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Post subject: Re: Is this a Tweed Deluxe 5b3 or 5c3?
Posted: Tue Sep 04, 2018 7:54 pm
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Location: Coastal Bend, Tx.
Here is a great resource for the evolution of the Deluxe model and many other models/mods/etc.
https://robrobinette.com/Fender_Deluxe_Models.htm


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Post subject: Re: Is this a Tweed Deluxe 5b3 or 5c3?
Posted: Wed Sep 05, 2018 6:53 am
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I will look into getting those new electrolytic main power supply caps!

Does my amp have the global NFL? I've got basic electronic skills but sadly, not enough to work that out...


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Post subject: Re: Is this a Tweed Deluxe 5b3 or 5c3?
Posted: Wed Sep 05, 2018 8:58 am
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"Does my amp have the global NFL? I've got basic electronic skills but sadly, not enough to work that out..."
I don't see one in your guts pic, but it could be hidden in another location.
It should be fairly easy to determine on your own by tracing the wires from the speaker to the 1/4" speaker jack and then from inside the chassis speaker jack connection to the board connection.
The tip portion of the 1/4" plug is hot/signal and the sleeve is ground. You only need trace the tip connection.
The 5C3 schematic shows a 1Meg resistor(GNF-resistance).
Generally in the layout view link from BMW2002's post, this 1Meg resistor is placed on the board(3rd resistor to the right from the bias resistor(250ohm 5watt) viewed from the tube side of chassis.
Your picture shows only 3 resistors (5B3) = no negative feedback.


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Post subject: Re: Is this a Tweed Deluxe 5b3 or 5c3?
Posted: Wed Sep 05, 2018 9:38 am
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Image

Check how the two yellow-arrowed resistors work in your circuit. They are in the place of the two 1 meg-ohm GNFB resistor divide, in the 5C3 layout.

Image


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Post subject: Re: Is this a Tweed Deluxe 5b3 or 5c3?
Posted: Wed Sep 05, 2018 10:13 am
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BMW, not sure where you're going w/ this.
This is how I understand GNF. A voltage supplied by the output transformer w/ a series resistor to the 6V6 output tube grid(5C3) is a negative feedback loop.
The resistor value difference you highlighted are merely to offset the grid voltage between the phase inverter 6sc7 triodes(250K & 7k), the other highlighted resistor is a cathode bypass. Supposedly this (250k/7k)makes a smoother output distortion in the paraphase phase inverter and better clarity of 2nd order harmonics, due to the common preamp distortion created in the circuit. Robinette says it is to decrease the gain.

In the picture, you missed the 250K when you rotated 90 degrees. Look back at the 1st gut picture he posted and you can see it. His amp doesn't have the on/off switch, aux. output jack or a NFL as best I can tell but does have the input caps increase. More a 5B3 than a 5C3.


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Post subject: Re: Is this a Tweed Deluxe 5b3 or 5c3?
Posted: Wed Sep 05, 2018 5:24 pm
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Eric, I believe the two resistors in question are part of the original 5C3 1-meg ohm/1-meg ohm GNFB voltage divide network.

Image

Now, replaced by a 2500-ohm and 6800-ohm resistor pair. He needs to trace the potential GNFB from the output transformer's secondary side, with a DVM, to be sure.

Image


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Post subject: Re: Is this a Tweed Deluxe 5b3 or 5c3?
Posted: Wed Sep 05, 2018 7:47 pm
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Thank you for posting photos, Jam. A thing of beauty is a joy forever.


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Post subject: Re: Is this a Tweed Deluxe 5b3 or 5c3?
Posted: Wed Sep 05, 2018 9:06 pm
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BMW, I think if you look at the 5B3 layout on Robinettes site, you will see exactly the same thing as shown in JamJuices picture as far as resistor values are concerned. Unfortunately I cant post as its an inactive pic on his site.

His amp only has a couple of the 5C3 changes. The input section(50k input resistors increased to 75k and mounted to board and increased input caps from .05 to .1) and the addition of a single 1/4" speaker jack(not 2).

The full picture of the three resistors in that stage(250K/6.8K & 2.5K) are the same as a 5AorB3(they used 7k as it was a standard component in the earlier 50's). The 250k & 6.8k are tied to pin three(grid) of V2 and the 2.5k is tied to pin 6(cathode) of V2.

The wire you see connected to the 1/4" speaker jack tip appears to me to run from the output transformer and terminate at the jack. There is no follow on wire(NFL) to the board from the jack.

The full 5C3 upgrades w/ NFL would have made the changes to 1meg-1meg-25k-2.5k.


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Post subject: Re: Is this a Tweed Deluxe 5b3 or 5c3?
Posted: Thu Sep 06, 2018 5:42 am
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Eric, you are correct. Very odd arrangement.


http://www.google.com/url?sa=t&rct=j&q= ... V_UJIK690I


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