It is currently Mon Mar 16, 2020 7:35 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 5 posts ] 
Author Message
Post subject: Bassman 135 problem
Posted: Wed Jun 01, 2011 4:00 pm
Offline
Amateur
Amateur

Joined: Mon Dec 17, 2007 11:30 am
Posts: 118
I have a Fender Bassman 135 amp, probably 1980 era (i.e. black face panel, mid control on the guitar channel). Ultra-linear design. I bought it as a cheap route to a Silverface Twin - looking for the Fender super clean sound.

However, for some reason, the amp doesn't seem to be putting out full-power. For example, running a 4 ohm load as prescribed and master volume turned to 5, the amp should be making the walls shake, but it doesn't, it just is a mildly loud. In comparison, my old '81 Silverface Twin Reverb could play a high school gym on 3 1/2. When I first got the amp about a month ago, my local tech had replaced all four screen resistors, replaced two of the power tubes (two blew and the other two were good and were easily biased) and replaced the preamp tubes. While it is a bit "chime-ier", there is no difference in output.

Any ideas what might cause this and where should we look next? I really don't want this amp to become a money pit, but if it is something easy to fix, I'm all for it. Thanks in advance!

Matt


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Bassman 135 problem
Posted: Wed Jun 01, 2011 5:03 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
Several possible causes for low output, Matt.

The first thing I'd look at would be the power supply to ascertain you're getting the full 500VDC to the plates of the output tubes. Inspect and measure the diode-stack rectifier for sufficient voltage then take a look at the filter caps and the voltage-dividing resistors underneath the cap can. If those check okay, I'd move to the output tranny and the elaborate set of self-switching speaker jacks. The OT has multiple secondary windings to allow matching to a variety of loads. Make sure nobody has modded anything there. Here's the schematic for the Bassman 135......

http://www.ampwares.com/schematics/bassman_135.pdf

Best of luck, HTH

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: Bassman 135 problem
Posted: Wed Jun 01, 2011 5:47 pm
Offline
Amateur
Amateur

Joined: Mon Dec 17, 2007 11:30 am
Posts: 118
Thanks Arjay for the leads and the better resolution schemo than I had. I'm taking your reply to my amp dude Chuck and see what he finds. I'll let know the verdict.

Matt


P.S. Checked out an early 70s, well-played, NMV, DSR this evening ---Sweeeeet sounding!!


Top
Profile
Post subject: Re: Bassman 135 problem
Posted: Wed Jun 01, 2011 7:13 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
Dual Showman Reverbs are pretty righteous rigs for loud/clean. Skip the OEM cab though -- it's a hernia waiting to happen. Mate that head to a 4 x 12 enclosure stuffed with Weber California's or 12A150's and lead your star-struck fans on a pilgrimmage to Alpha Centauri.

:mrgreen:

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: Bassman 135 problem
Posted: Wed Jun 01, 2011 8:01 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
I would replace all four output tubes as a matched quad, even if two of them "tested" OK. :idea:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 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: