Santiago Alvarez (electronics engineer, JVM, YJM, AFD...)

[PippPriss]

Could it be that HotRats issues stem from the same thing the TSL was suffering from? The PCB of those amps seemed to be made inferior, so that over time, when warming up the amplifier, the substrate between the PCB sides would become conductive:



I have no idea, but I read some comments where people were starting stuff like "the JVM suffers from the same issue, MARK MY WORDS" and other hyperbole language. I could imagine, IF that's true, that your device might be affected by that? I have no idea, if this is actually true and if that's the culprit of your issues, but just want to throw this in here for you to check.

 

[santiall]

No, those sounds came from the amp alone and all the issues I had happened with or without the pedal board connected.

As a further reference, I have to add that the first issue I had, with the original tubes, was a complete tube failure with wired noises, static, loud hum, power loss and so on.
The amp gave no signs of potential issues before the meltdown. I turned it in on and it was like that.

This time I get a brief intermittent loss of power that appears once the amp is warmed up and happens randomly every few minutes. Between the power losses the amp sounds perfectly fine.

Looking at the tubes I don't see strange glows, they illuminate correctly, evenly and just like the brand new tubes.

This morning , as a test, I've put on the "dead" tubes again and after few minutes ai got the power loss again therefore the issue is in the tubes (the cause unknown).

Since these tubes come form a JJ matched quartet that had a microphonic el34 right out of the box, I'm inclined to believe I've encountered a bad el34 batch.

I have no amp tech I trust near me (unfortunately the one I had died few years ago) therefore I'll wait and see what happens with these brand new tubes.

If they'll fail in the near future it will be proof that there's something else going on.

Thank you for your patience and support.

yeah, good luck with it but, as said, tubes are tubes. That they are new or matched doesn't guarantee anything (sadly I have to say), also, these low power amps don't stress the tubes at all so most likely you got a couple of faulty ones.
Fingers crossed that the bad luck with the tubes is gone and there is nothing else with the amp!

 

[santiall]

Could it be that HotRats issues stem from the same thing the TSL was suffering from? The PCB of those amps seemed to be made inferior, so that over time, when warming up the amplifier, the substrate between the PCB sides would become conductive:



I have no idea, but I read some comments where people were starting stuff like "the JVM suffers from the same issue, MARK MY WORDS" and other hyperbole language. I could imagine, IF that's true, that your device might be affected by that? I have no idea, if this is actually true and if that's the culprit of your issues, but just want to throw this in here for you to check.

I doubt as Hotrats amp has cathode bias, it is acompletely different to those JCM2000 amps, who knows... but the noises in the video to me look more like tube issues, arcing inside or the likes.

The original DSL and TSL series had a very poorly designed bias circuit, inherited from the JCM900 and 6100 series but it seemed to be particualrly bad in the JCM2000s... it is not the pcb but the circuit design as once the bias is gone, things get too hot, things start arcing, etc. The pcb material is the same as in anything else but if the design is bad... I can understand people saying that the "pcb quality is bad" because they see it burnt but you are killing the messenger so to say, the "poor pcb" has enough to try to stand conditions for which it hasn't been designed.

The JVM series, and for that matter, any other marshall apart from those designs from the 90s, don't have any 'bias drift' issues. I think all the amps designed from the early 2000 till today have the same bias circuit as you can find in a 1959 and plenty of other amps in the market, a simple circuit.

 

[wreckless]

Wow, I’ve learned quite a bit reading through this thread. Thanks so much for all the great info and anecdotes, @santiall !

Was going to do a few mods to my recently bought 410H, but now, it just doesn’t seem worth the bother.

Likewise, I was worried that the parallel/series loop was problematic somehow (drastically affecting volume and/or tone, as some claim…), but again, it looks like that shouldn’t be a problem either. Will try it at line level though (i.e., the +4dB setting).

 

[santiall]

Wow, I’ve learned quite a bit reading through this thread. Thanks so much for all the great info and anecdotes, @santiall !

Was going to do a few mods to my recently bought 410H, but now, it just doesn’t seem worth the bother.

Likewise, I was worried that the parallel/series loop was problematic somehow (drastically affecting volume and/or tone, as some claim…), but again, it looks like that shouldn’t be a problem either. Will try it at line level though (i.e., the +4dB setting).

hi, glad to know that this thread is of some use!

the loop should be OK, the first known issue is the volume drop when the MIX is set to 100%, which can be worse if the FX loop tube ihas low gain. If you keep the loop ON all the time, or the external effect is able to compensate the drop, you'll be perfectly OK. The second known issue was me/Marshall not being aware of people not knowing how to use a parallel loop