Tube Amp Trouble

[saturated]

Newly acquired Savage Rohr 15

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When I got it it seemed to work ok both channels four inputs...

I thought it didn't seem to have much gain but figured it was what it was.

I guess it had/has a problem because later it seemed to get quieter and quieter and finally one channel appearing inop and the other both volume knobs can be max and strumming a guitar 🎸 can be heard at low volume.

I worked up enough courage to take a look and perhaps see something.

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I looked at the chassis but did not touch or 🥢 chopstick anything.

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Also I reconnected the speaker before powering on.

Btw here is the tubes

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When I powered it on I noticed one 12ax7 was not glowing as well as the uncovered tube on the end which I presume to be a 12at7 (?)

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I guess I made a big mistake by not swapping a preamp tube to see if it was the tube or the chassis.

I carefully put everything back together and not too eager to further investigate until I can watch hours of reruns on YouTube about at least some basics of working on and around these units.

I also have read a bunch of the threads in this section so I'm expecting to be told check voltage ⚡ on pins xx on vx.

 

But alas I think this is gonna be on the back burner for a while.  I just don't yet have the stomach for poking around this amp.

Thanks

 

[saturated]

Maybe that tube being not lit up doesn't mean anything idk

But forgot to add I did have the reverb out of it idk if that matters

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[g1]

Sometimes certain ones don't light up as much as others.  But that one picture in the dark, it doesn't look like they are lit at all.  You could feel them to confirm. (just the preamp tubes, power tubes or rectifier tube will burn you)

The red and purple wires at the sockets are the heater wires.  Looks like they are all connected.  You can swap some preamp tubes around to find out if maybe the tubes themselves are bad.  Make note of where the 12AT7 belongs, but it can be swapped around for test purposes.

Once you have read up on safety for working in tube amps, you can measure those heater voltages at the tube sockets.  Should be about 6VAC with one probe to red and other probe to purple.

[Tassieviking]

If you are very very lucky it might be so simple its just a bad connection in the tube socket.
Pull the tubes out and reinstall them a few times just to make sure, if you have some Deoxit give the sockets a spray.

Just remember that there is high voltages in tube amps and the capacitors can stay charged for a long long time, be very careful so you don't damage the amp when you get knocked across the room from a charged capacitor.

[saturated]

Thanks guys you ROCK 



I was gonna name this thread something like the trials and tribulations of tubes

Then it got me thinking about a particular TV show episode.

Then I was gonna post a picture joking that it showed a rare sighting of some of our top ssguitar techs

I can only speculate who is who. 

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[saturated]

Man...I hate to bump this because I have yet to sit through  D-Lab and Uncle Doug video marathons 🍿🥤... but I got to thinking I hope I didn't lead y'all down the primrose path.

So here goes...I'm pretty sure I had the reverb tank disconnected and removed when I took those pics of the preamp tubes.  So maybe that's why one wasn't lit.

As stated before I have a lot of homework to do

Also it seems like the tube close to the doghouse (rectifier) looks kinda white ashen....idk.

I know...I need a schematic.

Meanwhile I hope you are enjoying the holidays.

 

[phatt]

Also it seems like the tube close to the doghouse (rectifier) looks kinda white ashen....idk.

 

If the Valve has a white haze then it has lost vacuum and it's DEAD.
Time for a new one, Phil

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Hi Mr Phil nice to hear from you thanks 

As embarrassing as it is I have to confess because I'm learning here it seems that what I saw and thought was coating or residue on the inside of the tube is a simply a component of rectifier tubes known as the

Insulating spacer

The little points on the circle threw me off.

Anyhow I haven't done anything to this amp whatsoever but I am going to today.  Today's plan

Remove chassis again and reconnect speaker (I think this is a big deal on tube equipment as in components can be damaged?) 

Reconnect reverb tank and see if dark tube lights up.

If dark tube doesn't light up then swap with another.

If that tube socket remains dark then very carefully do as suggested by the mighty G1 and try to get a voltage reading on the heater supply purple and white wires ?
(Quick edit...purple and RED wires )
Also I was wondering what the 🐶🐕 doghouse is all about I presume that's where the power supply capacitors are and maybe the voltage ⚡ is dangerously high and the doghouse protects people...idk.

 

[saturated]

Ok I took some measurements it had been a while since I read the helpful above posts so I had my meter on DC and couldn't get ANY voltage


But then I put it on AC and was rewarded   

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And for the heck of it checked the one next to it (12ax7 number three)

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So that was really cool 🆒

Meanwhile uggghh don't want to remove this chassis again but I guess I will so I can swap tubes

Also I had emailed Savage about a schematic but never heard back it's been a couple weeks.
But I get it they are a business after all and have families like everybody else.

 

Btw readings were done both with standby on and off and were very similar

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Ok the first thing I am noticing is one of the (assumed supposed to be) 12ax7 looks different than the other three.

I tried to remove a couple of tubes but pulling straight up gently but firmly they wouldn't so much as budge and I didn't want to start breaking stuff.

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So it's a big STOP 🛑 time for me until some elders comment on today's observations.

 

[saturated]

Ok I'm going to report some more info the give you guys a break 

Turns out there are three JJ EC83S and one Russian 12ax7

Markings are...

7025/12AX7WA
Made in Russia
0610

Anyhow I put some gloves on and preserved and was able to pull and remove swap tubes

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They all light up..and as was mentioned by a helper earlier turns out the Soviet tube doesn't illuminate much with the cover back on

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So I was kinda hoping that it would be easy enough and just buy a tube but idk at this point.

Also all of the tubes are lighting up good so idk...

Anyhow I enjoyed that anyway it was fun I still learned a bit.

Thanks

[saturated]

Well guys I promised I would give you a 💔 break but I have one more post to further confuse everything.  I put everything back together and the amp played very well normal then bright channel rockin like crazy and at 1/4 volume very loud


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About the only thing I can add is that (it seems maybe I'm wrong) that I lost some gain/overdrive after a few minutes like I had turned my tone knob down on my guitar.

And there is a hollow present hum/drone kinda like a distant vacuum cleaner.

But wow the bright channel was really nice and crispy just banging out the intro to lonely is the night then you shook me all night

Anyhow guys have a great weekend

Be safe

 

[g1]

Sometimes the removal and re-install of tubes will clean up (deoxidize) the sockets.  Maybe that got it working.

Depending on the droning sound, it could be a microphonic tube.  Try tapping them gently one at a time, or holding them with a rag or something to damp the vibration but keep from getting burned.  Generally, microphonic preamp tubes will be higher pitched whistling or squealing, where power tubes will more likely rattle or make low pitched rumbling sounds.

[Tassieviking]

Just remember that big power tubes can get VERY heavy, just pull one out when it's hot and try to hold it in one hand, I bet you can't hold it for too long.
But everyone has to learn that certain things are hot the hard way, I am constantly reminding myself that the soldering iron is too heavy to hold on the pointy end. (The hard way)

[saturated]

Thank you sir I am glad I did not have to touch any power tubes...in the back of my mind I had heard about tube biasing and was dreading having to do something like that.  But I looked it up and evidently preamp tubes are just plug and play...?

The two 12ax7 I switched positions were in there really tight.  To avoid broken glass and blood I put on a leather work glove.

I really appreciate everyone's help with this idk what we did but it's sounding really crazy nice it still has a little hum at low volume but I ain't touching it right now.