Amplifiers that are a total pain in the arse to repair and reason(s) why ?

Cabicular

ICBM said:

If they really wanted to protect the caps, they could still use the Zeners - just with the chain voltage *above* the normal operating voltage, so that apart from at power-up, it wouldn't be conducting. That would almost certainly prevent them cooking and failing, too.

Even aside from that, what idiot designs an amp with the main circuit board components inaccessible without unsoldering a dozen wires which are also glued down? Especially as the board is poor quality and unsoldering anything unnecessarily is likely to lead to traces separating.

Not impressed with them, never have been!

They also have the unfortunate trait of sounding dreadful
I really don't get the fascination with them.. marketing?

jpfamps

normula1 said:

jpfamps said:

Telejester said:

I've only ever owned one amp ,which after a tech nearly pulled his hair out trying to carry out a repair, that tech said to never bring that amp anywhere near him ever again. said amp was a blues junior, a truly dreadful amp.

I'm surprised by this. I've never had any trouble working on Blues Juniors and have never failed to repair one.

I repaired nearly 40 last year and current have 4 in the workshop.

They are one of easier amps to work on in my opinion.

Does repairing forty in one year imply that there's the odd design flaw in them?

There are some well known issues with the Blues Junior, for example ultrasonic oscillation and mains voltage wiring.

These can be sorted.

Most of the problems I see are caused by valve failures, a common trait in virtually all EL84 loaded amps (for what it's worth I've got 5 other EL84 loaded amps in the workshop waiting for repair, most I suspect will have power valve issues).

I think the Blues Junior at the moment is Fender's most popular amp, especially in London, and hence why I see a lot of them. 

Bear in mind that Fender have about 50% of the UK amp market too.

ICBM

jpfamps said:

I think the Blues Junior at the moment is Fender's most popular amp, especially in London, and hence why I see a lot of them.

I can understand why, given that a lot of people will be using public transport or taxis, and a Hotrod Deluxe is getting to the point of very big and heavy for that.

It just disappoints me that the Blues Junior is significantly lower in build quality - while not being so in price - compared to the HRD.

I see about the same numbers of BJs and HRDs for repair I think, which indicates the BJ isn't so popular in Scotland.

jpfamps

ICBM said:

jpfamps said:

I think the Blues Junior at the moment is Fender's most popular amp, especially in London, and hence why I see a lot of them.

I can understand why, given that a lot of people will be using public transport or taxis, and a Hotrod Deluxe is getting to the point of very big and heavy for that.

It just disappoints me that the Blues Junior is significantly lower in build quality - while not being so in price - compared to the HRD.

I see about the same numbers of BJs and HRDs for repair I think, which indicates the BJ isn't so popular in Scotland.

I see quite a lot of HRDs too. I've got 4 in work shop at the moment, but the BJ certainly more popular in London.

Beexter

jpfamps said

Most of the problems I see are caused by valve failures, a common trait in virtually all EL84 loaded amps (for what it's worth I've got 5 other EL84 loaded amps in the workshop waiting for repair, most I suspect will have power valve issues).

@jpfamps ;Are you saying that the EL84 is inherently unreliable or is it that it is generally fitted to poorly designed amps?
Are there any "reliable" EL84 amps in your opinion? 

ICBM

Beexter said:

@jpfamps ;Are you saying that the EL84 is inherently unreliable or is it that it is generally fitted to poorly designed amps?

The latter. Part of the problem with them is that many amp designers seem to think they should be run at well over their maximum ratings - for both voltage and especially for dissipation - much more so than with other valve types. This may come from the (wrong) belief that the Vox AC30 and similar amps are 'Class A' and so the valves need to be idling at 100% of their dissipation, but even that doesn't explain it fully - they're often run at up to 18W at idle, and more under full load - the valve rating is 12W. So it's not surprising that they die!

jpfamps

Agreed, designers do seem to regard the 12W maximum plate dissipation as a minimum.

EL84s are also rated for 300 V on the anode.

I've seen amps with over 400V on the anode and the max dissipation at idle I've seen is 21W!

