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#1 2007-12-02 03:10:54

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

R1, R7 and C1, C4 in v4/vt22

Ok.  I have an early 70s Vt-22.   and having worked on alot, i noticed that mine had places for resistors and capacitors that were not filled.  specifically R1,R7, C1, and C4.

they are right on the input of each channel. 

on the schematic,  it notes these components may not appear in some models.

I've always meant to put them in one of my channels to compare the sound.
has anyone else tried it?   doesn't seem like it would change the sound dramatically,  but i imagine it would change it.

anyone have a hypothesis one why ampeg would include them on some, but not all of the v-4s they made?

Last edited by hangman (2007-12-02 03:11:45)

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#2 2007-12-02 20:47:26

mojoman
Member
Registered: 2007-11-28
Posts: 36

Re: R1, R7 and C1, C4 in v4/vt22

Those components are not really necessary. The resistors are more commonly found on amps that have a dual input to one channel to prevent run-away isolation. The caps look to be in place to shunt RF interference than for any tone shaping design. So yes, your amp can happily run without them and most likely they were left off in production to save on cost of parts.

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#3 2007-12-02 21:41:08

hangman
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From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: R1, R7 and C1, C4 in v4/vt22

ok,  sure,  its a grid stopper,  with an added capacitor to shunt even more hf.    but certainly it must effect the sound to some extent. I realize ampeg was using a very small value (only 1k) were they simply trying to minimize signal attenuation while maintaining the hf roll off provided by the C1 and C4, in addition to the internal capacitance of the tube? 
are grid stoppers of such small values even that effective?

or were they really counting their pennies like that?   even today those parts would add up to like 30 cents.   

I'm gonna goof around with this just for curiosity's sake, and see if I do notice a difference.  even if I hear no difference a little extra protection never hurt anyone,  and besides... the parts are less than 30 cents!

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#4 2007-12-03 01:44:34

mojoman
Member
Registered: 2007-11-28
Posts: 36

Re: R1, R7 and C1, C4 in v4/vt22

Well when you multiply the cost of those parts by the thousands, yes it does really add up. And those values would not really effect the tone if at all. You can experiment and see.

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#5 2007-12-03 03:53:38

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: R1, R7 and C1, C4 in v4/vt22

i suppose you have a point mojoman. 

I'll just leave them out.

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