It is currently Mon Mar 16, 2020 9:30 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 12 posts ] 
Author Message
Post subject: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Fri Jul 18, 2014 5:03 pm
Offline
Hobbyist
Hobbyist
User avatar

Joined: Thu May 21, 2009 5:19 pm
Posts: 49
Location: Gulf Coast Florida
I DID it ! ... me thinks. I'd like those of you who are more experienced at it than me and my first time, tell me I did correctly OR I screwed up by forgetting something.
I took all yer advices and purchased a Bias Tester. Mine is a Duo from Amp-Head $65.

Here's what I did: pulled chassis out, connected speakers, turned on amp leaving it on standby.

- I pulled out the stock Fender Groove Tube 6L6sv power tubes, turned off standby making sure all dials were zeroed, and measured plate voltage on pin #3 = 461v (after 10 minute warmup). Put amp on standby.

- 2ndly, I attached the new sockets to the amp sockets and carefully stuffed the original Fender power tubes in the new sockets. My Dual Bias Tester switch is on #1 tube setting and both banana plugs are stuffed into my DMM. DMM setting is at 200m on Vdc section. Scale reads "0" on DMM until I flip the standby switch off. Instantly, tube #1 (V7) reads '32'. A flip of the Dual Bias Tester to position 2, reads V8 power tube as '42.4'.
This, pissed me off because I really liked the sound of these tubes yet they were far from being a 'matched' set!!! OK ... let's move on.

- 3rd - I stuck in the new Svetlana SV 6L6gc tubes and let them warm for 10 minutes.
Tube one came in at 28.9 and tube 2 was 28.3 - right out of the box. So now it's time for math. The manufacturer recommended that these tubes should be biased between 30 -37. The MPD chart for 6L6s says that factor is '30'.

@ 70% = 0.7 x 30(MPD)/461 = 0.046 .... way too high for a Super Reverb????
@ 60% = 0.6 x 30(MPD)/461 = 0.39 .... still to high for SR???
@ 50% = 0.5 x 30(MPD)/461 = 0.033 ... I set mine to 0.036

It plays well, sounds good, doesn't make me fart with joy and euphoria but at least, I believe it is set up properly. Oh yeah, I put in 4 new Tung-Sol 12ax7's, and a jjECC81 in V3, and pulled V1 out so it's all retubed except for the new rectifier tube which will arrive next week.

Did I miss anything? :roll:


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Fri Jul 18, 2014 7:10 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
bluezguy09 wrote:
...Did I miss anything? :roll:


Firstly, you are supposed to measure the Plate voltage with the tubes installed.

Any "recommended" current settings that don't include Plate voltage of your particular amp are BS. Your math is correct for the 50% to 70% range, that is all that matters. Except, use the Plate voltage reading that you get with the tubes installed, which will be much lower than with the tubes out. Your Plate voltage with the tubes installed should be closer to 430 VDC. With 430 Plate volts, your current range would be - 50%= .036 amps (36 mA), and 70% = .048 amps (48 mA)

Otherwise, you've just about got it. 8)

Personally, in this case I would go to about .040 amps (40 mA).

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Fri Jul 18, 2014 8:24 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
shimmilou wrote:
Firstly, you are supposed to measure the Plate voltage with the tubes installed


+1

shimmilou wrote:
Personally, in this case I would go to about .040 amps (40 mA).


+1 too.

Forty milliamps is a good datum point for most quality 6L6GC's. Tweak from there for optimum tone and tube life.

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: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Sat Jul 19, 2014 1:41 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
Allo toi !

Use bias calculator ; easier and faster ;

http://www.webervst.com/tubes1/calcbias.htm

Each time you change bias adjustment, you must check plate voltage

Hot bias = low plate voltage
Cod bias = hight plate voltage


Fender amp play very well at "cold" bias ( 50 % ) . Cold bias save tube , Do some hear test


Top
Profile
Post subject: Re: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Sat Jul 19, 2014 3:38 am
Offline
Hobbyist
Hobbyist
User avatar

Joined: Thu May 21, 2009 5:19 pm
Posts: 49
Location: Gulf Coast Florida
shimmilou wrote:
bluezguy09 wrote:
...Did I miss anything? :roll:


Firstly, you are supposed to measure the Plate voltage with the tubes installed.
Personally, in this case I would go to about .040 amps (40 mA).


