Hoffman Amplifiers
> Tube Amp Building - Tweaks - Repairs
> oscillation/snubbers&PI
<< Prev Topic | Next Topic >>
Author Comment
Tesno
Junior tube assistant
Posts: 6
(2/18/04 9:41 pm)
oscillation/snubbers&PI
--------------------------------------------------------------------------------
If I choose not to use the snubber capacitors how will I know or will oscillation occur randomly; then all of sudden while playing on stage live will it happen?
What does oscillation sound like?
On a Phase Inverter plates they seem to use this combination 82k/100k how does this matter and why?
Life is a jest and all things show it, I thought so once but now I know it.
coap01
Junior tube assistant
Posts: 99
(2/18/04 10:02 pm)
oscillations
--------------------------------------------------------------------------------
they will definitely NOT occur randomly. you will have to do something to make it go bonkers. like if you increase your gain/volume past a certain point, the amp will start to squeal and howl. or it might do that off the bat when you turn the amp on
as far as how it sounds, i had high pitched feedback type sounds or possibly motorboating. but regardless its NOT pleasant and you will definitely hear it.
i've been wondering about the 82k/100k thing myself and have yet to hear better answer then to balance the split push/pull signals. anyone has more info?
Lucid Alice
Senior tube assistant
Posts: 162
(2/18/04 11:01 pm)
Re: oscillations
--------------------------------------------------------------------------------
I definitely cannot provide an engineering explaination to this. But what is obvious to me is that the side with the 82K is the side of the PI that the preamp signal feeds directly into. My guess is that this triode receives a stronger signal than the other side of the PI. An 82K resistor on the plate would reduce the gain on that triode relative to the other side with a 100K resistor on the plate. Guess we all understand that it is supposed to balance the two sides.
Yes, it would be great if someone could explain how the second triode receives an inversion of the signal at the first triode. I never have fully understood how the PI does what it does. (Maybe I should read more books!)
gammelnalle
Junior tube assistant
Posts: 13
(2/19/04 2:48 am)
Re: oscillations
--------------------------------------------------------------------------------
www.tone-lizard.com/lesson8.htm about biasing
www.tone-lizard.com/lesson10.htm Maybe can be to some help... All his "lessons" are good AND fun!!
Tiny Daddy
I will work on all amps
Posts: 494
(2/19/04 4:19 pm)
Re: oscillations
--------------------------------------------------------------------------------
A small explanation:
If you set up a triode with plate resistor, grid bias resistor and UNBYPASSED cathode resistor, the resulting circuit has 2 (two) inputs: the grid which is inverting, and the cathode, which is non-inverting. The input impedance to the grid is high while the input impedance to the cathode is low. Now the cathode can be driven by connecting it to the cathode of another triode.
As for the uneven plate resistors, this unbalance is said to be the secret of Fender's great Bass sound. Some amps use a 100K and then 91K+9.1K for symmetyr and tap the sound off the junction of the 91K+9.1K. Don't know if there's a patent on that or not but using 100K and 82K seems cheaper, or a way to avoid a patent.
coap01
Junior tube assistant
Posts: 100
(2/19/04 5:36 pm)
tone lizard
--------------------------------------------------------------------------------
holy crap...i must have spent past 2 hours reading over this guys site. so much really cool info. i totally dig this his style...very blunt and to the point. i especially enjoyed reading his section on biasing. very....comical.
he actually explains the 91k and 9.1k idea and claims that removing the 9.1k resistor would give better results. but i guess as with everything, its probably subjective.
6G6
Junior tube assistant
Posts: 88
(2/20/04 8:58 am)
Re: tone lizard
--------------------------------------------------------------------------------
Yea, I'm still trying to read everything on that site.
There's a lot there!
gammelnalle
Junior tube assistant
Posts: 15
(2/20/04 9:31 am)
Re: tone lizard
--------------------------------------------------------------------------------
glad that even I could contribute with something...
Tesno
Junior tube assistant
Posts: 7
(2/20/04 5:36 pm)
Re: tone lizard
--------------------------------------------------------------------------------
Thanks for all the replys and help. The Tales from the Tone lounge is a neat site.
Life is a jest and all things show it, I thought so once but now I know it.
<< Prev Topic | Next Topic >>
Topic Commands
Click to receive email notification of replies
jump to: Tube Amp Building - Tweaks - Repairs (New)New Product Suggestions (New)Praises - Complaints - Suggestions (New)Buy - Sell- Trade (New)Archives (New)
- Hoffman Amplifiers - Tube Amp Building - Tweaks - Repairs - Hoffman Amplifiers -
Powered By ezboard® Ver. 7.32
Copyright ©1999-2005 ezboard, Inc.
Topic: oscillation/snubbers&PI (Read 3351 times)