Hacker Cavalier Loud Noise

[ricksteptoe]

I've just been overhauling an AL35 amp and discovered an interesting fault which may be relevant. While gently re-forming the reservoir/smoother, which I do in circuit with my trusty Heathkit power supply, I found that something broke down at approx 220 volts. This was eventually isolated to one of the ECL86's, which was happily sparking at the top of the main structure, and occasionally at the bottom as well. The flashover speed was voltage dependant and would obviously give rise to a loud crackle/roar as described.

I have never come across this before, and have always found EC86s to be reliable in the past. Hope this is of some help.

Rick.

[Station X]

C14 appears to have been a 100pF, wax coated, silver mica capacitor in which case it probably didn't need replacing in the first place.

[Nickthedentist]

Originally Posted by martinpinner

Thanks. Could you identify the type of C14 capacitor. Is it a silver mica and what voltage.

Regret that it doesn't say in the parts list. It's in the feedback circuit, so I'd be surprised if it had much in the way of voltage across it.

The original may well be one of those Lemco mica "slabs" as in the pics Michael and I posted. I'm sure an axial, polystyrene translucent modern one would be fine as a replacement.

Sorry, crossed with Graham.

[martinpinner]

Thanks to all. I note the problem with the valve and if I still have the issue after I have refitted/fitted all the necessary resistors and capacitors I will investigate. I have ordered the caps/resistors that are missing and located a 100pf 630v polystyrene capacitor for C14 as this is one of the missing caps.I will practicing my soldering and then start again.Obviously any more problems I will be back looking for advice being a "Novice". I am sure you will all look forward to that. Martin.

[Nickthedentist]

Martin, a few soldering tips:

Use traditional tin/lead solder, NOT lead-free.
Use flux-cored solder designed for electrical work, not plumbers' solder which needs extra flux.
Apply the solder AND the iron to the joint at the same time, keeping the iron touching both the tag and the component lead, and gradually adding more solder until the solder flows around everything and you get a nice shiny joint.
Remove the iron and solder, then leave well alone for few seconds until the solder sets.
A soldering iron of 25-40 watts is about right for this kind of work.

Good luck,

Nick.

[martinpinner]

Thanks for Tips.

[Station X]

Make sure there's always a coating of solder on the bit. It's that which conducts heat from the bit to the item being soldered.

[Nickthedentist]

Yes, and that the bit's nice and clean before you "tin" it or coat it with a thin layer or solder. A wipe on a slightly damp sponge usually does.

[martinpinner]

Just to clarify the fitting of the capacitors with the correct polarity. I note that on the component layout there is a + and - marked by C8 capacitor. Does this denote the polarity of the rail or just C8. Also is it only electrolytic capacitors that need fitting with the correct polarity.

[Station X]

Originally Posted by martinpinner

Just to clarify the fitting of the capacitors with the correct polarity. I note that on the component layout there is a + and - marked by C8 capacitor. Does this denote the polarity of the rail or just C8.

Why not look at the diagram in post #40?

Also is it only electrolytic capacitors that need fitting with the correct polarity.

You're unlikely to find modern non-electrolytic capacitors with polarity markings, so the question doesn't arise.

[martinpinner]

Thanks but I do not understand circuit diagrams. I was hoping to be able to change components based on how they were originally fitted. However I have messed up by not taking into consideration the polarity of the capacitors. From the information I have been given by forum members I now understand how to identify the polarity of the old components. Based on how these were originally fitted I believe the Tag rails are as identified on the component. However, based on previous information given with regard to the incorrect fitting of some of the capacitors this is in conflict with this.I was therefore seeking clarification as to whether the + and - denoted on the component list was relative to the complete rail. I will fit the capacitors on that basis. Thanks.

[Station X]

As a general rule, in valve circuits, electrolytic capacitors have their negative terminal connected to the negative rail or in this case the chassis which is the same thing. In the case of this player the negative connection is made via the fixing screws which hold the tag strips to the chassis.

There are exceptions though. For example in this player C3's connection to the negative rail is via the 100R resistor R5.

As regards reading circuit diagrams you should learn to do this. If you look at the circuit for this player you'll see that C8, C11 and C12 all have an earth symbol (three lines) shown on one end. This denotes a chassis connection. This is done to avoid cluttering up the diagram by showing these capacitors connected to the negative rail.

[martinpinner]

Thanks very much for your continued support of information.

[martinpinner]

I have now fitted the capacitors correctly and also the missing capacitors and resistors. I no longer have the loud noise but no volume at all.I attach a photo of the components as fitted. Any help would be appreciated. Thanks.

[Station X]

Are you sure the four blue identical electrolytic caps are the right way round? I think the negative ends should all be at the bottom of the picture. C3, C5, C9 and C10 I think.

[Lucien Nunes]

Agreed, C3 & C5 are reversed. Something strange about the larger electrolytic lying parallel with the tagstrip too, I can't see anything connected to its positive end. It's not on the layout drawing and if the dual section can is still in use, the reservoir, smoother and decoupler are all accounted for. Perhaps there's a wire link I can't see but which cap is this?**

Martin, your best bet now will be to post DC voltage readings from all pins except 4&5 of the ECL86s relative to the chassis. Take care when probing with the power on, pins 3 & 6 will have a few hundred volts on. When testing a faulty amplifier, it is first helpful to establish that all the DC conditions are correct, i.e. the voltages and currents that obtain in the absence of audio signal, because the valves will not function correctly without them and could be damaged. Once this is proven, if there is still a fault it is probably within the signal path and can be traced sequentially along the amplifying stages.

**E2A Looking at Nick's pic it seems to be C11, but in Martin's pic there is a red lead heading away from the tagstrip past the OPTX as though it were going to C11 in the dual-section. Puzzled!

[Station X]

The picture in post #50 shows a wire running from the positive end of the horizontal capacitor to......somewhere. Without knowing which cap it is I can't say where the wire goes to.

Were I able to read the colour code on the two resistors at the extreme left hand end of the tag strip I might be able to give designations to the other electrolytics.

[Station X]

OK. Got it.

The vertical capacitor at the left hand end of the tag strip is C8 and is specified as 8uF, the 10uF?? fitted will be OK.. I say this because it goes to one end of the 10k resistor R10.

The horizontal capacitor is C11 50uF. A wire is needed from its left hand +ve tag to the junction of R10 10k and R15 1.5k

[Lucien Nunes]

They are R15 (1.5K) AND R10 (10k), C8 is next along. C11 & 12 are supposed to be a dual section out of shot to the left, to which the orange and red leads passing the OPTX seem to be destined. All this looks OK, but that other cap seems to be a misfit. In Nick's chassis it's tied to the junction of R15 & R10 hence is C11, as an alternative to the smoother section of the dual.

Martin, when you fitted the dark blue cap parallel to the tagstrip, which component were you intending to replace?

Oops, posts crossed, what I was getting at was that C11 already seems to be present in the dual can out of shot, as per the layout dwg and the wire leading towards it. Hence, a wire-ended C11 is redundant, and from what I can see, not even connected.

[martinpinner]

Thanks. With regard to the capacitors negative being connected along the bottom rail. Based on information on how to fit them with the correct polarity. I have fitted them to the chassis(negative) via the fixing screw where appropriate and having read from the component layout that the rail at the bottom is positive!!! fitted the others to the top rail(negative) .Obviously this is wrong and I will correct this. With regard to the capacitor running parallel with the rail. I fitted this based on photo's seen on the forum but now believe that this relates to the GP42. I will remove this and then see if get the volume back.