JTM45 RI conversion

[PaisleyTube]

What's the B+?

Most reïssues I've seen were way below 400 Volts while a couple of real/old JTM45s were around 450 Volts....

Hi Chris! How are you?!

See my first post.

Pretty good.

Voltage: Kinda low ( but correct for a reïssue), the amp becomes much "larger" imo with a higher/"correct" B+

[Roe]

What's the B+?

Most reïssues I've seen were way below 400 Volts while a couple of real/old JTM45s were around 450 Volts....

yes, original voltage charts show 440 and 450v. I looked at one original recently that had ca 450v, depending on bias. most originals used the 1k flying resistor, but the RI omitted it, leading to screen voltage exceeding plate voltage

+1
+ different filtering

Is the choke right after the ot-centre-tap or in front? did forget to check that and/but the old schematics are pretty unclear to me regarding that.....

tia!

one schem shows CLC filter (before OT), but all known jtm45s seem to have the choke between OT and screens. only the latter has the right sound

[PaisleyTube]

Thanks!

It was a '65 or '66 I did measure, all voltages did match the schematic but I didn't look at the choke-position at that time....

Again: thanks!

[BIG Dave]

I have a JTM45 RI that I changed the filter caps to 16x16 and 32x32, then put in all NOS glass consisting of Mullard pre's and GZ34, and GEC KT66. Matched it up with a JCM800 2x12 (model 1936) loaded with Celestion Blues. Sounds pretty darn good so I'm done (for now).