It is currently Mon Mar 16, 2020 6:44 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 3 posts ] 
Author Message
Post subject: 60 cycle hum and a very hot power tube
Posted: Mon Mar 28, 2011 4:50 pm
Offline
Roadie
Roadie
User avatar

Joined: Tue Jan 04, 2011 8:21 am
Posts: 239
A couple of months ago..I pulled my 1963 Bandmaster (6G7-A) out of the closet (been there for the last 15 years or so). Plugged it in...works perfectly. I really had forgotten how great this amp sounded. Since then, used it almost everyday until about 2 weeks ago. Decided I would play thru it today..turned it on and got sound...but also what sounds like a 60 cycle hum thats not affected by volume control...and upon taking a look at the back...one of the power tubes..getting very hot (plates glowing red). Turned it all off..and here I am. Any ideas? Any help would be appreciated.

_________________
Image

This Ain't No Dress Rehearsal..We Are Professionals & This is the Bigtime - Waylon


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: 60 cycle hum and a very hot power tube
Posted: Mon Mar 28, 2011 5:10 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
I'd guess that the 470-ohm screen resistor on one of the power tube sockets finally gave up the ghost and the momentary voltage surge took one or more filter caps with it.

It's time for some servicing and a general overhaul, methinks.

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: 60 cycle hum and a very hot power tube
Posted: Mon Mar 28, 2011 8:17 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
I kinda remember an amp tech long time ago complained about how some early Bandmasters used kinda under-rated filter caps in their Bias Power supply. I looked up your schemo & sure enough! 8mfd/150VDC caps in parallel. The caps go dry and put AC onto the grid. The other source of hum was often burnt out "hum" pots.

He used to replace the diode with a good quality UF4004 and two 50/100 'lytics. Aybe worth a try. Good Luck!


http://www.prowessamplifiers.com/schema ... matic.html


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 3 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: