It is currently Mon Mar 16, 2020 1:46 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 4 posts ] 
Author Message
Post subject: Twin Reverb BF 1991 PRE186
Posted: Sun Jul 30, 2017 7:03 am
Offline
Hobbyist
Hobbyist

Joined: Sun Jul 30, 2017 3:56 am
Posts: 1
Hi Hi ...

First posting .... 8-)

Got a 65 Twin Reverb (1991) PR186 with bad static crackling noise ..

So to help everyone shorten their reading time here is what I have already did :

1. Crackling sound once power on ,without any plug in. Volume knob does not affect crackling
2. Clean all 10 control POTs and 4 input sockets
3. Replace R33 with dry soldered joint
4. Reflow solder on all tube sockets
5. Retension and cleaned all 10 sockets, no crackling when rattling tubes .. Good.
6. Replace all screen resistor with 1W R1.5k on power tubes
7. Replace all Plate R470 ohm with 1W on power tubes
8. Remove Output power tubes V8 and V9 to half the output.
9. Remove V1 ... just so to test CH2 only.
10. Change all 6x Preamp and 4x Power Tubes and re-bias to 65%. Tested and no microphonic fault.
11. Further chopstick poking with the amp ON ... did not find any loose components or loose ribbon cables.

Tested the Amp and sounded really sweet late into the evening ... happy and slept well.

Played again in the morning .... the damned static crackling noise just came back ... pops occur at random and not regular ...

I am pulling my hair out because I could not find where the fault is .... :(

Do I need to go into the doghouse to look at the caps ... or change out the plate resistors preamp tubes ?

Any great help will be greatly appreciated ... :D


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Twin Reverb BF 1991 PRE186
Posted: Fri Aug 04, 2017 8:07 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Tue Mar 01, 2011 3:10 pm
Posts: 5646
Location: Gateway to the West
Two suggestions:

Go back through the 11 items you listed and double check all your work and every connection.

Open up the Doghouse and see if there are anything looking out of order. If the caps are original they could certainly be ready for replacement at 20+ years old. Be careful with the caps, you seem to know what your doing, but a reminder never hurts and might keep you from getting killed.

T2

_________________
-----------------------------------------------------------
What time is it? It's Fender Time.


Top
Profile
Post subject: Re: Twin Reverb BF 1991 PRE186
Posted: Tue Aug 15, 2017 7:01 pm
Offline
Professional Musician
Professional Musician

Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1023
The lucky fix would be loose nuts on the input or speaker jacks.
Did you clean and exercise the ribbon cable connectors? There could be loose rivets on a control. You need to pull them to see if they wiggle. Squeeze the rivets until tight or replace the control.
There are electrolytics from that era that are broken internally, but aren't leaking. Give a good tug on the positive lead with needle nose pliers. If it pulls out, its junk.
But it sounds like a connection problem, not a component failure.
The next test will be to pull all the preamp tubes except the V6 phase inverter and see if it still crackles. If so, look at the main stage and power supply. If it quits crackling, add V5, then V4, then V3 etc until the crackling comes back.


Top
Profile
Post subject: Re: Twin Reverb BF 1991 PRE186
Posted: Tue Aug 22, 2017 3:23 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
TimsAudio wrote:

But it sounds like a connection problem, not a component failure.
.



+1

I guess it is a solder or tubes socket contacts


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 4 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: