The Guitar Refinishing and Restoration Forum Forum Index The Guitar Refinishing and Restoration Forum
This discussion forum is hosted by The Guitar ReRanch and was created to serve those interested in the arcane art/science of guitar refinishing and restoration. Those with all levels of experience are welcomed to participate.
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

very sad Marshall story... [update: very happy ending!]

 
Post new topic   Reply to topic    The Guitar Refinishing and Restoration Forum Forum Index -> Pick-ups, Amps and Electronics
View previous topic :: View next topic  
Author Message
tangelolemon



Joined: 26 Jan 2009
Posts: 2691
Location: Brooklyn, NY

PostPosted: Tue Jul 21, 2015 9:04 am    Post subject: very sad Marshall story... [update: very happy ending!] Reply with quote

Found a 1971 JMP50 Super Tremolo combo in a rare 4x10 configuration (model 1961) at a local store. It sounded amazing, and was priced such that I could just barely swing it if a trade situation came off right with an old Fender amp I could part with.

Right before I made an offer, I heard a crackle happening when I hit a big "A" chord. I showed a younger member of the staff the issue, and he offered to change the output tubes to see if that would clear it up.

Long story short, he forgot to hook the speaker back up, and he turned the amp on and left to deal with another customer. As soon as I realized there was no sound and figured out what happened, I switched the amp off. When I informed him and we got the speaker re-connected, the amp sounded horrible... lower-than-normal output and awful distortion.

It was only on for a very short time with no load... long enough for me to strum a few chords and puzzle over why there was no output before the light bulb went on. But I fear for the output transformer.

I didn't smell anything amiss or hear any arcing or other evidence of clear damage, but my experience with vintage Marshalls isn't the most extensive. I do know that they are MUCH more fragile in this regard than vintage Fenders, since a Marshall with no speaker connected is operating into infinite load (open) while a Fender with no speaker connected is operating into zero load (short).

If the amp is OK I want to buy it, as it was really awesome. And it's such a rare configuration that it will be a long time before another like it comes up for sale. It is/was beautiful and all original. The shop is sending it off to their tech for diagnosis.

I have my fingers crossed but my hopes aren't high. I suppose it's possible it just toasted the output tubes? But I fear the worst. Anyone with extensive Marshall experience have any instincts?
_________________
proud endorser of Curt Mangan strings, K&K acoustic guitar pickups, and Latch Lake Music slides


Last edited by tangelolemon on Mon Aug 03, 2015 3:50 pm; edited 1 time in total
Back to top
View user's profile Send private message Visit poster's website
statorvane



Joined: 21 Aug 2003
Posts: 1950
Location: Upstate New York

PostPosted: Thu Jul 23, 2015 2:56 am    Post subject: Reply with quote

I doubt they will get much for it sounding that bad unless someone knows the potential value of this item. I'd make them an offer that would allow you to replace the OT with an aftermarket item. See what they say.

There are no lack of replacement OTs for Marshall amplifiers.
_________________
"Good ideas are not adopted automatically. They must be driven into practice with courageous impatience."
--
Admiral Hyman G. Rickover
Back to top
View user's profile Send private message Send e-mail
ajeffcote



Joined: 09 Nov 2009
Posts: 2184
Location: Baytown,Tx

PostPosted: Thu Jul 23, 2015 3:29 pm    Post subject: Reply with quote

May have been the tubes he put in the amp? Most times, if an OT is gone there won't be any sound, good or bad. Right?
_________________
I can't remember what I forgot........
Back to top
View user's profile Send private message
statorvane



Joined: 21 Aug 2003
Posts: 1950
Location: Upstate New York

PostPosted: Thu Jul 23, 2015 5:16 pm    Post subject: Reply with quote

I agree, it could have been a bad power tube or two. Could also have been a preamp tube.

