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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Fri 25, 2016 5:53 pm 
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Location: Fayette County, Pa
That is about right for an 8 ohm speaker on an Ohmmeter. 8 Ohms is the AC impedance, not the DC resistance. DC will always be less than what a speaker impedance rating is. You will also find that speakers with the same impedance and a higher power rating will probably be a little lower simply because there is more iron in the core and a larger diameter wire may be used for the winding.


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Fri 25, 2016 10:40 pm 
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Location: South Jersey East of Philly
Sometimes the YouTube DIY stuff ain't as easy as it looks. I have a great local guy (South Jersey...http://www.soundremedynj.com/) that would recone your speaker for ~$55, but by the time you ship it the $$ would go up. You can try the recone, but the learning curve may be more expensive (if you mess it up) than getting a local pro to recone it. You will need special speaker shims to center the coil/spider assemble...if that's not centered perfectly, you will have problems from the get go..no redo's either. But, if you want to do a DIY recone, have at it.
AFA running pedals thru the ol' girl....let it rip. The only thing they can hurt is your ears (or a speaker that's on the edge of going out).


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Sat 26, 2016 1:44 am 
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thanks guys
I think I will play through the speaker a bit more as it seems to be clearing its self
up a bit the more I play it.
hopefully I can find a little time to work on it tomorrow .
this thing is very additive .I spent most of thanksgiving on the floor soldering and working on this thing.
I was showing some family members the inner workings of my new old amp when they came into my hobby room but all I got was blank looks on their faces lol ,,,,, they don't get it but I am having way to much fun .


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Sat 26, 2016 2:58 am 
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Joined: Oct Tue 30, 2012 9:33 pm
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If you had water half way up, it got into the gap and whatever dirt, dust, crud went in with it. We are talking just a few thousands of an inch gap. Especially a Jensen. That is why they were a better speaker. That and the paper had something to do with it. Could be just some rust in formed on the pole piece also. If you do recone, you will need to spend alot of time getting the gap clean. Just the least amount of crud and you will end up sounding just like you got. Sending to a good reconer and they will demagnetize, clean paint and then magnetize. I've reconed several speakers. Even a few Jensens. Have had pretty good luck. Only one I had to redo. I don't have the ability to magnetize. Kind of a expensive set up. One thing, if you do the recone or have it done by someone else, it will sound dead until broken in. It takes a few hrs before things loosen up and it starts to sing. I usually put mine in the cabinet, lay it face down on the carpet, plug in a mp3 player and let play while I'm away.
Really like this thread.....


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Sun 27, 2016 4:10 pm 
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first of the voltage testing ,starting with the last 4 tubes

Image

first 4 tubes

Image


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Sun 27, 2016 6:29 pm 
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Location: South Jersey East of Philly
All ballpark figures there..so far so good! Moving numbers part of the trem circuit?


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Sun 27, 2016 9:26 pm 
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Tbirdkid wrote:
All ballpark figures there..so far so good! Moving numbers part of the trem circuit?




you know I didn't think about that but I bet that's what it is as the different voltages that flash across the meter seem to be repetitive
I got a couple of tubes that make a loud noise when I tap on them ,they are 7025 tubes.
I don's have any 7025's but I do have a lot of 12ax7's on hand.I was reading on the net last night
that a lot of guys thought that a 7025 was the same thing as a 12ax7A,,,,,do you guys think that to be true and do you think I
could substitute the 7025's with 12ax7's with out hurting the amp?


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Sun 27, 2016 11:58 pm 
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Same tube. Just graded different. Find the quietest ones to put in the first two positions. I believe the 7025 was spec'd better is all.


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Mon 28, 2016 4:14 pm 
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Location: Fernandina Beach, FL
The RCA RC-30 tube manual says:

"Miniature type used as phase inverter or resistance-coupled amplifier in high-quality, high-fidelity audio Amplifiers...
This type is identical with miniature type 12AX7A except that it has a controlled equivalent noise and hum characteristic".

So, "No Worries" you can use a 12AX7 in place of it as mentioned above.

I don't know, does it have a spiral heater for AC hum reduction?

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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Mon 28, 2016 5:08 pm 
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thanks Don
so if I understand right the 12ax7A is a closer match to the 7025 tube then a regular 12ax7
I have plenty of 12ax7 and 12ax7a tubes so I should be able to eliminate the tubes as being a problem
as I have two of the smaller tubes that make a loud noise when I tap them
the 2ed one from the power tubes and the 2ed one from the end .
I am going to try and clean the pins with a Dremel rotary tool this time


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Tue 29, 2016 2:59 am 
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Location: South Jersey East of Philly
A 12AX7A was the next evolution of the 12AX7. I believe it was made to carry higher plate voltage. Just go ahead and swap them out..maybe stay with 12AX7A's for now, but I'm sure the old 12AX7 would be OK also. Whatever works.
I would just use a small hand file to clean the pins...the dremel could get carried away and shoot the tube 20 fee if you slipt!


