Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Instruments and Amps Everything that makes music, Especially including instrument amps.

Guitar amp
Guitar amp
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 24th April 2009, 06:49 PM   #1
argonrepublic is offline argonrepublic  Canada
diyAudio Member
Join Date: Apr 2005
Location: Simcoe Ont
Default Guitar amp

I have a problem with guitar amp. It is a Randall RG200. At idle it has a louder than usual 60hz hum. as I turn it up there is no signal until around "7 or 8". It kind of crackles through loud and powerfully. At full it will almost run. Signal does not decay it just drops out. Could someone please point me in the right direction? I would like to solve the problem myself (with help). I will try to upload jpegs.
  Reply With Quote
Old 24th April 2009, 08:55 PM   #2
mjf is offline mjf  Austria
diyAudio Member
Join Date: Jan 2009
Location: Austria
perhaps a (volume-)pot is damaged .have a look for bad soldering points............clean the pot with a contact spray.
  Reply With Quote
Old 28th April 2009, 07:59 PM   #3
argonrepublic is offline argonrepublic  Canada
diyAudio Member
Join Date: Apr 2005
Location: Simcoe Ont
Default Resistors Blown

Thanks for input. I checked pot fully and continued to inspect Amp. Found two blown resisitors. R68 and R69. I can't upload jpeg. if Anyone is willing to look at it I could email jpeg.
  Reply With Quote
Old 2nd May 2009, 07:06 PM   #4
spirod is offline spirod  Australia
diyAudio Member
Join Date: Sep 2006
Did it get worse over time or did it just happen suddenly?
What happend at the time it died?
I've seem guitar amps with T03 ouput devices sometimes the leads get dry joints as they see a lot of thermal stress. this is why i ask the above.

but heres my 2 cents worth:
You could have lost output from one rail by the sound of what you are saying. but the input cct may be fine.
I'd measure for:-
Dc at the output, should be close to 0 volts. ie across the speaker.
Also the VAS transistor voltage across the CE.
if you can measure the bias current would also be good to know if it still exists.
and post you findings.

also if you have an incircuit transistor tester it would come in hand.
but by the sound of it I would guess probably a driver and an ouput device have failed at the least, other than the 2 blown resistors.
  Reply With Quote
Old 3rd May 2009, 01:48 AM   #5
Artie is offline Artie  United States
diyAudio Member
Join Date: Jul 2007
Location: Jax, FL
Default Re: Resistors Blown

Originally posted by argonrepublic
Found two blown resisitors.
Ok. How do you define "blown"? Its like saying . . . My car goes thump, thump, thump. Found one flat tire. What else should I check?
  Reply With Quote
Old 4th May 2009, 02:16 PM   #6
argonrepublic is offline argonrepublic  Canada
diyAudio Member
Join Date: Apr 2005
Location: Simcoe Ont
Default Blown

As soon as I power up Amp, resistor begin to smoke until open. To of them are comming off tube heater circuit.
  Reply With Quote


Guitar ampHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
4x12 Guitar cab using guitar and bass speakers help andrewskaterrr Instruments and Amps 15 24th April 2009 12:43 AM
JLH Guitar Amp lcsegeng Instruments and Amps 1 14th March 2007 08:12 AM
DIY guitar BassAwdyO Instruments and Amps 41 8th January 2006 07:32 PM
Guitar to DIY amp? silentblackhat Instruments and Amps 2 27th July 2004 07:36 PM
6V6 Guitar Amp SHiFTY Instruments and Amps 2 5th August 2003 03:10 PM

New To Site? Need Help?

All times are GMT. The time now is 08:46 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio