The Amp Garage

I've been working on a 5b3, which is the same output section. I bumped the cathode resistor up to 270, then to 300... the dissipation didn't change significantly. Hence the term "auto-biasing" in reference to cathode bias. You can raise the resistance, but you're just going to see a bigger voltage d...

One other thing I should note. When I was about to mount the PT in the new location, I noticed that the mounting screws were designed to sandwich the laminations with a nut/star washer, and that all the nuts were loose. So I tightened all the nuts, and tried the headphone trick again. Jeez, it's ama...

Here's my issue... obviously moving the OT away from the PT lessens the noise. Changing the orientation helps a bit too. Problem is, even at the far end of the chassis, in the best orientation, there is noticeable line noise. Is there something else I can do to isolate them? Can you not find a diff...

Firestorm wrote:Fender were also masters of killing one hum by inducing another (out of phase).

Humbucking amp... I like it.

You'll see a lot of amps built by really good builders that have the PT right at one end, and the OT in about the middle of the chassis, so that's a pretty tried and true setup. Sometimes I end up with the OT being at a 45 degree angle, and I just go with that, even though keeping it at a 90 degree...

Have you considered trying new 6SC7's? These tubs can be quite noisy all by themselves. My guess is that if you separated the transformers - from end to end - and the noise is still there, the tubes might be the culprit. Just food for thought. In this case, not the tubes. There are no tubes install...

If it's truly the coupling of the transformer fields, only distance and orientation (plus, maybe shielding) can help. But noise may be radiating from the connections on the line side and the HT side. Marshall put 0.22s to ground on the HT side; Fender used only a single "death cap" on the line side...

On all smaller chassis, I cannot move the two transformers far enough apart to get zero noise out of the OT. Only on 24" chassis can I move it far enough. Not to worry, though. A very low amount of hum is present in all builds, and disappears below the noise floor on decent builds. Great observatio...

For about a month, I've been working on a vintage 5B3 that came to me in parts. It had a lot of ugly when I got it, including transformers that were replaced sometime around 1960 or so. They are not the original spec transformers, but would have gone into a Brown Princeton at that time. Pretty nice ...

Wow! Nice job on the tweed. A lot of guys use Bullseye amber shellac to tint the tweed. To my eye it looks a bit on the brown side so I would cut it more than 50% with denatured alcohol and try to sneak up on the desired tint. Also, you can go over shellac with lacquer if you want a more durable fi...

Got done with the cab work last night. First time I've ever done tweed; it's not perfect, but it came out better than I expected. Seeing a somewhat finished product has energized me to finish dealing with the cruddy electronics that are inside. I also need to figure out how to hit it with some amber...

Thanks guys-think I've got the right direction here. This amp does not have original transformers or speaker, and about 1/3 of the components on the board needed to be changed. The original push-back cloth wiring looks pretty deteriorated. I'm also in the process of replacing the long-gone tweed and...

Here is a gut shot, FWIW. You can't see it in the pic, but there is only one heater wire going from tube to tube, not a twisted pair.

[img764]http://i305.photobucket.com/albums/nn20 ... 69ccd7.jpg[/img]

It may be obvious if there's only one heater wire going from tube to tube, rather than a twisted pair. But before messing, bare in mind that improvements to the heater arrangement will only reduce noise from the heaters, ie 60Hz hum and possibly buzz. It can't help with 120Hz hum from the B+, or hi...

The two 100R resistors create an artificial center tap which centers the heater AC voltage around whatever the junction of the resistors is tied to. The simplest thing to do would be to put one 100R from pin 7 and one from pin 2 to pin 8 (cathode) on one of the output tube sockets. You could try it...