I've never the bias checked on this amp. Had to after I had a certified technician swap out the speaker and power tubes for the first time.  He was getting very low readings. If he maxed out the bias adjustment knobs, he was getting a maximum of 31 mV or 32 mV on both sets of testing ports.  He could not adjust any further. 

Interesting, I thought, so he put back the old tubes and speaker back (and he tried a combination of new speaker/old tubes, new tubes/old speaker).  ALL were relatively the same.  The highest reading he could achieve was around 33 mV.  He used multiple multimeters, so I'm quite confident that the readings were accurate. 

The older tubes were the original Marshall EL34's. The new tubes are JJ EL34's.  It has the original V-type speaker which I was trying to change to a 8-ohm Eminence Texas Heat (8-ohm jack was being used).  The tech is still investigating, but I figured I would ask  on the forum to see anyone had ideas as to the cause of low mV reading/adjustment on the bias.   

Thanks!

Chris

Hi,

A few months ago (Oct 2022), i buy in Reverb a Marshall Valvestate Bi Chorus 8280 and when i turn on, all feels ok, but one day i note only work one speaker. I change the cables and the other speaker are fine and i think the problem was in the output jack.

Finally, i found a tech who tell me he can check it and repair. When the amp is ready to go, i pay and check it in their local store and i notice a weak sound, but i thinked it was the room. The L and R speakers out works now but the problem comes when i push the chorus and the volume rise and have more body.

The guy tell me is because the amp only works in stereo when chorus is on (great sound and body), and in mono (sound lack and low volumen) when put off, but i don't believe it and that's why I'm looking for an answer here.

P.D. When i receive the amp, the first thing i do, is change the valve, so this is not the problem. If i disconected one speaker (L or R), sounds good and the chorus doesn´t affect the tone.

Please help me.

Edit: Replaced the tubes. Still cut out or no sound at all when taken off standby. Check the fuses. They look brnd new. Bypassed the FX Loop and it seemed to work fine foa  day then went right back to cutting outor no sound when taken off standby. 

Full discalimer I don't have a lot of experience with tube amps.  Not many tech options to take it to where I live. I recently bought a used DSL20C and it is in imaculate condition.  Still has the tag on it. For the first few days it worked perfectly as expected.  I turned it on this weekend and let it warm up for a couple of minute, plugged my guitar, flipped off standby  and no sound.  Not even the usual hum that let's you know it's on.  I tried different guitars and cables. I confirmed and visible conections. Eventually, after switching the standby switch a few times it did eventually make sound. There were some pops and volume changes but it worked. I didn't press my luck and turned it off.  I took the back off and made sure the tubes were still seated properly (it was shipped to me).

This is the first time I used it with the speaker instead of the emulated line out. I really had to crank the volume to get good volume in my headphones.  I don't know if that's normal or a symptom. BTW the Emulated line out worked even when the speaker wouldn't. 

Does this sound like it need new tubes or am I looking at something more complicated.  I appreciate any help.

Hello y'all,

I've been having a problem with JVM 205Combo.
During corona-lockdown, when we were not allowed to rehearse with the band, I had took my amp home with me....
As I'm always curious to find other sounds, I started experimenting with connecting other speaker cabs to my JVM. But, as I later discovered, the cable I used was no good and I think I blew up the main amplifier. I looked for the fuse, for it seemed logical to me that the fuse was blown, but couldn't find it. I also have a JCM 800 2205 head, a JMP MK2 2204 head and I've been having a JCM900 4100 head in the past. Now, all these amps were fused, so if anything went wrong, it was just the fuse that was blown. In fact, I've experienced that!
But no fuse on the JVM....is that correct? Because if it is, my problem is bigger than I thought. In that case, what was blown instead? The output transformer? My tubes?

I hope somebody can help me out on this one. And I promise never to experiment with other speakers or whatsoever.

Thnx anyway!
Cheers!

first time poster, long time tech. having experience with marshall amps I am familiar with issues stemming from problematic circuit boards (i.e.-DSL/TSL etc ) however my experience regarding this model is limited. can't say I have ever been a fan of DSP. for me ,as a player/tech DSP is a deal breaker. like the dreaded nintendo game format red circle of death, once the DSP bites it you're done.  I just seek a simple answer for my customer who bought one second hand,never re-tubed. amp lost power.sounds like a badly blown speaker (speakers test good). replaced output tubes and driver tube (original outputs tested badly). preamp tubes test good. supply voltages appear to be normal.overdrive channel LED switches from red to amber to slightly different amber but no green.  clean channel button switches normal. red-orange-green.master volume button doesn't come on.sometimes if you perform factory reset all buttons function but sound is still terrible. nice clean signal going thru to pin 7 of V7.  in between V7 and phase inverter something is haywire. my money is on the DSP board but not having a flow chart ??? tried to get a signal straight into the power amp but got nothing out. any input appreciated guys.  one thing more...i get the 2 separate heater voltages. V6 is 12vdc but the other for the remaining tubes originating at the tranny, is that standard 6.3 ? didn't see it on the schematic.

