Silver jubilee 2550 (50w) transformers

[jmrckr]

Hi,

I'm on the path of building a silver jubilee 50w 2550 clone. I found some good layouts and shcematics ... but I just want to be sure to choose the right transformers. From what I found, I would need a 3.4K or 3.2K primary OT, a 690VCT (at about 200mA ?) PT and a 5H 120 mA choke ... can someone confirm that ? I'm not that familiar with marshall designs, this is my first. But from what I see, it could be the same transformers as a JCM800 ? https://www.hammfg.com/electronics/tran ... cm-800-50w

Thanks !

[wpaulvogel]

Everything is correct that you stated but a plexi power transformer may not have all the voltage taps you need for a Jubilee. I’m not familiar with this amp but I think it has some relay switching and maybe some solid state circuits that require a low voltage supply. Someone else may chime in to give you more information.

[pdf64]

A regular 50W JMP/JCM PT looks like it should be fine, only need HT and heater secondaries https://drtube.com/schematics/marshall/2550psu.gif

[jmrckr]

Great ! Thanks for your answers. I did noticed that there si not fancy tap on the PT secondary looking at the schem. But yes, there is a a relay for switching for drive/clean, it seems like it is powered by the 6.3vac heater winding.

For the output transformer, I found some differences in primary impedences for 2 EL34s depending on the brand (50w). Some are at 3.7k, others at 3.6k (heyboer, and classic tone, don't remember wich is wich) and hammond at 3.2k ... weird. I guess tubes are not that "rigid" regarding the design and still work under different circumstances.

Hammond still make a 3.4k OT but with a different frequency response, maybe I'll try that ... https://www.hammfg.com/files/parts/pdf/1650K.pdf
Or Edcor https://www.edcorusa.com/cxpp50-34k

[timrobertson100]

If you need any measurements taken from an original I'll be happy to do so.

If you are in Europe, I also have some of the original grey tolex if you need some - I think there is enough for a head left. I restored a 2558 that was in tatty condition a while back. Came out like this: https://drive.google.com/file/d/1UfzEIE ... Pn-IDibECb

Please post pics of your build as you go - I am keen to follow it