Vox Night Train power cutting out

Marshall

Recently acquired through Reverb, it is the NTH15 head. It powered up out of the box OK, played perfectly for 5 minutes, then suddenly the Power switch jewel light went out and the output faded away over a few seconds. Thereafter it is hard to get life out of the amp again, however randomly with a bit of switching the standby/pentode/triode and/or power switches up and down and/or waiting a while it will work again and repeat the process as initially experienced.  Inspection of the valves shows the el84s still on/lit up after the output/power cuts out but the preamp valves go off. 

Wondered if this sounds like something obvious to any of the amp wizards here? old/dodgy valves? Or more like a faulty switch, or worse the preamp or power amp?  

ICBM

It sounds like the bridge rectifier for the DC supply to the preamp valve filaments (and the power light). I had one to repair recently with the same fault - the rectifier is a bit underspec for the current draw and overheats. This one had developed an internal fault rather than the more usual problem, eg on the Marshall DSL401, of desoldering itself from the board - although either is possible. I replaced it with a higher-spec one.

It's the black component in this (out of focus) pic at the far right-hand end, directly to the right of where the two twisted orange wires connect to the board.



The bad news is that the whole board has to come out to change it.

Marshall

Many thanks for this info @ICBM  

Presuming the "bad news" is bad because it means more time therefore more money?!

Can I reasonably assume the good news in as far as there is any is this amp is not dead in the water nor desperately expensive a fix? Any idea of an estimate, and would you take it on? Assuming replacing valves is a pointless exercise for now & save money for the repair? It sounded bloody great for the 5 minutes it worked  just as I'd hoped and very Voxy AC15 chimey in the bright position...

ICBM

Marshall said:

Presuming the "bad news" is bad because it means more time therefore more money?!

Yes.

Marshall said:

Can I reasonably assume the good news in as far as there is any is this amp is not dead in the water nor desperately expensive a fix? Any idea of an estimate, and would you take it on?

Not too bad. A decent tech will probably charge about £40 possibly including the new rectifier (if it doesn't just need resoldering) - they're pretty cheap - that's about the minimum charge via any kind of shop or professional business these days.

I could do it, but you're probably best to save the double courier fee and find someone local.

Marshall said:

Assuming replacing valves is a pointless exercise for now & save money for the repair?

Yes. There's no point in changing the valves since it won't fix it and there's almost certainly nothing wrong with them.

Marshall

ICBM said:

Marshall said:

Presuming the "bad news" is bad because it means more time therefore more money?!

Yes.

Marshall said:

Can I reasonably assume the good news in as far as there is any is this amp is not dead in the water nor desperately expensive a fix? Any idea of an estimate, and would you take it on?

Not too bad. A decent tech will probably charge about £40 possibly including the new rectifier (if it doesn't just need resoldering) - they're pretty cheap - that's about the minimum charge via any kind of shop or professional business these days.

I could do it, but you're probably best to save the double courier fee and find someone local.

Marshall said:

Assuming replacing valves is a pointless exercise for now & save money for the repair?

Yes. There's no point in changing the valves since it won't fix it and there's almost certainly nothing wrong with them.

 Much appreciated fella. Don't suppose you can recommend anyone in NW England (even NE)? Manchester or Liverpool is possible, though I'm slightly further up round Lancaster..thanks again for your advice and expertise   

ICBM

Not familiar with your part of the world unfortunately! Check out the ‘recommended amp techs’ thread, there should be someone in there not too far away.

Marshall

 Cheers bud 

jonnyburgo

Roland Lumby is the go to guy in Manchester

Marshall

jonnyburgo said:

Roland Lumby is the go to guy in Manchester

  thanks @jonnyburgo  I gave him a shout through his faceache page, quick response but several weeks wait time to get it in... mind you, still chasing up the Reverb seller to respond to the misselling of the amp as ‘Excellent and perfect working condition’ !

ICBM

Marshall said:

... mind you, still chasing up the Reverb seller to respond to the misselling of the amp as ‘Excellent and perfect working condition’ !

I’m reasonably sure this can’t be “shipping damage” either, if its the rectifier. There is a remote chance it could be something else in that part of the circuit, but the possibilities are fairly limited and not likely to be anything that could be caused by it being dropped.

Marshall

thanks again @ICBM  

Perhaps ironically he just got back to me and seems reasonably open to footing the repairs on the condition that I send him the initial fault report with cost to complete the repair before actually proceeding with the repair, which seems fair and reasonable.. he also wants a video clip of me playing the amp as the fault happens which incredibly I’ve managed to record but now have a dilemma on how to get it to him as it’s too big for email! 

Any idea on turnaround period with you @ICBM ?

ICBM

Marshall said:

thanks again @ICBM  

Perhaps ironically he just got back to me and seems reasonably open to footing the repairs on the condition that I send him the initial fault report with cost to complete the repair before actually proceeding with the repair, which seems fair and reasonable.. he also wants a video clip of me playing the amp as the fault happens which incredibly I’ve managed to record but now have a dilemma on how to get it to him as it’s too big for email!

Open a Dropbox account (free) if you don’t have one already. Upload the file to your Public folder and then send him the link.

Marshall said:

Any idea on turnaround period with you @ICBM ?

A couple of weeks should be enough I think - although I’m not in the shop this week, so a little longer if it’s soon.

Try to find someone local first though, it will save time and money. 

Marshall

@ICBM you’re the man 

I realised my google drive should do it..

re: local techs, seems I’m in the wrong part of the country for decent access to good techs and the few that are in range like Roland Lumby are consequently booked out for weeks.. unless anyone knows better!