WARNING: When using the DSL1HR head
for ‘silent’ practice or DI recording ALWAYS
disconnect the speaker cabinet from the
amplifier’s rear panel before switching on.
NEVER unplug the speaker cable from the
speaker cabinet while it is still connected
to the amplifier rear panel. This may stress
the amplifier’s power-stage and in extreme
cases may lead to valve and/or transformer
failure.

Can i use an emulated out with the cab speaker plugged in? 

Hello,

can I use my JTM60 speaker with a Marshall Origin 20H Head?

Also, my JTM60 has suffered some damage when my nephew tried to power on the amplifier, she cranked everything up but didn't succed, when I got home I didn't noticed it was all cranked up and powered it, it blew tubes and some more, I had it repaired but it didn't get back to the same sound as before... I'd like to have it checked by qualified personnel, can you indicate someone in Italy, please?

Thanks a lot,

Marco

Hi,

Have a few questions about attenuator usage with SC20H amp.

1. Do I need two attenuators? My cabinet has two speakers (8 Ohm each), and SC20H has two separate outputs for each speaker, so does it mean I have to buy two attenuators, one for each speaker? I didn't manage to find SC20H schematics, so I'm not sure if those two amp outputs are connected in parallel internally, and I can just use one attenuator.

2. Do I need attenuator(s) at all? I want to run the amp with overdriven tubes, thus I have to set max level, right? Consultant at my local store told me it's enough to reduce "Master" volume, and EL34 will still be overdriven, if I set "Pre-amp" volume to max. But folks at Marshall forum say that it's still better to use attenuator, even in 5W mode. Again, I don't have SC20H schematic, so it's hard to tell who is right.

3. What if my cabinet only have one 4 Ohm input (2 x 8 Ohm speakers inside)? Is it enough to connect it to the amp with only one cable? Or I have to rework my cabinet to have two different inputs (separate input for each speaker)?

Thanks!

Hello,

I am a recent ower of a Marshall Origin 20, which I got in July. I've really enjoyed the amp until I plugged in last night and got out absolutely no sound out of it. I couldn't figure out why, as nothing as happened to it and it worked fine two days ago. I took it apart to do some trouble shooting and found that when I have all the knobs max'd and output on 20 watts, I can hear a whisper of my guitar signal (nicely saturated, presumably by the preamp tubes) through the speaker. This sound is affected by all of the knobs. However, if I plug my guitar directly into the return of the effects loop, and activate the effects loop I get no sound whatsoever; no guitar, no hum, nothing. Because of this, I'm sure my speaker is not the problem. These things led me to think it was a power amp section issue, so I went down and purchased a new set of matched EL34's, threw them in there, and nothing changed. I'd really like to know if there's anything I can do to fix this, because this amp is not even a year old and I should not be having these kinds of problems with completely normal bedroom use.

Thanks,

Alex

I've noticed the outputs 2 & 3 differ, while the specifications on the speakers but the back of the cab (ORI212A) says x2 8ohms. Should I use the 16ohm output? And if not, which of the ohm outputs on the Origin 20H is the ideal one? The 16 ohm, the 8ohm or the 16x2 one?

Hello I'm considering to buy DSL1HR or CR for silent recording at home. But I would like to use fx loop SEND output to record raw valve soud to apply impulse response later.

Is it safe to unplug cabinet, and without connecting headphones use these amps in such manner? 

And if so, why? Usually valve amp needs speaker load

Thank you in advance for the answare!

Sergey

Hello everyone,,

I know that turning a "TUBE" amp on without a speaker load on the output will damage the amp.

(the no-load condition will cause the output voltage to increase until the output tubes burn out, which can then lead to other component  damage)

Is this also true for a CODE 100 amp?  Is there a risk of damage to the output section, with turning the unit on without a speaker cab load connected?

Would it be safe to operate the amp with just headphones connected instead of a speaker cab?

Would it be safe to operate the amp without either a speaker cab or headphones connected?

I ask because my computer (which is a desktop) is in a different location in my house than my amp.

Doing firmware updates or testing out patches requires either moving my computer or my amp, both of which are very inconvenient.

It would be much easier if all I had to move was the head.

Hey Mates,

Having issues with a clients amp, seems that after a retube that i did, he was playing and after about 30 min, it gradually started losing sound and then cut sound completely.  I did the re-tube myself, and biased it properly and i was able to play it for about 40 min with absolutely no issues.  List of troubleshooting steps i have done:

tried a different speaker cable

tried a different guitar cabinet

tried a different guitar and guitar cable

tried the old tubes, additionally bought a 12ax7 and tested each pre-amp tube

tried a different power source

Have tried different power tubes

have checked and replaced the fuses

Now this is what i am THINKING is the problem, I think it might be something with either the heater curcuit fuse, or i think it's called a BRT1 Rectifier?  I did alot of research and it seems that the people having MY issue, explain the same symptoms of what i am having.

