Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Nathan on April 27, 2022, 07:28:13 am

Title: Changed Output Transformer in a Blues Jr -Need Help!
Post by: Nathan on April 27, 2022, 07:28:13 am

Hey all,


I decided to swap OT on my Fender Two Tone (really a green board Blues JR).


Here's what I did:


1) Replaced the power resistors to the correct value (all 2W metal oxide)


2) Removed the small PCB with the speaker jack and the FAT footswitch jack by desoldering all 4 wires from the main board


3) Added a Hammond 1760H with 2 mono switchcraft jacks wired for 4 and 8 ohms.


I got everything back together and now nothing works. No sound, no hiss, controls do nothing but tubes are glowing normal.


Here's a pic.


FWIW this amp has had the reverb mod and cathode follower done previously as well as trim pot for bias, but all was working fine before yesterday!


Thanks if you can help

Title: Re: Changed Output Transformer in a Blues Jr -Need Help!
Post by: uki on April 27, 2022, 07:32:04 am

If you have the schematic, check all connections that have been changed, then check voltages.

Title: Re: Changed Output Transformer in a Blues Jr -Need Help!
Post by: sluckey on April 27, 2022, 07:56:22 am

Recheck your work. Take it all apart if necessary.

Title: Re: Changed Output Transformer in a Blues Jr -Need Help!
Post by: shooter on April 27, 2022, 09:06:44 am

Quote

Here's a pic.

did you take before pics? compare and contrast.
those spade lugs on the PS are pretty easy to get swapped if you just remembered

if you have to open it up again, look for broke solder connections, "loose teeth I call 'em"

Title: Re: Changed Output Transformer in a Blues Jr -Need Help!
Post by: PRR on April 27, 2022, 01:37:38 pm

> now nothing works. No sound, no hiss

How many Volts inside?

Title: Re: Changed Output Transformer in a Blues Jr -Need Help!
Post by: tubeswell on April 27, 2022, 03:01:48 pm

You possibly damaged one or more solder pad/traces removing those resistors or broke one or more jumper/ribbon cables by twisting everything around to get the main board out. Or didn’t put Humpty together again properly.

Title: Re: Changed Output Transformer in a Blues Jr -Need Help!
Post by: dude on April 27, 2022, 03:43:39 pm

I’d go with “Humpty/Dumpty Together Again”  :icon_biggrin:

Title: Re: Changed Output Transformer in a Blues Jr -Need Help!
Post by: mresistor on April 27, 2022, 05:07:20 pm

Well glowing tubes means your filaments are working..
Do you have voltage on the plates of the power tubes?



https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Blues-Junior-Schematic.pdf

Title: Re: Changed Output Transformer in a Blues Jr -Need Help!
Post by: Nathan on May 03, 2022, 08:39:04 am

Following up, I got it all sorted out.
It's the Hammond polarity which is reversed from the stock OT.
I also had to figure out the NFB and FAT bypass since they were on that small PCB I removed (easy fix). Sounding great too! Thanks for taking the time to respond guys.