Members LP Heaven Posted March 3, 2006 Members Share Posted March 3, 2006 I've personally never had a problem but my rigs were always pretty simple. I have no idea about plate voltage this and mercury magnet that - i also don't sniff the cork...but I know what wine tastes better then others.The advice I would give to ANY tube amp owner of ANY manufacturer, is when you get it, take it to a realllly good master amp technician for a complete checkup. If you have a really nice car, lawn, pool, diamond ring etc. your going to have it checked by an expert unless your an expert yourself...if your a tinkerer....well then you can most likely expect sub-par results down the road.Everything breaks down eventually and is unavoidable but I don't think the Plexi line of Marshall is more prone to faulting than others.I may be wrong..... but if anyone here works for Marshall/Peavey/MesaBoogie or is just a guy who has seen a few amps on the bench, feel free to chime in with some warranty/repair statistics wow...did I type that much...sorry Link to comment Share on other sites More sharing options...
Members 2B Posted March 4, 2006 Author Members Share Posted March 4, 2006 Originally posted by Voodoo Amps The old plexi trannies have great tone. But, they are not that well done (best quality). "Well-done" might sooner or later be like toasted "well-done". Can you explain how you came to this conclusion? We've worked on a great deal of older Marshalls and the transformers we always rugged. For what it's worth Trace Hi Trace.I've had some bad experiences with plexi 50W. I really do not trust this amp that much. An amp had the OT fried some years back for "no reason", like due to cranking the amp, wrong (or no load) etc..The other day, something else went real bad, also for "no reason".I guess just bad experience for my sake. "Experts" I've talked to have very often complained about cheap parts and "so-so" trannies for some of the oldies (not the 100W's or the JTM45's).As I mentioned in my first post, I've used old Marshall all years with no problems at all. But, I feel the 50W plexis do have some issues.For my sake, I do not trust these amps. Btw, I've heard that Marshall changed the OT and Main trannie for the post mid' 69 50W amps (transfer to metal-panel).Have You any info on this subject?As far as I know the 100W's did use the same trannies up to beg of '73.Is there a difference on the 50W amps transformers from '72 vs the '74's?The '74 OT looks a bit different, but I'm not sure about the tone.Cool with some info on these subjects.Thanks!T. Link to comment Share on other sites More sharing options...
Members 2B Posted March 4, 2006 Author Members Share Posted March 4, 2006 No one know about this...? Link to comment Share on other sites More sharing options...
Members Voodoo Amps Posted March 4, 2006 Members Share Posted March 4, 2006 Hi Trace. I've had some bad experiences with plexi 50W. I really do not trust this amp that much. An amp had the OT fried some years back for "no reason", like due to cranking the amp, wrong (or no load) etc.. Improperly running an amp or running it without a load can cause any OT to short. With that said OT's do not usually fry for not reason unless there is a defect (which tends to be more on the rare side). Is there an HT Fuse in that particular amp? Do you know what the primary is rated at? The other day, something else went real bad, also for "no reason". I guess just bad experience for my sake. "Experts" I've talked to have very often complained about cheap parts and "so-so" trannies for some of the oldies (not the 100W's or the JTM45's). There were some Marshalls that came with KT66's and many people try to install EL34's (with little luck) and tend to short the OT. As I mentioned in my first post, I've used old Marshall all years with no problems at all. But, I feel the 50W plexis do have some issues. For my sake, I do not trust these amps. Understood. I would recommend finding a tech who knows the ins-n-outs of those amps. They can make recommendations for you or you can of course just keep them at home and get a clone to jam on live. Btw, I've heard that Marshall changed the OT and Main trannie for the post mid' 69 50W amps (transfer to metal-panel). Have You any info on this subject? This seems to be a common statement and I would have to say yes they did change the transfrmer but then again I've seen so many different transformers on the 60's Marshalls it's not funny. Some of the 69's run around 450V while others run around 500V on average. Again they got a lot more consistant over all when they went over to PCB's. As far as I know the 100W's did use the same trannies up to beg of '73. If you are counting the 60's then they did not various different OT's. Keep in mind they were a small company and bought transformers as needed. Is there a difference on the 50W amps transformers from '72 vs the '74's? In general no but some of the PT's varied. The '74 OT looks a bit different, but I'm not sure about the tone. Are you referring to the mounting brackets? Have a great weekend Trace Link to comment Share on other sites More sharing options...
