp, move things around, poke and prod, and it works... for a while.

We don't know that the jacks are really an issue, all we know is when you changed them it helped for a week. Might not have anything to do with the jacks themselves. It seems unlikely the new jacks - no matter how cheap or expensive - would have the exact same problem.

Likewise the Molex headers. Yes, please do rresolder them, but they really are pretty reliable. The pins that fail are the ones carrying high curent, like the heater supply. Soldering wires around them might be a good idea. But if those fail, it causes the sound to fade in and out as the heaters come and go. They don't usually make oscillations and things.

Last time I looked, the jacks PV uses in those amps already are Switchraft. If the jacks are intermittent, it might not be the actual jack. WIggling the plug on the speaker cord flexes not only the jack, but also the circuit board the jacks are on, and other things in that area.

Even if it DOES turn out to be a molex connector failing, you need to find out which one and where. THEN you can hardwire it if you want. Otherwise, you take it apart, wire around the molexs, and it works, so of it goes and a week later, it is bad again, because it was never the molex in the first place. Until you find that AHA!!! spot where the problem lives, you just don't know.

Does it happen enough the guy would be able to demonstrate the symptom? Invite him and his whole setup into your shop. SHow me. There might be assumptions being made here. "That speaker cord can't be bad, I just bought it a month ago." Oh yes it can.

Have you looked into the old effects loop jack problem? Does plugging a cord from send to return "cure" the problem? The cutout contact on the return jack can cause you grief. ANy time someone calls you with any amp cutting in and out, tell them to try patching send to return an see if it gets them through the gig. Often as not that is the problem, and they'll think you are a genius.

Here is a tip. On any FX return jack, a power amp in jack, headphones jack, external speaker jack, or any jack that has the potential to cut out the signal - and things like footswitch jacks - I measure the resistance of the cutout contacts. The contacts should be touching and offer about zero resistance. if it measures more than a half ohm, clean it. If it measures something like 2 ohms, it will work fine, 2 ohms won't interfere with any circuit I can think of. But the fact it is 2 ohms instead of close to zero is evidence the contacts are not clean, and while 2 ohms today, they might go open of high resistance on another day. In other words, test with a meter, don't rely on "it works."

The most valuable tool you can have here is the symptom appearing before you. Then you can signal trace, and divide and conquer.

In my experience those PV anps are perfectly sturdy and hold up on the road well.

[Mars Amp Repair]

I really enjoy how succinctly Enzo explains things. I alway gleen something.
As far as the 6505 goes, I have not worked on one but it looks like it may be very similar to the 5150.
In those, the molex connectors that go from the main pcb to the preamp pcb are reknown for getting intermittent. As I recall, esp the longest one.

To remedy & preventative maintenance this issue I unplug the connectors & then lightly file the pins & then place some DeOx on the pins. By wiggling the plugs when you put them back on will in effect also burnish the female side of the plug connectors.

At this point having seen issues with so many of these (on the 5150's) I have made it a matter of course in the repair to do this whether or not it shows symptoms.

Also in the 5150 there is a main pcb screw near the input jack side that actually grounds the pcb there that gets loose. I beleive the result is a low grade hum, but certainly under certain circumstance could cause other issues. I routinely add a star washer to it & tighten it (on the versions that have the ground here).
Hope that helps some...glen

[Enzo]

The 5150 and 6505 are exactly the same amp. All they changed was the name when their agreement with Eddie ran out. Van Halen owns the trademark "5150," and was licensing it to PV. When they parted ways, PV changed the name and continued to produce the amp. Eddie owned the name, PV owned the amp.

The 5150-2 and 6505+ are also identical to each other.

[rf7]

Thanks guys for the replies.

[Dave Curtis, dB AudioTech]

[QUOTE= lightly file the pins & then place some DeOx on the pins.[/QUOTE]

Don't use a file, Glen. I don't use anything that removes the metal from the contacts (even Molex pins). Clean, burnish & polish them (a new $ bill works wonders), but don't file them, even lightly. Something like this is made for the purpose:

http://www.pkneuses.com/cont.htm

That said, I usually just hit all of them with the Deoxit Power Booster Pen.

The only residue-type treatment I'll use on tube pins is the GxL100 Pen, which is rated for the heat produced at power tube sockets (older formula). FWIW, the new stuff is called "ProGold" IIRC, and has a lower heat rating, but was assured by Caig that it can be used on tube pins.

-Dave

[Mars Amp Repair]

Hello Dave,
I'm curious why you would suggest against light filing of tube pins or molex pins.

I find if the contacts are slightly oxidized or badly oxidized, 'light' filing of the pins on the plug end or the tube pins will act to 'file' off the oxidation in the socket end of the tube or molex sockets when worked in & out a few times. If that doesn't work, then replacement is necessary.

I don't use this practice with the octal based tubes as they are made of aluminum & dont ususally oxidize like the novar based tubes do.

