Fender BJr repair

STRefugee said:
Some things never change it seems..
That's what brought me here. To get a good repair job done, I'd have to take my broken amp on travel. Otherwise, only cowboys round here pretending to know more than I do.
But it's great! It's not a high spec piece of kit so perfect for me to give it a go.
And I enjoy the experience so far thanks to you!
Click to expand...
What are you doing now?
Did you make any headway?
 
Amp Mad Scientist said:
I fixed a whole bunch of blues Jr.
I did mods on 3 of them I think.
One of them had Mercury Transformers and choke, JBL speaker, and Fromel preamp mods. I think the Fromel mods worked pretty good.
Click to expand...
No offense it's not you AMS your to kind with your time thing is every Blues JR I have serviced the bias was 120% dissipation stock
I shoot for 65% the day's are over when I could buy a case of 50 Russian mil spec EL84 at $2 per tube designed for ICBM use 450 volts on the plates
and shock resistant part # 6N14N-EP 5,000 hour service life as far as it goes I'm a student in this life not an expert
 
67plexi said:
No offense it's not you AMS your to kind with your time thing is every Blues JR I have serviced the bias was 120% dissipation stock
I shoot for 65% the day's are over when I could buy a case of 50 Russian mil spec EL84 at $2 per tube designed for ICBM use 450 volts on the plates
and shock resistant part # 6N14N-EP 5,000 hour service life as far as it goes I'm a student in this life not an expert
Click to expand...
Yes I understand, Fender biases the amps pretty hot.
I usually adjust it to 90% to make it run a bit cooler. I'm not the only one who does that.
It still sounds pretty good at 90% I think.
But still hotter bias sounds better is the general rule for a tube amp. It's just the usable life hours of components that become the concern.
 
Amp Mad Scientist said:
Here is the resistor R52 that you change to make the current lower.
I think I changed it from 22K to 42K, but whatever value works to get the current correct.
That why it's handy to have a resistor kit.
You can put 2 resistors in series or parallel to get the right value.

View attachment 105082
Click to expand...

Hi @Amp Mad Scientist
Finally found the time to get back to it.
In terms of capacitors & resistors I drew the list as:

C25 C26 C27 C28 Already acquired.

C30 and C32
2 x 470 50V Aluminium Electrolytic Capacitors - Radial Leaded 470uF 50V 12,5x20mm 105 C 2500h
Mfr. Part No: MAL214251471E3 Mouser Part No: 594-MAL214251471E3

C31
1 x 220 25V Mouser No: 581-REF0812221M025K Mfr. No: REF0812221M025K

C34
1 x 220 35V Mfr. No: MAL215090225E3 Mouser No: 594-MAL215090225E3

C33 Aluminium Electrolytic Capacitors - Radial Leaded 25VDC 100uF 6.3x11.2mm LS 5.0mm
1 x 100uF 25V 4,000 hr Mfr. No: EEU-FR1E101B Mouser No: 667-EEU-FR1E101B

R47
2 x 2.2K 2W Metal Film Mfr. No: CCF022K20JKR36 Mouser No: 71-CCF02-J-2.2K
2.2 K ohm (2200 ohm) or, in England: 2K2 ohm
Mfr. Part No. RW80U2201FB12 Mouser Part No 71-RW80U2201F Wirewound Resistors - Through Hole 2watts 2.2Kohms 1%.

R52
replace with a 42K. or Change R52 (22k) to 33k. This will raise the Bias Voltage to an acceptable level - Approx '-12.5vdc'.
1 x Mouser No:71-RS5-33K Mfr. No: RS00533K00FB12 https://mou.sr/44c5j7d
1 x Mouser No:71-CCF60-42.2K-E3 Mfr. No: CCF6042K2FKE36 https://mou.sr/4czeMI9
 
STRefugee said:
Hi @Amp Mad Scientist
Finally found the time to get back to it.
In terms of capacitors & resistors I drew the list as:

C25 C26 C27 C28 Already acquired.

C30 and C32
2 x 470 50V Aluminium Electrolytic Capacitors - Radial Leaded 470uF 50V 12,5x20mm 105 C 2500h
Mfr. Part No: MAL214251471E3 Mouser Part No: 594-MAL214251471E3

C31
1 x 220 25V Mouser No: 581-REF0812221M025K Mfr. No: REF0812221M025K

C34
1 x 220 35V Mfr. No: MAL215090225E3 Mouser No: 594-MAL215090225E3

C33 Aluminium Electrolytic Capacitors - Radial Leaded 25VDC 100uF 6.3x11.2mm LS 5.0mm
1 x 100uF 25V 4,000 hr Mfr. No: EEU-FR1E101B Mouser No: 667-EEU-FR1E101B

R47
2 x 2.2K 2W Metal Film Mfr. No: CCF022K20JKR36 Mouser No: 71-CCF02-J-2.2K
2.2 K ohm (2200 ohm) or, in England: 2K2 ohm
Mfr. Part No. RW80U2201FB12 Mouser Part No 71-RW80U2201F Wirewound Resistors - Through Hole 2watts 2.2Kohms 1%.

R52
replace with a 42K. or Change R52 (22k) to 33k. This will raise the Bias Voltage to an acceptable level - Approx '-12.5vdc'.
1 x Mouser No:71-RS5-33K Mfr. No: RS00533K00FB12 https://mou.sr/44c5j7d
1 x Mouser No:71-CCF60-42.2K-E3 Mfr. No: CCF6042K2FKE36 https://mou.sr/4czeMI9
Click to expand...

You checked the lead spacing of the caps?
It matches the holes on the board.
Dimension "F"
1743629718629.png
 
Amp Mad Scientist said:
You checked the lead spacing of the caps?
It matches the holes on the board.
Dimension "F"
View attachment 105753
Click to expand...
Hi,
Yes, as best I could without dismantling the whole thing apart yet, as I haven't got a dedicated place with a work bench where to leave a dissected body for weeks unfortunately. But noticed among the existing radial caps there are some slanted leads suggesting the spaces on the pcb between the holes are wider than how they pop out of the caps'base.
If in some instance the lead spacing is slightly different, I'll have to be creative I guess.
Thanks.
 
Last edited:
@Amp Mad Scientist ,
Hope all's good with you.
Hi, just got the amp out of the box and noticed the power transformer looking like it got a bit hot at some point.
Is this an issue? There's the same on the opposite side too.

Any test I should do to check the state of that transformer?
Cheers!


Screenshot_20250412_143152.jpg
 
STRefugee said:
@Amp Mad Scientist ,
Hope all's good with you.
Hi, just got the amp out of the box and noticed the power transformer looking like it got a bit hot at some point.
Is this an issue? There's the same on the opposite side too.

Any test I should do to check the state of that transformer?
Cheers!


View attachment 105875
Click to expand...
No worries.
That's part of the transformer construction, they welded the iron leaves together.
Nothing wrong, rock on.
 
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