Members 2B Posted March 4, 2006 Author Members Share Posted March 4, 2006 Hi Trace.Thanks for the cool info.Reg. the '74 trannie, yes I was referring to the mounting brackets.The 50W '74 has some small holes drilled on each corner, the earlier late '60 did not.Actually, I have been trying to get hold of a '68 OT, but this seems to be impossible to find. As a "close copy", I might install a Drake OT "784-139" from '74.Hopefully the tone will not suffer that much, some early '70 metal panels do have killer tone. They are not a "plexi", but a plexi do not IMO "define" great tone. Later Marshalls also have something real special going on in the tone dept. Different, yes, but not necessarily worse.I know the OEI is supposed to be a very good replacement for the '68 original, but I also think the '74 OT will be an equal match.Do You have any opinions on that subject?Thanks, and have a nice day!T. Link to comment Share on other sites More sharing options...
Members psychodave Posted March 4, 2006 Members Share Posted March 4, 2006 I have never had any problems with my 67 plexi....besides filter caps and tubes...which is normal. Link to comment Share on other sites More sharing options...
Members 2B Posted March 5, 2006 Author Members Share Posted March 5, 2006 Originally posted by psychodave I have never had any problems with my 67 plexi....besides filter caps and tubes...which is normal. .Hi.Cool to hear that You've not faced any problems at all.On the other hand, it makes me wonder how consistent these oldies really are.Hopefully I'll get my '68 Plexi 50W up and running ASAP.The TONE of this amp is really something on the bright side of life.T. Link to comment Share on other sites More sharing options...
Members BerkleeBill Posted March 5, 2006 Members Share Posted March 5, 2006 I played a guest appearance last night through a guy's rig - Metalfaced 4-input rebuilt to '68 specs thru an old basketweave straight-face 4x12. Man, that amp sounded gooooood !!! Link to comment Share on other sites More sharing options...
Members vlad Posted March 5, 2006 Members Share Posted March 5, 2006 For the record, I've never had any issues with my Super Lead. Aside from it being preposterously loud... Link to comment Share on other sites More sharing options...
Members Voodoo Amps Posted March 6, 2006 Members Share Posted March 6, 2006 Hi Trace. Thanks for the cool info. When ever I get some free time (not sure when that will be) I'll write all of our findings down in a book. Reg. the '74 trannie, yes I was referring to the mounting brackets. The 50W '74 has some small holes drilled on each corner, the earlier late '60 did not. The mounting brackets were employed because the stand-up transformers would bend where the feet are screwed into the chassis (seen this more times than I can count) so it helps to prevent the bending. Actually, I have been trying to get hold of a '68 OT, but this seems to be impossible to find. As a "close copy", I might install a Drake OT "784-139" from '74. '68 OT's are very hard to come by and while we have a few of the 60's plexi OT's we save them for refurbs. In all honesty the Mercury 68 clone sounds pretty cool and is much more affordable than '68 plexi OT. I would recommend giving that a try as it sounds and feels better than the 70's Drakes (in my humble opinion). Hopefully the tone will not suffer that much, some early '70 metal panels do have killer tone. They are not a "plexi", but a plexi do not IMO "define" great tone. Their circuits are fundamentally the same up until the converted over to PCB's. Even then they left of a bypass cap for less gain to compensate for the way the transformers sounded when the amp was cranked up to higher volumes. For an old plexi to sound amazing it pretty much has to have a PT, OT and choke that all work well together (there was a lot of mixing-n-matching back in the 60's), those that do sound phenomenal and sell for a great deal of money. Later Marshalls also have something real special going on in the tone dept. Different, yes, but not necessarily worse. Different transformers will make an amp sound, perform and feel different (even if the circuit is essentially the same). You are correct in that there is no right or wrong, there is just tone and if it works for you then that's all that truly counts. I know the OEI is supposed to be a very good replacement for the '68 original, but I also think the '74 OT will be an equal match. If all things were created equal then yes you would be correct. On the flip side of that a '74 OT is not designed the same as the OEI (or Mercury for that matter) and therefore they sound and feel very different from one another. Perhaps the best way to go is to try an OEI and then a Mercury to see which one your ear likes the most. Hope it helps Trace Link to comment Share on other sites More sharing options...