I guess if I ever had problems in the form of reworks I would change the practice, but I've been using this method for some 20yrs in all kinds of electronics & have as of yet to have any issues.

glen

[Dave Curtis, dB AudioTech]

Hello Dave,
I'm curious why you would suggest against light filing of tube pins or molex pins.

It's what I was taught. "never remove contact material". Every time it's lightly filed, metal is removed, getting closer to the base metal, which is very likely more susceptible to corrosion than the (silver? rhodium?) plating. A pink pencil eraser is a better tool for this job.

I find if the contacts are slightly oxidized or badly oxidized, 'light' filing of the pins on the plug end or the tube pins will act to 'file' off the oxidation in the socket end of the tube or molex sockets when worked in & out a few times. If that doesn't work, then replacement is necessary.

Oxidized sockets? Denatured alcohol or acetone and a torch tip cleaner, but don't remove the plating. If you file tube pins, they become rough enough to scrape the plating off the sockets, hastening corrosion.

I don't use this practice with the octal based tubes as they are made of aluminum & dont ususally oxidize like the novar based tubes do..

Not aluminum. Rhodium plated brass, IIRC. A Qtip & acetone to clean and crocus cloth to polish.

I guess if I ever had problems in the form of reworks I would change the practice, but I've been using this method for some 20yrs in all kinds of electronics & have as of yet to have any issues.

glen

You never know. If 3 or 4 consecutive techs over the years filed those connectors, it would be down to base metal (copper? brass?), and would corrode much easier. The Caig stuff helps stop that, but still...

It's what I was taught by a long time master electrician (dear ol' Dad).
Put the file away, use an eraser and a $ bill.

-DC
Master Electrician

[Steve Conner]

I never knew about the dollar bill trick, but for relay contacts and the like, I use a strip of stiff paper soaked in contact cleaner. I just close the contacts on it and rub it back and forth like dental floss. It works great on crackly Gibson-style pickup switches.

The file is probably best saved for really heavy duty contacts that arc so much that they actually develop high spots and pits, like the points on your '57 Chevy. Or octal tube pins with big oversize solder blobs on the ends that would stress your sockets otherwise.

[Dave Curtis, dB AudioTech]

I never knew about the dollar bill trick, but for relay contacts and the like, I use a strip of stiff paper soaked in contact cleaner. I just close the contacts on it and rub it back and forth like dental floss. It works great on crackly Gibson-style pickup switches.

The file is probably best saved for really heavy duty contacts that arc so much that they actually develop high spots and pits, like the points on your '57 Chevy.

Yes, use it to take down the high spots, then polish. Most contacts like that are silver. If you leave them too rough, they'll go bad in short order.

-DC

[Enzo]

As someone who has worked with relays for a long time, I would point out there are various types of contact surfaces. Some are plated and some are not. Low current contacts might be silver or gold plated, and it is in fact relatively fragile, but other contacts are meant to handle a bit of current - like those car ignition points - and are more likely solid tungsten something. You don't want to file or burnish plated contacts, since it will take the finish off. Use a dollar bill, a match book cover, a business card, whatever. SOlid contacts are serviced by filing and burnishing, that is why they make contact files and burnishers. I have a collection of point files and contact burnishers in my kit.

I also carry dollar bills, but not as large a selection as I'd like.

[Mars Amp Repair]

Cool everyone,
I know about the plating on relays contacts & switches & such, but never thought about it on tube pins.

The only pins with coating you know for sure about are those 'great' Realistic tubes of the 60's and you still find those nearly as bright as they were the day they were new.

Funny you should mention the '57 chevy...my first car (at 17) was the cheap 4 door model 500. This was 1970. My father taught me to set the points with a match book cover. I was told those had plating on them & only to file them in a pinch to just get the car going or when you didn't have any expendable dough, which was quite often in those days.

Too much. glen

[Dave Curtis, dB AudioTech]

As someone who has worked with relays for a long time, I would point out there are various types of contact surfaces. Some are plated and some are not. Low current contacts might be silver or gold plated, and it is in fact relatively fragile, but other contacts are meant to handle a bit of current - like those car ignition points - and are more likely solid tungsten something. You don't want to file or burnish plated contacts, since it will take the finish off. Use a dollar bill, a match book cover, a business card, whatever. Solid contacts are serviced by filing and burnishing, that is why they make contact files and burnishers. I have a collection of point files and contact burnishers in my kit.

I also carry dollar bills, but not as large a selection as I'd like.

While ignition points are likely a tungsten alloy (high-cycling), all of the motor contactors I've had apart used pads of silver/copper alloy (98Ag/2Cu) for the contact material. I wouldn't call these low current contacts, but they are very low cycling when compared to ignition points, so the contact material needed is less durable, but more conductive. That said, you can bet they arc considerably when opening the load on a 480V, 30HP motor.

It doesn't matter how many bills you have, pick the newest one.

Back to Molex pins, I wouldn't be surprised if they are tinned copper or brass. I know the older round, hollow ones are brass; I just scraped the solder from one on the board that came out of my old PV 600S. The newer small, square ones use sockets that incorporate a self-cleaning wiper that burnishes the pin when the socket is removed/seated.