Gibson GA-90 -- CF after Tone Control ?? (5879 > TS > CF > Gain Stage > ....)

[kagliostro]

As far as I can know pentode tube didn't like so much to drive directly Tone Controls

so some author council is to use a CF between the tube and the Tone Control

this acts as an impedance adapter and the pentode is not too higly loaded by the Tone Control (so we have less signal loss)

But the Gibson GA-90 seems a bit odd to this philosopy



V1 is a 5879 pentode that feeds directly the Tone Control then the tone control is connected to a CF

Not that a Tone Control is impossible to see after a pentode, but what is doing there the CF ????

May be the CF is there because the AG-90 is a dual chassis and Preamp is separated from the Power Amp ?



Franco

[sluckey]

May be the CF is there because the AG-90 is a dual chassis and Preamp is separated from the Power Amp ?

That seems reasonable.

[shooter]

Gibson GA-90 seems a bit odd

They seem a bit odd in most designs, hence my affinity for them
before I knew much,(ya, ya:), I used a CF as the last piece in the pre on 2 builds with good results, but there was no Good logic, just seemed *right*

[kagliostro]

.... but there was no Good logic

On the contrary

it is logic if you need to connect the pre to an external amp

it is perfect to drive cables

Franco

[Tone Junkie]

Franco it looks like you had that lovely amp on your work bench , the circuit is a very interesting design. my question would be how did it sound.
Thanks Bill

[kagliostro]

No, sorry but the photo is stolen from the Web

I've the bad habit to look to old amps as to study the circuitry .....

Franco

[sluckey]

I've the bad habit to look to old amps as to study the circuitry .....

That's a good hobby. Keeps you outta the bars and off the streets. 

[kagliostro]

....... Keeps you outta the bars and off the streets.

 

Franco

[sluckey]

Just keep in mind... Chasing old Gibson schematics is more likely to lead you down a blind alley than lead you to a pot of gold.

[kagliostro]

....Chasing old Gibson schematics is more likely to lead you down a blind alley than lead you to a pot of gold.

May be Steve, but I like them so much .....

@ Tone Junkie

( apply substitution ** = tt )

h**ps://www.youtube.com/watch?v=HoIRRzhM4es             

h**ps://www.youtube.com/watch?v=2WdJmMnOn9E

h**ps://www.youtube.com/watch?v=5cwGrlWi8DA

Ciao

Franco

[sluckey]

May be Steve, but I like them so much

I know. Plenty of other people like them too. The tube world is upside down. Anything with a tube in it is crazy popular these days. My prime example is the Silvertone 1484. The ONLY reason people bought them when they were new was because they could not afford a good quality amp. I know because I owned one. You could buy it new for $150. A Fender Super reverb would cost you $400. But that Silvertone is very sought after today. I don't get it, but I realize that plenty of others do.

My main beef with Gibson amps is that they could not produce two identical amps. And documentation was pathetic. That's part of the reason that Gibson did not survive in the amp business. Having said that, of all the electric guitars I've owned, Gibson is my choice.   

[kagliostro]

My main beef with Gibson amps is that they could not produce two identical amps. And documentation was pathetic.

I think nobody can reach avaiability of documentation that has Fender, they are unique

Franco

[sluckey]

You do realize all this talk is just my opinion, right?   

[shooter]

they could not produce two identical amps

Yup, I've repaired 3 GA5T and they were all unique!
My Uncle did necks and the pearl inlays on their mandolins in the mid to late 50's, my Dad, just sanded
I also like checker cars and Shakespeare fishing rods, must be that home-town thing

[kagliostro]

You do realize all this talk is just my opinion, right?

Of course   

Franco