69 Laney socket arcing over

[Doug]

60 watt. Arcing over between pins 2 and 3, blows mains fuse. Cleaned everything up and retensioned the socket. Powers up but then arcs over when you go to play the amp. Swapped tubes, same problem. The arcing has eaten away some socket structure between the pins. Time for a new socket or should I be looking somewhere else?

[52 Bill]

Time for a new socket or should I be looking somewhere else?

My vote is for a new socket and tube. You don't say what tube it is, but 2 and 3 on an EL34 is the filament and the plate.

You may be able to clean up the carbon arcing, but if you don't get it all, it will always conduct once the high voltage hits it.

[Enzo]

Once a socket has arced, it is almost always a good idea to replace it.

[Don Moose]

Replace the socket - a nice ceramic one would be (slightly) preferable.

[Buckeye]

Replace the socket!

Another vote for replacing the socket. Arcing often happens when you lose connection with the speakers... or forget to plug them in. As a result, there's a voltage kickback in the primary of the output transformer. The voltage can spike to well above the max rating of the tube socket or the tube base itself. Once a hole has been punched by the arc, the tube max voltage rating is drastically reduced, and the socket or tube are considered defective. If you continue to use a bad socket, it's possible that when it arcs (usually on hi power bursts) it can damage your tube base as well.

It is also very important that you check the impedance setting of your amp and make sure the speaker cabinet is what you think. I've seen this arcing happen when you blow some speakers too. If you have a 4x12 cabinet rated at 8 Ohms, it's often wired as two 8 Ohm speakers in series paralleled with the other two speakers in series. So each speaker is 8 Ohms and the impedance arithmetic is (2 x 8) / 2 = 8. If you blow one speaker, the impedance jumps to 16 Ohms. If your amp setting is 8 Ohms, this mismatch could be a problem. It would most definately be a problem if you blow the speaker while playing at a very loud volume. Arcing could result.

Other sources of the problem could be an intermittent connection in the speaker impedance selector switch, the speaker jack (amp or cabinet) or in the cable itself. If you're losing a connection to the speakers in any way, you run the risk of damaging the circuit on the primary side of the output transformer. Make sure you get the source of your problems fixed. If you just forgot to plug the speakers in, then you're probably OK with just the socket replacement. But make sure the problem isn't somewhere it could happen again.

Many manufacturers use a shorting speaker jack in tube amps to protect the sockets and all the circuitry on the primary side of the transformer -- including the transformer itself. Be happy it was only the tube socket that arced. Although much less likely, the arc could have happened inside the transformer itself.

Well, that was long winded... But the bottom line is make sure your speakers are ok and the impedance is set correctly. Don't run your amp without speakers plugged in. And replace your tube & socket.

[Prairie Dawg]

Once a socket has arced, it is almost always a good idea to replace it.

Yep, that's whatcha call carbon tracking. You can salvage a magneto cover by removing all the damaged material, baking it, and coating it with lacquer but nobody's going to do that with a $2 tube socket.

I'm kind of partial to the brown military surplus Amphenol sockets myself, but there is a guy selling sockets (Chinese) on fleabay that look pretty close to the black Amphenol sockets and the price is right-I may take a flier one of these days.

The Beltons are pretty good commercial sockets too, but it helps to have some old sockets with unused pins around because you're likely to break a few of them and need spares-the midpoint is kinda thin and when you go to bend the pins a little they break in the middle.

[HTH]

I've owned some of these amps (and repaired a few more too). The plate voltage is crazy on these (600v if I remember rightly) and they eat through EL34s like theres no tomorrow.

I just replaced the sockets on the ones I had in with arced sockets and they were fine after that (except the one with the shorted mains tx).

I'd be tempted to put 6550s in them if I got another at some point.

[Buckeye]

Ebay, China & Laney amps

Hey, thanks for answering guys.

Prairie Dawg, funny you should mention ebay & China in the same breath. I just bought some tube socket (base) spring clips from Beijing from some guy named Zhang Sheng (zhangsheng). They were reasonably priced, arrived in under 2 weeks, and of very good quality. The only problem is they were supposed to look like this:



But instead arrived looking like this:



They went into a Peavey Mace combo I repaired. They fit the socket rivets perfectly, work very well but don't match the appearance of the other clips. Minor detail I guess.

So I just registered on this board because I was looking for some schematics for a Laney Pro Tube 100 -- old style non AOR. Found some for the AOR 50 and posts that said it's very similar to the Marshall 2203. Between those two I should be able to get 'r done. Need to find some odd unique parts though. But first some pictures of this beast! Check it out, it's the 1,019th PT100 made:





This thing has been rusting away in someone's basement for a while. The chassis is corroded and rusted but the cabinet is in outstanding shape. It came w/o tubes, so I put some in and it powered up. Did a power check at 1kHz and got a whopping 112.5 Watts! What happened to the days when power was rated conservatively? The output waveform was a little asymmetrical with the plus half being a tad bit shorter than the minus half. That needs a look at, but I just grabbed some old preamp tubes out of the junk box and threw them in so don't know if it's the phase inverter or some RCs that drifted out of spec. (Hope it's not a few shorted windings in the primary of the output transformer.)

Looks to me like this thing is biased a little too hot and the EL34s probably won't last long. I'll back that off to something more reasonable. After reading HTH's post I tried to use 6550s and that's not so easy to do. The spring tabs that hold the tubes down are too close for the 6550s I tried to plug in -- old RCAs out of the junk box. They interfere with the 6550's big base and would have to come out. Probably wouldn't be a problem because the tubes are mounted with the base down.

Anyway, as you can tell from these pictures, the parts I need are the Voltage and Impedance selector switches. I don't really want to pay crazy Marshall prices either. Anyone know of any out there reasonably priced? So far I've found a Schurter V selector switch for $14 and a Marshall Ohms selector for $19. Would rather buy them from Beijing.

Here are the rest of the pics...





Due to message board limits, I will include the rest of the pix in another post.

[Buckeye]

Ebay, China & Laney amps, continued...

Here are the rest of the pics...







Any help in finding some original selector switches would be great. I don't want to pay big bucks for Marshall subs, though.

[pchilson]

Buckeye,

Contact the folks at this place and send them pics and as much model info as possible and they should be able to hook you up. They are supposed to be handling Laney "obsolete" items.

[Prairie Dawg]

[QUOTE=Buckeye;134688]Hey, thanks for answering guys.

Prairie Dawg, funny you should mention ebay & China in the same breath. I just bought some tube socket (base) spring clips from Beijing from some guy named Zhang Sheng (zhangsheng). They were reasonably priced, arrived in under 2 weeks, and of very good quality. The only problem is they were supposed to look like this:

Same dude. He's got these:

NEW Bakelite Tube Sockets EL34 6550A KT88 5U4G OCTAL X8 - eBay (item 290347576008 end time Jan-05-10 06:29:02 PST)

[Buckeye]

Those look like good sockets, and cheap too. Let's hope when you get them they look just like the pictures. I think it's more likely because my retainer clip listing didn't have all those close-ups. It was probably some old photo. Tell me how it goes. Good luck.

I sent an email to obsolete Laney amp support at MAJ Electronic this morning. Their info page said don't send pictures unless requested, so I didn't. Hopefully the prices are reasonable in US dollars and shipping is about the same as it is from Beijing.

I'll post what I learn.

[JerryP]

Yup, change the socket and find out why it happened. As mentioned the wrong impedance or no load connected will do it. An attenuator will do it too.
Jerry

[Buckeye]

I've been in touch with MAJ Electronic, the Laney parts supplier in England. They are on a morning schedule. My emails were answered promptly each morning, and it takes a full 24 hour cycle for each exchange.

They have no original Laney voltage & impedance selector switches. The originals were on 1 & 7/8" mounting centers, the new ones are on 1.5" centers. These are the same thing we can get stateside. Their pricing was very reasonable with shipping, competitive with local parts. They quoted me £12 including shipping -- that's around twenty bucks for both. They'll take a credit card but did not offer to take PayPal & I did not inquire about that because I bought the parts stateside.

Anyway, my main interest was getting identical replacement parts which are no longer available. To use the new parts, I'll have to mod the chassis.

Back to the original topic of arcing your tube sockets because speakers aren't connected...

You know how these old British amps don't use a shorting jack to protect the output transformer? If you put one in, the chassis isn't marked for a "Main" and "Aux" speaker so it's not obvious to the user how to plug the speakers in. Well, Re 'An makes a switched mono jack that's perfect for this situation. What's special about this jack is that it switches both the tip and sleeve circuits. That makes it easy to wire a protection circuit where it doesn't matter which jack you use for the main speaker. The Re 'An part fits panel holes in British amps, but does not fit the standard 3/8" Switchcraft holes. The Re'An part number is NYS2122.

Here's a drawing of the wiring:

[Prairie Dawg]

Those look like good sockets, and cheap too. Let's hope when you get them they look just like the pictures. I think it's more likely because my retainer clip listing didn't have all those close-ups. It was probably some old photo. Tell me how it goes. Good luck.

I sent an email to obsolete Laney amp support at MAJ Electronic this morning. Their info page said don't send pictures unless requested, so I didn't. Hopefully the prices are reasonable in US dollars and shipping is about the same as it is from Beijing.

I'll post what I learn.

I ordered twenty octal sockets and twenty tube retainer clips from the guy, the total including shipping came out to $52. He will combine shipping, you just have to go outside ebay to make the deal. Let's see what I come up with-I've got a couple Amphenols to compare them to.