Tube Amp Archive

Can anyone explain to me what's going on here. This is the secondary side of the Output transformer. Blue is ground the other colours are 4/8/16ohms. All of the top row have continuity with each other, all of the bottom row have continuity to each other. None of the top row have continuity with any ...

Now interestingly, when I switch off power to the amp, the capacitors are discharging themselves, my A+ reading drops over time which I assume means there is a short somewhere. The resistors that parallel, and balance, the stacked reservoir caps should discharge the amp when it's off. Ha that occur...

I believe the lightbulb limiter is now behaving the way I want it to. When i power up (with lightbulb limited in circuit) I have no sound at all. Not even hum or hiss. I have tested the guitar, cables, and speaker and they all work. I have gone through swapping out each power tube one by one but it ...

I started going through everything with the dcr meter, this is the grid screen resistor to socket 2. I have replaced it.

Now interestingly, when I switch off power to the amp, the capacitors are discharging themselves, my A+ reading drops quite quickly.

I don't'suppose you have access to an oscilloscope, do you? Don't tempt me I noticed that the wiring diagram shows a not on the NFB wire that it has to be kept close to chassis to prevent oscillation I believe I have it routed where it should be If it were me, I would be very tempted to move the ea...

This is the 3rd time im typing this out as TAG keeps making me log in again and deleting what i have written. Sorry If I am curt. I disconnected the NF wire from the 16ohm lug of my impedance selector. Lighbulb limiter flashed bright and then dimmed. I then reattached the NF wire, and swapped the OT...

3) a output tube socket is arcing. This was the issue, I have found it and fixed it. New Problem I plugged the amp in going through a passive attenuator (spl reducer) into my speaker cab, I powered it up with the tubes in, set the bias, left it for like 10 minutes, all was well. I plugged my guitar...

Is it possible that bringing it up slowly does something wonky to the bias... I do not know how i would test this asside from powering up at full voltage which seems dangerous Before re-inserting power tubes make sure you have sufficient negative bias voltage (e.g. -40V) at EL34 socket pins 5. I ha...

Hello everyone, thanks in advance for any guidance. I'm building a Matamp style GT120. I am building it from the Hillbish chassis and circuit board. I am in the UK 240v. This is my 2nd amp build and today was first power up and the HT fuse was starting to smoke when I got to around 60v on the variac...

[/quote]The hum pot should be connected across the heater winding, not in series with the pilot lamp.
[/quote]
Like this?

You did not add the essential ground connections I mentioned earlier. Yes sorry I did take note I'm just upset with DIYLC and am not redrawing the OT Were you planning on the same reservoir cap values as Rob Robinette' The answer is yes but are they not on the schematic? Almost all of HT fuses I've...

blacknick schematic 0.5.png Wow thank you for all of the input, any question of "why have you used x-value for y-component" the answer is always, that's what is on Rob's schematic. I'm very open to swapping in and out different values later, but I thought it best to just start in 1 place and adjust...

hopefully easier to look at

This was definitely on my list of concerns thank you

Hello, long time Lurker first time poster. I'm embarking on my first "from scratch" build. By "from scratch" I mean that I'm buying all the components individually and machining the chassis myself. I am a furniture maker so hopefully I'll manage to make the cabinet. In terms of the circuit I have ju...