Jeff Seal
New member
Chopstherocker sent his '66 Bandmaster to me, so I could convert it to three prong for him. With his permission, I'm going to show everyone what all is entailed to "restoring" the older Fender's to proper working specs and what to look for to make sure it's in great shape to last another 40 yrs.
This is going to be a little long....so bear with me...
Upon removing the chassis from the case, we can see the turret board with 100% original components...
The turret board being the large black rectangle with all the components on it..(in case you didn't know..). First glance reveals the large brown caps (cathode bypass) are indeed original and will need to be replaced...these were never intended to last 40 yrs, they are oil filled and dry up after time, regardless of how much use they have seen! Next we'll go ahead and check the tubes and determine what condition they're in...
This one is a "goner"...:blackeye:
The other 6L6 is even worse..
All four preamp tubes check out....
but all are 12ax7's and the PI calls for a 12at7...
Next we'll flip the chassis over and look in the "doghouse" (metal rectangular cover that hides the main filter caps)..
...obviously the two caps on the right have been replaced, but the three large gold caps are original and will need to be replaced...
A couple of things to notice... the two that have been replaced were originally 70uf/350v, and they have been replaced with 80uf/450v....normally I would have left these in there, as they will do just fine...but one of my personal pet "peeves" is cutting off the lead's and soldering new components to the old leads as shown here....why do people do this???:eek13:...since I actually have 70uf/350v caps on hand....I decided to replace them with factory values (again not a huge deal..)
The other thing to notice (if you can make it out) is the gold caps are actually "dry electrolytic caps" and not the Mallory oil-filled ones that "explode, rupture, etc" found quite often in these old Fender's....quite a few people are under the impression that these do not need to be replaced since they aren't oil-filled.....regardless, they're 40 yrs. old and they are going to fail sooner or later. So they're outta there!
I also checked the resistors to make sure they are within tolerance (very important!)...amazingly they check out fine which is pretty rare for an amp this old...
What is "within" tolerance you ask????... simple! Each resistor in this amp has a "maximum allowable" deviance from it's stated value. Fender's used +/- 10percent(most of the time..) of stated value to be within "acceptable".....thus a 100k ohm resistor can be anywhere from 90k ohm to 110k ohm and still be considered good....
BUT, there are four resistors in this amp that call for a much closer tolerance being in the 5 percent range...so in our above example 100k could be 95k to 105k ....make sense?
A quick check of EVERY resistor in here reveals only one resistor out of spec's...(again this is very rare and my guess would be this amp has seen little use!...probably sat in a closet for 30yrs.) Chop's made a killer score with this one...
I'm pretty sure I'm fixing to hit the max for a single post, so I'll end the first part here.......PLEASE WAIT FOR ME TO FINISH THE REST BEFORE RESPONDING....that way all the parts are together and more readily "examined"...thanks bro's
Jeff Seal
This is going to be a little long....so bear with me...
Upon removing the chassis from the case, we can see the turret board with 100% original components...
The turret board being the large black rectangle with all the components on it..(in case you didn't know..). First glance reveals the large brown caps (cathode bypass) are indeed original and will need to be replaced...these were never intended to last 40 yrs, they are oil filled and dry up after time, regardless of how much use they have seen! Next we'll go ahead and check the tubes and determine what condition they're in...
This one is a "goner"...:blackeye:
The other 6L6 is even worse..
All four preamp tubes check out....
but all are 12ax7's and the PI calls for a 12at7...
Next we'll flip the chassis over and look in the "doghouse" (metal rectangular cover that hides the main filter caps)..
...obviously the two caps on the right have been replaced, but the three large gold caps are original and will need to be replaced...
A couple of things to notice... the two that have been replaced were originally 70uf/350v, and they have been replaced with 80uf/450v....normally I would have left these in there, as they will do just fine...but one of my personal pet "peeves" is cutting off the lead's and soldering new components to the old leads as shown here....why do people do this???:eek13:...since I actually have 70uf/350v caps on hand....I decided to replace them with factory values (again not a huge deal..)
The other thing to notice (if you can make it out) is the gold caps are actually "dry electrolytic caps" and not the Mallory oil-filled ones that "explode, rupture, etc" found quite often in these old Fender's....quite a few people are under the impression that these do not need to be replaced since they aren't oil-filled.....regardless, they're 40 yrs. old and they are going to fail sooner or later. So they're outta there!
I also checked the resistors to make sure they are within tolerance (very important!)...amazingly they check out fine which is pretty rare for an amp this old...
What is "within" tolerance you ask????... simple! Each resistor in this amp has a "maximum allowable" deviance from it's stated value. Fender's used +/- 10percent(most of the time..) of stated value to be within "acceptable".....thus a 100k ohm resistor can be anywhere from 90k ohm to 110k ohm and still be considered good....
BUT, there are four resistors in this amp that call for a much closer tolerance being in the 5 percent range...so in our above example 100k could be 95k to 105k ....make sense?
A quick check of EVERY resistor in here reveals only one resistor out of spec's...(again this is very rare and my guess would be this amp has seen little use!...probably sat in a closet for 30yrs.) Chop's made a killer score with this one...
I'm pretty sure I'm fixing to hit the max for a single post, so I'll end the first part here.......PLEASE WAIT FOR ME TO FINISH THE REST BEFORE RESPONDING....that way all the parts are together and more readily "examined"...thanks bro's
Jeff Seal
