http://www.marshallforum.com/ Mods, amp repairs, tubes, maintenance, etc. en Fri, 20 Nov 2009 21:07:55 GMT vBulletin 60 http://www.marshallforum.com/images/misc/rss.jpg http://www.marshallforum.com/ http://www.marshallforum.com/workbench/9611-marshall-into-speakers.html Fri, 20 Nov 2009 20:10:40 GMT I've had an MG Series 15MSII as my practice amp for a few years now, and I've been looked down the route of using them as speakers for my Mac, by plugging my Mac into the CD In input. I picked up a 3.5mm - 3.5mm cable and a mini-jack-to-big-jack, and I was away. I had my Marshall as speakers for my Mac. Brilliant.

The only problem I've found, is that there's no pan at all. This wouldn't ordinarily be a massive problem, but whenever something is panned hard left, it ends up just being really quiet. Is there any way to either a) achieve a decent pan with my speakers, or b) just kill the pan completely and have a mono signal coming through?

Thanks in advance. ]]> The Workbench MHMaddo http://www.marshallforum.com/workbench/9611-marshall-into-speakers.html http://www.marshallforum.com/workbench/9605-problem-72-super-lead-100-a.html Fri, 20 Nov 2009 17:39:43 GMT Re-wired my presence control, as the former owned had the purple NFR wire on the center post of the pot. I put the wires on the proper terminals, only to experience more problems. The presence control was operation in reverse? Well, now I get no signal from the guitar? The amp makes scratchy sounds - and makes a loud pop through the speaker cab when I turn it off? I even put the wires back the way they were - but the same problem exists. Any help would be greatly appreciated... Re-wired my presence control, as the former owned had the purple NFR wire on the center post of the pot. I put the wires on the proper terminals, only to experience more problems. The presence control was operation in reverse? Well, now I get no signal from the guitar? The amp makes scratchy sounds - and makes a loud pop through the speaker cab when I turn it off? I even put the wires back the way they were - but the same problem exists. Any help would be greatly appreciated... ]]> The Workbench thegaindeli http://www.marshallforum.com/workbench/9605-problem-72-super-lead-100-a.html http://www.marshallforum.com/workbench/9602-dsl401-no-sound-no-glow-fading-out.html Fri, 20 Nov 2009 15:44:35 GMT OK heres my issue, I have no sound and NONE of the tube are glowing.

So like 1 1/2 months ago I replaced the tubes and re-biased, then the amp died a couple days later. The issue was W19's spade terminal and broken.

I resoldered it, but since I didn't have a new spade terminal it was probably not a good solder.

So in the past 2 weeks the amp would work, for say 5 minutes, then fade out, then start working again a few minutes later. I suspected a loose wire.

I ordered new spade terminals, and I replaced W19 and W20 and checked all other wires.

Now I fired the amp back up, and I blew the mains fuse. I rechecked my wiring, it looks correct, I did label each wire prior. So I replaced the fuse.

The amp powers on, but none of the tubes glow, and also, the channel selection lights are not on (no green/red/yellow).

I rechecked the marshall wiring schematic, but one wire on the mains and one on the transformer near the mains looks wrong in the scematic. I have seen photos of other DSL401's, and i compared my wiring and mine looks correct.

Does anyone have an ideas on what would cause just the mains to power on (i replaced fuses as well).

I was thinking either the onboard fuse OR the rectifier.

My amp is from 2002 and yes it did overheat. I actuallt put a heatsink on the rectifier just this past sunday because I thought thats why it was fading.

