Metropoulos Forum

Did the old jtm45s all have the same B+ voltage or did they vary? I know the standard for metro 45's are about 400v, but what are the chances every pt was made the same in the 60's? I also see the MM pt trans are about 420v on the metro site. My Mojo 45 kit has about 465v on the B+ with a tube rectifier (about 478v when I use a solid state rectifier ). Did marshall check for things like this back then?

Kyle

There were several different power transformers used over the years that original JTM45s were made (1962 - early 1967), so they probably did vary quite a bit. However, after things became a little more standardized, when Marshall had their own transformers made by Drake, the specs for the 1202-55 power transformer is around 450VDC B+. But even those did probably vary a bit. Typically transformers are rated for +/- 10% I believe...but most people seem to talk about 440-460VDC for a JTM45.

Cool info. Thanks.
Sounds like my pt is only slightly higher than normal .

Kyle

I've heard reports of 420-470v

Kyle, I have the same Mojo kit. I purchased it in 2004 from a musician friend (not Musicians Enemy) who had an amp/tv/electronics repair service and he got it cheap and built it nicely for me. Mine gets a B+ of 462VDC with the Weber Copper cap and 475VDC with an original NOS Mullard GZ34. I changed the filter caps to F&T 16x16ufs and run Shuguang KT66s. I recently tried EL34s in that amp and it cut way down on the overdrive and good tones so back went the Shugs. I really wish I'd have held out for the much better Metro Kit, from what I've heard the PT footprint on the Mojo kits is not the same as vintage or Metro PTs and I think the same goes for the OTs. Kind of stuck with the higher voltage Mojo iron unless you dont mind drilling more holes in the Mojo chassis. Will definitly go with one of the nicer Metro amps soon as the econ picks back up and I get back to work!