Tube Amp Archive

...to say how frigging great this place is. (so far ) I really got some top notch, practically one on one assistance with an issue I had with a first build over the last couple days.

Well, It's fixed!!! Between all the lead dressing, and tidying up, I've got it dead quiet with reverb! The thing I think did it was, I moved the filter cap grounds off of the damned reverb transformer lug! (DUH!!!) over to the PT lug. Quiet as a mouse!! I really want to thank you guys for all that h...

I'll redo my heaters. The twisting was a pain, so I admit, I gave up after V2. The tank is still connected. I only heard the station when I touched the probe to the pin. It's a local FM station. 100,000 watts and 35 miles away...

On Pin 3 I have 1.2V and a classic rock station...

[img:512:360]http://i272.photobucket.com/albums/jj16 ... 2707-1.jpg[/img]

Pin 1 = 144
Pin 6 = 143
Heaters = 6.0

[img768]http://i272.photobucket.com/albums/jj16 ... 134524.jpg[/img]

Sorry, the 377 was a mistake on my part. My PV is 347. Before all this biasing crap (I could shoot myself), I had an absolutely quiet amp. I could DIME bothe the volume and the reverb and there was no hum. There was a vibrato tick, which I handled with a lead dress issue. I did the biasing rigamarol...

I just spent about an hour dressing up and shortening leads, undid the bias test points and reconnected pin 8 of the tubes directly to ground, set the bias to exactly 70% (.7 * 14/347) made no difference at all... Could I have a bad reverb tranny?

I drilled 2 holes over by the power cord, installed two non-isolated RCA jacks, each with a 1 ohm, 1% resistor from its tip lug to its ground lug. Soldered a lead from pin 8 of each tube to a jack tip. I use an RCA cable broken out into two "banana" plugs to plug into the test meter for biasing.

everything seems OK there. Cables are good according to meter. Tank seems fine. Does it without the tank cables connected anyway. I have noticed that the lead from pin 7 to the place under the board where the grid resistor? is soldered is VERY microphonic and gets scratchy and makes the buzz louder ...

Yeah, shorting straight to ground from the grid (pin 2) shuts it up. (well, makes it "fine with me").

Pretty sure its the reverb circuit, pretty sure it's not the pan. Specifically, the reverb recovery circuit. Did you see Martin's suggestion to see what happens when you ground the grid on that triode? You can just short the ends of the 220K load resistor. Whether that shuts it up or not will be si...

Stand by...

Structo wrote:So you are positive this is coming from the reverb pan and not the power transformer?

Pretty sure its the reverb circuit, pretty sure it's not the pan.

Good strategy. What about the 220k to ground from the reverb recover tube's grid? Is that well connected and grounded I "chopsticked" the entire board yesterday, and all seemed well. No microphonic or loose parts. Wfhen I get home today, I'll check again with more concentration in the reverb area. ...

Firestorm wrote:Let's completely isolate this. Disconnect the in and out cables from the chassis and disconnect the footswitch and tell us if it still buzzes.

...yep