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

ecc83

I can see that for the one man band repair guy (JPF) and the fact that you techs are fixing products with the same function but of vastly different first cost (whether that cost is justified or not!) charges have to be somewhat more flexible than the bog S domestics guy.

The thing was  the "telly man" tended to be well known in his locale and people soon started to compare repair prices for what THEY thought was the same fault on very similar products. Then, guitar amp owners are, as said, generally attached to their kit and WANT it fixed and back. People with a second portable telly are not so fussed* and you often never see them again!

Time wasters are another problem. They want chapter and verse as to what MIGHT be wrong, how you are going to fix it and how much it will cost down to the last 2p. Hit them with a £20 charge up front and they piss off rapidly!

The design faults issue is really down to the very low cost of modern electronics and the emergence of the "pile 'em high, sell 'em cheap" Magnet type stores (yes chillen, we had cost slashers WAY before the infernal net!) . Back in the day companies would have an army of Technical Liason Officers scouring the country. These guys (promoted from years in off prod line servicing) would rock up every 3 months or so and go through fault trends and there would be a constant feedback loop twixt dealer and factory. Yer Pays Yer Money!!

*And EVERYONE should have a really solid, really legally sewn up "disposal of goods" policy.

Dave.

equalsql

Telejester said:

When I see pcb's with valve bases mounted on them I know it's an amp to avoid.

Not when it comes to Blackheart amps. Their PCBs use thick copper and there well designed board layouts have made then very popular with modders.

jpfamps

equalsql said:

Telejester said:

When I see pcb's with valve bases mounted on them I know it's an amp to avoid.

Not when it comes to Blackheart amps. Their PCBs use thick copper and there well designed board layouts have made then very popular with modders.

The problem with PCB mounted power valves is more an issue of the consequences of arcing between the pins, which thicker copper traces doesn't help you with.

jpfamps

ecc83 said:

I can see that for the one man band repair guy (JPF) and the fact that you techs are fixing products with the same function but of vastly different first cost (whether that cost is justified or not!) charges have to be somewhat more flexible than the bog S domestics guy.

The thing was  the "telly man" tended to be well known in his locale and people soon started to compare repair prices for what THEY thought was the same fault on very similar products. Then, guitar amp owners are, as said, generally attached to their kit and WANT it fixed and back. People with a second portable telly are not so fussed* and you often never see them again!

Time wasters are another problem. They want chapter and verse as to what MIGHT be wrong, how you are going to fix it and how much it will cost down to the last 2p. Hit them with a £20 charge up front and they piss off rapidly!

The design faults issue is really down to the very low cost of modern electronics and the emergence of the "pile 'em high, sell 'em cheap" Magnet type stores (yes chillen, we had cost slashers WAY before the infernal net!) . Back in the day companies would have an army of Technical Liason Officers scouring the country. These guys (promoted from years in off prod line servicing) would rock up every 3 months or so and go through fault trends and there would be a constant feedback loop twixt dealer and factory. Yer Pays Yer Money!!

*And EVERYONE should have a really solid, really legally sewn up "disposal of goods" policy.

Dave.

Valve amps are verrrrrrrry mature technology.

There, in my opinion, is no excuse for design faults in a modern valve amp.

Virtually all the faults I see in modern amps would have been cost neutral to solve if some more thought had been applied at the design stage. 

re "timewasters" or "weakeners" as we call them, I've learnt to politely decline their custom. In my experience someone whose first interaction with you is to demonstrate how little they want to pay you aren't the type of customer you want.

ICBM

Today's repair… Engl Powerball V2.

Unlike any other valve amp I've ever come across, part of the B+ chain is regulated by a stack of Zener diodes, fed from a large (5W) but relatively low-value resistor (I think 2K2, but the print has almost completely burned away and there's no easily available schematic for this version) - ten 33V Zeners in series to give 330V. So… when one of the Zeners fails, what happens? The voltage drops by 33V, which increases the current draw through the chain and makes the others overheat. So then another one dies… and another… and another… and another. By the time it's down to four left, the resistor is dissipating about 25W and so dies too.

What's so stupid is that this lash-up is completely unnecessary - if, like every other valve amp I know of, they simply used the current draw of the preamp valves through a *larger* resistor, they could achieve exactly the same voltage drop with only one component and no cascade-failure mode. A quick calculation and a test value showed that a 15K resistor gave exactly 330V, as before. The resistor dissipation is 1.25W, so a 5W is a very reliable near-overkill choice. This solution would also have saved the cost of ten diodes.

Next problem - all these components are on the underside of the PCB, which is impossible to remove without undoing a lot of soldered connections and glued-down wires. Oh joy. Except that, since I was simply removing and not replacing the blown diodes (which had burned their traces anyway), I just heated the joints and let them drop out of the board underneath, shook them out of the chassis and then fitted the new resistor on the trace side, which was easy. That saved me a great deal of hassle, and probably the customer at least £50.

I have no idea what they're thinking really.

jpfamps

I'm not a fan of shunt zener regulators.

I expect the thinking behind this is that this would give good regulation of the HT in the pre-amp, and is probably a product of some SS engineering mindset, as the HT to the pre-amp does not need to be that tightly regulated.

