It is currently Tue Mar 17, 2020 1:27 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 6 posts ] 
Author Message
Post subject: Tried to set bias on a fender hot rod deluxe
Posted: Mon Oct 22, 2012 12:05 pm
Offline
Hobbyist
Hobbyist

Joined: Thu Mar 24, 2011 3:01 pm
Posts: 50
Older model made in usa ,1996 I think , meter readings from lowest to highest point while turning bias ajuster are 12.0 to 45.2 , have 2 - JJ 6L6GC , and 3 smaller tubes with no letters or numbers , the info I got said to set it at 71.0 , tubes light up ,just got amp , don't know if it has any mods , it works , sounds ok , totally lost ! please help .


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Tried to set bias on a fender hot rod deluxe
Posted: Mon Oct 22, 2012 1:50 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Jul 30, 2007 9:35 am
Posts: 62
From EutoTubes "If you're after maximum headroom then set the bias to about 70mv. If you're after an earlier breakup you can go as high as 90mv. Remember there is no right, wrong or "perfect" bias setting within this range. It's where YOU like it best. I simply want you to have the knowledge to be in control of your tone! Try different settings to see what works best for you. "

So what is it you are after? Check out this link:
http://www.eurotubes.com/eurotubes-Hotr ... lts-mA.htm


Top
Profile
Post subject: Re: Tried to set bias on a fender hot rod deluxe
Posted: Mon Oct 22, 2012 2:30 pm
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
Mr. smith wrote:
Older model made in usa ,1996 I think , meter readings from lowest to highest point while turning bias ajuster are 12.0 to 45.2 , have 2 - JJ 6L6GC , and 3 smaller tubes with no letters or numbers , the info I got said to set it at 71.0 , tubes light up ,just got amp , don't know if it has any mods , it works , sounds ok , totally lost ! please help .


Where are you taking these measurements? Are you reading volts or millivolts? You should be measuring across the one ohm resistor, R66, from TP 30 to ground as shown in the schematic.

http://support.fender.com/schematics/gu ... ematic.pdf

If that is where you are measuring, then your amp has a problem and I suggest you take it to a good amp tech as soon as possible. Note that you also need to measure plate voltage (over 400 VDC!), but given the obvious uncertainty in what you are doing, I suggest you take the amp to a tech anyway.

The three smaller tubes are the preamp (V1 and V2) and phase inverter (V3) and should be labeled "12AX7".

_________________
Bill

Image


Top
Profile
Post subject: Re: Tried to set bias on a fender hot rod deluxe
Posted: Mon Oct 22, 2012 3:20 pm
Offline
Hobbyist
Hobbyist

Joined: Thu Mar 24, 2011 3:01 pm
Posts: 50
Using a multimeter on millivolts , neg on chassis , pos on bias test point (tp 30), turning bias ajust pot all the way left , get 12.0 , all the way right get 45.2 .


Top
Profile
Post subject: Re: Tried to set bias on a fender hot rod deluxe
Posted: Mon Oct 22, 2012 3:50 pm
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
Mr. smith wrote:
Using a multimeter on millivolts , neg on chassis , pos on bias test point (tp 30), turning bias ajust pot all the way left , get 12.0 , all the way right get 45.2 .


You have a problem in your amp. You are only reading 1/2 of the bias current flowing through the cathodes of the power tubes. It could be something as simple as a bad tube or you could have a failed component in the amp. I had a similar problem in my Blues Deluxe Reissue in that I was only reading 1/2 of the bias current. It turned out that the screen grid of one of the 6L6GCs had shorted which took out one of the screen grid resistors (R61/R62 in the schematic).

First, check the bias power supply voltage ("C" in the schematic) while adjusting the bias pot. It should be a negative voltage down to about -55 VDC. If that is OK, then with the amp unplugged and the power supply caps drained, you can measure across each of the two screen grid resistors and see if one of them is open. If that is the case, replace both of them. I used 2 watt metal film resistors instead of the 1 watt resistors used in the amp. If both resistors check out OK, try replacing both power tubes and measuring the bias again. Beyond that, take the amp to a good amp tech. Good luck.

_________________
Bill

Image


Top
Profile
Post subject: Re: Tried to set bias on a fender hot rod deluxe
Posted: Tue Oct 23, 2012 5:28 am
Offline
Hobbyist
Hobbyist

Joined: Thu Mar 24, 2011 3:01 pm
Posts: 50
Thanks bluesky for the info . update - tech wanted $180.00 to repair , that included new tubes , .............. so I sold it .


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 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: