Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: raza on October 21, 2017, 01:33:57 pm

Title: New Project! New Problems! can you help me?
Post by: raza on October 21, 2017, 01:33:57 pm

(First sorry for my English, Iam from spain)

I am in an other Project.
this:

(http://s2.subirimagenes.com/otros/previo/thump_9813861friedman004.jpg) (http://www.subirimagenes.com/otros-friedman004-9813861.html)

Well, the problem is, when I play with full gain I cant put the volumen more tan 11oclock,
A trebble noise scream apears and I can put the amp as loud that it can.

But when I put the gain at 9 I can putthe volumen at full.

What can I do?

Title: Re: New Project! New Problems! can you help me?
Post by: jim on October 21, 2017, 03:25:13 pm

The treble scream is an oscillation--a feedback of signal to an early stage.  These sounds could be from bad layout design or certain wires being too close to other wires.  Would you please post some pictures of the inside of the amp so that we can look at it.  It is wonderful the amp works but an adjustment is needed to play full gain.   Jim

Title: Re: New Project! New Problems! can you help me?
Post by: DummyLoad on October 21, 2017, 04:40:55 pm

you have an overall gain of 205k before the LTPI, assuming all the tubes are 12AX7. try eliminating c15 and see what happens. also, r26 and r27 are drawn incorrectly. r26 needs to connect to the jack end of r27 for r27 to function as a grid stopper.


veale pictura adjunto.



--pete

Title: Re: New Project! New Problems! can you help me?
Post by: 2deaf on October 21, 2017, 05:02:04 pm

I would try eliminating the 4n7 capacitor and the 220K resistor from the NFB loop first.