Regardless, if you did want to regulate the HT to the pre-amp then a simple MOSFET regulator would have been a much better choice.

ICBM

jpfamps said:

I expect the thinking behind this is that this would give good regulation of the HT in the pre-amp, and is probably a product of some SS engineering mindset, as the HT to the pre-amp does not need to be that tightly regulated.

That's what I thought too. The only rational explanation I can think of is that because this amp has a daft standby arrangement which leaves the HT fully on, when the amp is first turned on the following 450V-rated cap is briefly subjected to 470V until the preamp valves start to draw current… but this is also far from unusual and is not a major cause of cap failures (though not totally unknown).

jpfamps

ICBM said:

jpfamps said:

I expect the thinking behind this is that this would give good regulation of the HT in the pre-amp, and is probably a product of some SS engineering mindset, as the HT to the pre-amp does not need to be that tightly regulated.

That's what I thought too. The only rational explanation I can think of is that because this amp has a daft standby arrangement which leaves the HT fully on, when the amp is first turned on the following 450V-rated cap is briefly subjected to 470V until the preamp valves start to draw current… but this is also far from unusual and is not a major cause of cap failures (though not totally unknown).

Yeah that might be it too, although there are better ways of dealing with this.

Even if the amps has standby switch which kills the HT, you have to assume that the amps at some stage will be energised with it in the play position, so in my opinion it's good deign practice to ensure that all the electrolytic caps are rated for the full unloaded HT voltage.

If this looks like it will break the bank on capacitor expenditure, then you can always reduce the HT voltage from the mains transformer. This will also make the amp a bit more reliable at the expense of a few Watts, which in my mind is a good trade off.

ICBM

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!

jpfamps

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!

Proof that German engineering isn't always great......

Them and Hofner!

Misty

How are the modern Supros from a construction point of view? I see they are all PCB based, and with the valve bases PCB mounted as well. Even from a layman's perspective, with the valves hanging down from the chassis wouldn't there be potential issues from the heat they generate? Has anyone here worked on one?

jpfamps

I've only had one in, and it was a pre-amp valve failure so nothing major.

Any amp with the valves hanging down under the chassis is not ideal from a heat point of view, although virtually all Fender amps have been using this arrangement since the 50s, so it's manageable. 

Build quality seemed fine, although I've not had to remove the PCB in a Supro yet. This is often the main gripe techs have with PCB amps.

PCB mounted power valves can cause issues, eg in the Blues Junior where the solder joints to the PCB can fail due to heat.

In the say the Blues Deluxe the PCB mount power valve sockets have long mounting pins on them so less heat reaches the PCB.

Misty

jpfamps said:

I've only had one in, and it was a pre-amp valve failure so nothing major.

Any amp with the valves hanging down under the chassis is not ideal from a heat point of view, although virtually all Fender amps have been using this arrangement since the 50s, so it's manageable. 

Build quality seemed fine, although I've not had to remove the PCB in a Supro yet. This is often the main gripe techs have with PCB amps.

PCB mounted power valves can cause issues, eg in the Blues Junior where the solder joints to the PCB can fail due to heat.

In the say the Blues Deluxe the PCB mount power valve sockets have long mounting pins on them so less heat reaches the PCB.

Much appreciated, thanks.

Telejester

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.

shaunm

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.

It wasn't one of the made in China ones was it?

ICBM

I'm going to add another couple to the List Of Shame, two totally different amps but for exactly the same reason.

Fender Acoustasonic 30
Roland D-Bass 210

In both cases, there is a bundle of cables which runs from the amp section through the floor of the chassis compartment into the speaker compartment. In both cases, there isn't enough slack on the amp side to pull the chassis out of its slot to work on it. So you have to take the grille off, one of the speakers out, and undo the connections. And then you find that...

In both cases, the hole in the cabinet where the wires pass through is not only plugged but glued up very thoroughly - especially on the Roland. This makes undoing the cables and passing them back through so you can take the chassis out *extremely* difficult, without damaging anything - even if it didn't look like about a hour's work.

I did manage to undo the Fender - although I then had the joy of taking the PCB out of the chassis (which is the usual big job) to replace one pot, and the reverb unit turned out to be buggered as well… which is in the speaker compartment, but at least that was already open.

With the Roland I took off a cooling grille and managed to see far enough inside to confirm it as a switch-mode power supply (the amp just doesn't power up, so it's probably this), at which point I gave up and told the owner to take it to a Roland dealer, since even if I got it apart I would probably not be able to fix it anyway.

I would strongly suggest not buying one of these, which is a shame as it looks pretty well-made otherwise.

jpfamps

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.

ICBM

jpfamps said:

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.

They're certainly not difficult, unless the board has caught fire!

And the one of those I had to do recently, the owner simply bought a replacement board from Rat Mods, so that was very easy...

normula1

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?

DJH83004

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?

I think it is more to do with the volume of Blues Juniors that are out there, and yes there are a number of common problems with them, but once you have repaired a few, you can pretty much go straight to the problem, especially if the valve socket board has caught fire as per IC's previous post, which occasionally does happen