I have a 1977 Marshall Master Lead Combo 2x12. When I heard you say " Ill just slide the chassis out", I thought to myself, oh no you're not lol! It took me an hour (and much swearing!) to get mine out, and after checking the bits I understood and spraying cleaner into the pots, I then put it back together..... and its worse than ever! So, its sat in the spare room ever since, waiting for a miracle worker such as yourself to appear near me. Oh, how I wish I could post you my amp lol! I bought it for a tenner about 20 years ago so it owes me nothing, but one day it will sing again.... rather than hum, crackle and get very hot :(
Once again: Very nice. But I'm confused (?) that you never start to look att the schematic... (I ALWAYS start in that end- to see for expected voltages, odd components etc...) But I guess you have such a experience that you "know" what to expect. And that extra job on the lamp!!!! I know no technician that would do that.... because you can't charge the customer for all that extra work... RESPECT!!!
I too repaired and built amps in the late 70's and agree on there simplicity compared to the modern amps. However now amps have fancy anti distortion and clipping circuitry and DC protection. In the 70's amps if an output transistor failed as they often did then you could kiss goodbye to your speakers too more often than not. Keep up the good work. Love the videos.
Thank you for another entertaining lesson on working on these older amplifiers. I am learning much from your videos. I believe your systematic troubleshooting is the most valuable lesson I have learned. I picked up an old nonfunctional B&K 625 tube tester and was able to repair it by using your methodical, simple troubleshooting. Thank you for speaking to the newbies as there is much I have to learn. Wonderful video of amp I've never seen before. Thanks again, Stuart.
Great video. Old electrolytic caps make an amp sound very nasal. No low end, no sparkling highs and loss of definition besides hum. I have a lead 12 I have to recap. Love the amp in the video!
I thoroughly enjoy all of your videos and have learned so much from you. Thanks again for all the work you put into making these for other amp techs, you are very appreciated. Cheers from Chicago.
I have never seen this Marshall either. It was massive cool that you were able to deduce the crackling issue before removing the chassis! Brilliantly done, Stuart. Cheers!
You've never seen one in the shop because this is the first one to ever break down. Even at that, it wasn't actually broken, it just outlived the smoothing caps. Say what you want about solid state, but it's a fair bit more reliable and maintenance free than valves. Yes, it has a sterile tone, but that's what pedals are for. My favorite amp is my '77 Peavey BASS which looks very similar to that SS Marshall on the inside. It got its first cap change on its 45th birthday. Been rock solid, no issues at all for all these long decades.
Perhaps Stuart never saw one before because very few of them were sold, or maybe very few of them were sold in his general area. It's difficult and probably inaccurate to make generalizations when you only have a sample size of one. It's also kind of an oddball, funny looking amp with only a few knobs and a big cabinet, and so it's hard to imagine that it would be a "standout" that grabs people's attention in a music store and yells "try me"!. Not all products that sell well are "good" and not all products that sell poorly are "bad"; but it's difficult to know the difference if there were are very few of that particular device around that you can try as a player or work on as a tech. That said, from a tech's perspective (50+ years in electronics, myself) this is a very simple looking device and likely wouldn't be difficult to service as long as the transformer's okay and it doesn't use any unusual transistors that aren't easily obtained or substituted for.
Great video again Stuart. I remember a few of that design knocking around in the 1970's. Simple, effective and reliable as long as you didn't spill a pint of Watneys Red Barrel over them. Nice looking amplifier with the upright 2X12 configuration and it didn't look like a pain in the rear to repair either.
Good fix Stuart. Those amps look really cool from the outside. They were mail order amps. I can remember seeing them in the Bell Musical Instrument catalogue when I was a teenager.
13:30 ... About the transformer AC ... The common 3 lead center tap transformers divide the Mains in 2 phases that are 180 degrees from each other. If you put the leads on these points the meter sums the phases ex: 20 + (-20) and the result is close to 0. This doesn't happen if one lead is on a fixed voltage.
@@stuartukguitarampguy5830 , It's kind of funny looking and almost lopsided with a big cabinet and the half empty face plate with only a couple of knobs. It doesn't really look like a stage-performance amp and it doesn't really look like a practice amp, so it's neither fish nor fowl. Perhaps these just didn't sell well.
Back in the 1980s I had a Marshall Lead 20 solid state combo, which sounded pretty good for a solid state amp. There was a 12 watt version as well. The pots unfortunately were very low quality and subject to being noisy no matter how often you cleaned them, and there was some internal hum radiated into the audio signal due to the location and orientation of the transformer.
@@bjornstromberg7975, according to a guitarist and music shop owner I went to school with, yes, noisy, intermittent pots was indeed a common problem with Marshall solidstate amps of this era. My Lead 20 was probably a generation or two after this amplifier however because mine had all the pots mounted on a long strip of circuit board and not individually wired and mounted like they are on this amp. The pots in this same amp would be easy to change but they would not have been on my own amplifier....
i love your videos . i seem to learn something on everyone i watch . you explain everything so great even a beginner like me can understand and learn from them thank you .i do have a question about this one so on the cans when you was explaining the wiring the red wire is coming from the center tap then the purple is negative. the question is why wouldn't you ground the purple negative side and not the center tap wouldn't it just short out the can? this one has me stumped because i know it is right just don't understand how it works. thanks again i have learned a lot from your videos
It's a bit hard to explain simply but if you ground the centre tap of a secondary winding, the other two sides give you two equal antiphase signals. That probably didn't help!
lol well a little it does but i have no problem doing the research to learn how it works ..with you giving me the solution now i know exactly how to word it to get the rest. sometimes learning is having the beginning and the end. to learn why is the middle, lol i am just delighted that you replied. most of the time nobody replies anymore . thank you @@stuartukguitarampguy5830
I have a cheap dental mirror which is backlit by an LED that aims at the mirror, powered by a AA battery. Very very useful! The original mirror was plastic and eventually got scratched up so I replaced it with a glass one stolen from another inspection mirror.
I had one of these but it was a beige colour and it suffered from some sort of thermal run away problem, as it warmed up it made a motorboat sound, and you would have to turn it off untill it cooled down, if you turned it upside down you'd get another ten minutes or so before it happened again
The reason the amplifier sort of worked is because the amplifier has a plus/minus (+/-) power supply, and the power transformer therefore has ---- *must* have ---- a grounded centertap for the secondaries; and as one leg of the secondary intermittently disconnected itself from the circuit (touching the soldered connection intermittently or perhaps hanging by a cold soldered thread) You still had some voltage being fed to half of the project of fire by the one remaining secondary and the chassis grounded center tap. This would have given you only a half wave power supply with lots of ripple on it as either the plus supply or the minus supply went missing in action. There are other possibilities also involving maybe a shorted filter cap or some other way that you could still get plus and minus voltages to the output stage (are they a complimentary NPN/PNP pair, or not) , but regardless it's clear that you can disconnect one secondary and still get AC voltage to the bridge rectifier because of the center tap on the output side of the transformer, and DC output from the bridge....
PS, I looked more closely and the outputs are definitely complementary devices that run on a plus / minus power supply. Temporary loss of either could cause DC offset and fry the speakers (as well as loud hum), so it's probably just as well that a wire broke off of the speakers to protect them! 😉
A variable DC power supply is handy for experimenting with LED's to determine what voltage to run them at for a good brightness level without causing overheating of the LED; and since they only need about 3 V more or less at very low current a resistor-substitution switch box is also handy because it prevents you having to substitute different resistor values one at a time to figure out how to drop your 20 or 30 V power supply down to the 3 V needed for the LED. It's also generally best not to shove the LED right up against the front of the bulb jewel or colored lens because LED'S are far more "beamy" and don't have a more omnidirectional light pattern as an incandescent or neon lamp would.
The amp might not necessarily have been stored in terribly damp conditions, because the faceplate and the rest of the chassis looks pretty decent. The wood cabinet, however, probably absorbed sufficient moist air that it accelerated the process of the glues in the plywood or particle board (likely formaldehyde or urea/urethane based) corroding the screws. The other hardware appears to be stainless steel and wasn't affected, but it may also have had minimal contact with the wood cabinet. Anyway, screws in a wooden guitar, just like the screws in a wooden cabinet here, might be more likely to rust simply because the wood becomes a mildly thirsty, spongy trap for moisture, and the wood may also contain natural resins or artificial glues that accelerate or exacerbate the corrosion process. Add some finger schmutz and skin oils and salty sweat into the mix, and a guitar stored in a damp place is likely to undergo noticeable corrosion.
They always told me if you wouldn't lay your head down to sleep bec of the place or temperature overnight, it's best not to leave your guitar there either...
Just found this channel. 😊Very good. Question : i have a few solid state amps old, British when turn power switch on theres a loud crack/bang from speaker. I've used amps since 1980 and many have done this.. They work ok but i dont like thus turn on "crack * bang sound. Is there a way to stop this or does some cap need replacing? I thought i read years ago that there is a fix for this...? The amps i have that have problem is Vox Escort bass combo quite old.. Some caps were replaced about 20 years ago.. And other is that late 70's. Modelling amp built into flightcase by PA:CE, sorry i forgot name.. That really is scary bang on power up.. Its never been serviced and needs one.. Its missing the speakers and flight case box. Redmere is name, models a Marshall, Fender Twin and Vox its claimed and weird touch switches and built in sustain and chorus, flanger.. Thanks
Hi This is one of the more tricky things to sort and often cannot be. It's usually the design of the amp. A cap charges up quickly on power-on and this DC spike gets transferred to the speaker causing that bang. No easy answer I'm afraid.
Note the roll of self-adhesive numbers on the shelf, up behind the amp sitting on Stuart's bench. I presume Stuart uses them to number all his guitars, for when he's up on stage, like Pete Townshend does for his multitude of performance guitars!😉
Love seeing these uncommon amps...what were those speakers?...they looked like original 70's Green or Blackback Celestions.. interesting that Marshall didn't put cheaper speakers in an inexpensive line
Simples, the resistance value is Vs - Vf divided by If. Where Vs is the voltage applied, Vf is the forward operating voltage of the LED and If is the operating current of the LED.
@@stuartukguitarampguy5830 , I am continually surprised by the number of technicians who don't own a resistor substitution box, or in some cases forget they own it and just don't use it for some reason. I have replaced many hundreds of incandescent lamps in old hi-fi stereo receivers, and trying to achieve a suitable brightness level with multiple LED's by substituting individual resisters one by one would drive me nuts ( admittedly, that'd be a short trip in my case 😉).
All the resistors look discoloured, ie they look burnt. It's always a hard call on how much the owner wants to spend to make the amp playable or reliable.
