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Post subject: 5E8 circuit changes
Posted: Tue May 15, 2012 7:30 pm
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Hello, I am wondering about the 5E8 circuit. Which one did Fender use for the RI? Was it the 5E8 or the 5E8a? Does anyone know what if any tonal differences there are between the two circuits?

According to Ampwares
Quote:
There were several circuit changes to model 5E8 including the addition of a DC filter choke and a second negative feedback loop for the tone circuit. A selenium rectifier is used in the bias circuit. Model 5E8-A removed the treble section of the tone circuit from the second feedback loop.
Looking at the schematic I see that in the "A" circuit the bass pot is no longer connected to the treble pot.

Thanks,
Robert


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Post subject: Re: 5E8 circuit changes
Posted: Tue May 15, 2012 10:16 pm
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The re-issue schematic may provide your answers......

http://support.fender.com/schematics/gu ... ematic.pdf

Arjay

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Post subject: Re: 5E8 circuit changes
Posted: Wed May 16, 2012 11:58 am
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I tried to respond to this last night by my connection to the net went down for several hours. :shock: :cry:

Yes, the Fender 57 Twin Reissue is the 5E8A as Arjay noted in the link he posted.

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Post subject: Re: 5E8 circuit changes
Posted: Wed May 16, 2012 9:29 pm
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As "The King" would say, "Thank you very much" :lol: Is anyone aware of any tonal differences between the two versions?

Also, I am wondering why are there no input grid resistors used on the original?

Robert

Oops, I just looked at the schematic for the RI and I see they have added 1.5K grid resistors.


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Post subject: Re: 5E8 circuit changes
Posted: Wed May 16, 2012 9:43 pm
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bigampdaddy wrote:
As "The King" would say, "Thank you very much" :lol: Is anyone aware of any tonal differences between the two versions?

Also, I am wondering why are there no input grid resistors used on the original?

Robert

Oops, I just looked at the schematic for the RI and I see they have added 1.5K grid resistors.


Yeah, it is interesting to note that in the original 5E8A design, there are no grid resistor on the inputs, but there are on the power tubes. When Fender did the reissue, they added the grid resistors to the inputs. On the other hand, the original 5F6A Bassman circuit had 68K grid resistors on the input, but none on the power tubes. When Fender did the 59 Bassman reissue, they added 47 ohm grid resistors to the power tube. Go figure.

When I built my Weber 5F6A Bassman clone, some forums recommended adding 1.5K grid resistors to the power tubes like the 5F6 Bassman had. I did not and have no problems.

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Post subject: Re: 5E8 circuit changes
Posted: Sat May 19, 2012 4:15 pm
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Thank you for the information. If I could continue this thread a bit further, what is the purpose of the 2nd set of 100K's that are in parallel with the 100K plate resistors on the first gain stages? Is it a passive resistance mixer as in the 5F6/JTM45 circuit?

Thank you,

Robert


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Post subject: Re: 5E8 circuit changes
Posted: Sat May 19, 2012 6:51 pm
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bigampdaddy wrote:
Thank you for the information. If I could continue this thread a bit further, what is the purpose of the 2nd set of 100K's that are in parallel with the 100K plate resistors on the first gain stages? Is it a passive resistance mixer as in the 5F6/JTM45 circuit?

Thank you,

Robert


Exactly, with some differences.

If you look at the 5F6A circuit

http://ampwares.com/schematics/bassman_5f6a.pdf

You will see that a single 12AY7 is used to perform preamp duty. One half of the tube is for the high and low gain inputs of the normal channel, the other half is for the high and low gain inputs of the bright channel. The two 270K ohm resistors are then used to mix the two channels together after the volume controls and the combined signal is fed to the cathode follower.

In the 5E8A, one half of one 12AY7 performs preamp duties for the low gain input on the normal channel while the second half handles the high gain input. A second 12AY7 does the same thing for the bright channel

http://ampwares.com/schematics/twin_5e8a.pdf

The two halves of the normal channel are mixed together by one of the 100K ohm resistors and the two halves of the bright channel are mixed together by the second 100K ohm resistor. Those two signals are then mixed together by the two 270K ohm resistors and fed to the cathode follower just like in the 5F6A circuit.

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Post subject: Re: 5E8 circuit changes
Posted: Sat May 19, 2012 7:26 pm
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Quote:
The two halves of the normal channel are mixed together by one of the 100K ohm resistors and the two halves of the bright channel are mixed together by the second 100K ohm resistor. Those two signals are then mixed together by the two 270K ohm resistors and fed to the cathode follower just like in the 5F6A circuit.


I thought that is what they did. Thank you for the info. I want to say that the people on this board are just about the most helpful of any board I have been on. On some other boards I am lucky to get a reply at all. On this one I have never had to wait more than one day. :) :)

Oops, I almost forgot to mention that my neighbors, one in particular, just do not have any appreciation of good, cranked, tweed tone. Especially around midnight. :lol:

Robert


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Post subject: Re: 5E8 circuit changes
Posted: Sat May 19, 2012 10:50 pm
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bigampdaddy wrote:
Quote:
The two halves of the normal channel are mixed together by one of the 100K ohm resistors and the two halves of the bright channel are mixed together by the second 100K ohm resistor. Those two signals are then mixed together by the two 270K ohm resistors and fed to the cathode follower just like in the 5F6A circuit.


I thought that is what they did. Thank you for the info. I want to say that the people on this board are just about the most helpful of any board I have been on. On some other boards I am lucky to get a reply at all. On this one I have never had to wait more than one day. :) :)

Oops, I almost forgot to mention that my neighbors, one in particular, just do not have any appreciation of good, cranked, tweed tone. Especially around midnight. :lol:

Robert


You're welcome. :D

Your neighbors need a little education in good tone. They probably listen to rap or metal from highly compressed MP3 through ear plugs. :lol:

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Post subject: Re: 5E8 circuit changes
Posted: Sun May 20, 2012 12:55 am
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Hey Big, this ain't a bad village at all. Don't have the Tweed experience. You're spot on, about most folks around here!!! JMHO Art

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