Re: Issues with one of my blackface bandmaster heads NEED HELP
Posted: Mon Jan 13, 2020 2:25 pm
the amp is quiet on both channels, i have turn up to 6 or so before it gets anywhere near audible really, when it's dimed you can hear it fine enough but it's not loud.Igorilla wrote: ↑Mon Jan 13, 2020 1:59 amSome corrosion and warping in the board is normal.panoramic wrote: ↑Sun Jan 12, 2020 6:45 amhttps://www.flickr.com/photos/54099386@ ... ed-public/
https://www.flickr.com/photos/54099386@ ... ed-public/
https://www.flickr.com/photos/54099386@ ... ed-public/
https://www.flickr.com/photos/54099386@ ... ed-public/
Last night i went through all of my amps just to spray the pots etc, you know the old annual save myself a trip to the tech evening. Great news, i have my new HRD running in TIP TOP shape, not so great news is what i found inside bandmaster number 2 above (i have 2 of them yes)
here are some pics of it, there is some oxidation inside that is visible, there is also a warp in the board if you look close
I don't know if those have anything to do with what happened to the amp.
I plugged it in last night and tried to play through it, it passes a signal fine just EXTREMELY QUIET which is worrisome, the pots are clean and work fine and the trem still works too, it's just CRAZY quiet and breaks up super easy
Is your amp quiet on both channels?
You mentioned in the OP that you did try different tubes with no results. As andy-tchp and mbene085 suggested I would suspect the filtering caps too. Swap them out for fresh ones anyway as the amp is'nt been serviced in recent years. But MAKE SURE TO DISCHARGE EVERYTHING of relevance before doing anything. And double check with a multimeter.
You should check the cathode bypass caps, cathode resistors and plate resistors belonging to the preamp and phase inverter tubes next. These are basic amplification units besides the tubes. Your cathode bypass caps look old, so I would simply install fresh ones. The carbon comp resistors drift in value, but sometimes old CC resistors are broken physically which you can check by chopsticking them or by trying to move them.
From the pics, the electrolytic cap in the bias circuit for the power amp looks pretty old. Replace it with a fresh one and check the carbon comp resistor parellel to it as well as the bias pot and the resistor attached to it.
Check for cold and/or broken solder joints.
If you know what you are doing, you can measure the voltages across the circuit and compare to the schematics. This will show you to some extent in which shape the circuit is.
If you don't feel comfortable with doing this yourself and don't know how to discharge the caps before replacing them bring the amp to a tech. It should be an inexpensive and easy fix unless it is transformer related (in which case it is expensive and easy).
I'll take this in for service, i was hesitant due to $$$ worries on it. I know the OT works as it passes a signal it's just the volume drop off was crazy and so sudden