Members Duesentrieb Posted March 6, 2006 Members Share Posted March 6, 2006 Hey Trace, isn't part of the "hyped sound" and the "bad reputation" that both share two common things? In 50 Watters (at least from the 76s I have here) both, screen grid resistors and grid stoppers are missing. On the one hand this will give you the sparkling excellent sound, but makes them very sensible to tube failures (--> OT frying). And those reissues with screen grid Rs and grid stoppers don't sound as good as this old stuff does. Or am I wrong? Link to comment Share on other sites More sharing options...
Members Voodoo Amps Posted March 9, 2006 Members Share Posted March 9, 2006 Hey Trace, isn't part of the "hyped sound" and the "bad reputation" that both share two common things? I'm not following my friend? It's early and I haven't had any coffee so please forgive me if it's obvious (ha, ha). In 50 Watters (at least from the 76s I have here) both, screen grid resistors and grid stoppers are missing. Some are and some are not. That comes down to who ever (most seemed to be women for a long while) was responsible for assembling that particular day. Keep in mind those assembling were not techs and naturally as the company grew more people were hired to assemble. A new person on the job may have made numerous mistakes until they got a handle on it (IE: on-the-job-training). On the one hand this will give you the sparkling excellent sound Yes and no...I guess it depends on who you are talking to. Generally speaking; On average most had screen grid resistors and input resistors. We've seen a lot without input resistors but most of the time the screen grids were there. I'm not a big fan of leaving off the input resistors because when you crank the amp up you get a very non-musical smearing type of sound happening because the grids are getting pounded so hard. Some guys like it (to each his own) but personally speaking I've never liked the smearing sound. , but makes them very sensible to tube failures (--> OT frying). Tube failures yes but not blowing OT's. As long as you have a HT Fuse in place and it's properly rated then the OT should never blow/short. Granted there are those who put larger fuses, slo-blo fuses, tin foil, etc. and naturally this can result in shorting an OT. And those reissues with screen grid Rs and grid stoppers don't sound as good as this old stuff does. There are several reasons for this, the most obvious are transformers. Or am I wrong? When it comes to tone there is no right or wrong, there is just tone. If it works for you then that's all that counts. Have a great day Trace Link to comment Share on other sites More sharing options...
Members Duesentrieb Posted March 9, 2006 Members Share Posted March 9, 2006 As always very helpful and interesting reading. Thanks Trace. Now hurry to the coffee Olaf Link to comment Share on other sites More sharing options...
Members LiquidPCB Posted March 9, 2006 Members Share Posted March 9, 2006 Theres a couple of mods that really help your marshall be more reliable these are easily reversable and dont change the tone. People wonder why marshall never did these mods to begin with because he knew about them and did them on his parks of the same era.Maybe it was payback to the company that bought marshall to give them more trouble who knows a lot of {censored} went down when jim sold his rights. See this website I think it has some mods but there are other books if the mods arent covered here. http://www.tone-lizard.com/Marshall_Myths.htm Link to comment Share on other sites More sharing options...
Members Voodoo Amps Posted March 9, 2006 Members Share Posted March 9, 2006 Theres a couple of mods that really help your marshall be more reliable these are easily reversable and dont change the tone. That would depend on what mods you are referring to. For example; There are those who say adding screen grid resistors and input resistors have no audible difference. Personally speaking I have no idea why anyone would suggest that there is no audible difference because it is audible. People wonder why marshall never did these mods to begin with because he knew about them and did them on his parks of the same era. It's important to realize that people did not design guitar amps to distort. No engineer every conceived that someone would turn an up to the point of distortion (this came from players pushing their gear to the limits). Enter in the concept that Marshall, Fender and Gibson were now faced with voicing amps that were also going to be used wide open. This was an entirely different way to look at things, one that had not occurred up to this point and no one wanted distorted guitar amps. Maybe it was payback to the company that bought marshall to give them more trouble who knows a lot of {censored} went down when jim sold his rights. See this website I think it has some mods but there are other books if the mods arent covered here. http://www.tone-lizard.com/Marshall_Myths.htm It's important to keep in mind that the website you've listed comes with a lot of the author's opinions as as info taken from numerous other sources. For example; The JCM800 mods on this website were directly taken from the mod-section on Schematics Heaven.com. Several of those mods are in fact ours but I do not see credit being given on the tone-lizard website. For what it's worth Trace Link to comment Share on other sites More sharing options...
