bjp

To everyone,

I own a Super Lead 100 head made in Sept 1971, when I aquired it in 1991, it was not working. It needed a power transformer, rectifier diodes, and one grid resistor (all burnt out ). I rebuilt the power supply, replaced all the valves and other components that looked damaged or were out of spec. I used it a couple of times , then let it sit for some time till recently ( Last month ). Naturally it didn't sound too good after so long and there was a lot of hum. So I replaced all the filter caps as they were about to let go.This reduced the hum significantly, but it seems to persist a bit, particularly when the volume controls were turned up ( without anything plugged in). The hum is a 50hz, also the presence control introduces a scraping sound when it turned up or down and the hum increases as it is turned up. Yesterday I replaced the presence pot and nothing has changed.

When I tried the amp out after recapping, despite the abnormal hum, it sounded great. Loud and really quite majestic, so potentially this amp holds a lot of promise and I would like to use it at gigs ( now that I'm playing in a band again ). When testing I noted that under heavy use valve 3 would glow differently than the others intermittently, all valves remained an orange color. I have decided I will replace all the valves, output with winged c's .

Last night I planned to use / trial the head at a gig, I set it up turned it on - let it warm up and did a sound check at low volume it was all good until the end of the sound check. Just before switching to standby there was a crackle/pop sound, which made me leave it on for a while longer, the frequency of this increased. I switched the stand by on back off again and it started to motorboat, I turned the amp off and swapped amps. It was disappointing as the super lead sounded so much better .

Has anyone any ideas as to why

1) the hum is occurring ( there is a slight humming sound from the power transformer when the amp is turned on but it remains moderately cool in use. )

2) Why the presence control causes this scraping sound

3)what could be the cause of the motor boating now occurring

Any ideas, knowledge, solutions ( no matter how technical ), or experiences anyone can share I would be really appreciative.

Thanks for reading this

Best regards to all BJP

Jesstaa

I'd suggest replace the preamp tubes, just to make sure none of them have gone microphonic, clean ALL the contacts in the amp, even the tube sockets. Vacuum all the dust out of it, and make sure the transformers are still fine.

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bjp

Thanks for your quick reply. Will do exactly what you said and replace all three preamp tubes this week and check over the whole amp for dirt/dust and dry solder joins. From my knowledge of valve amps I would say both transformers are okay judging from the results of my basic tests, i.e. check for short circuits and heating up from prolonged high-level testing. Thanks again-BJP.

Jesstaa

The best way to tell if your transformer is acting up is to check if it's vibrating, I'm sure all tube amps will vibrate a tad, but if it's vibrating lots, and making alot of noise (Not from the speakers), then the transformers are definitely on the way out.

If you have to put new transformers in, don't settle for anything other than Mercury transformers.

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bjp

Thanks for your reply Jesstaa
The power transformer is vibrating slightly, I think I'm more aware of it, because I'm looking for faults and scrutinizing every part now. The power transformer has had a maximum use of 10 hours and was a fresh Marshall replacement which I purchased from a service tech who used to be our Marshall service agent. The output transformer appears to be perfect as, I said , I have checked it for shorts and readings of the taps seem to be right. Through out testing it remained cool, and the amp did sound good. I am aware that there is a hell of lot more to testing transformers than I have carried out, but I think they are good. Thanks for reassuring me though
, in the past I sold many Marshalls but it never occurred to me listen to the amps when they were just switched on, these amps being new I guess I never really looked for anything other than that the amp worked and sounded good. Many thanks for your reply. All the best

BJP

Jesstaa

You say it was a proper Marshall replacement, meaning it was one of the transformers they fit into stock Marshalls? If you got it in 1991 and it was a new transformer, there is a good chance that even just the sitting around could've weakened it (The transformers Marshall has used in recent years have been dodgy from what I've been told). But you might wanna ask some experts, I'm not exactly a good source of knowledge, I just go off my experience and what people tell me, and then choose which seems most logical.

And remember, when checking a valve amp out, remember to listen to it, feel it and smell it. If the feel, sound or smell of it is a little odd, then it's most likely got something wrong with it.

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rockinr0ll

The ones I have used all hummed and had some pot noise.

bjp

Thanks guys'
This is what I wanted, IE as many relevant comments as possible from as many people possible. Because I've been out of the game along time and never really thought I would seriously play again, I feel a bit out of the picture as to what is happening these days.

Jesstaa, I go with you on the intuitive side of things, but no wrong smells, signs of over heating, and I have heard worse hums/ vibrations than my amp's trannie. Though it sitting around for so long doing nothing is no good for sure. I have heard what you have said about Marshall transformers and there is no doubt about Mercury transformers being really well engineered your comments have tipped their me way, if I need to change transformers.


RockinrOLL Thanks, My very 1st 100w Super Lead ( 1975 MK.ll ) I was 17, it used to hiss a bit and from time to time have a scratchy / crackly pot, I just pulled it out of it's case and cleaned the pot with pure spirits from the chemist, no noise. The presence control on this amp, when turned makes the sound like the wiper is wrecked a sand papery sound. But the control does work !

Thank you for your posts.

Oh, will be getting a whole new set of valves in a couple of days
These will be the EL 34 winged c' s and the Tesla ECC 83s has anyone got further comments?

Thank you for your help all and best regards
BJP

Jesstaa

N.O.S tubes are the way to go, especially for the preamp. They don't make tubes like they used to.

Also, some newer tubes run the risk of blowing on the high plate voltages that Marshalls have.

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HAMPAMP TUBE AMP SERVICES

If new tubes do not cure the motor-boating, check your coupling caps. Motor-boating is usually caused by too much bass frequencies. Also check your by-bass caps on the cathodes of the preamp tubes, especially the electrolytics, these can cause motor-boating. Another possible source of hum are the electrolytics in the bias circuit, I've run across that problem in vintage marshalls. If New tubes don't fix your problem, look at the caps next, the filter caps aren't the only ones that can cause problems after aging for 30 years.

__________________
Pie are not squared, Pie are round

Due to inflation, I can no longer afford to put in my 2 cents worth.


'81 Gibson SG jr
'97 Gibson SG Special
'82 Gibson Explorer
'63 Fender Strat
'00 Fender Strat
'76 Ibanez Doubleneck (Gibson copy)
'08 PRS Paul Allender
Kramer (parts box) V
Peavey Vandenburg (parts box)
Marshall 1959
Marshall VS100R
Marshall 1960/A x 2
Line 6 Flextone III
Peavey Triumph 60
Gibson GA-5
Danelectro Cadet Model 122

bjp

Thanks everyone,
I hear what you say about the valves, living in Australia, makes NOS valves pretty hard to get. If the prices ( exchange rate ) aren't bad enough then shipping kills it. At this stage I will have to settle for the quad set Winged Cs and JJ ECC83 ( gold tip pins ) valve no. 1 and JJ ECC83 s for valve 2 and 3. I will confirm the order tomorrow with my supplier. If anyone has a better suggestion please let me know.

Hampamp ? I don't want to be disrespectful, I think your advice technically is totally sound, and makes perfect sense. I have considered changing every electrolytic in the amp but have been cautious about altering the amps sound. My 1959 MKll ( 76 Model )was a cracker, this one is really sweet sounding even though it's not right, it' must sound insane when it's working well. You obviously have experience with these amps, what can go wrong if I change all the electrolytic caps with precisely the same spec and type as the originals. Can / do modern production methods have a detrimental effect on the sound etc. when these are used ? would NOS caps be a real option ?
Thank you both for your help it is greatly appreciated

BJP

Jesstaa

Woah dude, you live in Australia? Where abouts?

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bjp

Windsor (ish) NSW

HAMPAMP TUBE AMP SERVICES

No, don't change all of the electrolytics, just give them a check if it still hums after trying new tubes. I was just giving you some areas to check if your hum problem still remains. As far as the bias circuit, changing the the elecrtolytics would not change your sound. The motor-boating problem is another story. If one of your by-pass cap have drifted off, it could possibly be increasing the gain enough in the bass frequencies to cause motor-boating. If you have a meter that will measure capacitance, just check and see if one has drifted way up in value. Parts do drift and that is what makes old marshalls sound sweet so I'm not saying change them all, just look for one that is way off. If you do have to replace one, try getting several that are within %20-%30 of the original value and try a few until you find one that gives you the desired "sweet spot". If you don't find a bad by-pass cap, check the coupling caps on the first couple of stages to make sure they haven't drifted way off, again. if the value is too high it can cause motor-boating. Only change the one(s) that is/are bad.

__________________
Pie are not squared, Pie are round

Due to inflation, I can no longer afford to put in my 2 cents worth.


'81 Gibson SG jr
'97 Gibson SG Special
'82 Gibson Explorer
'63 Fender Strat
'00 Fender Strat
'76 Ibanez Doubleneck (Gibson copy)
'08 PRS Paul Allender
Kramer (parts box) V
Peavey Vandenburg (parts box)
Marshall 1959
Marshall VS100R
Marshall 1960/A x 2
Line 6 Flextone III
Peavey Triumph 60
Gibson GA-5
Danelectro Cadet Model 122

Jesstaa

Aww, that's all the way up there.

And man, I hear you about the expenses over here, it's insane. Marshall cabs are twice the cost new over here compared to the US.

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bjp

Thanks hampamp,
I've got a quote on the valves at a pretty good price, so will go ahead with what I said. I do have a meter that measures capacitence, so I will get busy tomorrow measuring and cleaning etc. Jesstaa I will recheck the valve sockets as you suggested, thanks mate. By the way, the cost of quad boxes has always been ridiculous even back in the 70s and 80s( the 80s is when I worked in music retail ). There have been some excellent local boxes produced but even these were really expensive. So much for the excuse of " they are so expensive because we are shipping air" I would loved to have a had a dollar for every time a wholesaler said that to me. In 1990 when I was working in retail a 1960a rec. retail was $1195.00 AUD. At least they have come down a couple of hundred since then, yeah I know that's cold comfort. Anyway thanks for all your help it has been invaluable, I hope to be able to help out others as you guys have helped me so far . This is a great forum and people like you make it what is. Will stay in contact
All the best
BJP

Jesstaa

I've seen the 1960A cabs for like $1600.

And make sure you tell us how it all goes and what you do to rectify the situation. And if you're ever in gippsland, drop us a line man.

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bjp

Jesstaa thanks man I promise to let you all know how it goes. Got to get some zzzzzs got a busy day ahead of me. You keep well - Marshalls are the best- at least for me.