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Post subject: Use of negative voltage regulation in Bias Power Supplies
Posted: Wed Jan 16, 2013 1:22 pm
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Anyone use an LM-137 or LM-337T in a modded bias power supply to help stabilize the negative voltage? Trick seems to work well in older EICO and Dynaco amps.

http://www.tronola.com/html/ps_mods_for_st-35.html

http://www.linear.com/product/LM137?utm ... _medium=SE

Thanks!


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Post subject: Re: Use of negative voltage regulation in Bias Power Supplie
Posted: Thu Jan 17, 2013 2:53 am
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IMO you don't need regulate power supply for bias. The bias don't swing to need that.

If you read an unstabilize bias voltage , your amp have another problem. Many amp have poor bias pot .

What amp do you what to mod ?


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Post subject: Re: Use of negative voltage regulation in Bias Power Supplie
Posted: Thu Jan 17, 2013 6:07 am
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Stratele, I was thinking about modern amps with circuit boards that sometimes seem to make less consistent negative voltage. At least, I have worked on a lot of lower to mid-end amps that lose bias control and let the output tubes go ballistic.

Many old school hi-fi amps --- which have their circuits upgraded to modern boards, can have this same issue. This negative voltage regulator mod only costs a few dollars and seems to yield a more consistent negative voltage supply. It has been a well-known mod, in EICO, Dynaco, and Scott upgrades. I remember using an LM-137 in an ST-70 that was modded for guitar use --- about 20 years ago.

I believe that some of the issue is not just the supply itself, but some recent issued output tubes are not as tolerant to changes to negative voltage on the grid (actually, not as tolerant to changes in internal current flow). Allowing the tube to orange-plate more easily. That seems to be the word on amps that push their tubes hard. These amps sometimes do not sound too good, even slightly biased cold.

Often those amps that have their sockets soldered onto the circuit board. These are the worst offenders. They change the electric parameters of the circuitry around them, the most. With too hot biasing = permanent damage with capacitance and resistant changes to the tracings. I have not worked on many Fender amps with this issue. More than a few Peaveys and Crates have had this issue. Where after frying an output stage and tubes --- simple replacing of parts and pots does not yield an amp that has long-term stability.

I usually end up putting the bias supply onto a small, extra circuit and jumpering the signal chain and output to OPT. A messy affair, to get the amp stable and sounding good. Just wondered if this would have happen to such extent, if an LM-137 was in the bias supply, initially.

Anyhow, just a thought I would run up the flagpole and see if anyone saluted it.

Thanks!


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Post subject: Re: Use of negative voltage regulation in Bias Power Supplie
Posted: Thu Jan 17, 2013 12:00 pm
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The bias typically follows (line voltage and subsequent transformation to bias and the HV voltages. In my opinion a relationship exists so the HV and bias kind of in essence follow each other as line and signal voltage changes. it can be seen by monitoring bias as you vary signal levels..if you regulate the voltage but the HV swings a bunch..i feel the relationship (ratio) between the two may go way outta there....

take a look at oddwatt series of amps (power amps) using Ultra-linear tannys (super clean) and an LM317HV and a spanning resistor to supply a constant CURRENT not voltage to the Cathode of the power tubes (ALSO look at supertex and their line of Ldr's and HV mosfets

http://oddwattaudio.com/ the oddblock...the pod watt i am thinking of doing...asap

notice the drive tube is operating as a constant current bootstraped amplifier..cool stuff so cool that i am doing a Jazz amp for myself basically using a trainwreck minimalistic front end with a tone section derived from the jazz channel of a Dumble to a 12DW7 loop and to an oddwatt kt-66 power amp (5751 driver) that heavy but nice puppy should howl......read up on it

i MAY as in MAY (with my trash rusky 5881's try that in the vibro king i have a few 117HV in to-3 cases...my fav. if i do i'll post..heck i could do it today because after i am done messing with the SS22 i have to bring the VK back to the bench for tube testing and final selection...so i may get silly -i have been wanting to try it. i'm going to load 1 ohms in the cathode ckts anyway...so while i'm at that why not try?...if i blow a tranny i'll go order some Mercs....Rollo :shock:

