Another JTM45/100 is born

[shakti]

Hmmm, just can't figure this one out. I think maybe it's something I just have to live with. To be fair, my other amps exhibit just a tiny bit of this same phenomenon, it's just more obvious with this amp. May have to do with the high voltages involved, and the proximity of the transformers. I may be able to get my first build back on the bench for a comparison. I'll report back if that brings any new insight.

How are other people's 45/100 builds in this respect? If you turn down all the tone controls except the bass (to get rid of the hiss), and crank the high treble volume to 10, do you get any hum?

[JimiJames]

hmm. well, it might well be a charactoristic with the orientation of the trannies like you say but, hopefully with your last question someone will answer this. I would like to know too, because this build is on my list for next year...

[Roe]

my 66 45/100 is pretty quiet. my 67 with el34s is probably the most quiet amp I have (out of 17). the metro 1203-80PT in my 1959 hums but the marstrans are pretty quiet

[shakti]

My Black Flag amp is also very quiet, and one of the reasons why I'm puzzled by the hum in this amp. It's dead silent at idle, and only above 8 on channel 1 it is noticeable (and the bass has to be turned up as well).

Which way do you have your PT turned, Roe? And I assume you're using the 490V secondaries? Mine runs on 560, which may be part of the reason?

Another thing to consider is the orientation of the OT. I have the primary side closer to the PT, which I believe is what the originals had. My previous amp was the same in this regard.

[Roe]

I think both the 66 and 67 have the 1204-43 turned the right way. I'm using the 490 secondaries and the 230v primary with the 66 and 240v primary with the 67 el34 amps. the former has 510v on the plates, the latter 495v. btw, the new genalex does not handle 560v, they tend to redplate

[shakti]

Sorry, what do you mean with "the right way"? If you check the photos at the start of this thread, do you have the PT oriented the same way, or 180 degrees around?

[Roe]

sorry, I mean the same way as shown on the first page here: with the heather taps oriented towards the front, not the back