OK ... that's why I hang around here :oops: :!: Back to the drawing board. As you can tell, I went in to the top of the tube socket with tube removed. I will pull the chassis right now before too much caffeine begins to flow through my veins which then, I'll have to re-bias with red wine to adjust :lol: .
So, I will measure from bottom of tube socket exposed in chassis.

Thanks again!


Top
Profile
Post subject: Re: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Sat Jul 19, 2014 4:25 am
Offline
Hobbyist
Hobbyist
User avatar

Joined: Thu May 21, 2009 5:19 pm
Posts: 49
Location: Gulf Coast Florida
Here I am - I/2 an hour later - to tell you my plate voltage when measured with tubes "IN" is 458 ... if you recall, my original measurement was from the tops of the tube sockets with tubes "OUT" and that was 461.
Is the difference kinda negligible? Anyways, if it's to be from the bottom and tubes "IN", so be it ... that's the way it'll be done!
Thanks again for checking me. Have a great weekend!


Top
Profile
Post subject: Re: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Sat Jul 19, 2014 7:39 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Something is not right. :?

I am not sure what you are measuring, but the voltage can not be that close with tubes removed vs installed. From the bottom, count the pins in a clockwise manner, from the pin immediately to the left of the key which is pin 1. VDC correct? Negative meter lead on the chassis, positive meter lead on pin 3.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Sat Jul 19, 2014 8:22 am
Offline
Hobbyist
Hobbyist
User avatar

Joined: Thu May 21, 2009 5:19 pm
Posts: 49
Location: Gulf Coast Florida
shimmilou wrote:
Something is not right. :?

I am not sure what you are measuring, but the voltage can not be that close with tubes removed vs installed. From the bottom, count the pins in a clockwise manner, from the pin immediately to the left of the key which is pin 1. VDC correct? Negative meter lead on the chassis, positive meter lead on pin 3.


Respectfully, I am sure what I am measuring - including correct pin holes both top and bottom backed by about 50 years experience soldering and using prehistoric multi-meters when I used to do Heath-Kit projects for nerd type hobbies :) :)
I just never got around to messin' with guitar amps as there was never any need to ... until I joined a couple forums a few years ago and got taken by this 'mod' bug :roll: Fun, interesting BUTTT - expensive.

I'll call Fender support on Monday and let them know waz happenin' to see what they say. There are various posts on other Fender Discussions with folks having Plate Voltages in the 460s. The suggested solution was to get a rectifier which would reduce this voltage. Such is the case with the RCA 5R4GB to replace the 5AR4.

I approve this message. Written with no malice, no offence taken or given and with complete appreciation for your concern!!!!!!!!!!!!


Top
Profile
Post subject: Re: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Sat Jul 19, 2014 11:02 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
bluezguy09 wrote:
There are various posts on other Fender Discussions with folks having Plate Voltages in the 460s. The suggested solution was to get a rectifier which would reduce this voltage. Such is the case with the RCA 5R4GB to replace the 5AR4.


Personally, I think you're pissing in the wind.

You should have 465 VDC at the output tranny's center-tapped primary, 460 VDC at each of the primary's outboard legs.

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: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Sat Jul 19, 2014 1:15 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
shimmilou wrote:
Something is not right. :?

I am not sure what you are measuring, but the voltage can not be that close with tubes removed vs installed. From the bottom, count the pins in a clockwise manner, from the pin immediately to the left of the key which is pin 1. VDC correct? Negative meter lead on the chassis, positive meter lead on pin 3.



+1, or the bias is very very cold .


bluezguy09,

Tubes are a load for the plate voltage , with tube in , plate voltage must drop at least 10 volts . Or your tubes are not properly biased , are defective, or you make some mistake somewhere ?


Top
Profile
Post subject: Re: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Sat Jul 19, 2014 1:16 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
Retroverbial wrote:
bluezguy09 wrote:
There are various posts on other Fender Discussions with folks having Plate Voltages in the 460s. The suggested solution was to get a rectifier which would reduce this voltage. Such is the case with the RCA 5R4GB to replace the 5AR4.


Personally, I think you're pissing in the wind.



Arjay



+1


Top
Profile
Post subject: Re: My '65 Reissue Super Reverb Re-biased By Moi
Posted: Sat Jul 19, 2014 2:57 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
stratele52 wrote:
Tubes are a load for the plate voltage , with tube in , plate voltage must drop at least 10 volts . Or your tubes are not properly biased , are defective, or you make some mistake somewhere ?


+1

I should've mentioned that voltage drop as well, Stratele.

Mercí, mon amí.

:oops:

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
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 12 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: