Blown primary of the mains Tx, isolated removed from chassis, draws 1.2 amp at 20V variac "mains" and temp climbs 20 deg C in 4 minutes or so. Secondaries measure l27V, 16.3V and 2V so that side presumably ok. DC of primaries measure 1.2R and 2.2R, would they use 2 bifilar primary windings where stressed midpoint would show half way short and half measured ohms?. I will poke around in the winding/ try delaminating out of curiosity but stock fault/ batch fault ? Other than "marinating" in paint stripper , any tips on delaminating ? Are replacements available from Marshall ? or a grey market source UK ? or anyone use 2 or 3 separate Tx ? Googling Tx model Dagnall, TXMA 00061, D2105 only shows up suspiciously low priced dollar quotes
We get parts direct from Marshall. Used to be a Marshall dealer, but we are not any more, and they still supply us with parts ok, so it must not be a requirement. It may be that you have to be a 'legitimate' business though, and not just 'Joe Punter'.
I've had parts direct from Marshall also. I was never a Marshall dealer, when you talk to their service dept, they soon suss you out as competent or not. Great service and killer 'on hold' music on the telephone ;)
At least its the outer 120V primary at fault and a split bobbin so once the laminations are apart , easy to inspect. Tomorrow I will try a 125W iron concentrating on the central sliver of the first "E". Laid thin ptfe sheet heat insulation under the other 3 slivers. What will be the softening temperature of the lacquer and any guesses as to time of heat application at the exposed end only ? At least I can monitor the other end with a pyrommeter.
I wouldn't have thought so. I would have said that Gareth's estimate was probably not far short of the mark, based on transformers that we've ordered from them in the past. I've always found them pretty reasonable. Just give them a call and ask. They're a friendly enough 'family' company. Jim Marshall's daughter did run spares. As far as I know, she still does.
I've always found them very good - except when they are on stock-take ! Then, you can wait a couple of weeks for your parts ... But yes, in general, anything you need, and very reasonably priced.
The one problem that I have got with them, is that dreadful system of providing access to their service information. I actually find it difficult to use, and to search, and on several occasions, have 'caught them out' with sections of schematic that simply aren't on there. I'm sure they thought it was a good idea to have their service info archive 'front ended' by that Image Bank user interface, and then to give access only to registered (=pre-approved by their service department) users, but every time I go there to download a manual, I just find it an awkward and frustrating process.
A long time ago, I found another Marshall specialist site, and they have an archive of pretty much everything that Marshall have ever produced, right back to the start, arranged by 'class' and date. I always go there first to look for service info, and treat Marshall's Image Bank as a port of last resort. I wish, if they are basically happy to let people have service info, they would just list everything, and let you get it on a one-click download, as other manufacturers do. I can sort of understand that they would prefer to have some control over who they are giving data out to in order to try to preserve a degree of professionalism in repairs to their equipment, but given the fact that they must know that info on every one of their products is already out there for download by the determined searcher, it just seems a bit 'prissy' of them to force this poorly designed service info search and download software on their registered users. They could still restrict registered users to a password protected area on the website, that gave access to a simple list of all the manuals available.
Normal single filament winding. Normal failure mode , for slapdash wound Tx these days. Slipped turn at one end of a layer dropping into a lower layer, then presumably chaffing of lacquer to marginally spot weld. Not at all obvious "weld" point , about 80 turns from lead out of outer primary. 195 turns in all of .75mm wire for one 120V primary. Not a problem here as 240 V use, but would be for this Tx used in USA . There is tape covering the inner primary but not extended at the leadout point of the inner primary so first turn of the outer primary directly crosses that point so a full short is very likely there with a bit of normal in service vibration/ chaffing. For
240V use those 2 points are at near enough same mid-mains potential (2 tails to options bridging point on pcb) At least I now know how to delaminate the E/I iron laminations.
** The turns wound on that transformer do no move or chaff - you wanker.
Those Dagnall power transformers ( TMXA00061 etc) are made with low temp grade enamel coating the copper and the tranny is under sized for the job it has to do - not to mention working in a very high ambient temp from the heat of the output valves.
As a result the windings run DAMN hot, the enamel gets soft and when two soft spots meet under pressure you can get a short.
I have THREE dead ( internally shorted) examples of the exact same tranny sitting here right now.
I would expect it to probably be a ringer for what was already in there. If the amp is really from 1998, then duff construction or not, it ain't done bad, and if the new one does another 13 years, it's not going to come back on you, is it ? And, if in the intervening 13 years since it was made, Marshall have had a lot of them fail, then maybe they've taken this up with Dagnell, and got them to improve the situation ? I would stop agonising over it, and just stick the new one in, and write out the hundred quid bill for the owner ...
Only way to fix the problem is to find someone willing to rewind the original transformer with high temp enamel wire - ie 180C rate instead of the 120C rated stuff used by Dagnall.
Or you could fit a small fan blowing on the tranny....
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