Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: kagliostro on April 25, 2013, 07:21:36 pm

Title: Old Italian Guitar amp - I Need Help - Please give a look to the schematic
Post by: kagliostro on April 25, 2013, 07:21:36 pm

For a friend I'm drawing the schematic of an old italian guitar amp

it is a mixed amp with SS and Tubes

as I didn't understand SS at all, I'm not sure the schematic I've draw following the layout is correct

I'm not able to recognize if the Base - Emitter - Collector of the BC209 transistors are connected consistently

with the schematic, if I swap a grid or a cathode I can see by myself the mistake, but transistors are like arab language for me

Thanks for any help

K

Title: Re: Old Italian Guitar amp - I Need Help - Please give a look to the schematic
Post by: PRR on April 25, 2013, 09:25:45 pm

Q1 and Q2 are reasonable.

Q3 is surely wrong. So is the connection from Q2 to Intensita pot and tube grid.

Q3 *seems* to be a "switch" to short-out the tremolo signal. To do this, I would expect B and E the other way, and a source of current to the Base.

And it is still odd, because the Trem signal can go on the wire out to the foot switch, no transistor switch needed. So maybe Q3 is an emitter follower to buffer the trem signal?

Here's one way it might be done. I think you need to study it some more.

Title: Re: Old Italian Guitar amp - I Need Help - Please give a look to the schematic
Post by: kagliostro on April 26, 2013, 07:22:46 am

Many thanks PRR

Q3 was the principal doubt I had (not thet Q1 & Q2 weren't a problem for me, but looks less odd to my eyes)

I'll further investigate about Q3

So may be there is a reason for which someone disconnected the wire from FottSwitch and Q3

I am indebted to you, really thanks

Franco

Title: Re: Old Italian Guitar amp - I Need Help - Please give a look to the schematic
Post by: kagliostro on April 29, 2013, 10:55:40 am

The investigation give some result

the situation seems to be this (see schematic)

there is a wire that connect the wiper of the 10k trimmer to the emitter of Q3

there is also an unconnected wire, the wire that previously I've draw as connected between the emitter of Q3 and the FootSwitch

if someone can say something as to arrive at a solution he is welcome

Many Thanks

K

Title: Re: Old Italian Guitar amp - I Need Help - Please give a look to the schematic
Post by: PRR on April 29, 2013, 11:57:20 pm

BC109 data with pin-out:

http://www.tekkna.it/open2b/var/catalog/product/files/1428.pdf (http://www.tekkna.it/open2b/var/catalog/product/files/1428.pdf)

Perfectly modern NPN Silicon. (Yes, 40 years old!)

Pinout is referenced to a flat-spot on the body. I am not sure what I am seeing in the picture. However my *guess* is that C is grounded, E shorts-out the guitar signal through Intens knob, and B gets a portion of the trem oscillator, plus DC bias, through the pre-set trim pot.

And grounding the Base with jack or pedal stops the trem.

Title: Re: Old Italian Guitar amp - I Need Help - Please give a look to the schematic
Post by: kagliostro on April 30, 2013, 01:08:45 am

Many thanks PRR

Now I know how is connected the transistor, how to connect the wire and, very important for my knowledge, how the circuit acts

Again I'm in debt to you

Franco