Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: lego4040 on June 24, 2015, 01:23:48 pm
-
How is everyone doing? I've been incognito lately due to work and stress and no time. I have a issue with my revibe, I just brought all my equipment home from my shop where I had my own little setup. I set up my stack: I have my revibe going into the Vox clone into a 12" cabinet. I get only a very low volume output out of amp, I took revibe out of signal and went straight into amp and it's perfect. I reseated tubes and even moved the 12ax7's around and still low volume. I left my job last week(new job starts Monday)and brought all my gear home but haven't set myself up at home yet. Was hoping i can get some ideas thrown at me before I see what's going down on. Miss building
-
Bad output impedance from the tank somewhere?
What are the voltages like?
-
I haven't even gotten that far yet, I've been cleaning out my section of the shop and all my equipment is now sitting all over the place at home. After 11 years in my current plant and not being appreciated I got a offer and Went back to my first chiller plant. I will pull out Sluckeys prints and run some tests and see what I find. I will discharge caps and check all tube socket tightness as well. Some pins felt loose when I inserted and rolled some tubes, you have anything in mind I should be looking for?
-
First think to check is whether all the (power supply rail, and plate, and cathode) voltages are looking normal.
Then check solder points and socket pin connections (incase you've got a cold-solder joint or crack somewhere?)
Then check coupling caps for DC leakage. (could be affecting grid bias, and hence amplification?)
Then we'll take it as it comes.
-
It worked perfectly at shop on my bench and when I brought it home it got moved around. I had it carefully boxed up and protected too. What I didn't realize was that I had the bottom plate off when I packed it up so I need to check all my connections and pinch all the tube socket connections. I will get to that this weekend
-
Should I have the revibe connected to a speaker when I start checking volts? I can't remember on this. I know for Amos you do
-
Got the meter out and this are my numbers after I found a bad solder on the heater wire on v4. I hooked it all up and I still have very low volume
-
:w2: So I have negative voltage on V1 pin 7 & V2 pin2. Well now I need to ask for help
-
All voltages look normal except the two pins that are negative. Both of those pins should be zero. Also, they are tied together and should be exactly the same, but you show two different readings for each pin, so I don't trust either reading. Please recheck those pins.
Divide and conquer. Pull V2. This will kill the reverb circuit. Also turn the MIX to zero (MAX CCW). Now your guitar signal path is INPUT jack, V1B, V4, and OUTPUT jack. Got signal now? If so, put a fresh 12AT7 in V2.
-
I'll do that, a 12at7 I might not have another. Can I throw a 12ax7 for a quick check
-
Can I throw a 12ax7 for a quick check(?)
Totally
-
Happy Fourth of July Folks, have a great weekend. I haven't gotten any further then what you guys suggested, I removed the 12AT7 and I put mix to zero. I got I straight thu guitar signal no reverb and that was a good sign. I put a 12AX7 in(out of 12at7) v2 and same issue with extremely low volume. With the extra day off I hope I can find something, I have not found anything touching but I did find a heater wire off one off the 12ax7's. I re soldered that on and my high voltages on the B+, A,B&C come down to respectable levels. I wonder if I might have did some thing to the other tubes or even reverb pan parts?
-
Update, I pulled ALL the tubes and put a complete different set in and the Revibe came alive. I pulled the 12AX7 I had in V2 and put in 12AU7 and it sounded even better and I was very Happy. I found the only 12AT7 I had that was in there and put that back in and it worked nicely, I preferred the 12AU7 tho. I might put that one back in for now, my only nuisance is a pulsating sound when I use the Range switch. When I first built it I had it all the time and I was informed to pull the ground off that is coming in from the power cord cause it could be a ground loop issue between the head and the amp. If like to get ride off that completely to finalize this amp.