ANY advice would be appreciated! ]]> The Workbench dsheehan2005 http://www.marshallforum.com/workbench/9602-dsl401-no-sound-no-glow-fading-out.html http://www.marshallforum.com/workbench/9600-bias-question.html Fri, 20 Nov 2009 13:43:56 GMT Okay, I know this has probably been discussed before (many times)... How can I bias my JMP 2203 (changing from 6550s to EL34Ls) without the bias probe/tube socket... I am an electrician and have many multiMeters (Digital and Anaolog)... Can I just measure across the pins or do I need to install a resistor...? Image: http://i188.photobucket.com/albums/z135/custom53_photos/Image002.jpg?t=1258724806 Okay, I know this has probably been discussed before (many times)... How can I bias my JMP 2203 (changing from 6550s to EL34Ls) without the bias probe/tube socket...
I am an electrician and have many multiMeters (Digital and Anaolog)... Can I just measure across the pins or do I need to install a resistor...?

]]> The Workbench custom53 http://www.marshallforum.com/workbench/9600-bias-question.html http://www.marshallforum.com/workbench/9582-jcm-800-shorted-speaker-wire-when-purchased.html Thu, 19 Nov 2009 21:01:49 GMT I bought the amp years ago, never really looked closely at it. I new the amp sounded bad, I thought a retube would do the trick. I found the speaker wire shorted so that was the first thing I fixed. Retubed and replaced caps the amp still sounded weak. So I then changed the power transformer and the output transformer also installed new caps with the power transformer. Biased tubes, the amp does sound better but not marshall quality and still very weak in volume. I'm just about ready to give up on it unless someone has any other ideas.The model is 4210 and the inspection year is 1982 if that helps. ]]> The Workbench knk2691 http://www.marshallforum.com/workbench/9582-jcm-800-shorted-speaker-wire-when-purchased.html http://www.marshallforum.com/workbench/9580-late-70s-jmp-50w-master-volume.html Thu, 19 Nov 2009 19:25:36 GMT I am taking my late 70's 50w MV head out of storage and using it again after about fifteen years of it sitting idol. Everything seems to be working fine but the tubes are old GE stuff that I would like to replace. What are some good options as far as brands? I have 6550's in their now. Is that the best power tube for this amp?

Thanks! ]]> The Workbench RockinRon http://www.marshallforum.com/workbench/9580-late-70s-jmp-50w-master-volume.html http://www.marshallforum.com/workbench/9577-parts-spares-etc.html Thu, 19 Nov 2009 15:41:15 GMT Anybody looking for genuine Marshall bits...components, boards etc.. Contact us at Marshall Amp Spares (http://www.marshallampspares.com). We ship to USA as well for Example on shipping prices: DSL 100 Main Board £75 ($125 approx) Royal mail Airsure(fully insured and tracked) £16.99 ($28.25 approx) This went on the weight after being packed. Any questions please contact us. MAS Marshall Amp Spares (http://www.marshallampspares.com) Anybody looking for genuine Marshall bits...components, boards etc..
Contact us at Marshall Amp Spares.

We ship to USA as well for
Example on shipping prices:
DSL 100 Main Board £75 ($125 approx)
Royal mail Airsure(fully insured and tracked) £16.99 ($28.25 approx)
This went on the weight after being packed.

Any questions please contact us.

MAS

Marshall Amp Spares ]]> The Workbench Marshallampspares http://www.marshallforum.com/workbench/9577-parts-spares-etc.html http://www.marshallforum.com/workbench/9572-need-help-jcm-800-master-model-50w-mk2-lead-head.html Thu, 19 Nov 2009 08:38:26 GMT OK, new to the forums, not sure if this is the right place for this thread but here goes.

So, I bought this JCM 800 from a guy on Ebay. The guy lists this amp as a "Marshall 2204 JCM 800 50w head". By the way I am not very knowledgeable about the technical side of amps, I wanted an all original working vintage JCM 800 and had some gear head friends of mine help me figure out which model I want. The amp we come up with is a vintage 50w JCM 800 with vertical inputs, and this is exactly what I find on Ebay. I ask the seller about how well the amp works, if it has all the important original parts, and if it has been modded at all. Apparently the amp works fine, all original, no mods...So I buy it.


Here is my dilemma...At this point I had owned the amp for about a week, I am jamming with my band and I suddenly smell burning plastic coming from the 800. I immediately turn he thing off and refused to turn it back on til a repair man sees it.

