Old DSL2000 Crackle after using A/B/Y Switch

[Robert Machine]

I was using 2 guitars into a DSL2000 50w head using an A/B/Y switcher it wasn't but 3 minutes & a couple strums & I started to get a crackle & the volume cut out then came back. I plugged straight into the head & it did the same. I checked all the tubes & they seem fine. It played fine the other day & today it started again. It's like almost having a noise gate cause after the crackle I strum the volume kicks back in then crackles & kicks out but when it kicks back in it doesn't have as much amp noise. Any ideas?

 

[fitz]

I was using 2 guitars into a DSL2000 50w head using an A/B/Y switcher it wasn't but 3 minutes & a couple strums & I started to get a crackle & the volume cut out then came back. I plugged straight into the head & it did the same. I checked all the tubes & they seem fine. It played fine the other day & today it started again. It's like almost having a noise gate cause after the crackle I strum the volume kicks back in then crackles & kicks out but when it kicks back in it doesn't have as much amp noise. Any ideas?

Probably nothing to do with using an A/B/Y.
Check the easy stuff first - clean all the jacks (input, loop & speaker).
Try different cables.
Tubes can "seem fine" and not be functioning properly.
If you have any spares, try changing pre-amps one by one - then try changing power tubes & re-bias.

 

[Mitchell Pearrow]

Also try a patch cable in the FX loop
This is something I have to do with my 3210’s
And what @fitz said

 

[Robert Machine]

Thank you guys! I checked the tubes with a multi-meter & they all seem fine. My bais was 22mAh & 38mAh on the powertube I reset that so both are at 38mAh. I've used several different cables & it happened with each cable. Now it stopped doing it. The one tubes print is slightly dull compared to the others but I don't see red plating. I will try some deoxit. I don't have any extra powertubes but I do have 2 new pre-amp tubes. I didn't find any microphonic tubes either.

 

[Robert Machine]

As I was cleaning the connections I realized I recently switched out cabs. My old cab I had wired in Series 2 - 8 ohm speakers = 16 ohms & this cab I just seen Mono 8 ohm & the amp was not seeing enough resistances as I had it connected wrong. I had 16 ohm from amp to 8 ohm cab. A big no no. Any advise as to what I should check?

 

[fitz]

As I was cleaning the connections I realized I recently switched out cabs. My old cab I had wired in Series 2 - 8 ohm speakers = 16 ohms & this cab I just seen Mono 8 ohm & the amp was not seeing enough resistances as I had it connected wrong. I had 16 ohm from amp to 8 ohm cab. A big no no. Any advise as to what I should check?

If you weren't running full throttle for hours on end, your amp is probably fine.
That's not a severe ohms mismatch.
Might have been a little more stress on the power tubes, so perhaps another good reason to get some spares.

 

[Robert Machine]

If you weren't running full throttle for hours on end, your amp is probably fine.
That's not a severe ohms mismatch.
Might have been a little more stress on the power tubes, so perhaps another good reason to get some spares.

Thanks Fitz! Good to know. I was running a hair past 2 crunch channel but the amp was on for about 6 hours but not being played constant. More just learning a song. I will have to order some tubes. I have the switch on the amp set for 8 ohm. I take it I could plug into either tap just not the 16 ohm?

 

[anitoli]

16 ohm tap 16 ohm cab. With the switch on 8 ohm two 16's or one 8 ohm cab goes there. Two 8's if set to 4.

 

[fitz]

Thanks Fitz! Good to know. I was running a hair past 2 crunch channel but the amp was on for about 6 hours but not being played constant. More just learning a song. I will have to order some tubes. I have the switch on the amp set for 8 ohm. I take it I could plug into either tap just not the 16 ohm?

If you weren't putting the spurs to it, the ohms mismatch would probably just change the tone a bit from what the speakers are designed to run at.

Do you mean the speaker jacks by "either tap" ?
I think that amp has one 16 ohm jack and a switchable pair of parallel jacks that can be set for 8 or 4 ohms.
With the switch on 8, you can run a single 8 ohm load to either jack, or a pair of 16's.
Likewise, with the switch on 4 you can run a single 4 ohm load to either jack, or a pair of 8's.

 

[anitoli]

I honestly think newer amps are engineered to take the mismatch. Imagine how many amps would be returned if this mismatch fried the transformers every time? Not happening. Amp companies do not want warranty returns. Case in point are the 900's which most have the output fail fuse's. Technically if you lose a pair and the fuse blows you are running a mismatch at the OT. Also if you use the half power switch it has the same effect two tubes out of circuit results in a mismatch at the OT. No where in the documentation does it say to change the switch to 8 ohms to compensate. I tested a 6100 on half power dimed into an attenuator knowingly running the mismatch on the OT purposefully trying to make it explode and it took it, and took it for 6 months.

I think you are ok there.

 

[Robert Machine]

16 ohm tap 16 ohm cab. With the switch on 8 ohm two 16's or one 8 ohm cab goes there. Two 8's if set to 4.

anitoli Thank you! Much appreciate the info.​

 

[Robert Machine]

If you weren't putting the spurs to it, the ohms mismatch would probably just change the tone a bit from what the speakers are designed to run at.

Do you mean the speaker jacks by "either tap" ?
I think that amp has one 16 ohm jack and a switchable pair of parallel jacks that can be set for 8 or 4 ohms.
With the switch on 8, you can run a single 8 ohm load to either jack, or a pair of 16's.
Likewise, with the switch on 4 you can run a single 4 ohm load to either jack, or a pair of 8's.

Yep I was talking about the speaker jacks. I never used anything other then the 16 ohm with the switch always selected to 8 ohm. After realizing my mistake I was unsure if the other 2 output speak jacks were in parallel & if it mattered or didn't matter which speaker jack I plugged the cab into.

 

[anitoli]

You can see in this pic the small line under the jacks that says 4 & 8 Ohm parallel with the line also going to the switch. Those two are for two 16's switch on 8, one 8 or two 8's switch on 4, or one 4. The lone 16 is for 16 only.

 

[Robert Machine]

You can see in this pic the small line under the jacks that says 4 & 8 Ohm parallel with the line also going to the switch. Those two are for two 16's switch on 8, one 8 or two 8's switch on 4, or one 4. The lone 16 is for 16 only.
View attachment 140747

Thanks for the picture & explanation. I was able to read it better (Need new glasses). So that makes sense as 8 + 8 = 4 ohms & the cab I got is the 1936 2x12. When I hooked it up I seen 16 ohm & miss the Mono 8 ohm on the Left at the top. After reading the online manual I realized it's an 8 ohm cab. So now I used the 8 ohm switch & plugged into the 8 ohm jack on the amp.

 

[Robert Machine]

I wanted to update in case anyone else runs into this. I took my tubes & had them tested turns out one PT was wore & the other failed. With the DMM both were fine & no visual signs of them being bad. I also found 2 cracked soldier joints on the one PT socket & the factory didn't soldier the ohm switch good.

I do however have concerns as the guy I bought this from 3 years ago said he put new tubes in it & they are only a year old. The tubes were GT & I always kept the volume just a hair past 2 on crunch & lead channel gain 7 & 6. The bias was set to 38mV & Marshall Service Bulletin said 45mV. I know when playing it would reach into Low & high 50's when I turned it to 3 once. The chassis on this amp has a date stick of 2002 but the sticker on the back of the amp is 2003. It has the green board JCM2-60-00. I also noticed after setting the bias with the new PT's it was holding but after 45 mins. it dropped 1 to 1.3mV. I'm wondering if I should dump it & get something else?

 

[fitz]

I'm wondering if I should dump it

If it's working now, that's a cool amp to have.

& get something else?

By all means, more Marshall amps is never a bad idea.

 

[Robert Machine]

If it's working now, that's a cool amp to have.

By all means, more Marshall amps is never a bad idea.

I like the amp just worried. I'm playing about 45mins now the the bias dropped 1 to 1.3mV. I had it at 38mV now both sides are 36.9mV

 

[fitz]

I like the amp just worried. I'm playing about 45mins now the the bias dropped 1 to 1.3mV. I had it at 38mV now both sides are 36.9mV

New tubes?
They can take a few hours to "burn in" and stabilize.
Just re-bias after a few more days.

 

[anitoli]

How many times have i heard "new tubes" on a second hand amp. Even worse is when you buy a "new" amp and the power tubes are cooked. Little tell tale sign is when the bases are brown and the top half is black. Unfortunately this bs is prolly gonna get worse as tube prices have increased so much.
I just factor in now that any used amp buy or open box buy is gonna need a set right off the bat. If i get lucky and it doesn't cool, if it does it doesn't upset me anymore, just the way it is.

 

[Robert Machine]

New tubes?
They can take a few hours to "burn in" and stabilize.
Just re-bias after a few more days.

Yep I bought them yesterday. Thanks for the info. The shop said about leaving the amp on 24hrs to burn in but I was worried about that especially with this amp. I will recheck like you said.