On occasion, I have powered up an amp and taken it out of standby without having a speaker load connected - just for a few seconds until I realized what was wrong - probably not unlike tangelolemon. I did not notice any problem after securing power, reconnecting the speaker and restoring HT. OTOH, Marshalls are notorious for blowing OTs, so I wouldn't rule it out without further checking for open/short in the Pri or Sec windings.
_________________
"Good ideas are not adopted automatically. They must be driven into practice with courageous impatience."
--
Admiral Hyman G. Rickover
Back to top
View user's profile Send private message Send e-mail
Johnson82



Joined: 27 Aug 2007
Posts: 1733
Location: New Castle, IN

PostPosted: Thu Jul 23, 2015 8:37 pm    Post subject: Reply with quote

My gut says OT...no blown fuses, though, so who knows. I've had explosive failures with mine, where you get flyback voltage and the plate shorts to the filament. Of course, that takes out the B+ fuse, which sounds like that's not what happened...maybe pop the old tubes back in and see if the new ones are cooked/duds?
_________________
Plaid Sabbath wrote:
What kind of operation is that? No sawdust...no empty beer bottles...no one is using extremely foul language...no one is spending 2 hours looking for lost tools...no dust on the bodies in the finishing room…
Back to top
View user's profile Send private message
tangelolemon



Joined: 26 Jan 2009
Posts: 2691
Location: Brooklyn, NY

PostPosted: Fri Jul 24, 2015 5:48 am    Post subject: Reply with quote

Thanks guys.

I've gotten advice from a lot of places. It varies. I'm waiting on the shop to call me back-- they were going to take it to their tech for diagnosis.

The reason Marshalls are so much touchier than Fenders and other amps is that, unlike Fender amps, they don't have a mechanism that shorts the output when no speaker is connected... the output remains completely open-circuit. Fender uses a shorting jack that short-circuits the output when no speaker is plugged in. In a tube amp, "zero load" (short circuit) is MUCH safer and less catastrophic than "infinite load" (open circuit).

I've also run Fenders with no load for a short time with no issue, but Fenders and Marshalls are really apples-to-oranges where this kind of thing is concerned.

A really good tech friend of mine told me it IS possible that a winding could've burned through insulation and partially shorted without so much as a whiff of smell or smoke, and without blowing a fuse, in this amp. A short to the transformer core would obviously cause a fuse to blow, but an inter-winding short, not necessarily.

As far as negotiating a good price on the amp with a blown OT... I'm not really sure I'd want to buy an "unknown quantity." I wasn't really in the market for an amp, I wanted to buy THIS one because (exactly as it was) it was one of the most awesome-sounding amps I had ever heard. Bummer.
_________________
proud endorser of Curt Mangan strings, K&K acoustic guitar pickups, and Latch Lake Music slides
Back to top
View user's profile Send private message Visit poster's website
tangelolemon



Joined: 26 Jan 2009
Posts: 2691
Location: Brooklyn, NY

PostPosted: Mon Aug 03, 2015 3:52 pm    Post subject: Reply with quote

OK! here's the update.

Transformer was fine. Tubes were no good. With new tubes, there was still a slight crackle when I'd play a low Ab loud. Negotiated a good deal for it as-is from the shop.

Took it back to the studio, opened it up, tapped wires with a chopstick and found one that seemed a little fussy when I tapped it. Re-flowed the solder joints on both ends, and re-positioned a preamp tube grid wire that crossed it a little too close (seemed like when i tapped it, it had the vaguest hint of wanting to oscillate).

Then I chopstick-tapped the impedance selector switch, and it was intermittent too. I think this may have been the actual problem. First I re-tensioned the socket and cleaned the plug with electrolube and taped it down-- this fixed it, but then I thought "you know what? this thing is a combo. No need to risk it with this highly failure-prone impedance selector mechanism." So then I hard-wired it to the 16 ohm setting internally, bypassing the impedance selector completely, and then P-Touch labeled the chassis where the impedance selector is, saying "hardwired for 16Ω."

Thing works a damn treat, and sounds amazing. Couldn't be happier. Glad for the happy ending, and thanks for the advice of everyone here!

