Tube Amp Archive

Thank You! Since the chassis/cabinet layout was so different than the original I just tried hard to make it "period correct". Although I'm no industrial designer, it was great fun and I think it came trough with the '50's vibe. Particular thanks to you, Ian. Your "GA50 Aspirations"" posts (2017?) an...

Promised I'd post finished pictures.... Couple developments; Went with Weber alnico 12" and 8" per original GA50. Sound was good before with the old Fender Blues Junior speaker. Now it's fantastic (at least to me). Interior temperature was getting a little warm after I put the bottom on the chassis....

Hello... Some unexpected developments but, a good outcome. :D While I was waiting for my filter caps I went ahead and built a small board with the pre-amp output circuit. Everything from V1, P8 to V2, P1. Pic is below. It didn't help but, it pretty much eliminated that part of the circuit as the cau...

Hey Gang... Ordered caps. Extras for some spares. Two 47uf & four 22uf. Plan is to replace the two 10's with 22's first and evaluate. Pulling the 6SN7 kills the 60Hz. So my thinking is that it is not coupling between the PT and OT or anything down stream. I think there is still a grounding issue in ...

Junction R5-R6-C11 and RP2...these are connected to the white wires that fly over the B+ rail... I would relocate those white wires to run under the tag board. Tried going under the board but was making a big, uncontrollable rats nest. Decided to go over the top. I think the leads are actually furt...

Hey gang.... Is pin 1 on your 6sj7 tied to the it’s metal case? I wonder if grounding that might help? I knew better but let it slide. Now grounded but no improvement. Once through again noticing that L1 is not the 159P in my build, but the significantly smaller 159M. I had both the 159P and 159M. I...

Hey gang... Yes, phase inverter abbreviated is "PI". Thanks. For some reason i read it as PL (lower case). :oops: didit suggested unfastening the pots. No change. However, when I touched RP2 the buss increased. With RP2 pushed against the chassis the buzz went back to "normal". RP1&3 didn't do this....

Back again.. Disconnected C12 & C14 C14 only connected; no buzz C12 only connected; about 1/2 to 2/3 buzz. Reversed cap, no change. Both connected; the usual buzz. So...since the grid of V2b, is fed from the anode of V2a it, V2b, would would amplify the buzz coming from V2a. This would account for t...

First off, the easy one. On the 120Hz buzz: These can come from "slam-off" in solid state diodes (which you don't have) or from spikes on the AC mains wiring riding through the PTs interwinding capacitance, among other places. I have checked the 120ac line. Looks clean. I also moved everything from ...

Egad! That isn't lead dress. That's lead pants. No, no, no. I can't decide if you're pranking me or not. It was a "funny" hence the :D . I did this to turn the OT 90deg. I had to splice the wires and drag them over the edge to hook them back up. It was a temporary expediency to see if there was any...

Went ahead and rotated the OT. Pic below. No change to scope trace or audible noise. Still has very, very faint 60Hz hum and annoying 120Hz buzz. While my component placement isn't optimum, I think we can take it off the table as the cause of the buzz. Included a pic if the bottom as well so you can...

Quick one...

To turn the PT I will have to move the OT as well. So, turning the OT is the way to go if it will help the noise issues. I would leave the PT alone.

Disconnected L2 and jumped the connection. 60Hz hum went up. No change to the 120Hz. Borrowed a GZ34 from another amp to replace the 5V4. No change. Replaced the JJ 6sn7 with a new Tungsol. Can't conclusively say it helped but, the grid waveform amplitudes were just about equal as opposed to the 2:1...

Been trying to dress some of the wiring. Some of the pot leads and the "Blue Wire" ground. No silver bullet . At least not yet. Also, the blue wire running to V3 & V4 P1 comes from C2. I'm using the empty P1 for the screen resistor connections to P4. With the scope set to line (thanks, sluckey) I wa...

Try sitting the amp on a sheet of Aluminum foil that makes good contact with the chassis . Are your output tube heaters wired pin 2 to 2 and pin 7 to 7? Forgot to mention that I tried shielding the bottom. No effect Heaters are wired per the schematic. I used a blue and white wire to keep track. It...