Page 1 of 1

JTM45 Up and running

Posted: Tue Dec 20, 2011 4:33 pm
by mercerism
Amazing sounding amp.

used the Metro amp instructions.

Used Magnetic components xformers from Triode. good company!

Big B+ voltage of around 464v. i earlier posted that it had been at 485v but that was before the Kt66 was added.
Rocking a bias of 38ma on one Kt66 and 45ma on the other using a 100k 2 watt resistor as my bias resistor.

Lots of voltage to the ecc83s too. Maybe too much. 20% above spec.

used JJ 32uf+32uf cap
used ARS 16uf+16uf cap
used Valve Art KT66
used Harma ecc83/JJ ECC83 and some other Ecc83
used Sprague Atom 16uf 475 cap and 8uf Sprague Atom caps
Used sozo caps
Used 1w carbon composite resistors where needed.
no allen bradley nonsense.

I have a 1961 vox Ac30 and this Marshall sounds every bit as good through a Marshall 2 12 cab with Celestion Vintage 30 speakers
wired for 16ohm,

Loving this amp so much. Very Fender. Very Fender sounding.

Thanks everyone

michael de a :jimi:

Re: JTM45 Up and running

Posted: Tue Dec 20, 2011 6:56 pm
by mathd
Try having a hot bias (70% maxplate dissipation MAX) this will help reducing the B+ voltage a few volts.
For 485 V its a max of 36mV.
The valve art can handle that voltage/hot bias, just make sure the caps are not overvolted(at least 500v main cap rating not 450v).