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Post subject: Re: Use of negative voltage regulation in Bias Power Supplie
Posted: Thu Jan 17, 2013 12:05 pm
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BTW :shock:

I ordered an anniversary VK once it arrives and i load it the way i want...i'm taking this current one and it's going to be a head....

for the obvious reasons. and as a young man hauling a twin reverb up three flights of stairs (quietly) in the humid south Pacific air...well the VK weighs more than that..and i am OLD

i need a head..sold my el84 rev version VK head...

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Post subject: Re: Use of negative voltage regulation in Bias Power Supplie
Posted: Fri Jan 18, 2013 6:22 am
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rollo, interesting design. Wodner why Fender went to extent of adding a current limiter to the primary side of the PT (potentially noisy). And not a voltage regulator to the bias supply (not as potentially noisy)?

Thanks for post!


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Post subject: Re: Use of negative voltage regulation in Bias Power Supplie
Posted: Thu Jan 24, 2013 10:04 am
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BMW2002Ti wrote:
rollo, interesting design. Wodner why Fender went to extent of adding a current limiter to the primary side of the PT (potentially noisy). And not a voltage regulator to the bias supply (not as potentially noisy)?

Thanks for post!

Hey there 3.0CSI.....Black and proud parked in front of the Vail condo....on Swedish tires...after exercising a Vail cop's SAAB...night before christmas.... :mrgreen:

i was just messing around doing a supply for a mic pre i am whipping up...and am in the mood for a change from the ole 317 beast...check out the LT stuff like the neg ver of this beast

http://www.linear.com/product/LT1085 (look around the site)

here are some tech on tweaking 3 leg term..LT stuff...bears a read

http://cds.linear.com/docs/en/application-note/an2.pdf

"She had fun fun fun 'till her daddy took her 930 turbo away"....cuz she crashed it in the freaking snow..... :x :x :x :cry: $$$$ "fly fly away old dollars"... :evil:

And now, unlike the late 60's..i must do an acid wash...on the honey do list- tile job...then i am freeeeee!!! (guest bathroom....) :shock: Brahahahahawwwha..and more amp tweaking to come..... :mrgreen:

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Post subject: Re: Use of negative voltage regulation in Bias Power Supplie
Posted: Sun Feb 03, 2013 4:24 pm
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BMW2002Ti wrote:
Anyone use an LM-137 or LM-337T in a modded bias power supply to help stabilize the negative voltage? Trick seems to work well in older EICO and Dynaco amps.

http://www.tronola.com/html/ps_mods_for_st-35.html

http://www.linear.com/product/LM137?utm ... _medium=SE

Thanks!

Hey Beemer,

check out this nuttiness...slam that in a vibrok king and see what happens with KT-66..

this is nuts read it all......hummmm?????

http://www.partsconnexion.com/prod_pdf/conn_76156.pdf

:shock: :mrgreen:

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Post subject: Re: Use of negative voltage regulation in Bias Power Supplie
Posted: Fri Feb 15, 2013 10:25 am
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BMW2002Ti

Stumbled on a ton of hideously cool biasing data with CCS and bypassed CCS (partial), and a tube based CCS for the silicon snobs

Then stumbled on sick regulated HV rails etc...ZERO ripple...easy to do....(solid sate INDUCTOR circuit that is sick out of Italian Alps my AES base is expanding. THIS dude is using it and using regulation at each tube...VIA THE SUPERTEX REGULATORS

Off island...and when i tried to access my servers from the hole i am in..i couldn't - called the wife she said "the little light in back of the rack is blinking" can't remote in either... when i get back i will grab the stuff and post it.

Still have a 2002Ti? :?:

3.0CSI (had) :(

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