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Old 22nd November 2011, 10:51 AM   #181
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hello,
is there any link with a class a tube pre amp,if any for bass guitar,using 3 pcs of 12ax7
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Old 22nd November 2011, 09:48 PM   #182
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guitar amp schematics are downloadable from the web, you have lots and lots to choose from......electric guitar amplifier - Hanapin sa Google
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Old 22nd November 2011, 11:50 PM   #183
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thanks boss tony,
what particular model can you suggest,implementing class a pre amp using 3 pcs. 12ax7
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Old 23rd November 2011, 03:01 AM   #184
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i do not understand why 3 12ax7's, the spitfire i made only used 2 and if you have this 6C10 compactrons you can make a guitar amp using 3 tubes only or 2 tubes if you use an 832 tube, gerry sta maria has these tubes, 400-2762.....
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Old 5th December 2011, 10:28 AM   #185
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Old 12th December 2011, 02:36 AM   #186
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Default Test Tube

Hi, I am totally new to working with tube amp circuitry. I have a Marshall 8080 and I am trying to repair it. I turn it on and no sound comes out when I play. Could this be due to a broken tube? If so, how do I test the tube with a multimeter?
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Old 21st December 2011, 01:51 PM   #187
GloBug is offline GloBug  Canada
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Your best approach is to find somebody local with a tube tester, just to rule out a bad tube.

You can't really check them with a DVM other then to see if the heaters are intact. Find a "datasheet" or google "pinouts" for your particular tube.

In this case you only have one tube in the amp which is a 12AX7, the heaters are pins 4,5 and 9.

You likely have a buddy who you can snag a known good 12AX7 to try out.

Read up on safety before diving inside the amp.

If your tube is OK then time to start learning a little more about it. Your is is a Hybrid so you have twice the fun ahead of you.
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Old 21st January 2012, 02:38 PM   #188
kees52 is offline kees52  Netherlands
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I thought yes, this is learn material, it is very nice to see how a tube works, in real time manufacuring by a DIY man.

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Last edited by kees52; 21st January 2012 at 02:44 PM.
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Old 21st March 2012, 07:01 PM   #189
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what is the maximum life of a tube amplifier ?
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Old 21st March 2012, 08:02 PM   #190
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Decades, even a century if properly designed and constructed. I have some some RCA-3 45 push pull amplifiers from early 1920 that still function flawlessly. The capacitors may dry and and need replacement or the resistors drift and need replacement, but the basic amp should last a long time.

Note: This is not necessarily true for circuit board based tube amplifiers. Traces lift, the material degrades and starts conducting, audio sound gets worse and worse, and eventually it is trash. Point-to-point is what lasts.
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