It is currently Tue Mar 17, 2020 2:53 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 4 posts ] 
Author Message
Post subject: Would bad tubes cause bias voltage to spike?
Posted: Thu Mar 01, 2012 11:23 am
Offline
Hobbyist
Hobbyist

Joined: Thu Mar 01, 2012 11:05 am
Posts: 2
I have a Hot Rod Deluxe III that is about 2 years old. I'm trying to determine if the problems it is having could be just from bad tubes or if in needs warranty repairs done to it. Here is what it is doing:
My son said it was acting up, but when I checked it there was no power and the fuse had blown. I replaced the fuse with a slo-blow fuse with the same rating as the original. When powered on it has occasional pops of static which eventually turn into a motor-boat sounding pattern and then disappear. After the amp has been on for several minutes, it begins to have a low hum that gradually increases to load volume. While this is happening, one of the power tubes begins to brightly glow blue. I also notice an electrical smell coming from the amp.
I went ahead and ordered 2 new matched power tubes with the same model number as the originals. I read how to bias the amp on the internet and wanted to see what the current mAmp rating was set to before replacing the tubes. While doing this, the voltage started spiking as the hum began and the one power tube started to burn bright blue. At this point I shut the amp back down again. My question is whether bad tubes could cause this increase in voltage and simply replacing the tubes could fix the problem. I don't want to take it in for a warranty repair if its not something that is going to be covered anyways. If I did that I was told I would end up having to pay the cost of them testing it and replacing the bad tubes.


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Would bad tubes cause bias voltage to spike?
Posted: Thu Mar 01, 2012 1:16 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Yes, an intermittent problems with the output tube can cause your symptoms. However, other parts in the output section may be the fault or may have been damaged. Prolly best to carefully inspect the output section. And look for damaged components, burnt or other overheated signs. Fried tracings.

You'd need to unplug the amp & remove the chassis of the amp from the cabinet. And discharge the main filter caps. If you feel uncomfortable or unfamiliar doing this, may want to take the amp to a good tech.


Top
Profile
Post subject: Re: Would bad tubes cause bias voltage to spike?
Posted: Sat Mar 03, 2012 10:27 am
Offline
Hobbyist
Hobbyist

Joined: Thu Mar 01, 2012 11:05 am
Posts: 2
Well, I put the new power tubes in last night and they seem to have solved the problems. :D I biased them to 70 mAmps, they were around 64 when I first put them in. I think the V1 preamp tube needs replacing as well because if I tap on it with the amp on, I get a kind of an echoing metallic sound coming through the amp. I'm thinking about trying a tube with a lower gain factor. This is my son's amp and is used mostly in our house. He can not turn the volume past 2 without it being very loud. He plays mostly jazz and also classical acoustic using the clean channel. I know basically nothing about guitars or amps, just trying to help maintain his equipment for him. Does anyone have any suggestions on tube designation and brand for this style of play?


Top
Profile
Post subject: Re: Would bad tubes cause bias voltage to spike?
Posted: Sun Mar 04, 2012 5:47 pm
Offline
Roadie
Roadie
User avatar

Joined: Tue Jun 28, 2011 11:54 am
Posts: 271
Location: Baytown, TX
A 12AY7 in V1 will lower the gain factor considerably. Do a search on my thread about my Blues Deluxe Reissue. Bluesky has a list of recommened tubes that will also work for the HRDlx listed there. And somewhere in this forum there is a list of tube types with gain factors also. Here's my thread:http://www.fender.com/community/forums/viewtopic.php?f=13&t=63584&hilit=blues+deluxe+reissue

_________________
2000 American Deluxe Stratocaster
2011 Gibson Les Paul Trad Pro 50's
2007 Epi Les Paul Custom
90's ESP Eclipse
JH-1B Jimi Hendrix Crybaby
Analogman KOT
Korg Pitchblack
Boss NS-2 PH-2
Blues Deluxe Reissue
1999 & 2007 Marshall TSL 100 w/1960BV cab


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: