FDP Home Page / FDP Forum / Classifieds / FAQ's / Links / Cookbook

The FDP is made possible by the following companies and individual members like you.
Please use the links below to show them we value their sponsorship.

The Music Zoo

Antique Electronics Supply

Musician's Friend

Jensen Loudspeakers

Sweetwater

www.thetubestore.com

Bill Lawrence Pickups

Guitar Center

Amplified Parts

WD Music

Amazon

MOD KITS DIY


* God bless America and our men and women in uniform *

* Illegitimi non carborundum! *

If you benefit and learn from the FDP and enjoy our site, please help support us and become a Contributing Member or make a Donation today! The FDP counts on YOU to help keep the site going with an annual contribution. It's quick and easy with PayPal. Please do it TODAY!

Chris Greene, Host & Founder

Registered Members: 64,000+

LOST YOUR PASSWORD?

......................................................................

  For Sale/Wanted Classifieds

 
FDP Jam
Calendar
Find musicians
in your area!
  Search the Forums  

ALL FDP MEMBERS CAN NOW POST IN MOE'S

FDP Forum / Amp Mods, Repairs, and Projects / power tube question

capecod bluesman

usa

Nov 20th, 2009 05:45 PM   Edit   Profile   Print Topic   Search Topic

Hey fellas, I have a Bogner alchemist that seems to be blowing power tubes every other month. I do not have a tube tester, will it ruin my amp if I put in another 6l6 tube just to see if my sound comes back big.

I feel like my amp is missing it's soul, gain is weak and just doesn't have any balls, usually I can put it on 1 and it's loud. I have a matched set of JJ's in there and all brand new JJ pre-amp tubes.

I have a ruby 6l6 sitting around, I just want to pop it in for a second to confirm what I think I already know. Why would an amp blow so many power tubes. My fender superchamp has blown 2 pre amp tubes in less than a year as well. I test ac outlet, seems fine according to my meter and polarity tester gatchet thingy I have. Thanks for any advice or comments anyone might have.

pauln
Contributing Member

Houston

Nov 20th, 2009 07:09 PM   Edit   Profile   Print Topic   Search Topic


I'm no expert, but I would first suspect the bias if power tubes are only lasting 60 days...

Not familiar with the Bogner - does it have a bias pot? If so you should get a bias tester, there are several good ones out there. If not you should take it by a shop and have the bias checked.

capecod bluesman

usa

Nov 20th, 2009 07:39 PM   Edit   Profile   Print Topic   Search Topic

Just had the bias done about 2 months ago. Bogner himself said the bias should be set at 35mA so that is what my amp tech set both sides at. My amp has 2 trim pots for bias, one for each power tube. This amp also blew a tube when the bias was set cold at only 23mA from the factory so i'm lost

I'm mainly concerned with just throwing in a random 6l6 tube in there, I don't know if it will hurt the amp or not. I don't think tubes were matched back in the old day's but nonetheless I have a matched set of JJ's in there now. Just want to troubleshoot and be positive it is a tube. Thanks

RussB
Contributing Member
****

Connecticut

a little out of tune
Nov 20th, 2009 09:11 PM   Edit   Profile   Print Topic   Search Topic

Please explain what "blown tubes" means to you?

(This message was last edited by RussB at 09:12 PM, Nov 20th, 2009)

Blue Strat
FDP Business Member

USA

Nov 21st, 2009 06:28 AM   Edit   Profile   Print Topic   Search Topic

It's ok to pop one in for a few minutes to see if everything seems normal. Beyond that, I would be sure to have the bias checked.

Mike K

KCA NOS Tubes & Amp Repair/Mods

capecod bluesman

usa

Nov 21st, 2009 04:47 PM   Edit   Profile   Print Topic   Search Topic

(This message was last edited by capecod bluesman at 05:43 PM, Nov 21st, 2009)

capecod bluesman

usa

Nov 21st, 2009 05:38 PM   Edit   Profile   Print Topic   Search Topic

thanks

(This message was last edited by capecod bluesman at 06:20 PM, Nov 21st, 2009)

RussB
Contributing Member
****

Connecticut

a little out of tune
Nov 21st, 2009 06:32 PM   Edit   Profile   Print Topic   Search Topic

your welcome?

capecod bluesman

usa

Nov 21st, 2009 08:33 PM   Edit   Profile   Print Topic   Search Topic

Russ what I mean about blown tubes is they sound weak, Have lost there power, gain on the amp is terrible, volume is low. Maybe it's not the proper term but it's always something i've said referring to a tube that craps out. I put a known good 6l6 in my amp and it sounded big and crunchy again.

I immediately took it out because I could tell right away that the amp needs to be biased with some new matched tubes, the mismatch tubes sounded good but I could tell it wasn't balanced, something was off can't put my finger on it. Thanks for all the replies, now off to get mores tubes. I have blown 2 sets in 2 months, something is not right there. I just play at home,no gigging or really loud playing.

Btw if anyone here could point me in the right direction, I would like to buy a tube tester and a bias meter. I want to learn how to bias my own amps, i have to many to keep having to pay tech to do it. I am a tech by trade(different profession)not amps or guitars obviously but I am pretty quick learner, I just need to learn the math behind bias'ing and which is some decent equipment that won't break the bank. Thanks agian

(This message was last edited by capecod bluesman at 08:47 PM, Nov 21st, 2009)

RussB
Contributing Member
****

Connecticut

a little out of tune
Nov 21st, 2009 09:48 PM   Edit   Profile   Print Topic   Search Topic

I think you're chasing your tail. Time to have the amp looked at...

Then again, there could be nothing actually wrong with the amp, it's you're just not diggin' it anymore

Rick Plays The Blues

Austria

ooops, I changed that tube again ...
Nov 22nd, 2009 02:16 AM   Edit   Profile   Print Topic   Search Topic

Capecod Bluesman,

you find some calculating formulae for bias setting and a bias test adapter at Weber.
Having bias pots, maybe you even have bias test resistors already installed in your amp so you might even get away without a test adapter?

However, with or without adapter, it is fairly easy to bias an amp (okay, easier with adapter, as it gives you direct access to all relevant measurement points without having to search for it).


Regarding your issue: I think it is not usual, that tubes wear out that fast. I was already dissatisfied when my power tubes were worn out after a year.
I agree you can hear it by the sound. In my case, it went along with a major bias drift (went up from 35mA to 55mA) on both tubes.
But I can absolutely not believe that tubes wear out as fast as you report.
Either you had absolutely bad luck with your tubes (where did you buy them. were they from same delivery? sure you did not get b-stock or something?)
or you amp is defective
or you just don't like the amp so much any more?

capecod bluesman

usa

Nov 22nd, 2009 01:47 PM   Edit   Profile   Print Topic   Search Topic

I absolutely love the sound of my amp, it's pretty clear when you play something 3 hours a day that it is not right. The volume at 1 was chunky and full of resonance and now it's on 3 and lifeless. I will contact eutotubes and see if I can send them back.

The first tubes that went, well one of them went was the original tubes, but the amp was only 1 month old and sent to me brand new. I will get some testers and tubes and have a go at it. THanks Rick for the information on testing.

THe results of putting a known good 6l6 into the amp were great, sound came right back but I could tell that it should not be running that way without bias, they are 2 completely different tubes and I like to get matched set's and bias. I do not know what to do with all the extra tubes I have, is there a way to balance different tubes to work together?? That would be something I would love to read about.

Rick Plays The Blues

Austria

ooops, I changed that tube again ...
Nov 22nd, 2009 11:06 PM   Edit   Profile   Print Topic   Search Topic

"is there a way to balance different tubes to work together??"

Since you have two individual bias pots, you can pair different tubes of same type (e.g. both 6L6GC) together - simply set up the same bias on both tubes.
It is not exactly the same result as if you have really matched tubes (not only bias matched but also matched amplification etc.) but it is okay.

Link to Weber's Bias Calculator page

capecod bluesman

usa

Nov 23rd, 2009 10:10 AM   Edit   Profile   Print Topic   Search Topic

Rick that is great to hear, at least this way I have backups now. I just placed an order for some tubes and bias probe's. I would like to do it with my multimeter but I have never done it that way and am a little skiddish without knowing all I have to do.

I was surprised to see that this amp had 2 trim pots being it was made in china in order to keep the cost down, everything else in the chassis looks like nice parts as well. Sounds amazing when everything is in harmony together,best 1200 I ever spent on an amp,it was tagged wrong got 400 off price:) Well Thanks again Rick

Rick Plays The Blues

Austria

ooops, I changed that tube again ...
Nov 23rd, 2009 11:16 PM   Edit   Profile   Print Topic   Search Topic

No need to thank me - I feel good giving back something to the board that helped me as well :-)

I guess the point about the bias pots is more due to Bogner design - nothing to do with where it has been produced.

Once you have the bias measurement adaptor, it is quite easy to adjust the bias.

1st, you can measure the voltage between anode and cathode of the tube (volume totally off, meaning voltage at idle) - this is the plate voltage for the bias current calculation.

2nd, there is a small resistor inside (usually 1 ohm) where you can read the voltage drop caused by the bias current. E.g. 30mV at 1 ohm means you have 30mA bias current. You then adjust the bias pot until you get desired voltage/current and there you are.

Don't forget to set your multimeter to 500V range for 1st step, otherwise you will blow your multimeter or at least a fuse inside.
For 2nd step, of course you need to set to minimum range like 50mV or 100mV.

There should be a description with the bias probe's, which measurement contact is which point in the circuitry.

Don't forget to bias each power tube separately ;-)

capecod bluesman

usa

Nov 23rd, 2009 11:40 PM   Edit   Profile   Print Topic   Search Topic

good stuff, yes I was given some pretty good directions today by the company that I am buying my tubes and bias probes from. They sent me pics and all sorts of amp specific directions on where to hook up what lead to what and where the trim pots were. Some I knew some I din't. People like them and yourself should feel good knowing your helping somebody out, one day I will give back what I know. Peace

capecod bluesman

usa

Nov 24th, 2009 10:56 AM   Edit   Profile   Print Topic   Search Topic

edit-answered me own question

(This message was last edited by capecod bluesman at 12:11 PM, Nov 24th, 2009)

FDP Forum / Amp Mods, Repairs, and Projects / power tube question




Reply to this Topic
Display my email address             Lost your password?
Your Message:
Link Address (URL):
Link Title:




Moderators: Black Hole Gang  Chris Greene  EA6B  Iron Man  reverendrob  

FDP, LLC Privacy Policy: Your real name, username, and email
are held in confidence and not disclosed to any third parties, sold, or
used for anything other than FDP Forum registration unless you specifically authorize disclosure.

Furtkamp.com 
Internet Application Development

Copyright © 1999-2014 Fender Discussion Page, LLC   All Rights Reserved