For some reason many manufacturers use 100 ohm screen grid resistors. Almost certainly because VOX did it and this means we don't have to think about it.

1k screen grid resistors will improve reliability.

I get through more EL84s than any other valve, including pre-amp valves.

Beexter

Interesting stuff @ICBM and @jpfamps. This thread is particularly relevant as I'm in the market for a new amp and many of the contenders on the shortlist to try are EL84 based (Bad Cat, Morgan and Dr Z) but if reliability is that much of an issue, should I be re-thinking my options? 

jpfamps

Beexter said:

Interesting stuff @ICBM and @jpfamps. This thread is particularly relevant as I'm in the market for a new amp and many of the contenders on the shortlist to try are EL84 based (Bad Cat, Morgan and Dr Z) but if reliability is that much of an issue, should I be re-thinking my options? 

Depends how much you like sound of those amps. 

In my experience Bad Cat and Morgan amps run their valves (and other components in the case of Morgan) pretty near their limit. For example, in a current production Morgan amp I've seen > 450 VDC on caps rated for 450 VDC, which is in my experience not good design practice. It's not as if 500 VDC caps aren't available at a sensible price either.

I've not seen enough DrZ amps to draw any conclusions on this.

EL84s certainly can be employed reliably, for example I don't see so many Orange amps with dead EL84s.

kipple

ICBM said:

Beexter said:

@jpfamps ;Are you saying that the EL84 is inherently unreliable or is it that it is generally fitted to poorly designed amps?

The latter. Part of the problem with them is that many amp designers seem to think they should be run at well over their maximum ratings - for both voltage and especially for dissipation - much more so than with other valve types. This may come from the (wrong) belief that the Vox AC30 and similar amps are 'Class A' and so the valves need to be idling at 100% of their dissipation, but even that doesn't explain it fully - they're often run at up to 18W at idle, and more under full load - the valve rating is 12W. So it's not surprising that they die!

Hmmm.. Reading this stuff about the EL84 thing has got me wondering...

Do you have any experience of problems with Fender 15 watt EVH 5150III LBX. It runs on EL84
Do you know anything about build quality reliability .Is it easy to work on

Do you know can the Amp be biased when it is time to change tubes or does it need tubes that fall within a certain range. 
Thanks 

ICBM

kipple said:

Do you have any experience of problems with Fender 15 watt EVH 5150III LBX. It runs on EL84
Do you know anything about build quality reliability .Is it easy to work on

Do you know can the Amp be biased when it is time to change tubes or does it need tubes that fall within a certain range.

Sorry, I don't have any experience with them at all.

It doesn't look particularly fun to work on…

https://www.gitarrebass.de/wp-content/uploads/2016/03/EVH-5150-III-innen.jpg

There's a trimmer at the right hand side of the pic (blue, partly hidden by a cable tie) but I don't know if that's a bias control or not.

kipple

ICBM said:

kipple said:

Do you have any experience of problems with Fender 15 watt EVH 5150III LBX. It runs on EL84
Do you know anything about build quality reliability .Is it easy to work on

Do you know can the Amp be biased when it is time to change tubes or does it need tubes that fall within a certain range.

Sorry, I don't have any experience with them at all.

It doesn't look particularly fun to work on…

https://www.gitarrebass.de/wp-content/uploads/2016/03/EVH-5150-III-innen.jpg

There's a trimmer at the right hand side of the pic (blue, partly hidden by a cable tie) but I don't know if that's a bias control or not.

Thank you for that pic 
I have had one of the 15 watters on loan for almost a year now and I have given it a right caning without any problems so far and as a result I have just bought one for myself so I am hoping it's not going to give me any problems...

looking at that pic and comparing to the layout of my own amp it does appear that the power tube sockets are PCB mounted so I hope that is not a recipe for disaster.
I don't seem to see many people on forums etc complaining of issues with the 15 watters but I have noticed a few problems with the 100 watters.
Fingers crossed it will stand the test of time.. 

ICBM

If the board is high quality and properly designed regarding trace spacing then there is no issue with having the power valve sockets mounted on it, especially in an amp with the valves above the chassis so the heat goes away from the PCB rather than onto it.

It's hard to see enough in the pic to be able to tell either way though.

ICBM

New-version Peavey Valve King with 'Vari-Class' output section, which is where this bit of the circuit is…



From the remains here that looks like a diode that's burned itself out, but there's probably also trace damage and board carbonisation, and it might be quite difficult to repair - even if none of the other components have failed as well. I'm currently waiting on a quote for a complete new PCB as the simplest solution, but if that (as expected) works out uneconomical, I'll have to see if I can clean up the mess, scrape away any carbonised board material, bridge any burned tracks and fit a full-size diode over the top, check the other parts then hope it works. This will still not be particularly cheap.

Personally, I wouldn't buy one of these amps.

DJH83004

This is all too common IC with modern SMT amps, you could end up spending an hour or so cleaning the board, repairing the tracks, replacing the diode, and just hope it has not taken anything else out, (like the op-amp). They are just a nightmare 

ICBM

DJH83004 said:

This is all too common IC with modern SMT amps, you could end up spending an hour or so cleaning the board, repairing the tracks, replacing the diode, and just hope it has not taken anything else out, (like the op-amp). They are just a nightmare 

I know…

To be perfectly honest I'm actually hoping that either the owner accepts the quote for the new board - which means that I make about £20 out of an expensive repair, since swapping the board isn't that much work, the cost is all in the part - or that he just refuses the whole thing, since even the quote for the manual repair will be fairly big. I don't really want to spend an hour or two trying to fix this mess and end up finding that it still needs other stuff or that it just fails again.

I may be in danger of turning into a Luddite, but components and construction like this do not belong in valve amps.

Telejester

ICBM said:

If the board is high quality and properly designed regarding trace spacing then there is no issue with having the power valve sockets mounted on it, especially in an amp with the valves above the chassis so the heat goes away from the PCB rather than onto it.

It's hard to see enough in the pic to be able to tell either way though.

ICBM I'm an advocate in the belief that tubes have no place on a circuit board, I've had two absolutely shite experiences with victory amps, sheriff 22 and V40 and returned both immediately. Next head I'm considering is the Laney lionheart lh20 which has pre and power tubes chassis mounted, thing is they are mounted so as the tubes are inserted upwards into the sockets.  As heat rises, do you think there could be reliability issues down the line and do Laney push el84s beyond their limits ?

ICBM

Telejester said:

ICBM I'm an advocate in the belief that tubes have no place on a circuit board, I've had two absolutely shite experiences with victory amps, sheriff 22 and V40 and returned both immediately. Next head I'm considering is the Laney lionheart lh20 which has pre and power tubes chassis mounted, thing is they are mounted so as the tubes are inserted upwards into the sockets.  As heat rises, do you think there could be reliability issues down the line and do Laney push el84s beyond their limits ?

The only Lionheart I've worked on so far was simply because someone had failed to solder a joint on a valve socket, the wires were just poked through the hole so they were intermittently not making contact.

Some Laneys aren't well-made and heat can be an issue, particularly the LC15, but that does have PCB power valve sockets. PCB preamp sockets are not an issue on any amp I know of other than some 90s Trace Elliots and Marshalls, and that's because the sockets themselves are crap, not because they're on a PCB. I've come across terrible chassis-mounted valve sockets on at least one Laney (Iommi model) too, although mostly they seem OK.

Under-rated transformers are a fairly common Laney fault too, although I haven't heard of it being a problem on a Lionheart.

Bear in mind that all Fender BF and SF amps have the valves mounted under the chassis, and they are generally very reliable. (As well as easy to work on!)

normula1

I've had a Lionheart for a good few years now. The only problems I've had are the handle surface disintrigating (common fault) and the tolex coming away way underneath the chassis so that it catched when removing the chassis. A bit of gaffer tape fixed that.

ICBM

normula1 said:

the tolex coming away way underneath the chassis so that it catched when removing the chassis.

This is the single most irritating fault with Laneys, to be honest! Not serious in the grand scheme of things, but it can make working on them a real chore. I use a staple-gun on them if I can be bothered...