Ashdown Fallen Angel Repair 17/1/13
There is a big effect difference between voltage levels that break through the skin conductivity – which happens to be in the 400 to 500V DC range of our amp circuits! BE CAREFUL! Drain the secondary capacitors when the circuit is off and always check the circuit with a multimeter on both AC and DC sides before touching components or working on it – with the mains UNPLUGGED. If the Mains is plugged in, the plug socket and switch contacts are LIVE still, with the switch in the OFF position.
If you are testing the circuit after a change, make sure all your test leads, probes and croc clips are well insulated from your fingers and chassis contact points (chassis edges can be sharp too). I always connect the croc clips and meter and double check. I then plug in the fused mains side. I use the mains toggle switch to power the secondary with the indicator light connected so I can SEE power also, as well as checking the on/off position of the switch BEFORE I plug in the mains. I switch OFF and unplug the mains, checking the meter voltage or current level has dropped to 0V, (or use a drain lead on the capacitors ASWELL) before I move any croc clips to a new circuit point for another measurement.
For the sake of a few extra seconds, why risk safety by not switching off and draining the circuit?
A 240V AC shock will certainly help you not make that mistake again if you ever forget any of this – if you are lucky enough to not get away with it! My last one left my right arm aching for an hour!
A 500V DC shock may mean you don’t get to worry about any of this ever again…but now you know why.
I learned a lot about the more tedious mechanical practicalities of repair with this amp.
The story behind it, was that it was working fine up to a few years back when the owner – who also likes to “tinker” a bit – pilfered the original Celestion (?), the handle and the feet to put on a smaller amp cab he had built from old wine crates.
I’m now not convinced that was the whole story, personally, because of what I found when checking the amp.
The first thing I learned you should always do with none working “spare/repair” buys from Ebay or anywhere, is open the amp and physically look for any basic, obvious problems first.
Burn marks, blown fuses, or re-soldered joints are the obvious and easiest to check for, initially.
If a fuse has blown, you have to consider it may have been more than a surge, and a (possibly) expensive component repair, like a mains or output transformer winding (like the dead Fender Champ I have now). This also means that just replacing that fuse may cause further damage if you just replace it and turn on – but then you have to start somewhere – and the cost/time spent looking over the risks are up to you.
With this amp, I took the prior owner at face value – the amp had worked, but had been unused and moved around a lot since, so the story went. With valve amps, you can at least check each of the valves in other amps first if you have them, as another aid in what you may be up against. You should always look inside first if qualified/knowledgeable enough/happy to do so. It may save doing more damage and you have an idea what state things are in, or if it is even safe enough to power up in the first place. A mains wire may be disconnected, damaged etc. If it is an older amp, looking at the electrolytic capacitors for corrosion or bubble patches etc. is a good idea. Rectifier diodes can be checked in situ, with the diode setting of your multimeter – about 0.7 ohms +ve to –ve direction, no conduction in the opposite direction, across each one.
Anyway, I had already bought a 60W Marshall Marquee speaker on Ebay, which would be perfect for this 40W amp, so I made up a patch lead from Klotz cable with a Nutriks jack on one end, and soldered the other to the speaker connectors. This amp has 3 speaker connection options – 4, 8, and 16 ohm jack sockets – so I connected the 16 ohm Marquee, as valve amps should ALWAYS have a speaker load connected to them when powered to prevent output stage damage, though you can have all volumes turned down and not damage anything in most cases, without a load connected.
Best to get into these good habits – CORRECT speaker load connected and volumes down before turn on. See the Briggs Amp PDF here for a tech explanation.
I plugged in my guitar and I fired it up, with all the volume, gain etc. pots on 0, so hopefully no surges or other unpleasantries would go through the new Marquee. Tentatively I brought the gain and volume controls up, but got no sound for either channel.
Time to look inside. I removed the chassis. This looked like a nightmare to do at first, as it seemed the whole baffle (6 very tight woodscrews) and back plates have to come out to allow for the front VU meter holder to be removed while attached to the chassis. I searched the web to see if anyone had done this, and got dismayed reading Champ Electronics site review of this:
which is incorrect as it goes, as I realised you don’t have to take the baffle right out, just tilt the top and the chassis and front VU meter plastic can be angled back and over the top of the baffle. You don’t have to remove the Benton reverb tank either;
but I like to clean everything on second hand amps – hoover the dust out and wash the Tolex with a nail brush and soapy water, then towel dry.
Once I saw the circuit board looking a bit intimidating, I thought I’d wait for a schematic before doing any serious work, but for now, the immediate thing was a blown fuse at the bottom left of the board:
I went and bought some replacement 1600mA fuses and then the temptation was too much! I talked myself into that maybe it was a just a surge that had caused the blown fuse, so wanted to see if it would work (and it had done supposedly…), as all else looked fine. Unprofessional I know, and stupidly impatient of course.
I turned on again with all knobs off, but I had a big surprise when I got a really loud squeal through the speaker, then silence! A bit shocked by this I turned the amp off immediately.
I decided I should check all the valves first to see if any were (now!) duff. This is where having spare amps comes in handy for those of us who don’t own a £200+ 1950’s valve tester! The Marshall Mercury has an EL84 and the Aston amp uses 12AX7 pre amp tubes (and a 6V6 output, so I checked the Fender Champ 6L6 tube also), so between the two amps I could test all 4 of the Fallen Angel’s Sovtek and 1 Electro-Harmonix 12AX7 valves, and 4 EL84s which were all good except the last EL84.
This is where life got tedious. When pushing the last EL84 valve into the Marshall, it didn’t feel like it was in all the way, and when I looked closer, it had a rubbery silicon type crap round some of the pins:
I removed this crap with a small screwdriver then tried the last valve again but it seemed dead (started wondering if the scream I heard was this valves last dying microphonic breath), but then broke this valve later when trying to put it in the Marshall again after a double check it was fitting properly, due to a slightly bent pin, and awkward floor position looking at the underside of the Marshall with a torch. Luckily I had a spare new JJ from the Marshall project.
Checking the valve holders on the FA also, there was a load of this glue stuff inside pin 6 and 7 sockets of one holder also. As pin 7 is the gate for the valve, a bad connection here means no signal out.
At least it may be the cause of no power valve output. I spent ages digging out bits of “glue” from the valve pin holders and taking the opportunity to tighten them, using a sharp, modified corn on the cob spike and a magnifying glass!
Knowing all the valves were ok, and the holders clean, I tried it again but still had no Ch 1 or power output, and only a low level distortion from channel 2 once turned up quite high, to hear anything at all. It sounded like the pre-amp stage only with no power amplification – really tinny and distant – a bit like the Marshall Mercury had done before its repair (which had lost its pre amp stage 1 of 2).
I wasted a few days waiting after this, as I had read on a forum that Ashdown Tech support are a helpful bunch and had sent someone a schematic on request, so I had emailed requesting access for a schematic, but got no reply so phoned up, and though the test engineer was willing to talk about possible fault causes – test for pot dry/broken joints, test dirty jack inputs etc. – they don’t give out schematics to Joe Public. That’s understandable but disappointing. I searched the web and found one for a 60W anyway, eventually, close enough and better than nothing, so here it is:
Ok, next option? I thought output transformer, as at least its only de-soldering a few wires at worst to check for open/short windings.
This is where it got even more tedious – but an important lesson was learned about tight spade connectors!
These are a great idea for ease of removal of transformer wiring – provided they haven’t welded themselves to the board spade! In wiggling these with pliers, I pulled the spade clean out from the solder on the underside of the board on an OT secondary winding – Doh! – which I think was already a dry joint (so explained the lack of speaker output if true). After a second spade came out too, for the mains secondary windings, I squirted the now invaluable Servisol switch cleaner/lubricant down the shrink covers of the rest, so no more would break –which they didn’t. These were all REALLY tight. Once removed, I tested the windings for continuity and sensible values with the meter, with the experience gained from the Aston build.
These readings are:
Ashdown Transformer Tapped Primary
170.5 ohm Black-Brown
Black (HT +ve)
Red – CT Hi-Tension Tap
Brown (HT –ve)
Blue – Green (earth) 2.1 ohm
Yellow – Green (earth) 2.5 ohm
White – Green (earth) 2.9 ohm
Note this amps OT is centre-tapped at the Primary, as in this 60W schematic, but there are two EL84s in push-pull mode each at HT +ve and +ve side of the centre (red), but this 60W diagram shows only 1 EL34 (higher output) valve, where my FA 40W (2003 model) has 4 x EL84s instead (2 x 20W push-pulls). The rest of the circuit seems to correspond – the transformer wires were correct, and the channel 1, stage 1 components I checked.
Now I was committed to removing the board to be able to re-solder the 2 detached spades to the underside.
This was a pain because all the 13 x VR pots front and 1 rear (FX return level), and 8 jack socket nuts had to be removed to get the board out. At least this gave me a good look at the solder joints. As the channel 1 stage had not worked, I checked continuity from R1 to about R7 and C1 to C11 between components for the first pre amp valve pin connections etc. to its output stage capacitor. I also checked all the VR pot joints and jack connections to the board, which all seemed ok. This was the advice from the Ashdown guy, as the channel 1 stage goes to the FX send/rtn, and he said these jacks can be stuck open circuit with dirt, whatever, stopping the signal going to the 2nd Op amp circuit and transistor in the chain, which then goes to PS_In, which is the gate of a pre amp valve.
Servisol was squirted in all jacks and a plug shoved in and out a few times to clean them off.
I found more glue in another valve holder, and tightened ALL the valve holder pin sockets, and gave them another spray with Servisol.
I felt pretty sure in my mind that the OT spade connector had been a dry joint, so thought I’d try the amp now as all mains and OT transformer connectors were clean, and the valve holders were clean with tighter connections. All this took a few hours but I wanted to be quite thorough before re-assembly as it is a hassle to remove the board because of the VR pot nuts.
The other major hassle was that Warranty protection glue that manufacturers stick to some components so they know it has been tampered with – this was all over the 2 pin VU and LED meter connections which have to be undone else the wires stop the board from turning over. I had to use a Stanley knife then brute force to pull these off. Luckily they still reconnected after even though the bases came right off the board pins, but I wasn’t bothered at this point, about having a gimmicky VU meter anyway. It only moves at full volumes anyway as I found out later – hardly a benefit or necessity for the hassle it causes in maintenance. I know – “Looks Cool…”!
Once the board was back and the mains and OT connectors connected, I plugged in the Marquee and guitar, setting the VRs to 0 of course, and turned on. I was pleasantly relieved when I got a decent sound from the speaker on channel 1.
Channel 2 was good also, and now the reverb too, which had not worked before either. With that, I put it all back in the cab to give it a better sound check at higher volumes without thrashing it yet, as the speaker at least is brand new, and these should have a “run in”period also according to some web sources.
I’m not sure if I like the overall tone of this amp – I was a bit disappointed actually – the clean sound is great, but the overdrive is a bit characterless for me – but I’m probably spoiled by the Vox AD30VT.
The reverb is nothing great either, but I’ll have to play it more yet. I also suspect the push-pull EL84s need to be bias checked, as I added the extra JJ for the broken one ,and the cheaper Sovteks aren’t most people’s favourite on the web either.
I’ll look into biasing later for this amp. I still have to check the FX send/returns and the other 8 and 4 ohm outputs also, but for now – she’s done!
The mains lessons re this fix was just the mechanical side of aging, ware and tare really, with a period of non use. Dirty pots, connectors, dry joints, switches and loose/bad connections can all be causes of failure, when no components are actually faulty. At such high DC voltages and heat with valves, there is bound to be a lot of pin connector oxidisation and other things like contraction/expansion related events (solder joints) to consider and be aware of that may cause issues over time.
Most people also overlook waiting for the valves to cool down before moving the amp about, or waiting a few minutes for the heaters to warm up before turning the standby switch on , or turning on or off with the volumes turned down first. All these can be factors in stressing the valves or the components. If you don’t have valve retainer springs to hold them in when upside down, make sure the pin holders are squeezed together tighter from time to time – DON”T GLUE your valves in if they get loose!!! How will you change them when/if they burn out without MAJOR surgery??
Common sense people…don’t ruin an amp through laziness.