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Tue 29, 2016 5:27 pm 
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Hmmmm
well the amp was playing pretty dang good
but then after I tested my volts on the tube sockets I powered it up the next day and got this weird
high pitch Squealing and hissing sound.the guitar would play at first a little bit though the weird noise
but then the guitar quite playing at all but I could still hear the Squealing and hissing .so I UN-plugged the guitar
from the tremolo side and plugged the guitar into the normal Chanel and the guitar plays well on that Chanel .I can
still hear the the squalling and hissing but the guitar at least sounds nice and strong on the normal Chanel
so I cleaned the pins and tested the tubes again and replaced the smaller ones 1 at a time with 12ax7a tubes that tested strong and no change ,I swapped the two big tube and no change ,the problem was still on the the tremolo Chanel.
I taped on all the capacitors and the brown board it self and I can hear almost all of the taps through the speakers,it kind of sounds like tapping on the head of a microphone.is that normal ?
I am now trying to find a .03 cap to replace the mustard cap as I know it is reading .08 and I have been told that they almost always leak DC the wrong way.any thoughts ?


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Tue 29, 2016 6:57 pm 
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Joined: Oct Tue 30, 2012 9:33 pm
Posts: 73
Make sure that the ground is good on the input jacks. That is a starting place. Ever heard of the chop stick test method? Use a wooden stick to prod around solder joints while power is on. Helps locate cold solder joints, loose components etc. If you are not comfy doing this, DON'T!


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Tue 29, 2016 9:01 pm 
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Joined: Aug Sun 23, 2015 6:01 pm
Posts: 984
Location: South Jersey East of Philly
Scurry is right with the chopstick method.... Since you've eliminated the tubes and the 'Normal' channel as the source of the hiss/squeal, the push and probe chopstick method is in order to do now. Many times I have found the offending part by nudging around the tube sockets/circuit board/components with a chopstick. Hiss is sometimes a carbon resistor going 'bad' sound...also it could be a gassy tube sound, but you seem to have eliminated that by changing tubes. Squealing could be a bad/intermittent ground in the circuit causing oscillation.
If you try all the above and it doesn't help, you may have to start isolating the trem channel's stages and see when the sound stops.


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Wed 30, 2016 3:01 am 
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well after a very long search through my stash I found some caps that may work in place of the yellow mustard Cap
the cap that is in the amp is a .03 400v
the caps I found are
.02 MF 400v
.033 400v
.0033 400v
I think they may be the black beauty's
do you guys think one of these black caps can work in the place of the .03 yellow cap ?

Image

Image

this is the cap I think I may need to change

Image

the amp is playing and the squealing and hissing is not so bad but I have almost (no tremolo).
I did do the wooden stick tap test and much of the board make noise through the speaker when I tap on it .
doesn't this yellow cap control the tremolo ?


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Wed 30, 2016 3:47 am 
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Joined: Aug Sun 23, 2015 6:01 pm
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Location: South Jersey East of Philly
Any of those .03 caps values should be OK for testing...are these old (unused) caps or ones you may have bought new in the last 5-6 years? If they are old stock caps, I wouldn't trust them, but no harm in trying them and see what happens...Just unhook one side of the yellow cap and jumper the new cap in place, and see what happens. I can't quite read the pic and schematics to piece together what the yellow cap does, but it's looks to be in the area of the trem circuit. The trem is very dependent on the caps being in spec, any deviation from the norm, and the trem circuit may quit. The noise you get thru the circuit board is probably some caps that (normally in many cases) get almost microphonic when they are in hi-gain circuits...or, you have a microphonic tube.


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Wed 30, 2016 2:42 pm 
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thanks tbird
I did lift one end and use a jumper wire to test the .02 cap in circuit
the tremolo did sound a little deeper (better) but not as good as it did before .
I have learned that these old yellow cap leaks almost all the time when they
are out of specs as bad as this one was so I went ahead and put the black cap in. the black cap read
.03.9 (almost .04) not great but better then what the yellow was doing.and I am hoping the black caps don't
have as bad of history of leaking as the yellow caps do.


Image

Image

I did notice that one of the small tube sockets was really noisy when tapped so I put a 12ax7A in it.
the amp still has a little squeal but not as bad as it was.


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Wed 30, 2016 8:55 pm 
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well the chop stick really paid off for me guys, after poking around a bit I found a broken solder on tube 4
from the end.now the amp sounds nice and strong again.the only thing I notice that is questionable
is I now can hear a very small amount of tremolo when the tremolo knob is tuned all the way off. its really not noticeable
unless you really look for it so I can live with it.I guess it might have something to do with the black cap I replaced
the yellow one with .
I have been thinking about the power cord .I kind of hate to lose that cool old original look.and I am going to always run this thing on 110v.I can see no good reason to run modern day voltage through the old girl with all these older parts.
but if I decide to put a 3 prong cord on this thing I am assuming that I should wire it up like it is now but just wire the green of the new cord to the chassis right?
now moving on to the cabinet


Image


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Nov Wed 30, 2016 9:31 pm 
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Joined: Oct Tue 30, 2012 9:33 pm
Posts: 73
When adding a grounded 3 wire plug, the ground switch and cap must be removed from the circuit. They can be left in place so you are not left with a hole in the panel. Just not connected. Hot (black wire) goes to fuse-switch-transformer out of the transformer and to the neutral (white). The green wire will go to a machine screw holding down the power transformer. This "mod" is a must in my book. As a playing musician and having the crap zapped out of me a few times and reading of guys actually dying from electrical shock because of ground loops, I do it on all my builds and vintage stuff that I've gathered for my use. The decrease in value does me no good if I'm dead.


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 Post subject: Re: DIM BULB LIMITER ON A FENDER BANDMASTER
PostPosted: Dec Thu 01, 2016 1:16 am 
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As long as you don't run the amp above its rated ac voltage it should be fine.

I'd only recommend running the amp at 110 volts if that's what is specified on the amp itself or the schematic.


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