JTM45 troubleshooting

[Louie]

Just thought of sharing this with everyone:

Last night I plugged in my freshly restrung LP Special into my 100% stock 2013 Marshall JTM45 Reissue, turned the amp on, waited for almost 2 minutes and when I turned the stand-by switch on, there was some static noise for a few seconds, no guitar sound whatsoever and immediately the amp died. The pilot light went off and there was no more sound coming out.

I pulled the fuses out and the mains fuse was blown. I replaced it with a new one, turned the amp on again, waited a minute and as soon as I flicked the stand-by switch on, the amp died again.

After browsing a few forums last night, it seemed that one cause might be the rectifier tube. This morning I bought a new JJ GZ34, put it in along with a new mains fuse, turned the amp on and everything was ok.

I'm glad it wasn't anything more serious, but it seems there's a known issue with the stock GZ34 that Marshall uses.

If you have a similar problem, check your rectifier tube first. But my concern is, could there be another component that's causing the rectifier to fail?

Cheers,
Louie

 

[THDNUT]

The same thing happened to me once with my Metro JTM45. Rectifier tube went kaput.
Many owners (myself included) flip the on and standby switch at the same time with the volume turned down to get more mileage from their recto tubes. I learned that from the Metroamp forum.

 

[Louie]

I always wake the amp up from standby with the volume off and no guitar cable plugged in (except the channel jumper).

 

[madryan]

The same thing happened to me once with my Metro JTM45. Rectifier tube went kaput.
Many owners (myself included) flip the on and standby switch at the same time with the volume turned down to get more mileage from their recto tubes. I learned that from the Metroamp forum.

This...

Don't leave your amp sitting there with the heater's cooking the tubes for long periods without high voltage present.

The voltage in a guitar amp, while seemingly high isn't anything compared to the voltage tube circuits ran at back in the day. You're not going to hurt the tubes by hitting them with the relatively low voltage tube amps produce these days, plus, your rectifier tube tends to provide a more gradual increase anyway.

 

[Ozzy Mandeus]

My experience is that JTM45s don't like standby, and eat rectifier tubes for breakfast if you use it. My power on routine is to always have standby "on" and only use the power switch for startup, it's easier on the amp. The rectifier then can charge the caps while the power section is still warming up and you don't get a huge surge all at once like you do when you warm up then apply HT with the standby.

 

[Louie]

My experience is that JTM45s don't like standby, and eat rectifier tubes for breakfast if you use it. My power on routine is to always have standby "on" and only use the power switch for startup, it's easier on the amp. The rectifier then can charge the caps while the power section is still warming up and you don't get a huge surge all at once like you do when you warm up then apply HT with the standby.

Do you do this with the volume knobs on 0?

 

[madryan]

Do you do this with the volume knobs on 0?

It won't make any difference.

The rectifier tube warming up and the filter caps charging will have the effect of raising voltages in the rest of the amp relatively slowly. You don't need to keep the volume down.

 

[Ozzy Mandeus]

No, there is no need. I leave the volumes wherever I had them last. The warmup time on the valves takes care of soft starting for me, and the volumes don't control the DC current draw on the power section anyway.

The problem is that the standby switch isolates the HT after the rectifier, but before the first filter cap. If you use the standby to fully warm the valves before starting up the rectifier then has to fill four 50µF caps and supply around 70-80 mA to the power valves all at once which isn't good for it. If you don't use standby, the rectifier starts to conduct first and fills the caps before the big power tubes have woken up.

Amps with a silicon rectifier won't care what you do with the standby.

 

[Louie]

Thanks, guys.

Would you recommend I do the same with my new YJM100 or is this a JTM45-specific issue?

 

[Ozzy Mandeus]

I think the YJM is a silicon rectifier, so it won't matter either way. I'd recommend getting in the habit of only using the power switch though.

 

[roeg]

My experience is that JTM45s don't like standby, and eat rectifier tubes for breakfast if you use it. My power on routine is to always have standby "on" and only use the power switch for startup, it's easier on the amp. The rectifier then can charge the caps while the power section is still warming up and you don't get a huge surge all at once like you do when you warm up then apply HT with the standby.

this.But i must say,once i switched to vintage mullard GZ34's i have not had a recurrence...i'm also careful with the startup...as suggested.Make sure not to be hitting the strings when you come off standby,if thats what you do....

 

[porkster]

I just bought a new jtm45 clone & its bassy as hell & the overdriven sounds are muddy is this because its new
& the tubes are new, i hope it gets better over time..

 

[Cjsinla]

No, that doesn't sound right to me. You shouldn't have to wait for an amp to improve over time. Also, you might want to state this question as a new thread and put in more details about what brand the amp is. Some forum members might not see your question posted at the end of an old thread.

 

[porkster]

No, that doesn't sound right to me. You shouldn't have to wait for an amp to improve over time. Also, you might want to state this question as a new thread and put in more details about what brand the amp is. Some forum members might not see your question posted at the end of an old thread.

yeah thanks man..

 

[ac/dcfan87]

I just bought a new jtm45 clone & its bassy as hell & the overdriven sounds are muddy is this because its new
& the tubes are new, i hope it gets better over time..

A lot of folks complain about the bassiness of the JTM45 and it can get muddy quick if there's too much bass.

My advice is try turning the bass to 0 all the time.

If there's still too much bass, mods can be done to correct this. If you still don't like, sell it and buy an Avatar 45. All the tone of the JTM but without the boomy bass or piercing treble. Avatar has fixed the JTM45 circuit's weaknesses and highlighted its strengths. This amp is my #1 and one of the most affordable JTM45 clones on the market. High quality components and build quality is exceptional.

I've been beating on mine several years and haven't even rolled tubes in it.