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Post subject: Red knob Dual Showman tube chart
Posted: Thu May 02, 2013 5:21 am
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Hi there,

I just picked up an old red knob Dual Showman and was going to change all the tubes to start from scratch on it, and noticed that there is no tube chart sticker inside the cab. I found a schematic for the amp, but have no idea how that relates to the physical layout of the chassis. From what I've found so far I think it uses 2 12AT7's and 5 12AX7's, in addition to the quad 6L6's. Logic would say just pull a tube and replace it with the same that you pulled out, right? I thought that and started pulling tubes, and they are all 12AX7's (obviously not the power tubes). If anyone can help with a pic of their tube chart or give me a description, that would be great. Thanks!

Dave


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Post subject: Re: Red knob Dual Showman tube chart
Posted: Thu May 02, 2013 5:42 am
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Location: Natural Bridge, Virginia
According to this, it uses four 7025s (low noise 12AX7s, rare and expensive these days) and one 12AT7. The 12AT7 is the phase invertor.

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

http://www.webphix.com/schematic%20heav ... _schem.pdf

Note the typo in the schematic: two tubes are labled V3A/V3B. One should be V2A/V2B. Both are 7025s/12AX7s so it doesn't matter.

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Post subject: Re: Red knob Dual Showman tube chart
Posted: Tue May 07, 2013 4:48 am
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Thanks for the files bluesky636. I'm having trouble matching what the schematic shows to the physical layout of the chassis though. I'm guessing from the schematic that one of the two tubes next to the quad 6L6's is an 12AT7...which one though? Maybe someone could help with this crude diagram of the physical tube layout looking at the bottom of the chassis as if you were changing the tubes:

(front of amp)
1 2 3
o o o
4 5 6 7 8 9
o o O O O O

1-?
2-?
3-?
4-?
5-?
6-6L6
7-6L6
8-6L6
9-6L6

Somewhat blindly guessing from the schematic, I'd say maybe #5 is the 12At7? Also is it that big of a deal if I don't use the "low noise 12AX7's"? Thanks again.


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Post subject: Re: Red knob Dual Showman tube chart
Posted: Tue May 07, 2013 7:20 am
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Dmerch1969, a kind of rule-of-thumb is that most Fender amps have the phase inverter (12AT7) next to the output tubes. Or V5 in your diagram.

You are most likely correct.


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Post subject: Re: Red knob Dual Showman tube chart
Posted: Thu May 16, 2013 5:30 pm
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Dmerch1969 wrote:
Hi there,

I just picked up an old red knob Dual Showman and was going to change all the tubes to start from scratch on it, and noticed that there is no tube chart sticker inside the cab. I found a schematic for the amp, but have no idea how that relates to the physical layout of the chassis. From what I've found so far I think it uses 2 12AT7's and 5 12AX7's, in addition to the quad 6L6's. Logic would say just pull a tube and replace it with the same that you pulled out, right? I thought that and started pulling tubes, and they are all 12AX7's (obviously not the power tubes). If anyone can help with a pic of their tube chart or give me a description, that would be great. Thanks!

Dave

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Hope this helps...Congrats on the red knob Dual Showman. An underrated amp in my humble opinion.


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Post subject: Re: Red knob Dual Showman tube chart
Posted: Mon May 20, 2013 3:07 pm
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Thanks a bunch man! Perfect!!!! :)


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Post subject: Re: Red knob Dual Showman tube chart
Posted: Mon May 20, 2013 3:08 pm
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And yes, I agree, underrated and outright awesome amp!


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