I take it to a guy in Colorado. This guy is like the exclusive amp repair guy for this big time studio in Ft. Collins, CO. that I interned at, so I figure hes reliable. I tell him the problem and I also ask him if he can figure out if the insides of the amp look all original and if it really didn't have any mods, because I don't really know how to tell. He fixes it up and says it looks all orignal, no mods.

Now that I have the amp back I notice that the Treble knob seems very strange. This is how it works: When I turn the knob DOWN it seems to BOOST the the higher frequencies and DRASTICALLY boost the volume. The exact opposite happens as I turn the knob UP. Does that sound right at all??
SO what I do is have my gear head friend take a look at the amp, I don't know what exactly he is talking about but he says "The treble pot is sitting farther back than all of the other pots". This gear head friend also says the 800 looks like someone may have been trying to install some mod.

All I want is for the insides of this amp to be like factory default...what can I do?? does the "pot" thing sound weird to anyone else??

Also I'm looking at the back of the amp now and it almost looks like it says "Model: 2206"

If you guys could help me I would like to know what year the amp was made and whether it is a 2204 or 2206. Also what can I do to get this thing to factory default without some repair guy jerking me around? I feel ripped off, the repair guy said the amp is back to normal and it's not. If it will help I will open the 800 up, take some pictures, and post em up here. Sorry about the long read, thanks for reading though.

Here are the specs:
Marshall JCM 800 Master Model 50w Mk 2
Serial number S/A: 42681R
It has vertical inputs
Need anymore info? Let me know. ]]> The Workbench Triscuithead http://www.marshallforum.com/workbench/9572-need-help-jcm-800-master-model-50w-mk2-lead-head.html http://www.marshallforum.com/workbench/9568-parts-source.html Thu, 19 Nov 2009 05:42:04 GMT I have a Marshall G15Rcd practice amp with a broken gain pot (250K linear taper) and a broken instrument input jack. The only linear pots I can find are too big, and the generic 1/4 phone jacks are not black. Is there a source for this stuff? Thanks. JD I have a Marshall G15Rcd practice amp with a broken gain pot (250K linear taper) and a broken instrument input jack. The only linear pots I can find are too big, and the generic 1/4 phone jacks are not black. Is there a source for this stuff? Thanks. JD ]]> The Workbench JayDee http://www.marshallforum.com/workbench/9568-parts-source.html http://www.marshallforum.com/workbench/9550-mg15dfx-trouble-occasional-horrible-loud-squeal-crackle-death.html Wed, 18 Nov 2009 23:51:34 GMT Hi, joined just now to ask about this. I have a Fender DeVille at home, but I'm up at college right now so I brought over my little Marshall MG15DFX instead. Trouble is, at some point something went wrong with I think the input jack--I've tried different cords and different guitars, but the same thing happens every time. After a little while (it varies) the guitar will suddenly stop going through and the amp generates an exceptionally loud noise--sometimes a high-pitched squeal, sometimes a loud buzz, etc. And sometimes the sound just cuts out completely. Whenever that happens, fiddling with the cord where it's going into the input brings it back to normal, but it never lasts very long. It's kind of driving me crazy, because I get enough shit from people in my dorm for playing guitar all the time without this. Is there any way I can fix it myself? I don't really know anything about amps. ]]> The Workbench Cosijo http://www.marshallforum.com/workbench/9550-mg15dfx-trouble-occasional-horrible-loud-squeal-crackle-death.html http://www.marshallforum.com/workbench/9544-dead-tube-socket.html Wed, 18 Nov 2009 21:52:01 GMT Hello there, not really new here just first time posting.

My Marshall dsl100 has recently crapped out on me. One of the preamp tubes went out at a studio I went to so I figured no biggie, just replace em. It'd been a while so I decided to just get a full retube kit from Eurotubes. But when I replaced them, the same preamp tube was not lighting up which is the V2 tube I believe. Right next to the one in the silver cylinder. I tried switching around tubes but still no go. Every once in a while it lights up and the amps fine except for this cracking static sound but its done that for quite a while now.