Members LiquidPCB Posted March 9, 2006 Members Share Posted March 9, 2006 The marshall paying back his buy out company by ommitting parts is my opinion not one of the tone lizard site and I am in no way affiliated with the tone lizard site or the authors views or opinions. I just offered the site as a reference for others. If they in fact did take your mods and not credit you with it , that is a shame but they may have collected them from some where else too. I just enjoyed there site and found the mods and information helpful my opinions in my posts are mine and not that of the tone lizard site thankyou and I hope you can use any extra info from the site Its is a shame people are sometimes not credited but information sharing is so wide spread due to the net maybe just be happy in the knowledge that your knowledge is helping people. Link to comment Share on other sites More sharing options...
Members JerryP Posted March 9, 2006 Members Share Posted March 9, 2006 Originally posted by psychodave I have never had any problems with my 67 plexi....besides filter caps and tubes...which is normal. There you go, take care of your amp with basic maintenance and it will last forever. They need to go in the shop for a little TLC every now and then. Take care of things before they become problems and cause other problems.One thing to remember is back in the early day Marshall was building their amps with surplus parts and free samples they were given by suppliers. That's why the early amps weren't consistent.Jerry Link to comment Share on other sites More sharing options...
Members 2B Posted March 10, 2006 Author Members Share Posted March 10, 2006 Originally posted by Voodoo Amps Hi Trace. Thanks for the cool info.When ever I get some free time (not sure when that will be) I'll write all of our findings down in a book. Reg. the '74 trannie, yes I was referring to the mounting brackets. The 50W '74 has some small holes drilled on each corner, the earlier late '60 did not.The mounting brackets were employed because the stand-up transformers would bend where the feet are screwed into the chassis (seen this more times than I can count) so it helps to prevent the bending. Actually, I have been trying to get hold of a '68 OT, but this seems to be impossible to find. As a "close copy", I might install a Drake OT "784-139" from '74.'68 OT's are very hard to come by and while we have a few of the 60's plexi OT's we save them for refurbs. In all honesty the Mercury 68 clone sounds pretty cool and is much more affordable than '68 plexi OT. I would recommend giving that a try as it sounds and feels better than the 70's Drakes (in my humble opinion). Hopefully the tone will not suffer that much, some early '70 metal panels do have killer tone. They are not a "plexi", but a plexi do not IMO "define" great tone. Their circuits are fundamentally the same up until the converted over to PCB's. Even then they left of a bypass cap for less gain to compensate for the way the transformers sounded when the amp was cranked up to higher volumes. For an old plexi to sound amazing it pretty much has to have a PT, OT and choke that all work well together (there was a lot of mixing-n-matching back in the 60's), those that do sound phenomenal and sell for a great deal of money. Later Marshalls also have something real special going on in the tone dept. Different, yes, but not necessarily worse.Different transformers will make an amp sound, perform and feel different (even if the circuit is essentially the same). You are correct in that there is no right or wrong, there is just tone and if it works for you then that's all that truly counts. I know the OEI is supposed to be a very good replacement for the '68 original, but I also think the '74 OT will be an equal match.If all things were created equal then yes you would be correct. On the flip side of that a '74 OT is not designed the same as the OEI (or Mercury for that matter) and therefore they sound and feel very different from one another. Perhaps the best way to go is to try an OEI and then a Mercury to see which one your ear likes the most. Hope it helps Trace .Hi Trace.Thanks for all the cool info, I appreciate it!Btw, I just got hold of an old original Drake OT, taken from a '67 plexi a while back. This OT is told to have a GREAT tone, and is 9/10 all original condition.After searching all around for the last two weeks, I guess I was real lucky to come by this (from UK).These oldies are so hard to find that I nearly just gave up my search. I've got a lot of contacts, still not an easy task.I'm looking foreward to get my '68 back in shape in a week or so.In the long run it's the TONE that matters.And yep, its cool to have the amp back with the original parts.Have a nice day!T. Link to comment Share on other sites More sharing options...
Members LiquidPCB Posted March 10, 2006 Members Share Posted March 10, 2006 What are the repro drake copies like are they close at all or are they just average. I hear the Mojo transformers are very good reproductions though. Link to comment Share on other sites More sharing options...
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