Some pics (sorry for blurry):



Inside looks pretty original (didn't realize that my hand must've shaken when I snapped it. I had the impedance selector taped down here as a test, before deciding to hard-wire)


_________________
proud endorser of Curt Mangan strings, K&K acoustic guitar pickups, and Latch Lake Music slides
Back to top
View user's profile Send private message Visit poster's website
statorvane



Joined: 21 Aug 2003
Posts: 1950
Location: Upstate New York

PostPosted: Mon Aug 03, 2015 5:32 pm    Post subject: Reply with quote

Congrats! That is a really cool piece Cool
_________________
"Good ideas are not adopted automatically. They must be driven into practice with courageous impatience."
--
Admiral Hyman G. Rickover
Back to top
View user's profile Send private message Send e-mail
BluesmanDave



Joined: 17 Nov 2008
Posts: 2816
Location: Sacramento CA

PostPosted: Wed Aug 05, 2015 3:57 pm    Post subject: Reply with quote

Too hip! I love it when these stories end well.
_________________
www.davesegalmusic.com
Back to top
View user's profile Send private message Visit poster's website
twangster



Joined: 05 Aug 2005
Posts: 9513
Location: Nashville Tennessee.

PostPosted: Thu Aug 06, 2015 6:00 pm    Post subject: Reply with quote

Congrats, that is a thing of great beauty.
Back to top
View user's profile Send private message
tangelolemon



Joined: 26 Jan 2009
Posts: 2691
Location: Brooklyn, NY

PostPosted: Thu Aug 06, 2015 8:20 pm    Post subject: Reply with quote

man it has really made a believer out of me. I've never been a "marshall guy" but I just hadn't played the right ones. This thing is awesome, and way more versatile than I ever could've anticipated.

My favorite thing is how "sculpted" the low end is. It's not round-big like a Fender, and as a result it doesn't ever get bloated; the low end is definitely there, it's just tucked in nicely. I'm not talking about the kind of thing you accomplish by turning the bass knob down a bit... there's something about the way the amp just naturally sits in the low end that's right.

And it has this nice glossy, silvery thing in the upper midrange (what I suppose you would call 'top end" in a guitar amp) that's so appealing.

I never really thought of "Marshall cleans" as a thing that I'd seek after, but the clean sound in this amp is as or more impressive to me as the overdriven sounds. I could just play it all day.

The feeling of a light bulb going off reminded me of when I got my first vintage Telecaster. Suddenly these sounds from all of these amazing records that I'd been referencing and chasing after were just automatic. It was like "man, if I had just had this thing years ago I could've saved myself so much headache."

It also reminds me of when I got my first good soldering iron. Everything is just so much easier when you have the right tool for the job.
_________________
proud endorser of Curt Mangan strings, K&K acoustic guitar pickups, and Latch Lake Music slides
Back to top
View user's profile Send private message Visit poster's website
BluesmanDave



Joined: 17 Nov 2008
Posts: 2816
Location: Sacramento CA

PostPosted: Mon Aug 31, 2015 1:08 pm    Post subject: Reply with quote

HEY! When are we getting sound clips? Very Happy
_________________
www.davesegalmusic.com
Back to top
View user's profile Send private message Visit poster's website
tangelolemon



Joined: 26 Jan 2009
Posts: 2691
Location: Brooklyn, NY

PostPosted: Mon Aug 31, 2015 1:27 pm    Post subject: Reply with quote

Haha. I'm not sure. I've got a pretty full schedule lately. Generally any time I'm plugging in a guitar or setting up a microphone lately it's because I'm working. Which is cool, but there's less time/energy/inclination to do sound clips for funsies. Sad
_________________
proud endorser of Curt Mangan strings, K&K acoustic guitar pickups, and Latch Lake Music slides
Back to top
View user's profile Send private message Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic    The Guitar Refinishing and Restoration Forum Forum Index -> Pick-ups, Amps and Electronics All times are GMT - 6 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group