I contacted Bob from eutotubes and he told me it was probably a cold solder joint. I'm fairly good at soldering. I've fixed guitar jacks and cables before. Is this something that I might be able to do myself or would it be better to take it to a tech? And if so, what should it run?

Thanks for any help you guys can throw my way. Its much appreciated. ]]> The Workbench zaviere http://www.marshallforum.com/workbench/9544-dead-tube-socket.html http://www.marshallforum.com/workbench/9515-my-amp-stops-producing-sound-after-5-minutes-use.html Tue, 17 Nov 2009 18:22:08 GMT I have a JCM 2000 DSL 401

Usally after 5 or 10 minutes the amp doesn't produce anymore guitar amplification, it fades away. The power light switch stays on as well as lights on four tubes...

Can anyone help? ]]> The Workbench rlancas http://www.marshallforum.com/workbench/9515-my-amp-stops-producing-sound-after-5-minutes-use.html http://www.marshallforum.com/workbench/9490-all-8-tubes-80-00-your-thoughts.html Mon, 16 Nov 2009 15:00:47 GMT I found a place to buy all 8 tubes for my DSL100 at $80.00 plus shipping. They are all matched Svetlana tubes. If anyone wants the info send me a pm. I found a place to buy all 8 tubes for my DSL100 at $80.00 plus shipping. They are all matched Svetlana tubes. If anyone wants the info send me a pm. ]]> The Workbench KTLucy http://www.marshallforum.com/workbench/9490-all-8-tubes-80-00-your-thoughts.html http://www.marshallforum.com/workbench/9486-marshall-1987x-retubing.html Mon, 16 Nov 2009 07:05:29 GMT Hi there can anyone help me??I would like to change my stock tubes to new ones but I got a bit of a prob due to limited tubes brand down here. For the power I got JJ, Mesa and sovtex and the preamp EH, Mesa, JJ and sovtex,for a bit more gain which one should I use??iplay classic rock such as zepp and deep purple thx a lot Hi there can anyone help me??I would like to change my stock tubes to new ones but I got a bit of a prob due to limited tubes brand down here.
For the power I got JJ, Mesa and sovtex and the preamp EH, Mesa, JJ and sovtex,for a bit more gain which one should I use??iplay classic rock such as zepp and deep purple thx a lot ]]> The Workbench sabun http://www.marshallforum.com/workbench/9486-marshall-1987x-retubing.html http://www.marshallforum.com/workbench/9480-why-its-important-always-get-your-amp-rebiased-when-replacing-power-valves.html Mon, 16 Nov 2009 00:46:39 GMT Here's a perfect example of the importance of getting your amp rebiased when replacing power valves. I have a homebuilt amp that came in for repair that came in with a set of Valve Art KT66s. As a troubleshooting measure, I installed a pair of Gold Lion KT66s we had here at the shop and biased them up.

The first thing I immediately noticed with the Gold Lions was that at maximum cold bias of -61VDC on the control grid, they were only pulling about 15-16mA whereas at that cold bias setting the Valve Arts were pulling about 23-24mA at the same negative voltage. When I biased up the Gold Lions, I ended up at -53VDC on the control grid for a plate current of 35mA, which was at about 64% plate dissipation.

Well, the valves weren't the issue so I reinstalled the Valve Arts. Started at max cold bias again and biased them up. Once I ended up at 35mA plate current, I checked the bias voltage and those required -55.4VDC to hold them at 35mA! Only 2.4 volts difference at pin 5...had it been the other way around, say the amp came in with the Gold Lions and I'd popped the set of Valve Arts in without rebiasing, I'd have overheated a brand new set of valves!

This is why it is VERY important to ALWAYS have the amp rebiased when replacing power valves. You just never know where a given set is going to bias in at. ]]> The Workbench Wilder Amplification http://www.marshallforum.com/workbench/9480-why-its-important-always-get-your-amp-rebiased-when-replacing-power-valves.html