Now i have to make this clear, I AM NOT A PROFESSIONAL TECH, just a guy helping bands out with tech stuff that they don't know how to do.  So any help is appreciated.

Thanks!

So I've been thinking about buying a Celestion F12-X200 speaker for my code 50 and was wondering it this would work. The reason I need to know this is because even though I know you can use an 8ohm speaker on a 4ohm tube amp, I'm not sure about a digital amp. Could anyone tell me if this is possible.

High, first off, I am new to the modeling world, my main rig is peavey and Line6 DT25 tube rigs.

I bought a Code 50 as a quick and reliable solid state backup/practice amp to gig with if needed.

I love the sounds of it but at times the BASS just takes over even when Bass knob is rolled to

zero. no matter what settings i use the Bass is booming. I am thinking of a speaker upgrade

possibly but is there any advice on settings that may help me pull the mid range out more. I 

use Super Cleans and Gritty Gains. Hard Rock/Metal sounds

Wes

I'm using a Origin 50 combo. I find when I crank the master volume and play at higher volumes, I get what sounds like glassy tube rattle. There is also just generally more noise than I would expect. I tried it with a different cabinet. It seems to be worst when using the internal speaker or when the amp is sitting on top of the external cabinet... my assumption is that the physical vibrations due to high volume are causing the tubes to rattle. The rattling is getting passed through the speaker, meaning that it is not just simply a physical rattle, but it is a transferred into the signal.

It sounds similar to some of the problems on the internet with the Class 5 that had rattling. Someone suggested that tube rings would fix it. Any suggestions?

Hello,

I've noticed that there is rattling/jangling coming from the amp (not the speaker) when playing notes between low  A and C and their respective octaves above. It sounds like it is coming from the EL34 valves - is this due to the way that they are mounted without spring dampers? They have not gone microphonic as far as I can tell, and are otherwise performing as expected, so I feel this is more a mechanical issue with the chassis/mounting, or it's just an undesirable characteristic of the valves themselves. What I'd ideally like to know is, do all Origin 20Cs do this or is this the first anyone has heard about this?

I've removed every external variable there could be, moving the amp to another location and isolating it from floor vibrations in the studio. I've taken the 'amp' out of the cabinet so that I could lightly tap the valves, and check the screws around the supports are not loose. You can generate the rattle (or very similar) just by tapping lightly with the handle of a screwdriver, on both valves. This is what I was expecting if it was just physical vibrations from the speaker causing them to rattle in sypmathy. The rattling sound does not get amplified, so it's not in the audio path.

It's enough to be offputting when tracking/practicing in the studio unless pushing out really high volume so that you can only hear the guitar. I play fairly clean a lot of the time so it is more obvious under those conditions.

Would really appreciate some advice. If the answer is, "It's the same for all and there's not much that can be done..." then ok, I just need to know. That said, I spotted there was some sort of similar issue perhaps on Class 5 amps that a kit was developed for to resolve? I may have misunderstood though.

If there is any further mechanical troubleshooting to be done then please let me know. I wouldn't want to void the warranty status if possible. For what it's worth, I'm a systems and support engineer for a large format mixing console company, so I'm competent enough to poke around as required... just figured someone may have alreday solved this one before I carry on!

Kind regards,

Ed

Hallo,

I got a doubt on well interpretating the manual where it states:

WARNING: When using the DSL1HR head
for ‘silent’ practice or DI recording ALWAYS
disconnect the speaker cabinet from the
amplifier’s rear panel before switching on.
NEVER unplug the speaker cable from the
speaker cabinet while it is still connected
to the amplifier rear panel. This may stress
the amplifier’s power-stage and in extreme
cases may lead to valve and/or transformer
failure.

can someone confirm what I understand: if I want to play using an headphone for silent practice (connecting my headphone to emulated line Out), I shall prior disconnect the external speaker from the rear of the amplifier (shouted off), (and never from the rear of the speaker cabinet). So I can Play the amplifier using headphone without connection to the cabinet? is that correct? An this is applicable also if I connect the amplifier to a mixer (by using Line out). That is quite strange because all other amplifiers recommend to never disconnect the speakers, with or without an headphone or something helse. Please help! I don't want do damage my DSL1HR. Thanks. Cheers.

I have had this amp for a few months and still can't seem to dial in a good sound. It is my first Marshall and first tube amp. I have looked on-line for settings to no avail. This also has the upgraded Creamback speaker from Sweetwater.

I use this mostly at home and am looking for a good clean tone and a good distorted tone.  Any help would be greatly appreciated. I use the 20 watt setting.

Thanks