SVT 70's silver face question

19s · #1 05-09-2010, 11:58 AM

I'm new on the forums, so forgive me if I'm posting this in the wrong area.

Below is kind of a block of text with a little more detail, so here's the short version:

I heard a pop come from the head (not the speakers) followed by a sizzle, then shorty after an electrical smell. It still works.

Am I dealing with a blown tube? or something else here?

Any help or insight would be appreciated.
Thanks in advance to any replies.

/start back story

I got lucky with finding a 70's SVT with the original Magnavox "branded" tubes still in it. (back from when they owned ampeg)
From what i was told, it was gigged with for about a year when it was bought by the sellers father. After that, it sat for years moving from garage, to closet. They said it had been serviced, but i kind of doubt it judging by the amount of dust it had inside when I got it.

/end back story

What happened last night:

All channels and inputs work great, loaded up, headed to rehearsal. Unloaded, set up, power on *stand-by*, got a drink and gave it a bit. Played for half an hour, band took a break, and I turned down and kept playing. I pause for a bit, and all of a sudden, I hear a pop come from the head, not the speakers, followed by a sizzle. I was hoping the noise had came from elsewhere, but then i started to smell an odd electrical burn with a bit more nasty to it. I threw the amp in stand by for a few, and turned it off. 10 minutes later, i power it back up, give it a few, take it out of stand by and start to play. I didn't check each channel or input, but nothing appeared to have audibly changed. The smell however was still there.

(*one note, I'm running a Morley A/B/Y to channel one bright, channel 2 normal.)

I took the cover off to take a look, and all the tubes still had the dim orange glow, equal intensity from what i could tell.
Back to standby/power off.

I didn't get to mess with it much more than that, and don't want to further damage anything if i can avoid it. I left it at the rehearsal space, unplugged.

So here I am.

Any guess as to what I'm dealing with?
Blown tube? Something worse?

If I remember right, these amps tend to keep going without much loss if a tube goes out.

Any help or insight would be appreciated.
Thanks in advance to any replies.

BurningSkies · #2 05-09-2010, 12:03 PM

Capacitor failure?

Its been sitting around for 25+ years and to add to the trauma, it was 'cold powered' after a long sleep. I would guess that the pop was a capacitor reaching it's death and the sizzle was it's last cry of pain.

Really all old amps, no matter how good the condition should be checked and powered up by a tech who knows their was around a tube amp.

johnk_10 · #3 05-09-2010, 12:04 PM

well, IME, a blown tube doesn't give off a weird electronic scent/smell. foreign 'electronic' smells are usually from blown caps, resistors and transformers on their way out.

19s · #4 05-09-2010, 12:21 PM

Any idea on range of cost to repair? Low to high ballparks?

I just want to have an idea of best/worst case senario walking in.

Thanks for the help!

BurningSkies · #5 05-09-2010, 12:24 PM

It will really be up to what component has actually gone, if it's taken out any others and if there are any other components that need to be replaced.

Find a qualified and trustworthy tech its hard for even the most qualified person to diagnose a problem based upon a sound (or sounds) as posted.

I would suggest that you don't power up the amp until you do so.

anderbass · #6 05-10-2010, 05:12 PM

Hey 19s, you should post where your located, someone might know a good SVT tech in your area.

19s · #7 05-10-2010, 05:27 PM

Roanoke, VA

coreyfyfe · #8 05-10-2010, 05:47 PM

There may be someone listed in here:

Good amp techs!

gbazinet · #9 10-01-2010, 01:31 PM

I'm having the same problem with my vintage SVT. I didn't notice a pop, but it sure smells like an electrical short. All tubes look good though and the tonal quality has not been comprimised in any way. It just smells like burning. Wondering if the OP ever got his checked out?

Alex1984 · #10 10-01-2010, 02:34 PM

"They taste like burning!" ~ Ralph Wiggum.

Sorry...I digress.

KramerBassFan · #11 10-01-2010, 03:00 PM

Sounds like a blown resistor.. but who knows. It could be a whole lot of things that can't really be diagnosed over the internet.

Tech time matey!

gbazinet · #12 10-01-2010, 03:07 PM

I brought it to a local tech today. I hope they find something, as i have not always had the best luck with this place. Will keep you posted.

gbazinet · #13 10-04-2010, 02:06 PM

Tech called today... HE told me the smell i was experiencing was due to a loose tube that also apparently was glowing brighter and he seemed to think was going to blow soon. He pretty much told me to switch the tubes over to 6550's or sell it since i would "never find a set of matched 6146b's!" But otherwise it was fine to use the amp as is now. Thoughts?

anonymous02282011 · #14 10-04-2010, 02:11 PM

6146b power tubes are certainly available and in matched in sextets.They are also a lot cheaper than 6550s.

I know because I have a blue line SVT with original 6146bs.

Also, the burning smell is most likely a resistor.

I think you may need to find a new tech.

I got mine here a few years ago:

http://www.tubedepot.com/nos-6146b.html

40 bucks per NOS tube = 240 bucks for a matched 6tet. You can get new ones from China for less.

Good luck.

KramerBassFan · #15 10-04-2010, 02:13 PM

Quote:

Originally Posted by adbass

6146b power tubes are certainly available and in matched in sextets.They are also a lot cheaper than 6550s.

I know because I have a blue line SVT with original 6146bs.

Also, the burning smell is most likely a resistor.

I think you may need to find a new tech.

+1

Loose tubes smell funny?

BurningSkies · #16 10-04-2010, 02:31 PM

Sounds like maybe your tech has a tube loose.

I was chillin' with my tech the other day and he was working on a mid-50's Gibson tweed amp...we discussed the 'smell' of a tube amp and how that's an enjoyable part of having and using a tube amp. Like a nice childhood memory...

gbazinet · #17 10-04-2010, 03:26 PM

Yeah, the guy has a tube loose for sure. I had to bring back my Musicman HD130 twice when he couldn't find a simple bad connection and a Kustom combo that went back tons of time and was never right. Just not enough good tube people in Maine.

I thought i had read online that new 6146 tubes are available. The tech told me not to buy new ones from china "cause they won't sound good". I will look into that site posted above.

metron · #18 10-04-2010, 04:19 PM

I had a DB 728 once uopn a time. Fired it up and *POP* SSSSssssss. It let out the magic smoke. A cap in the power supply was visibly melted. It would still turn on but no sound.

timv · #19 10-04-2010, 11:32 PM

Almost every old svt I have worked has had the 10 ohm 5 watt resistors blow at some point. Always black marks on the pcb.
If a tube goes bad or is running hot, it may take this resistor out and save the rest of the amp. I once had an svt with 3 blown resistors. I actually didn't know how low the power was until I checked the bias and saw how off it was....
6146's can be found.
I personally would keep 6146's....
Good luck...

MAMMOTHvolume · #20 10-05-2010, 04:57 AM

Quote:

Originally Posted by gbazinet

Tech called today... HE told me the smell i was experiencing was due to a loose tube that also apparently was glowing brighter and he seemed to think was going to blow soon. He pretty much told me to switch the tubes over to 6550's or sell it since i would "never find a set of matched 6146b's!" But otherwise it was fine to use the amp as is now. Thoughts?

translation - the valves are fine, i want to stick in some cheap sovteks and keep the 6146's and stick them on ebay.