I had the good fortune of restoring San Diego harp phenom Billy Watson’s Masco PA head. This is a very popular and highly sought after vintage amp by harmonica players. The amp was in good physical and cosmetic shape but was full of hum, buzzes and crackles when I first tested it. All of the electrolytic caps were replaced first. That cured most of the hum issues and brought the voltages up to spec.
It still had lots of hiss and crackling noise and the volume and tone controls were scratchy. I subbed out one of the pots with a new one and it still had the scratch. A tell tell sign that there were dc voltages on the pot. This typically indicates leaking signal/coupling caps. After removing and testing random caps for leakage I decided that they were all bad and replaced all of the signal/coupling caps.
Now all that was left was hiss and crackling/pops during the first minute or so of operation. I knew that was coming from the old carbon composition plate load resistors. I replaced all of the plate load and cathode resistors with Allen Bradley NOS carbon comps. All of the high wattage power supply dropping string resistors were replaced with modern metal oxide power resistors.
So we now had a wonderfully quite vintage amp. We were fortunate that all of the tubes were functional and not exhibiting and microphonics. Harp tone to die for.
Next on the agenda was a speaker cabinet. Billy wanted the cabinet to match the look and color scheme of the head. He also liked to experiment with speakers. After a little searching I found Tolex in colors that went well with the Masco. For the speakers I made the speaker baffle removable from the back and then made separate baffles for various combination of speakers. I believe I provided baffles for 2X10, 1X12 and 2- 6X9 and 4- 6X9 speakers.
Masco Restoration
I had the good fortune of restoring San Diego harp phenom Billy Watson’s Masco PA head. This is a very popular and highly sought after vintage amp by harmonica players. The amp was in good physical and cosmetic shape but was full of hum, buzzes and crackles when I first tested it. All of the electrolytic caps were replaced first. That cured most of the hum issues and brought the voltages up to spec.
It still had lots of hiss and crackling noise and the volume and tone controls were scratchy. I subbed out one of the pots with a new one and it still had the scratch. A tell tell sign that there were dc voltages on the pot. This typically indicates leaking signal/coupling caps. After removing and testing random caps for leakage I decided that they were all bad and replaced all of the signal/coupling caps.
Now all that was left was hiss and crackling/pops during the first minute or so of operation. I knew that was coming from the old carbon composition plate load resistors. I replaced all of the plate load and cathode resistors with Allen Bradley NOS carbon comps. All of the high wattage power supply dropping string resistors were replaced with modern metal oxide power resistors.
So we now had a wonderfully quite vintage amp. We were fortunate that all of the tubes were functional and not exhibiting and microphonics. Harp tone to die for.
Next on the agenda was a speaker cabinet. Billy wanted the cabinet to match the look and color scheme of the head. He also liked to experiment with speakers. After a little searching I found Tolex in colors that went well with the Masco. For the speakers I made the speaker baffle removable from the back and then made separate baffles for various combination of speakers. I believe I provided baffles for 2X10, 1X12 and 2- 6X9 and 4- 6X9 speakers.