Amp Mad Scientist
Ambassador of Heresy
Nice one.
Fender BJr repair
- Thread starter STRefugee
- Start date
Whew, 11 pages. Just a suggestion. 
www.guitarcenter.com
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Amp Mad Scientist
Ambassador of Heresy
I do it for fun it's a hobby.Whew, 11 pages. Just a suggestion.
Used Neural Dsp Gear | Guitar Center
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OP
STRefugee
Well-Known Member
Whew, 11 pages. Just a suggestion.
Used Neural Dsp Gear | Guitar Center
Save money on Used Neural Dsp gear at Guitar Center. All pre-owned items are rated and scored. Buy online or at your local store today!
Enjoy!
OP
STRefugee
Well-Known Member
Hi @Amp Mad Scientist
I checked that German dealer in tube amp parts again, queried about their replacement transformer.
Product information "MAINS transformer for Fender Blues Junior, Pro Junior
Has a higher current capability than the Fender original. So it would stay cooler would it not?
The primary side of this transformer also features all wires of the original too. So, any wall outlet voltage is possible including 240V.
Sounds like a great quality product and an upgrade to the original one do you agree?
But man it doesn't come cheap. I'm not decided yet to bother with replacing it but if I am to bother some day, I rather put an upgrade in than change like for like. What do you think? Waste of money?
I'll first wait to hear what it sounds like after the mods.
Cheers!
I checked that German dealer in tube amp parts again, queried about their replacement transformer.
Product information "MAINS transformer for Fender Blues Junior, Pro Junior
Has a higher current capability than the Fender original. So it would stay cooler would it not?
The primary side of this transformer also features all wires of the original too. So, any wall outlet voltage is possible including 240V.
Sounds like a great quality product and an upgrade to the original one do you agree?
But man it doesn't come cheap. I'm not decided yet to bother with replacing it but if I am to bother some day, I rather put an upgrade in than change like for like. What do you think? Waste of money?
I'll first wait to hear what it sounds like after the mods.
Cheers!
Amp Mad Scientist
Ambassador of Heresy
You don't need to spend a lot.
The Hammond transformer will work pretty good.
It runs hot because the bias was set too hot.
OP
STRefugee
Well-Known Member
Hi,
Won't touch it tonight.
Haven't slept over the last 48hrs and i'm dying for some serious dtinking session.
So, party night tonight!
Amp Mad Scientist
Ambassador of Heresy
OK I get it now.
Took me a while to get thru my thick head.
There's a thermal fuse inside the transformer and apparently it's blown.
Apparently bypassed the defect thermal fuse, hence the wiring is changed.
The transformer may have overheated because:
the bias was set too hot
the capacitor was in backwards, and probably screwed up the bias voltage, and made it run even hotter.
The transformer may still work OK but it's been abused.
It has been overheated.
I can fully understand why you might want to change it.
I don't know if the replacement has a thermal fuse as the original does.
Sorry I didn't get it sooner.
OP
STRefugee
Well-Known Member
You're Brilliant mate!! No need to apologise. The fact you confirm it, is Awesome!
Thank you so much for taking time to ponder over the issue and come back to me on it in that way.
Makes me feel real good of having you supporting me in my discovery journey.
Hadn't it been for your involvement, I had never dared getting started on it.
And thanks to you, I've already learnt so much and still enjoying the journey.
So thanks so much!
OP
STRefugee
Well-Known Member
So looking for a replacement mains transfo. I list the wiring required below (though the colorurs may be different).
This one would do the job. But at over £100 is irritating as it seems the most basic type on offer.
I have a freind who's got a freind.... Basically I could get one over from the US. So any suggestion for an upgrade to the stock one within a reasonable price range?
Connection with Board labeled 2001, 2002, 2003, 2010 (Blues Junior III)
Primary:
Purple wire (Thermo) to P4
BLK/RED wire (0V) to P7
BLK/GRN wire (120V) to P9
BLK/YEL wire (0V) to P10
White wire (100V) to P5
WHT/BLK wire (110V) to S2B
Black wire (120V) to P6
Secondary:
HV Red To P11
HV Red To P12
Bias Brown To P13
0V Brown To P14
6,3V Green To P15
0V Green To P16
This one would do the job. But at over £100 is irritating as it seems the most basic type on offer.
I have a freind who's got a freind.... Basically I could get one over from the US. So any suggestion for an upgrade to the stock one within a reasonable price range?
Connection with Board labeled 2001, 2002, 2003, 2010 (Blues Junior III)
Primary:
Purple wire (Thermo) to P4
BLK/RED wire (0V) to P7
BLK/GRN wire (120V) to P9
BLK/YEL wire (0V) to P10
White wire (100V) to P5
WHT/BLK wire (110V) to S2B
Black wire (120V) to P6
Secondary:
HV Red To P11
HV Red To P12
Bias Brown To P13
0V Brown To P14
6,3V Green To P15
0V Green To P16
Amp Mad Scientist
Ambassador of Heresy
No power tubes installed.
Go ahead and hook up the transformer, test the voltages.
Test the bias voltage.
You don't need the thermal fuse to test it.
If I was buying a transformer
I would buy the original Fender part, or the Hammond.
I wouldn't spend a lot if I could help it.
OP
STRefugee
Well-Known Member
Measured resistance across each side of the output transformer with the amp turned off and Ohms set to 200 on multimeter.
P2 to P1: 145.9 ohms
P2 to P3: 148.2 ohms.
Turned amp On.
Set bias from 13.7 to 12.3
Test DC on PIN 7: 339DCV
and Pin 9: 339DCV
Amp Mad Scientist
Ambassador of Heresy
Can you measure the DC voltage across D7 and the voltage across D5?
There should be about 15VDC across each diode.
Can you measure the DC voltage on pin 9 of the output tube sockets?
each socket should have high voltage in Pin 9.
The after you do that,
Plug in the output tubes and plug in the speaker.
Remember there are 2 jacks, one for speaker and 1 for footswitch.
Then it should work I think.
OP
STRefugee
Well-Known Member
Will get to it tomorrow.
A couple of mates dropped by and ended up having a bit of a party again
Will defo get to it tomorrow
Thank you!
OP
STRefugee
Well-Known Member
Hi,
II'm thinking of ordering this one:
https://mou.sr/44bSvxU
Mouser No:546-1750F
Mfr. No:
1750F
Should be a drop-in with all the required wiring, am I right?
Thanks
Amp Mad Scientist
Ambassador of Heresy
It says on the data sheet that it's "drop in." Should work OK.
Well at least you learned something about fixing your amp. It's great when people take the time to learn about it.
OP
STRefugee
Well-Known Member
Ah! I didn't see that.
Thank you!
OP
STRefugee
Well-Known Member
Totally! That was the main motivation I had, and been able to reach people like yourself, ready to support and share some of their knowledge just got me started.
It is brilliant! It's been my escape from all the pettiness, meanness of daily life and it is doing a lot of good to my mental health.
So thanks again for your support.
I now ordered that transformer so I won't put the amp all back togethet yet.
I will have to look at the reverb tank then. There is a bad contact somewhere which I have yet to locate. The parts are so tiny I'll need to look at it with a magnifier glass I think.
OP
STRefugee
Well-Known Member
I turned the amp on.
Placed the red probe at the with the stripe, and the black probe at the other end of the diode.
Multimeter set on DC voltage 200.
Reading D7: 14.5
Reading D8: 14
Reading D5: 26.5
Pin 9 reading: 337V and 337
