Amp...Eh.. No!

[Ian]

Hi Guys,

Well those of you who expressed jealousy at my amp can now relax, because I just tried it and it doesn’t work, !! Only kidding about the jealousy!

OK;- more specifically;- I put in a complete new set of valves, and then tried switching it on.

For the first 10-15 sec. it seems fine, the Power Lamp lights and there’s no smell of burning or whatever, but then an alarming "growling" type noise rapidly builds up, sounds like rising thunder !

Obviously I assume the sound is coming from the speakers? But of course after 1 or 2 seconds of that noise building up, I quickly shut off the power.

I tried it twice; first with the guitar plugged in, and then I unplugged the
guitar just in case it was a problem with that input Jack, but same problem
either way.

All the controls were set to zero, and of course there was no input signal from the guitar.

Any ideas

Thanks guys,

Ian.

[loverocker]

Yikes!

Did you try with the old set of valves - did you get the same sound?

Ian - No disrespect to any of the gurus here (or anywhere else on the Net), but I reckon that amp is SO important/valuable/etc that getting it looked at professionally is the only answer if tube swaps don't work. Remote diagnosis, trial-and-error and guesswork could be VERY costly in this case.

Fingers are crossed over here!

[Plexi]

Yep. I've helped alot of people on Ampage,but all you can do is listen to what they describe the amp is doing..and give it a guess. Sometimes you guess right,sometimes its something completely different..


But having the original caps in the amp.. and the amp sit since the seventies.. My first guess would be the filter caps. As the amp voltage rises, which is about 15 to 30 sec.. the hum would get louder.
One thing about it, it can be fixed. Those caps go back to when the beatles first came to America..or there abouts..thats a longggggg time.

A good amp repair man should be able to figure out your problem in a few mins..(with the amp in front of him) If its just the caps, its not that expensive. Like loverocker posted.. lets hope thats all it is,and a simple fix.. hopefully you didn't get a bad tube in the new ones you bought..And lastly hope the Power transfomer is ok... But my first guess would be a filter cap.



Richie

[bluevibeamps]

Well, first question, did the amp make this noise before you changed the tubes?

Second, if yes, I can't say a thing about it unless I had some reading from the trusty ol' fluke. If no, then it is definitly your powertubes. Did you try the old tubes to see if the problem still happens?

[loverocker]

Those caps go back to when the beatles first came to America..or there abouts..thats a longggggg time.

Hmmm... maybe there's some sort of musical memory effect - they have to be reformed by playing a few bars of Day Tripper at max volume?

I reckon Richie's right - if it's not the valves, the solution will probably still be simple and cheap to repair. Just don't smoke those trannies!

[Ian]

Hi Richie, Loverocker, Bluevibeamps;-

Thanks for the quick response guys. Yes, it’s a bit sad, but I guess after all these years the Caps have dried out at the very least.

Bluevibe;- the saga of this amp has been going on since late May. So you may not have seen, & everyone else may have forgotten or got totally bored with most of the original details LoL! But just to recap;- the last time I used it was over 20 years ago, at which time it was all working fine. However, after such a massive time lag it's probably no longer relevent for me to claim it was working OK before I swapped to the new valves (the change of EZ81 was forced, because the original was cracked).

OK, well I tried swapping back to the old original set of tubes (except for a new EZ81), and the character of the problem has changed slightly. It still has this initial period of about 20 seconds when all seems fine, & then the audible problem sets in, only now it sounds more like a typical electrical hum (as opposed to the more worrying sound of “growling thunderâ€

[servant]

Hey Ian,

Maybe Jim Marshall would be willing to have a go at it! Now that would be a story...

Dean

[Ian]

Hey Dean,

You know that’s just not funny! OK, it is slightly funny, but not funny enough!! When I posted that message saying “it doesn’t workâ€

[Dai]

[quote="Ian"]Hi Richie, Loverocker, Bluevibeamps;-

Thanks for the quick response guys. Yes, it’s a bit sad, but I guess after all these years the Caps have dried out at the very least.

Bluevibe;- the saga of this amp has been going on since late May. So you may not have seen, & everyone else may have forgotten or got totally bored with most of the original details LoL! But just to recap;- the last time I used it was over 20 years ago, at which time it was all working fine. However, after such a massive time lag it's probably no longer relevent for me to claim it was working OK before I swapped to the new valves (the change of EZ81 was forced, because the original was cracked).

OK, well I tried swapping back to the old original set of tubes (except for a new EZ81), and the character of the problem has changed slightly. It still has this initial period of about 20 seconds when all seems fine, & then the audible problem sets in, only now it sounds more like a typical electrical hum (as opposed to the more worrying sound of “growling thunderâ€

[Ian]

Hi Dai,

Thanks for that.

Glad you liked the photos, and I appreciate your comments about the historic value of the amp – I feel the same way about it!

As I say, I’m just not technically qualified to try more than a few basic tests;- anything more ambitious & I’d probably fuse the lights all over London, not to mention sending both the amp & myself into orbit (first Marshall on the Moon, maybe!) !!.

Seriously, if it were a less important amp then of course I’d have a bash at it, but in this case I think it’s best to look for a “tameâ€

[loverocker]

Depending on where you are in London, it might be quick to pop the amp over to Dennis Cornell (see http://www.dc-developments.com) who's in Southend, Essex.

I've heard good things about him (aside from the well-known Eric Clapton connection), but never used him myself. If it is as simple as the caps, he might be able to do it on a while-u-wait basis if you arrange so beforehand. Let us know what transpires (not what expires!)

[drgork]

Ian,

Loverocker's suggestion is probably a good one with regard to Dennis Cornell. I read a great article about him a while back and he has worked for just about every British amp company except Marshall. He does make his version of the 20 watt which he calls the "Plexi 20" so he is certainly familiar enough with the lower wattage Marshall circuits. It's actually a cool amp. I had the opportunity to try one out in Atlanta for an hour or so. We compared it to my 18 and it sounded great but distinctly different than the 18.

Good luck and get that 18 fired up! Maybe we should all pitch in and get Richie a ticket to fly over and fix it in person! He could get some persective on the tonal differences. Graydon, how are your frequent fly miles looking? An deals with Delta, BA, Virgin, etc. out there?

Danny

[EBE]

I am with "Servant/Dean", since this amp was verified by Jim Marshall as an amp personally done by him what would be the harm in asking? All he could do is say no. If you had an amp made by Jim Marshall in 196X and fixed by Jim Marshall in 2003, what a time piece you would have.

Norm

[Plexi]

HA.. the only plane i've flown in had duct tape on the wing..
I did have some friends just leave for England the first of the week,they are playing there somewhere. Should have gone with them,except they are staying trough middle of Aug. Might look at there site and see where they are playing.I've also heard good things About Dennis. I don't think Jim would work on it.. He's a pretty busy man, and Ian said Jim told him he'd damaged the nerves in his hand,and used his special pen to sign the book with. But he may have his A-1 tech fix it.. Sounds like there are a few people that might be able to look it over. I don't know if any of our members might be close to you there,one of them might be able to help.
Richie

[bluevibeamps]

Just a little off the subject,


Where are at in Chattanooga, TN. drgork?

[servant]

I am with "Servant/Dean", since this amp was verified by Jim Marshall as an amp personally done by him what would be the harm in asking? All he could do is say no. If you had an amp made by Jim Marshall in 196X and fixed by Jim Marshall in 2003, what a time piece you would have.

Norm

Whew! Thanks for the vote of confidence. I was really concerned that I had (gulp) seriously offended Ian. But then I did see all those in his post.

Richie's got a good idea with Jim's A-1 tech. Worth a shot!

Dean

[gtrmac]

I think the amp deserves a professional restoration. The filter caps should surely be replaced and little things like tube socket pin cleaning and cleaning and relubing the pots is another good idea. It's wise to be selective about who to take it to since the amp is obviously very valuable.

[Ian]

Hi Guys,

Thanks for all the suggestions.

Sorry Dean, I was just pulling your leg LoL!

GTRMac;- thanks for your comments, & I entirely agree that it deserves professional attention. The financial value doesn’t really concern me, because I’m never likely to sell it. But the historic value does interest me, and I just wonder how much of that would be left if half the circuit board has to be replaced (inc. the transformers)

Loverocker’s suggestion of Dennis Cornell looks promising;- thanks for that Loverocker! I may end up taking that route. But I’m also thinking this way;- people here who’ve been following this story (along several threads) appreciate why it’s important to retain as many of the original components as possible. But I’m not sure I could impress that quite so clearly upon anyone outside this Forum .

Obviously, if I lived within driving distance of Richie then he’d already have the amp by now (assuming he’d agree to do it, of course) ! But Kentucky is a heck of a long way from West London.

On the other hand there are several people here on 18Watt.com who do live within driving distance of me here in the UK, plus another in Holland (not too difficult now, ie with â€

[Plexi]

"" (assuming he’d agree to do it, of course) ! But Kentucky is a heck of a long way from West London.""

HA there is a London Ky..and it is west of me..

Yeah if you were that close ,i'd fix it for free. I owe ya one anyway..

Just to let eveyone else know, My Jim Marshall autographed Doyle book from England,has made it to Kentucky.. Thanks!

Whoever you get to work on the amp, if they needed extra info on it, I'm sure they could find it here.. It should be easy to fix.

Richie

[Gabi]

Ian...


Check that .005 "flying" disc capacitor (red color) that sits right between the TREMOLO input jacks.

I am afraid that is accidentaly touching the ground bus there. I am attaching a pic here to know what I am talking about...

Gabi.