Question about biasresistors

[Roly]

Zener (or Reg chip)

Zener yes, reg chip no - these operate in quite different ways and the power dissipated by a reg chip is pretty well = output current times voltage difference across reg, the self operating current normally so small it can be neglected.

E is voltage (ElectroMotiveForce or EMF)

A zener regulator is a shunt form, when it's unloaded the maximum available current goes through the zener.

The three pin regs are series regulators where a series transistor is adjusted to pass exactly the right amount of current to maintain the output at the required voltage.

Generally the main dis/advantage is that having a single supply is cheap but requires a regulator that will get fairly hot, while having a specific low voltage supply is more expensive but more elegant and (literally) cooler.

[Rutger]

Thanks Enzo, I placed new resistors and have a decent voltage on the IC's now.  :dbtu:

No problem Phatt, I got my answer, so the thread can go about anything else we can learn from!  :cheesy:

[phatt]

@ Rutger, Glad to hear it worked out. :dbtu:

I just made a fluff up job of using a pre existing power amp board to run multiple opamps for a foldback I'm trying to get up and running on the cheap and forget to check the Zener regulation.  :duh
So now I have to pull the 1k resistors (need 330 R) off a small tight space and I've stuffed the cheap PCB tracks from the power amp circuit board.
So back to the bench to make a whole new board for the power amp and PSU,,,,which I should have done in the first place. xP
Serve me right for cheating too much.


and Thanks Roly,, yep I hang my head in shame, should have known what E stood for.
I doubt I'll ever totally conquer the mountain but I pick up a lot from wonderful folks like you and I feel more confident to take on slightly harder stuff but I try not to get in too deep cause I know darn well I'll get caught out if I'm to cocky about it.

I say that as I take on another repair which erks me a bit,,I don't like PCB Valve gear much. :grr
Can't even get the red knobs off the front on this Fender, broke the pot shaft on one already. :duh

Surprising how little electronics is actually involved in repairs
as a lot seem to be more mechanical issues.

The leaky power caps where easy to fix but now it's turned into a major
headache that will take a lot longer to fix.
Such is life.

Phil.

[Enzo]

I don't like PCB Valve gear much.
Can't even get the red knobs off the front on this Fender,

Surely you don't think the knobs were stuck because it is a tube amp?  Like the same pots and knobs on a solid state amp would slide right off?   Maybe a little heat will help loosen them.

[Roly]

Dunno if I mentioned that I had a Jensen up on the bench needing a clutch of new pots.  Everything went well, including getting a couple of unobtainium tapped pots ... until I tried to get the last knob off.

I did, eventually, but not before Murphy had extracted his pound of flesh.  "Electronics"?  What's "electronics"?  :lmao:

[phatt]

I don't like PCB Valve gear much.
Can't even get the red knobs off the front on this Fender,

Surely you don't think the knobs were stuck because it is a tube amp?  Like the same pots and knobs on a solid state amp would slide right off?   Maybe a little heat will help loosen them.

Sorry Enzo,, Badly worded on my part.
No I mean I hate pcb Valve stuff because they have heaps of room but persist in making the high current traces way too fine and narrow.
Causing a real big headache to fix de-laminated tracks from 10 Watt resistors that run far too hot and too close to boards. :grr :grr

(I think JM Fahey touched on this a while back,, noting that SS guitar Amp pcbs should be wide as possible if you want then to survive long term.)

In this Amp ,, a Fender Red knob super 210 there is heaps of pcb real estate to spread the tracks,, but NO they decide to use fine tracks in the wrong places.

IMO,,No excuse,, just plain bad design and planning.

Anyway it's all working now with the help of some eyelets through the board I've been able to rescue the high current traces which had lifted from the over heated fiberglass.

Heating knobs may sound like a good idea but you likely need a heat gun and even then you may end up with a melted blob by the time you finish.
I have no doubt it would work but you have to be setup for it.

I've had this disaster happen a few times and my advice to folks is pull them off and wipe some Vaseline (Petroleum jelly) that will stop the Aluminum shafts from oxidizing and gripping the press fit plastic knobs.
But of course you need to do this long before they clamp on. xP

In the old days these shafts where likely Brass which did not oxidize,,, so much for advancement. :duh
Phil.

[phatt]

Dunno if I mentioned that I had a Jensen up on the bench needing a clutch of new pots.  Everything went well, including getting a couple of unobtainium tapped pots ... until I tried to get the last knob off.

I did, eventually, but not before Murphy had extracted his pound of flesh.  "Electronics"?  What's "electronics"?  :lmao:

Tapped pots ?
So They still exist?

I think I have a couple of those in a bucket under my bench but hifi era so lower values.
I'm assuming You are working on Valve stuff and are in need of high values like 1Meg?
Phil.

[Enzo]

A heat gun, or borrow the wife's hair dryer.  Bonus, hair driers are far less hot than heat guns.

[Roly]

Um ... 300k tapped at 75k, apparently standard on some early Fender, Jensen decided to use them for their tonestacks, and thankfully still being made.  Managed to find some locally rather than having to pay $50 shipping on a couple of $5.50 pots from the US, the balance of my find have gone to Mac at EVACO, troops, for the use of.


Freeze the pot shaft to make it shrink?