Traynor YBA-3. in with cooked tube sockes. OT varistors previously removed

[SoulFetish]

Traynor YBA-3 brought with note “maybe overheating. Smells burnt?”.
Some HV Transient must’ve flashed over the primary and cooked a tube socket and a good bit of wire.
Cleaning all that out, and Replacing what i need to.
The amp had been previously serviced, and the protection MOVs across the OT primary where removed. (But not replaced)
After a brief web search trying to find specs on the MOVs traynor used, it seems like it’s common practice in some circles to remove them all together as a matter of course.
Are these parts know to be faulty, or cause problems? Or do people remove them because they don’t understand what they are, and think it messes with thier “tone”?
If it was left in the amp may have saved this dude what I hope is a very prompt payment for service.
Anyone have any data on the original part? I cant read part#s on the schematics ive seen online.

[Enzo]

Or one of the odd parts fails, they take it out, and have no idea where to get new ones. So they leave them out. I am sure there are knee-jerk guys who take them out because the internet said to some place.

For some reason I am reminded of a cooking story my mom told. It seems her mom made a killer roast ham. Grandma went to the butcher for a ham, and always had the guy cut the ham in half before she took it home. She then tucked the two halves into her roasting pan and did her cooking magic. Mom duplicated this procedure for years and years, with great results. I still like mom's ham.

One day, mom asked grandma why she had the ham cut in half. "Does it make more surface area so it bakes faster? SO the seasoning gets into more meat? Grandma said, "Nah, it was the only way the ham would fit in my small roasting pan." But all those years, mom had her hams cut in half too, even though her pan was larger.

SO just because the internet says so, isn't always a good reason.

There is more than one way to skin a cat, if you can't find the MOVs, add a couple flyback diodes like a zillion other amps.

[g1]

They all seem to eventually fail. The factory used to tell us to remove them if we found them still present in any old amps.
Like Enzo said, the standard flyback diode type arrangement will work fine as a replacement.

They are thyrectors, part numbers in linked thread, specs. in attached pdf

http://music-electronics-forum.com/t37122/

[The Dude]

......add a couple flyback diodes like a zillion other amps.

^^^^^^That!

[Chuck H]

Most important, zillions of amps have no MOV's or flyback diodes in similar working environments. What caused the failure. THAT is primarily what needs to be fixed. It didn't fail because the MOV's weren't there.

[SoulFetish]

They all seem to eventually fail. The factory used to tell us to remove them if we found them still present in any old amps.
Like Enzo said, the standard flyback diode type arrangement will work fine as a replacement.

They are thyrectors, part numbers in linked thread, specs. in attached pdf

http://music-electronics-forum.com/t37122/

Just got a chance to catch up and thank you guys for the replies.

G, you're exactly right. I misread the schematic symbol, and couldn't read the part number til I got to work and looked at the schematic in the head-cab.
They are thyrectors. I was able to follow up and read a little bit about it. But ultimately, I opted to put in some MOVs I had in overstock. I would have definitely gone with the diode stack if I didn't have those MOVs handy. There are several viable options to tackle this, like Enzo says.
As for the status of the amp, the transformer tested good; rewire came out good. But, I was suspicious of the tubes on the side that flashed over. I cleaned the base on the burned one as good as it was going to get, but I was really weary that the tube probably didn't survive. But, I was guessing. I don't have the experience yet with what is common in faults like this. I'm still a bit green and this is only the second occasion where I've actually had my hands on a repair when this has happened. I've learned that when I have more assumptions than information, it's easy to come up with an idea that seems totally reasonable... and is completely wrong.
So, it was time to test the out. I put them in pairs at a time and used the variac to bring the voltage up. While watching the current draw in the mains, I thought I noticed the indicator needle slightly "breathing". Like it wasn't stable at idle?? With my finger on the power switch, I gave the tube in question a mild stress test. After a second or two of mild tapping, the tube went, the meter dimed, and I cut the power.
I returned the 3 working tubes and all that was left to do was set him up with a new quad. After a quick bias, and putting them through the paces to make sure they were solid, I was able play it and give it a test run. One thing that struck me was that even with the open, unshielded chassis, this amp was Dead quiet - even at high volumes. No Hiss, Hum, static. It's a nice amp. So far, in my limited experience with Traynors, I dig their stuff.

Chuck, to answer your question. You're right, it certainly didn't fail because the thyrector was removed. The speaker went open during a session. I went through what happened and how it happened with the customer. He's getting a clean, restored, working amp head. What he plugs into after that, is beyond my purview

[Chuck H]

The speaker went open during a session. I went through what happened and how it happened with the customer. He's getting a clean, restored, working amp head. What he plugs into after that, is beyond my purview

A little sideways of the topic, but...

Ain't that the truth. I don't do repairs often, but a few times it's been for purchasers of amps I've built. It's usually implied that "Your amp failed and I had to finish the gig with the spare." or something like that. It's always been user error and the amp is actually fine. In one case it was a dying battery in a tuner that gets left in the pedal chain. Somehow the tuner wasn't swapped to the spare amp and the customer didn't put together on site the 'add tuner, have problems' equation. Another time the guy had failing guitar electronics. Not recognizing the guitar as the problem he switched to the spare amp. Still having a problem he switched to the spare guitar, but never plugged back into the main amp. Then he used that rig for the next two gigs without calling me. When he did he told me there was a problem with the amp and that it wouldn't work with his main guitar. I couldn't find a problem with the amp and had to suss out through questioning that he couldn't use that guitar with the spare amp that night either.?. Fortunately I haven't had an actual failure of one my built amps yet, unless you include very beaten up and microphonic power tubes that needed replacement. They were so bad that you couldn't even get a modest volume clean tone. The amp just sounded like it had a rattling cough with every note. How do you not catch that sooner? I guess my point is, these guys don't often really know what they're doing so mistakes and misconceptions happen.

[Mick Bailey]

FWIW if I get a cooked tube socket I always replace it. Once the socket has tracked it's always a weak spot - even if its a ceramic socket - and can fail again in the same place due to microscopic cracking of the surface, residual carbon traces or metallic oxides. An arc will form much more readily and at a lower breakdown voltage over a contaminated surface. Some people clean them up and they can be OK, but I never trust them.

I did some experiments with this using an automotive coil powered off a multivibrator circuit driving an IGBT, set up so I could vary the coil voltage. A side-project from ignition systems I was (still am...) working on. An arc across a socket face between pins would always break down again in the same place no matter how well it was cleaned up. This was compared on the same socket to a pair of unaffected pins. How I compared them was to increase the voltage between the previously affected pins until it arced, then repeat with the same voltage on a 'clean' pair of pins. These didn't break down and needed a fair increase in voltage for them to eventually fail.

The one thing that changed this was spearing a very thin film of silicone grease over the phenolic socket surface and wiping it off. This restored the entire socket so there was no preferential breakdown of any previously affected section. In fact the siliconed socket performed way better. The problem is I've no idea how long this would last for or whether there could be a migration issue.

[g1]

The one thing that changed this was spearing a very thin film of silicone grease over the phenolic socket surface and wiping it off. This restored the entire socket so there was no preferential breakdown of any previously affected section. In fact the siliconed socket performed way better. The problem is I've no idea how long this would last for or whether there could be a migration issue.

How about corona dope?

[TimmyP1955]

Just replace the socket - it's only a few bucks and a few minutes, and you know it will be good.

[Mick Bailey]

Never tried corona dope.