1974x PT replacement

[foreverstrung]

heres the link. Under the P18RS is a link to the spreadsheat.
https://www.mercurymagnetics.com/produc ... ransformer

[foreverstrung]

Sorry. that link doesn't open up to the P18RS. I'm challenged today posting pics n links

[zaphod_phil]

Don't worry, Mercury Magnetics' transformers are ridiculously overpriced IMHO

[JMPGuitars]

Sorry. that link doesn't open up to the P18RS. I'm challenged today posting pics n links

I fixed it for you. You were missing the first bracket on the /URL...but you don't need to do that manually anyway, you can just paste the link and the board should make it work.

[geoff 1965]

That MM spec sheet does’nt show the HT current rating anyway!
Have you tried contacting Marshall? They are the ones to confirm if 120mA is enough for the 1974X,they are hitting the el84’s hard with the 92R biasing and why do the new upgrades have a 150mA HT?
I agree with ZP on the mercury transformers and if you get the upgrade dagnall it’s a straight swap out for the wiring and peace of mind with the HT,I have’nt seen any negative feedback with the new upgrades also you have to consider if you sell or pass the amplifier on,you don’t want any comebacks if you use a 120mA and it fails!
Tough decision and hope you get it resolved

[foreverstrung]

Thx. I've emailed Marshall and Dagnell. We'll see what's what after they respond. This PT coming today I'll send back. Someone on the Marshall Forum mentioned a Hammond 290PAZ, At least to compare specs as to what to compare too, though this PT has 140mA

https://www.hammfg.com/files/parts/pdf/290PAZ.pdf

[geoff 1965]

That looks better at 140mA,is there any specs printed on the PT that failed?
Quote the serial number of the amp when asking Marshall so they know you are a genuine owner.if any of us tried the “reverse engineering” alarm would go off!
Good luck

[foreverstrung]

I added the amps serial number to marshall. No specs for the bad tranny. it's a a D4909 Dagnall electronics. TXMA 00115 Batch:1294800446

[geoff 1965]

Keep us posted with your progress on this,will be of interest to me and future reference.the amp is nearly 20 years old now so it might be worth renewing the electrolytics while you are in there.

[foreverstrung]

Marshall responded to my email. Sent a replacement tranny out today. I did not expect that.
I'd appreciate any info on installing a PT. Anything easily confused or that can get wired backwards.

[geoff 1965]

That’s good of Marshall,should be just a straight swap regarding wiring,take some pics of the old transformer wiring before you remove it or draw a diagram showing which wires go to which terminal.just ask if you are unsure and post some pics.

[foreverstrung]

OK, so I received a Hammond 290PAZ replacement PT. I'm enclosing some pics before I pulled The Dagnell 4909 PT and then sitting side beside the Hammond. I've got different color wire. I was pretty sure I would.....I'm hoping someones got a spec sheet for the dagnell. As I said, this is my 1st tranny replacement, would like to get it the first time.........Marshall still is sending me a free replacement, but IDK when that'll be here. I've got this one now, I'd like to put it in. Kinda OCD about it now. Any help laying this out would be appreciated.......also, I snipped the wires long from thew tranny

[foreverstrung]

not sure how to post these pics. Help!

[JMPGuitars]

not sure how to post these pics. Help!

Click the "Attachments" tab under message post box where I typed all this text into. You click "Add Files" and you can also click "Insert Inline" if you want after uploading them.

[foreverstrung]

dagnell1.jpg

danall2.jpg

danell3.jpg

These show the Dagnell 4909 PT before I pulled it

[foreverstrung]

hammond1.jpg

hammond 2.jpg

[geoff 1965]

Marshall-1974X-18W-Schematic.pdf

you're quite a bit off! here's the 2004 version of the 1974X schematic for you to study and see where your mistakes are i.e. you can't have both the 120V & 240V pirimary wires going to the switch,the red/yellow HT centre tap goes to ground via the HT fuse,the 2 red HT wires go to pins 1&7 of the ez81,the yellow/black wire is rectifier filament 5V and is not used etc,etc
note someone has been in there and changed the 91R bias resistor to 200R.
see if you can work out the wiring also do the mounting bolts of the 290 paz match your existing holes?
good luck

[JMPGuitars]

The unused wires get clipped and covered with heat shrink tubing.

Why are you using the Hammond if Marshall is sending you a replacement? I would use the Hammond for another build.

[foreverstrung]

Mounting bolts line up perfectly.
No telling when the Marshall replacement might be here. Maybe a couple weeks, IDK, but I've got this one here now

[foreverstrung]

Does anyone know where I might find a Dagnall 4909 PT drawing? I can't find one anywhere and Dagnall has not responded to emails.