The Amp Garage

So with the tubes out I have a nice, stable -46v on the bias. With the tubes in it drops to less than 1 volt. I take it this means tube failure?

I would also put my meter on the bias voltage and vary the bias pot to see if it changes smoothly with no drop outs along it's rotation.

Thanks to all of you for your help. When I get home from practice tonight I'll pull the output tubes and check the bias voltage, then report back.

I took an old Bandmaster Reverb head I haven't used in a year or so to band practice a couple of nights ago. I never really liked the sound of that amp but for whatever reason is was sounding great this night.....until the last tune when one of my bandmates said "Do you guys smell something burning?...

There has been quite a bit of discussion on the Steel Guitar Forum about the Little Walter amps now favored by a number for Nashville A-listers including Paul Franklin and Vince Gill.

http://bb.steelguitarforum.com/viewtopi ... sc&start=0

I building a Dumbleator using Structo's schematic based around the Fender reverb power transformer. My question is: Should I ground the nodes of the power supply separately (one at the preamp ground and one at the main ground), use one star ground for the power supply and preamp, or ground the power...

Thanks for the replies guys. I found an article in an old Vacuum Tube Valley magazine where there is a quick mention of the fact that Tesla made some xf-1 knock-offs with a wide base and everything. I've also seen pictures of Teslas with the same kind of overlapping halo getters. Who knows? Anyway, ...

I picked up a pair of lightly used "Mullard" xf-1, large base EL-34s at a local electronics surplus shop VERY inexpensively, and I have my doubts that they are the real deal. They do sound fine in my AX84 build. The most obvious thing that makes me suspicious is that the silkscreening doesn't rub of...

I bet the Adjust-A-Volt has a pretty high build quality.

http://www.edcorusa.com/p/429/cxpp25-ms-8k

Looks like a nice fit for a half power rocket. Anyone used this one?

Thanks for the encouragement. I just took the Rocket to band practice for the first time and got to hear it in context with drums, bass, and keyboards. The tone is better than I could have hoped. My bandmates were impressed! I'm really pleased with the sound of the Hammond 1650n but I don't have any...

Thanks for the reply Rooster. I certainly am under no illusion that I have figured out something new in grounding the center tap to the top of the power tube cathode resistor! Perhaps I didn't make it clear enough that I had de-soldered and wrapped the center tap and used a pot to make an artificial...

Thanks for the replies. I'll try it again. With my signal generator set at 1 Volt and 600 Hertz I attached the the leads from the signal generator to the leads from the transformer that attached to the plates of the tubes (the primary right?). Then I measured 26 Volts AC on the output (secondary?) s...

For the record: In my rocket build I used RJ's em0708 power transformer, which has a center tap for the filament winding. Originally I used the center tap and grounded it to the top of the cathode resistor of the power tubes. The amp had a slight to moderate hum. Tonight I removed the center tap, in...

Finished off my first Rocket today and it sounds better than I could have imagined. Very detailed and dynamic. I put some of the filter caps on the board and used a 32/32 can cap for the first filtering stage. The PT is an Edcor from RJ and the OT is a Hammond 1650N. I grounded the preamp stages to ...

Hey guys, I have a fairly hefty output transformer pulled from a Hammond that I want to do something with. I used a signal generator to measure the turns ratio and figure out the primary impedances at different frequencies. At frequencies from 100 to 1K, the primary impedance would be 2.7k into 4 oh...