The Amp Garage

Since 2010 started out a very slow year for amp customers, I had lots more time to tinker. I wanted to try to build a 2xEL84 Rocket in a small (12" x 6") chassis. So I built and changed and whatever, but just wasn't happy with it. For reasons I can't recall, I had, at some point, bought a Hammond 26...

Thanks for your kind words. I work with lots of vets.

My dad was Air Force, and when we were in Taiwan in 68 - 70, several families we knew PCSed home without a dad.

I invite y'all to check out my new video on youtube. The words/music are mine, and I've got friends singing and playing bass, drums and organ. http://www.youtube.com/watch?v=bnyuGP2bpUc I did this to honor our men and women in uniform and to benefit the Wounde Warrior Project. The electric guitar pa...

I had an amp I built a couple of years ago come in with nasty hum. It turned out that the cathode resistor on one triode--the V2a--V2b was the cathode follower-- was the culprit. I replaced it and the amp was quiet again.

Interesting problem. I had a Tiny Terror come across my bench that had suddenly developed really bad 120Hz hum. It hummed even without the power tubes. In this case, with the power tubes pulled, the only electrical connection to the OT is the center tap. So this means that either a. the noise is cou...

OK, I learned something already. On page 93 of the 1967 RCA manual, figure 126 shows why some Hammond transformers have a center tap on the rectifier filament winding--that can be the HT output tap, rather than one of the cathode pins.

Must fill brain with more tube stuff.........

I love the opening sentence of the 1967 RCA manual:

"The electron tube is a marvelous device."

Couldn't agree more!

Very cool books. Thanks a million for the link!

If that speaker, dated 36th week of 1956, works well, it's probably worth some nice cash in that pristine condition.

It could find a nice home in an amp whose speaker was done in by the flood in Nashville, for example.

My approach to using T-nuts is to slightly countersink them, as suggested, but I put a dab of 5 minute epoxy under them to hold them for ever to the wood. Then if you want a really smooth outside, use a bit of bondo after the epoxy is set.

After messing about some more, and doing more careful tube substitution, it turns out that one of the 6550s is quiet, the other hums, no matter which socket it's in. So now I wait for the owner to give me with word to order new tubes. He has some vintage RCAs in there, so it's too bad one of them we...

My bad on the nomenclature. The sticker on the back says MK II.

Thank you all for your suggestions. However, filter problems would not manifest themselves on only one socket. I will check the cathode ground and the grid load resistor ground.

One more thing.

The noise is there even with no 12ax7 in the PI socket.

So my choices of source are:

--bias
--ground
--screen
--coupling cap from PI
--??

I'm working on a 1974 Marshall 50 watt super lead that has, at some point in its life, been modded to run 6550s. A couple of months ago I recapped the amp, it it was working fine. Now it has a nasty hum--dark. like 120 Hz. All the caps check out fine, as do the tubes. Here's the thing: The noise is ...

On your filters, remember that the Lightning runs the plates at about 350 VDC and has an extra dropping resistor of 22k to a 33 mF cap in order to drop the screens to around 250 VDC.