Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Papa Jim on March 14, 2019, 08:28:20 am

Title: Same o'le, same o'le.
Post by: Papa Jim on March 14, 2019, 08:28:20 am

Another Blue's Jr. redplating V6. Working on a friends amp. Also output sockets have melted solder on their terminals. It has -11.7 vdc on the R31, R32 and they both ohm fine. Is there anything else I should check before resoldering the sockets and trying it again? Watched BillM video on Jr. bias and at 1:40 point I'm not understanding what he does. The amp did not have the voltage that he talked of either. He gives no help what to do if it fails that test.

Title: Re: Same o'le, same o'le.
Post by: sluckey on March 14, 2019, 08:38:19 am

It's important to check for bias ***DIRECTLY*** on pin 2 of the socket. Even better to check it on the top side of the socket.

Title: Re: Same o'le, same o'le.
Post by: Papa Jim on March 14, 2019, 08:56:42 am

Good point Steve. After seeing the socket connections I know why now. I think I will fix up the socket connections. (some traces may need replaced with wire from the socket to the between socket and main board  flex cable. Then recheck the bias.

Title: Re: Same o'le, same o'le.
Post by: Papa Jim on March 15, 2019, 07:20:27 am

Fixed traces. Not tried. It has .003 uF piggybacked to R20 with amatuer soldering  :dontknow: :dontknow: Why I wonder?  Removed it. Next step, retry bias.

schematic location section/area  C-5 pre PI/master volume.
https://el34world.com/charts/Schematics/files/Fender/Fender_blues_junior_rev_a.pdf

Title: Re: Same o'le, same o'le.
Post by: Papa Jim on March 15, 2019, 09:45:18 am

Not redplating now. Bias  -10.74 vdc. Amp no loud.  Looks and smells like OT may have go hot in the past. Probably need to get new output tubes and OT. What ya think.

Title: Re: Same o'le, same o'le.
Post by: Slimtim on March 15, 2019, 08:18:49 pm

do you have any other el84 tubes you can try?

Title: Re: Same o'le, same o'le.
Post by: Papa Jim on March 15, 2019, 08:26:28 pm

Nope I sure don't unfortunately.

Title: Re: Same o'le, same o'le.
Post by: Slimtim on March 15, 2019, 08:31:41 pm

what do you get at tp 17 and 18?and are you saying you're getting low sound or no sound at all?

Title: Re: Same o'le, same o'le.
Post by: Papa Jim on March 15, 2019, 08:42:47 pm

Like a 1w bedroom amp volume. It can remain dimed in a bedroom.

Title: Re: Same o'le, same o'le.
Post by: Slimtim on March 15, 2019, 08:53:09 pm

well i dont know much about this stuff but if all your test points are checikng out ok id say its a tube.

Title: Re: Same o'le, same o'le.
Post by: Papa Jim on March 23, 2019, 06:35:44 pm

Got it working with volume now. It was the OT. It evidently got too hot at one time or another. Went ahead and replaced the output tubes just to be sure since I have no idea how long the guy let them redplate for. Anyway all is good.

Title: Re: Same o'le, same o'le.
Post by: Slimtim on March 23, 2019, 10:28:46 pm

damn i hate that it was the trans.

Title: Re: Same o'le, same o'le.
Post by: Papa Jim on March 24, 2019, 05:52:40 am

Yeah, I got to looking and there was some black stuff that was coming out of the old one.