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Frankie schematic issue / calling Bill [message #22047]

Fri, 02 January 2015 06:27

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Hey Bill do you own a Frankie PA head? And if so what year is yours? And have you seen any other schematics for these amps other than what I have, let me explane!
I was into my head (early 1966 model) yesterday to finish off cleaning and lubing the pots from 6 months ago and I also took a look at the schematic to see what could be done in regards to the somewhat muddy reverb these heads have.
My schematic says the reverb board is pc401, however mine is just etched with a copper 4, on top of that the signal output wire off of the preamp feeds into a 4,700 ohm resistor and that feeds a 10 uf cap that THEN goes to the center lug of the reverb pot.
Also I took note that my head has no .005uf cap on either channel to make for a brite input, this I can understand on the channel with verb as that was ment for a Mic, but I though that it would at least have the cap on the non effect channel!

Any thoughts any one,does any one have a earlier or latter production head than mine that they can peek into?
It would seem that mine was made on the 23rd week of 66.
Thanks in advance for any info!

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Re: Frankie schematic issue / calling Bill [message #22053 is a reply to message #22047]

Sat, 03 January 2015 02:05

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

I do have one Steve, I'll try and pull the chassis this weekend to let you know.

I do know that there are no bright caps on any of the inputs. I have only seen the one schematic for all of the Frank heads.

I always assumed that all of the inputs were meant to be used with mikes and only the left side had reverb. Before I owned one, I thought that the reverb would work on both channels.

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Re: Frankie schematic issue / calling Bill [message #22062 is a reply to message #22047]

Mon, 05 January 2015 19:22

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

Steve- I pulled my Frankie PA head and checked things out. Mine is an early 1967 with the same board that you have with the number 4 etched in the middle.

My board is just like the schematic with the input from the preamp board going directly to the reverb control and to the base of Q401. The output from the reverb return circuit goes to the other end of the reverb control, with the output to the power amp coming from the wiper of the reverb control, going through the 10uF C409 and the 4k7 resistor R413.

Remember that the reverb control is like a balance control, the signal to the power amp is either connected directly to the output of the preamp or to the output from the reverb return circuit. The pot itself is used as the mixing resistor.

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Re: Frankie schematic issue / calling Bill [message #22063 is a reply to message #22047]

Mon, 05 January 2015 22:10

riverboat
Messages: 49
Registered: November 2014
Location: United States

Member

Hello and HELP!
I too have a Frankie head in need of repair, actually it's in the repair shop now. The tech called me today and asked if I could get a schematic for him as it's easier working with some kind of road map. It's a model C595-no reverb- no vibrato. How can I get a copy of this coveted secrete document? Thank You Keith.

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Re: Frankie schematic issue / calling Bill [message #22064 is a reply to message #22063]

Mon, 05 January 2015 22:25

pleat
Messages: 1452
Registered: June 2004
Location: Belding, Mi

Senior Member

On the technical tab on the left, click and go to schematic amp models and scroll down to K200-A all models is the frankie schematic. So far the schematics can't be copied, so your tech will have to have a computer opened up to the schematic page.
pleat

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Re: Frankie schematic issue / calling Bill [message #22065 is a reply to message #22047]

Mon, 05 January 2015 23:55

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

The schematic in the technical section is marked K200 and has "Wide Panel" written on it. One page contains the circuits for all three versions of the Frankie amps.

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Re: Frankie schematic issue / calling Bill [message #22066 is a reply to message #22047]

Tue, 06 January 2015 00:46

riverboat
Messages: 49
Registered: November 2014
Location: United States

Member

Thanks, man. I am not very computer savvy but somehow I pushed a wrong button and all of the schematics printed out including the illusive wide panel.
Thank You again, Keith

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Re: Frankie schematic issue / calling Bill [message #22067 is a reply to message #22047]

Tue, 06 January 2015 00:55

riverboat
Messages: 49
Registered: November 2014
Location: United States

Member

Thanks, Man. You have saved the day! I am not very computer savvy but somehow I pushed a wrong button and all of the schematics came pouring out of the printer,including the illusive wide panel. Now lets see if we can bring the monster back to life!
Thank You Again...Keith

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Re: Frankie schematic issue / calling Bill [message #22068 is a reply to message #22047]

Tue, 06 January 2015 06:51

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Thanks for the check out nd the info Bill!

Keith if your tech finds that your amp has a output stage problem these amps are very easy to repair due to the phase splitter transformer they have driving the 4 output transistors .
A younger tech who has never seen such a output stage my not see that he can just unhook the secondary side of this transformer that feeds the output transistors and just deal with the dc voltage issues he finds with the transistors on there own!

This also means that any issues with the driver stage on the primary side of the phase transformer will not effect the power transistor side of the output stage.

While the amp is in the shop no even if the mp has no output stage issues have the tech replace all the emitter resistors and bias resistors on all 4 output transistors .

These should be replaced with resistors that are 1% in tolerance as in these amps if just one of these resistors are off 1.7 ohms OR LESS the amp may only output 60 watts and not the 100 that it should!

The stock 5 watt resistors should be upped to 7 watt and the others should be upped by 1 watt in rating.
Also take note that these early Kustoms had only a fuse to protect the output stage, not a true protection circuit like the latter amps.

What this means is that if you have the amp on and a speaker cable plugged into the amp and you then plug the cable into the speaker cabinet you are shorting out the output stage and the fuse can not react fast enough and damage may take place , on the other side of the coin if you are unplugging the cable from the speaker with the amp on you are creating a short also!
If it turns out that this phase splitter/ drive transformer is bad you may be SOL!
If your tech needs any help point him here!

[Updated on: Tue, 06 January 2015 06:59]

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