Re: waddaya think about biasing..........

 :

4/19/2000 2:51 PM

Trace

Re: waddaya think about biasing.......... quote: "ok, then how about the tranny in the silver jubilee 50 watter? do you know if it's similar or the same as a regular 800,"     As I recall I think it's a different tranny but it pretty much looks the same as the 800's. Speed might know answer for sure.     quote: "...and with this tranny and EL34LS at 457 volts, what would you consider a low bias setting that won't compromise the tone while being lower than the max so that the tubes will last a bit better?"     I think 30-32ma is a pretty place to be in my opinion. You can also change the bias splitter resistors to 100K's, as I recall there are 220K's in there now. The 100K's will make your power tubes last longer as well.     As a side note on these amps: If you decide to ever run these amps as part of a multiple amp set up you will find that the Jubilee is out of phase with pretty much all other amps (Fender's Vox's, Boogies, etc.)     Hope it helps!   Trace

 

4/19/2000 4:36 PM

dale

As a side note on these amps: If you decide to ever run these amps as part of a multiple amp set up you will find that the Jubilee is out of phase with pretty much all other amps (Fender's Vox's, Boogies, etc.)     trace,     can you expand on this point for me? i use a peavey classic 30 with the marshall onstage in stereo, and i haven't noticed any out of phase problems. it sounds nice and thick. but i'd really like to hear more about what your saying. for all i know, maybe reversing the speaker leads on one of the amps WOULD make a difference is what you're saying is true. maybe it's just not as obvious for some reason.

 

4/24/2000 1:58 PM
J. Vincent Collins	Pick up the book:     Tube Amp Talk for the Guitarist and Tech   by   Gerald Weber.     He describes the use of multiple amp setups and   how to set up all your stuff so it will always be in phase.   Hope this helps.   ISBN# 0-9641060-1-9

 

4/19/2000 5:16 PM

SpeedRacer

Dale - the OT in your Jubilee is that same as the regular 800 AFAIK. I don't believe that Marshall used different models for different amps of the same output power.   As far as biasing though, the whole point of my post was to suggest using your ears and your guitar to set the bias - within the limits of the tubes' dissipation ratings.   35mA sounds great in my amp, Trace's amp sounds great at 30mA and I've heard amps with idle sttings from 20mA to 45mA which all made their users happy.   There is no one right answer!   You have a range to work with, but ultimately it's up to YOU to see what works the best for YOU.   Just plug in and tweak.

 

4/19/2000 5:24 PM

dale

thanks all. i decided to just set it 5 ma under the max. it doesn't seem to sound any better at max, so i figure take it a bit easier in them 34's and have max tone to boot. what i'd like to know is why i run into so many techs who will literally get mad at you if you even suggest that theres are different points at which an amp can be biased depending on the amp. they'll tell you any lower than the max and tone will suffer, any higher and your amp will go poof ! and they tell you this in no uncertain terms. amazing what money can do to a person's personallity, eh? *S*

 

4/19/2000 5:45 PM

Rebel420

quote: " i run into so many techs who will literally get mad at you if you even suggest that theres are different points at which an amp can be biased depending on the amp" Exactly!!! Remembe a while back, I had the marshall that the tubes would runaway, turns out it was an issue with the OT being too close for comfort, and between the hotplate and my speakers having lower imp, the y woul overdissipate, so with that setup, I could bias the amp with the tubes at 20mA to kepe them from running away, and when cranked, it sounded pretty good. with different speakers I could get away with a higher biasing and still sound just as good. Biasing too hot is not recommended by anyone, WITHIN reason... however there is no dispute you will wear out your tubes quicker. AND some tubes can handle running hotter than others.. AN old set of mullards are pretty much bulletproof, whereas some of the chinese el34's have been reported to go within a fewminutes in MusicMans or old plexis (never understood why if you coud afford a plexi, oyu coundt afford good tubes..) Have I ever blown an output tube, even by biasing too hot by mistake no. I've only ever heard 2 output tubes go in my lifetime.. the first was about 10 years ago in a Fender Bassman 10, and last month on a BFSuper Reverb. Did the OT go with them in these cases. No.. could it have.. .yes.. honestly, 20-30 years ago, a lot of people didnt ever bias their amp. Fenders and marshalls were biased slightly cold from the factory, and in most cases people just popped in new tubes and went with it... heck most of the time the tubes werent even matched. And as for tone suffering.... if what they did back then was so 'wrong' why are we today trying to clone the sounds of yesterday! Yea the tone will suffer.... do you like the supposed 'suffering tone'? if yes, then thats what it's all about.... My theory is, the specs are a guideline on where to start, but they cna go either way... remember, we generally try to bias at 70% of the max, so you ahve a bit of play onthe hot side. NOW if the plates start to glow when cranked, or especially when idling, then definitely back things off a bit--here is a case where your tubes are gonna go quick... if the amp will never be cranked, and they are good up to and above where you normally play it, enjoy it! I'm not encouraging anyone to do crazy things, but as long as you know the POSSIBLE outcomes of what you do, remember after all, it is YOUR equipment... you are free to do whatever you like with it...just remember to keep yourself safe.     To summarize, I"m NOT telling you it's OK to grossly bias your tubes too hot, but saying 1 or 2 mA over what is recommended in some cases IS ok, as is way under what is recommended....Maybe i should'nt have posted this...but I AM entitled to my opinion....     P.S. ideas contained in this commentary are not necessarily reflective of the views of this BBS or any of the users on here. Of all things, you are on your own, and do at your own risk. These are strictly the opinion of myself and NOT textbook fact!

 

4/20/2000 12:30 AM

Ray Ivers

Dale,     This isn't really to the point of your posting, but I wanted to put it out anyway.     Certain amps - 50 watt, JCM900, 30th Anniversary, DSL and TSL Marshalls, some Ampegs, the Vox AC100, etc. - derive their bias supply from the HV supply. This really sucks, because the bias voltage varies with the high voltage - and since the HV voltage supply in a non-regulated supply will vary with bias voltage, a 'vicious circle' is created - the HV drops, the bias drops, the tubes suck more current, the HV drops more, etc. I ended up having to bias my 30th Anniversary head by the most bullshit method imaginable: enough voltage to ensure that the plates don't glow red after being on for an hour, minus about 10 mils. Older 100 watt Marshalls have a separate bias winding (and a choke) so the bias voltage only varies with line voltage, as it should unless everything is regulated.     My advice - keep an eye on your plates if you own one of these amps, especially in a place with unfamiliar line voltage.     You ever see the schematic for the output stage on a Music Man RD100? 15 mils quiescent current (total!), almost no crossover distortion, a really clean sound. I've changed the original Sylvania 6L6GC's in these amps after 5 years of hard use and heard no difference at all - it was like the tubes had 3 months on them.     Ray Ivers

 

<<First Page

<Prev

Page 2 of 2