Weird whooshing sound on M-125

A get an aperiodic whoosh sound out of my L.H. M-125 amp. It's not tube rush, it's a after all the hacking, tube-rush and barfing noises leave. Kinda sounds like the dishwasher, 'cept it's not.
The pre-amp is not an issue; just every five or six minutes I get this 30-second whooosh.
Tubes are biased OK and interconnects are fine. Any ideas?
Have I got a tube going south?

deepee99 wrote:A get an aperiodic whoosh sound out of my L.H. M-125 amp. It's not tube rush, it's a after all the hacking, tube-rush and barfing noises leave. Kinda sounds like the dishwasher, 'cept it's not.
The pre-amp is not an issue; just every five or six minutes I get this 30-second whooosh.
Tubes are biased OK and interconnects are fine. Any ideas?
Have I got a tube going south?

a 'southward' tube was my first thought......

Possibly a tube.  My expensive Black Treasure CV-181 recently started making mild rushing and popping noises then quietens down for a bit.  Replace the tube and all quiet.

Could be a coupling cap.  I've had bad ones in the past make strange noises and even periodic sounds as they charge/ discharge.  Freeze spray is sometimes helpful in isolating.

I've also had carbon composition resistors make funny noises on their way to electron heaven.  You probably don't have any of these older resistors.

Thanks, guys. I'm suspecting an output tube. These KT-120s have been in their slots for two years. I don't think my old RCA drivers could give up the ghost that quickly.
The amps sat silent for a month while Troy and Roy re-tweaked my pre-amps, so I'm wondering if maybe being shut off that long could have sent a cap south, but I'm leaning toward the KT-120s; the getters are completely white now.
Dr. Bob, any thoughts?

deepee99 wrote:Thanks, guys. I'm suspecting an output tube. These KT-120s have been in their slots for two years. I don't think my old RCA drivers could give up the ghost that quickly.
The amps sat silent for a month while Troy and Roy re-tweaked my pre-amps, so I'm wondering if maybe being shut off that long could have sent a cap south, but I'm leaning toward the KT-120s; the getters are completely white now.
Dr. Bob, any thoughts?

so how are the preamps now???

I don't have the PH-16 back from Troy yet, but it's due tomorrow. The SP-13 sounds very sweet.
Problem with going to woodies is you don't have that giant ground-plane of a metal chassis anymore; takes a lot of finesse.
I've traded what I had (perfection) for near-perfection but damn good aesthetics.

My advice to anyone thinking about going "woodie" is maybe put the power xformer and pwr supply board in a separate metal box and umbilical it to your wood box.

That was Troy's fix, and while I haven't heard it yet, it makes sense.

BTW, bought some cool old Bakelite knobs for the SP-13, they should be here next week. Photos forthcoming.

deepee99 wrote:I don't have the PH-16 back from Troy yet, but it's due tomorrow. The SP-13 sounds very sweet.
Problem with going to woodies is you don't have that giant ground-plane of a metal chassis anymore; takes a lot of finesse.
I've traded what I had (perfection) for near-perfection but damn good aesthetics.

My advice to anyone thinking about going "woodie" is maybe put the power xformer and pwr supply board in a separate metal box and umbilical it to your wood box.

That was Troy's fix, and while I haven't heard it yet, it makes sense.

BTW, bought some cool old Bakelite knobs for the SP-13, they should be here next week. Photos forthcoming.

yes, my custom SP9/PH10 preamp is also in a woodie, I found out after some trial and error that I had to ground ALL metal plates and that fixed ALL of my hum problems, nice 'n quiet now.
All my future builds will be in woodies, at least now I know what needs to be done. I have even added a small 3mm hole to all my alum plate designs for that ground connection!
Component layout too is vitally important, that is, the pcb's, tubes, transformer etc, I try and keep the distance between transformer and other hardware as far as practically and aesthetically possible.

deepee99 wrote:but I'm leaning toward the KT-120s; the getters are completely white now.

Milkish-white getter flashing? That's usually a bad sign. The tubes are losing vacuum (going gassy).

skriefal wrote:

deepee99 wrote:but I'm leaning toward the KT-120s; the getters are completely white now.

Milkish-white getter flashing?  That's usually a bad sign.  The tubes are losing vacuum (going gassy).

I know how that feels...going gassy that is........  

In the guitar world, GAS means Gear Acquisition Syndrome......

audiobill wrote:In the guitar world, GAS means Gear Acquisition Syndrome......

and not just in the guitar world!!!....trust me!!   

MontanaWay wrote:

skriefal wrote:

deepee99 wrote:but I'm leaning toward the KT-120s; the getters are completely white now.

Milkish-white getter flashing?  That's usually a bad sign.  The tubes are losing vacuum (going gassy).

I know how that feels...going gassy that is........  

Funny thing is, the flashing got that way after about 100 hours on them, and they've probably got close to 3,000 now. Ran it for about 5 hours yesterday and no untoward whooshing/pharting noises, outside the usual start-up racket.
One lesson I've learned, having suffered many years with my wife's 1966 Mustang (289) is that an intermittent problem either gets worse, so you can identify it, or it goes away. (In the Ford's case, it most always got worse).

my first thought when you mentioned white was same as Skiefal, any white inside is usually a sign of the tube loosing vacuum, the white is oxygen (or whatever other atmospsheric gas) interacting with the getter inside, if that's what it is, eventually that tube will be totally dead (a white ghost!)

tubes4hifi wrote:my first thought when you mentioned white was same as Skiefal, any white inside is usually a sign of the tube loosing vacuum, the white is oxygen (or whatever other atmospsheric gas) interacting with the getter inside, if that's what it is, eventually that tube will be totally dead (a white ghost!)

But one man's white is another's light grey...

The odds of all four tubes having an atmospheric leak are VERY long to say the least. Badly depleted getters will often look quite close to white, but they will not have the exact same look. You can see this "whitish" coloring on the edges of the silver getters in some tubes.

One last thing - a tube does NOT require a getter to work. But once the getter is gone the tube will eventually have issues with gas molecules building up in the tube. And that can cause trouble for sure.

It sounds to me like it's time for some new tubes!

Jim McShane wrote:

tubes4hifi wrote:my first thought when you mentioned white was same as Skiefal, any white inside is usually a sign of the tube loosing vacuum, the white is oxygen (or whatever other atmospsheric gas) interacting with the getter inside, if that's what it is, eventually that tube will be totally dead (a white ghost!)

But one man's white is another's light grey...

The odds of all four tubes having an atmospheric leak are VERY long to say the least. Badly depleted getters will often look quite close to white, but they will not have the exact same look. You can see this "whitish" coloring on the edges of the silver getters in some tubes.

One last thing - a tube does NOT require a getter to work. But once the getter is gone the tube will eventually have issues with gas molecules building up in the tube. And that can cause trouble for sure.

It sounds to me like it's time for some new tubes!

There was still silver getter flashing inside the white/grey rings, but I think asking 3,000 hours out of an output tube is probably enough; I had a spare quad of KT-120s from Jim McShane from a couple of years ago, so I just put them in. Also replaced the drivers as well with NOS RCA clear-tops, BH7As; the old ones did yeoman's duty, maybe 6k hours all in as I swapped around the output tubes over the past couple of years.
I had forgotten how much fun installing new output tubes can be. One went KER-BANG with a lovely light show inside for a second or two; was sure I had a red-plate but it was just crud falling off the plate and lighting up, a fairly common occurrence, apparently. They're holding steady bias after 1/2 hour.
Bob, I am getting a bit of hum out of that channel -- it was there before I replaced the tubeage, but it persists with the new tubes. Not pre-amp related and not particularly annoying, but it's recent. Ideas?
One hour now; bias holding steady, the fire-extinguisher has been returned to the kitchen and secured.

Maybe it's the black helicopters hovering overhead ...

I'm thinking the white halo may not mean what it once did due to production changes. Lot of the rare metals they used to use have either been banned or are no longer available, and could affect how the stuff ages.

Here's what I'm seeing with maybe 500 hours on the tubes ...



Granted, that's highly accentuated using a polarizing filter, but taking pics of shiny glass can be a challenge. A lot of it is actually refraction due to the flash being denser in the middle I'd think. Using MOE (the Mark One Eyeball), it's just a thin border of a lightish gray ...

Anyway ... they're all like that, and I couldn't really say if they weren't like that when new. I do plan to track any changes and will report back.

(Dang ... if ida knowed they'd be homework ...)

sKiZo wrote:Maybe it's the black helicopters hovering overhead ...

I'm thinking the white halo may not mean what it once did due to production changes. Lot of the rare metals they used to use have either been banned or are no longer available, and could affect how the stuff ages.

Here's what I'm seeing with maybe 500 hours on the tubes ...



Granted, that's highly accentuated using a polarizing filter, but taking pics of shiny glass can be a challenge. A lot of it is actually refraction due to the flash being denser in the middle I'd think. Using MOE (the Mark One Eyeball), it's just a thin border of a lightish gray ...

Anyway ... they're all like that, and I couldn't really say if they weren't like that when new.

Well, I'm going to pay closer attention to the flashing nowadays. But I think asking 3-4k hours out of a Russian output tube is probably pushing my luck, anyway.
Besides, I need a whiff of de-oxit. Nice buzz, and the hum, well, I'm liking it now. And yeah, I can never take a decent photo of the toobs when they're lit; the glare from the flash whites out the filaments and that beautiful red-plating thing   

If there is an atmospheric leak the ENTIRE getter flash turns white - whiter than the greyish white in the picture. There won't be any silver left if the tube has a leak. The tube in the pic is showing 100% normal getter wear.

Jim McShane wrote:If there is an atmospheric leak the ENTIRE getter flash turns white - whiter than the greyish white in the picture. There won't be any silver left if the tube has a leak. The tube in the pic is showing 100% normal getter wear.

DAMN! Let me dig 'em out of the Dumpster before Wednesday. Maybe it was a driver . . . .

deepee99 wrote:I had forgotten how much fun installing new output tubes can be. One went KER-BANG with a lovely light show inside for a second or two; was sure I had a red-plate but it was just crud falling off the plate and lighting up, a fairly common occurrence, apparently. They're holding steady bias after 1/2 hour.

Did you turn the bias down (reducing the bias current) before installing the new tube? If you didn't the new tube may have been passing a lot of current for a bit. But keep an eye on it - sometimes it's just residual gas built up in the tube while sitting (it's NOT likely to be any solid material), but it's not likely to be as "impressive" at lower bias currents.

Or here, if you've got FaceBook:

Jim McShane wrote:

deepee99 wrote:I had forgotten how much fun installing new output tubes can be. One went KER-BANG with a lovely light show inside for a second or two; was sure I had a red-plate but it was just crud falling off the plate and lighting up, a fairly common occurrence, apparently. They're holding steady bias after 1/2 hour.

Did you turn the bias down (reducing the bias current) before installing the new tube? If you didn't the new tube may have been passing a lot of current for a bit. But keep an eye on it - sometimes it's just residual gas built up in the tube while sitting (it's NOT likely to be any solid material), but it's not likely to be as "impressive" at lower bias currents.

Yeah, Jim, I went all the way clockwise with the bias pots before setting the tubes in and brought 'em up (resistance down) carefully with my Fluke. The're holding steady at 1.1 per pair, which is where I prefer to set them. I won't turn my back on the bastards for a couple more hours but so far, so good. Gave the sockets a tweak inwards and de-oxit'd everything first. Get that order for me Wednesday. I always like backups. Good in a firefight, too.

Nice looking setup in your pic ... was I supposed to be able to see getter flash? My eyes are good, but they're not THAT good ...

Worth mentioning, I've been running the bias on mine at 60mA per KWard's suggestion ... 5AR4 didn't like that, but either a copper cap or my GZ37 dial it right up. Can't imagine that making a difference, as the KT120's are happy at 75mA if your amp can drive them. From what I hear, they don't even object that much to 100mA or thereabouts in an amp made specifically for them. With my ST120 Monarch, I just get a lot more punch.

PS ... first glance at DP's pic and I thought I saw chicken wire on the window. Say high to Jake and Elwood for me ...   



Second glance, looks like blinds and a fence outside ...

PS ... you don't need Facebook to look at linked pics ... just to move around once you get there.